diff --git "a/ferrimagnetic_-_abstract.csv" "b/ferrimagnetic_-_abstract.csv" new file mode 100644--- /dev/null +++ "b/ferrimagnetic_-_abstract.csv" @@ -0,0 +1,25344 @@ +publicationDate,title,abstract,id +1998-10-09,Magnetic Properties of Quantum Ferrimagnetic Spin Chains,"Magnetic susceptibilities of spin-$(S,s)$ ferrimagnetic Heisenberg chains are +numerically investigated. It is argued how the ferromagnetic and +antiferromagnetic features of quantum ferrimagnets are exhibited as functions +of $(S,s)$. Spin-$(S,s)$ ferrimagnetic chains behave like combinations of +spin-$(S-s)$ ferromagnetic and spin-$(2s)$ antiferromagnetic chains provided +$S=2s$.",9810112v1 +1999-01-08,Quantum Ferrimagnets,"We study quantum ferrimagnets in one, two, and three dimensions by using a +variety of methods and approximations. These include: (i) a treatment based on +the spin coherent state path-integral formulation of quantum ferrimagnets by +taking into account the leading order quantum and thermal fluctuations (ii) a +field-theoretical (non-linear $\sigma$-model type) formulation of the special +case of one-dimensional quantum ferrimagnets at zero temperature (iii) an +effective description in terms of dimers and quantum rotors, and (iv) a quantum +renormalization group study of ferrimagnetic Heisenberg chains. Some of the +formalism discussed here can be used for a unified treatment of both +ferromagnets and antiferromagnets in the semiclassical limit. We show that the +low (high) energy effective Hamiltonian of a (S_1, S_2) Heisenberg ferrimagnet +is a ferromagnetic (antiferromagnetic) Heisenberg model. We also study the +phase diagram of quantum ferrimagnets in the presence of an external magnetic +field h ($h_{c1} < h < h_{c2}$) and show that the low- and the high-field +phases correspond respectively to the classical N\'eel and the fully polarized +ferromagnetic states. We also calculate the transition temperature for the +Berezinskii-Kosterlitz-Thouless phase transition in the special case of +two-dimensional quantum ferrimagnets.",9901063v2 +2012-07-29,Ferrimagnetism of the Heisenberg Models on the Quasi-One-Dimensional Kagome Strip Lattices,"We study the ground-state properties of the S=1/2 Heisenberg models on the +quasi-onedimensional kagome strip lattices by the exact diagonalization and +density matrix renormalization group methods. The models with two different +strip widths share the same lattice structure in their inner part with the +spatially anisotropic two-dimensional kagome lattice. When there is no magnetic +frustration, the well-known Lieb-Mattis ferrimagnetic state is realized in both +models. When the strength of magnetic frustration is increased, on the other +hand, the Lieb-Mattis-type ferrimagnetism is collapsed. We find that there +exists a non-Lieb-Mattis ferrimagnetic state between the Lieb-Mattis +ferrimagnetic state and the nonmagnetic ground state. The local magnetization +clearly shows an incommensurate modulation with long-distance periodicity in +the non-Lieb-Mattis ferrimagnetic state. The intermediate non-Lieb-Mattis +ferrimagnetic state occurs irrespective of strip width, which suggests that the +intermediate phase of the two-dimensional kagome lattice is also the +non-Lieb-Mattis-type ferrimagnetism.",1207.6771v1 +2017-10-21,Correlation between Compensation Temperatures of Magnetization and Angular Momentum in GdFeCo Ferrimagnets,"Determining the angular momentum compensation temperature of ferrimagnets is +an important step towards ferrimagnetic spintronics, but is not generally easy +to achieve it experimentally. We propose a way to estimate the angular momentum +compensation temperature of ferrimagnets. We find a linear relation between the +compensation temperatures of the magnetization and angular momentum in GdFeCo +ferrimagnetic materials, which is proved by theoretically as well as +experimentally. The linearity comes from the power-law criticality and is +governed by the Curie temperature and the Land\'e g factors of the elements +composing the ferrimagnets. Therefore, measuring the magnetization compensation +temperature and the Curie temperature, which are easily assessable +experimentally, enables to estimate the angular momentum compensation +temperature of ferrimagnets. Our study provides efficient avenues into an +exciting world of ferrimagnetic spintronics.",1710.07779v1 +2011-02-16,Collapse of Ferrimagnetism in Two-Dimensional Heisenberg Antiferromagnet due to Frustration,"We study ferrimagnetism in the ground state of the antiferromagnetic +Heisenberg model on the spatially anisotropic kagome lattice, in which +ferrimagnetism of the conventional Lieb-Mattis type appears in the region of +weak frustration whereas the ground state is nonmagnetic in the isotropic case. +Numerical diagonalizations of small finite-size clusters are carried out to +examine the spontaneous magnetization. We find that the spontaneous +magnetization changes continuously in the intermediate region between +conventional ferrimagnetism and the nonmagnetic phase. Local magnetization of +the intermediate state shows strong dependence on the site position, which +suggests non-Lieb-Mattis ferrimagnetism.",1102.3244v1 +2012-11-01,Spin Seebeck effect in antiferromagnets and compensated ferrimagnets,"We theoretically investigate the spin Seebeck effect (SSE) in +antiferromagnets and ferrimagnets, and show that the SSE vanishes in +antiferromagnets but survives in ferrimagnets even at the magnetization +compensation point despite the absence of its saturation magnetization. The +non-vanishing SSE in ferrimagnets stems from two non-degenerate magnons. We +demonstrate that the magnitude of the SSE in ferrimagnets is unchanged across +the magnetization compensation point.",1211.0123v1 +2015-02-04,Instability of a ferrimagnetic state of a frustrated S=1/2 Heisenberg antiferromagnet in two dimensions,"To clarify the instability of the ferrimagnetism which is the fundamental +magnetism of ferrite, numerical-diagonalization study is carried out for the +two-dimensional S=1/2 Heisenberg antiferromagnet with frustration. We find that +the ferrimagnetic ground state has the spontaneous magnetization in small +frustration; due to a frustrating interaction above a specific strength, the +spontaneous magnetization discontinuously vanishes so that the ferrimagnetic +state appears only under some magnetic fields. We also find that, when the +interaction is increased further, the ferrimagnetism disappears even under +magnetic field.",1502.01071v1 +2018-04-05,Stochastic ferrimagnetic Landau-Lifshitz-Bloch equation for finite magnetic structures,"Precise modeling of the magnetization dynamics of nanoparticles with finite +size effects at fast varying temperatures is a computationally challenging +task. Based on the Landau-Lifshitz-Bloch (LLB) equation we derive a coarse +grained model for disordered ferrimagnets, which is both fast and accurate. +First, we incorporate stochastic fluctuations to the existing ferrimagnetic LLB +equation. Further, we derive a thermodynamic expression for the temperature +dependent susceptibilities, which is essential to model finite size effects. +Together with the zero field equilibrium magnetization the susceptibilities are +used in the stochastic ferrimagnetic LLB to simulate a $5\times10$ nm$^2$ +ferrimagnetic GdFeCo particle with 70 % FeCo and 30 % Gd under various external +applied fields and heat pulses. The obtained trajectories agree well with those +of an atomistic model, which solves the stochastic Landau-Lifshitz-Gilbert +equation for each atom. Additionally, we derive an expression for the +intergrain exchange field which couple the ferromagnetic sublattices of a +ferrimagnet. A comparison of the magnetization dynamics obtained from this +simpler model with those of the ferrimagnetic LLB equation shows a perfect +agreement.",1804.01724v1 +2023-12-01,Compensated Ferrimagnets with Colossal Spin Splitting in Organic Compounds,"The study of the magnetic order has recently been invigorated by the +discovery of exotic collinear antiferromagnets with time-reversal symmetry +breaking. Examples include altermagnetism and compensated ferrimagnets, which +show spin splittings of the electronic band structures even at zero net +magnetization, leading to several unique transport phenomena, notably +spin-current generation. Altermagnets demonstrate anisotropic spin splitting, +such as $d$-wave, in momentum space, whereas compensated ferrimagnets exhibit +isotropic spin splitting. However, methods to realize compensated ferrimagnets +are limited. Here, we demonstrate a method to realize a fully compensated +ferrimagnet with isotropic spin splitting utilizing the dimer structures +inherent in organic compounds. Moreover, based on $ab$ $initio$ calculations, +we find that this ferrimagnet can be realized in the recently discovered +organic compound (EDO-TTF-I)$_2$ClO$_4$. Our findings provide an unprecedented +strategy for using the dimer degrees of freedom in organic compounds to realize +fully compensated ferrimagnets with colossal spin splitting.",2312.00367v2 +2014-02-19,Theory of Ferrimagnetism in the Hubbard Model on Bipartite Lattices with Spectrum Symmetry,"In this paper we developed theory of the ferrimagnetism in the Hubbard model +on bipartite lattices with spectrum symmetry. We then study the defect-induced +ferrimagnetic orders in three models and explored the universal features.",1402.4634v1 +1998-03-12,Frustrated quantum Heisenberg ferrimagnetic chains,"We study the ground-state properties of weakly frustrated Heisenberg +ferrimagnetic chains with nearest and next-nearest neighbor antiferromagnetic +exchange interactions and two types of alternating sublattice spins S_1 > S_2, +using 1/S spin-wave expansions, density-matrix renormalization group, and +exact- diagonalization techniques. It is argued that the zero-point spin +fluctuations completely destroy the classical commensurate- incommensurate +continuous transition. Instead, the long-range ferrimagnetic state disappears +through a discontinuous transition to a singlet state at a larger value of the +frustration parameter. In the ferrimagnetic phase we find a disorder point +marking the onset of incommensurate real-space short-range spin-spin +correlations.",9803150v1 +2000-12-19,Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O,"In response to recent nuclear-magnetic-resonance measurements on a +ferrimagnetic chain compound NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O [Solid State +Commun. {\bf 113} (2000) 433], we calculate the nuclear spin-lattice relaxation +rate 1/T_1 in terms of a modified spin-wave theory. Emphasizing that the +dominant relaxation mechanism arises from the direct (single-magnon) process +rather than the Raman (two-magnon) one, we explain the observed temperature and +applied-field dependences of 1/T_1. Ferrimagnetic relaxation phenomena are +generally discussed and novel ferrimagnets with extremely slow dynamics are +predicted.",0012342v1 +2002-06-27,Intrinsic double-peak structure of the specific heat in low-dimensional quantum ferrimagnets,"Motivated by recent magnetic measurements on A3Cu3(PO4)4 (A=Ca,Sr) and +Cu(3-Clpy)2(N3)2 (3-Clpy=3-Chloropyridine), both of which behave like +one-dimensional ferrimagnets, we extensively investigate the ferrimagnetic +specific heat with particular emphasis on its double-peak structure. Developing +a modified spin-wave theory, we reveal that ferromagnetic and antiferromagnetic +dual features of ferrimagnets may potentially induce an extra low-temperature +peak as well as a Schottky-type peak at mid temperatures in the specific heat.",0206555v1 +2006-06-12,Defects in CrAs and related compounds: a route to half-metallic ferrimagnetism,"Half-metallic ferrimagnetism is crucial for spintronic applications with +respect to ferromagnets due to the lower stray fields created by these +materials. Studying the effect of defects in CrAs and related transition-metal +chalcogenides and pnictides crystallizing in the zinc-blende structure, we +reveal that the excess of the transition-metal atoms leads to half-metallic +ferrimagnetism. The surplus of these atoms are antiferromagnetically coupled to +the transition-metal atoms sitting at the perfect lattice sites. The needed +condition to achieve half-metallic ferrimagnetism is to prevent the migration +of the $sp$ atoms to other sites and the atomic swaps.",0606286v1 +2007-05-25,Ferrimagnetism and antiferromagnetism in half-metallic Heusler alloys,"Half-metallic Heusler alloys are among the most promising materials for +future applications in spintronic devices. Although most Heusler alloys are +ferromagnets, ferrimagnetic or antiferromagnetic (also called fully-compensated +ferrimagnetic) alloys would be more desirable for applications due to the lower +external fields. Ferrimagnetism can be either found in perfect Heusler +compounds or achieved through the creation of defects in ferromagnetic Heusler +alloys.",0705.3731v1 +2008-05-23,Frustration Induced Quantum Phases in Mixed Spin Chain with Frustrated Side Chains,"A mixed Heisenberg spin chain with frustrated side chains is investigated by +numerical and perturbational calculations. A frustration-induced quantum +partially polarized ferrimagnetic phase and a nonmagnetic spin quadrupolar +phase are found adjacent to the conventional Lieb-Mattis type ferrimagnetic +phase or the nonmagnetic singlet cluster solid phases. The partially polarized +ferrimagnetic phase has an incommensurate spin structure. Similar structures +are commonly found in other frustration-induced partially polarized +ferrimagnetic phases. Numerical results also suggest a series of almost +critical nonmagnetic ground states in a highly frustrated regime if the side +chain spins weakly couple to the main chain.",0805.3604v2 +2008-11-15,Half-metallic ferrimagnet formed by substituting Fe for Mn in semiconductor MnTe,"A ternary ferrimagnetic half-metal, constructed through substituting 25% Fe +for Mn in zincblende semiconductor MnTe, is predicted in terms of accurate +first-principles calculations. It has a large half-metallic (HM) gap of 0.54eV +and its ferrimagnetic order is very stable against other magnetic fluctuations. +The HM ferrimagnetism is formed because the complete moment compensation in the +antiferromagnetic MnTe is replaced by an uncomplete one in the Fe-substituted +MnTe. This should make a novel approach to new HM materials. The half-metal +could be fabricated because Fe has good affinity with Mn, and useful for +spintronics.",0811.2455v1 +2010-02-24,Evidence of Ferrimagnetism in Ferromagnetic La0_{67}Ca0_{33}MnO_3 nanoparticle,"The present report is dedicated to show that ferromagnetic La0.67Ca0.33MnO3 +(LCMN) particles can be better described in the framework of ferrimagnetic +model. To confirm the ferrimagnetic signature in ferromagnetic LCMN particles, +the temperature dependence of the inverse of magnetic susceptibility in the +paramagnetic state of the samples was taken as a tool of data analysis. The +observed ferrimagnetism is understood as an effect of of the core-shell spin +structure in LCMN particles.",1002.4574v2 +2013-01-21,Ferrimagnetism of dilute Ising antiferromagnets,"It is shown that nearest-neighbor antiferromagnetic interactions of identical +Ising spins on imbalanced bipartite lattice and imbalanced bipartite +hierarchical fractal result in ferrimagnetic order instead of antiferromagnetic +one. On some crystal lattices dilute Ising antiferromagnets may also become +ferrimagnets due to the imbalanced nature of the magnetic percolation cluster +when it coexists with the percolation cluster of vacancies. As evidenced by the +existing experiments on $Fe_pZn_{1-p}F_2$, such ferrimagnetism is inherent +property of bcc lattice so thermodynamics of these compounds at low $p$ can be +similar to that of antiferromagnet on imbalanced hierarchical fractal.",1301.4754v3 +2014-03-06,Spontaneously magnetized Tomonaga-Luttinger liquid in frustrated quantum antiferromagnets,"We develop a theory of spontaneously magnetized Tomonaga-Luttinger liquid +(SMTLL) in geometrically frustrated quasi-one-dimensional quantum magnets by +taking an $S=1/2$ ferrimagnet on a union-jack lattice as an example. We show +that a strong frustration leads to a spontaneous magnetization because of the +ferrimagnetic nature of lattice. Due to the ferrimagnetic order, the local +magnetization has an incommensurate oscillation with the position. We show that +the spontaneously magnetized TLL is smoothly connected to the existence of a +Nambu-Goldstone boson in the canted ferrimagnetic phase of a two-dimensional +frustrated antiferromagnet.",1403.1513v2 +2021-02-22,A review of modelling in ferrimagnetic spintronics,"In this review we introduce computer modelling and simulation techniques +which are used for ferrimagnetic materials. We focus on models where thermal +effects are accounted for, atomistic spin dynamics and finite temperature +macrospin approaches. We survey the literature of two of the most commonly +modelled ferrimagnets in the field of spintronics--the amorphous alloy GdFeCo +and the magnetic insulator yttrium iron garnet. We look at how generic models +and material specific models have been applied to predict and understand +spintronic experiments, focusing on the fields of ultrafast magnetisation +dynamics, spincaloritronics and magnetic textures dynamics and give an outlook +for modelling in ferrimagnetic spintronics.",2102.11004v1 +2012-08-31,Magnetic symmetry of the plain domain walls in the plates of cubic ferro- and ferrimagnets,"Magnetic symmetry of possible plane domain walls in arbitrary oriented plates +of the crystal of hexoctahedral crystallographic class is considered. The +symmetry classification is applied for ferro- and ferrimagnets.",1209.0004v1 +2023-04-26,Direct observation of Néel-type skyrmions and domain walls in a ferrimagnetic DyCo$_3$ thin film,"Isolated magnetic skyrmions are stable, topologically protected spin textures +that are at the forefront of research interests today due to their potential +applications in information technology. A distinct class of skyrmion hosts are +rare earth - transition metal (RE-TM) ferrimagnetic materials. To date, the +nature and the control of basic traits of skyrmions in these materials are not +fully understood. We show that for an archetypal ferrimagnetic material +DyCo$_3$ that exhibits a strong perpendicular anisotropy, the ferrimagnetic +skyrmion size can be tuned by an external magnetic field. Moreover, by taking +advantage of the high spatial resolution of scanning transmission X-ray +microscopy (STXM) and utilizing a large x-ray magnetic linear dichroism (XMLD) +contrast that occurs naturally at the RE resonant edges, we resolve the nature +of the magnetic domain walls of ferrimagnetic skyrmions. We demonstrate that +through this method one can easily discriminate between Bloch and N\'eel type +domain walls for each individual skyrmion. For all isolated ferrimagnetic +skyrmions, we observe that the domain walls are of N\'eel-type. This key +information is corroborated with results of micromagnetic simulations and +allows us to conclude on the nature of the Dzyaloshinskii-Moriya interaction +(DMI) which concurs to the stabilisation of skyrmions in this ferrimagnetic +system. Establishing that an intrinsic DMI occurs in RE-TM materials will also +be beneficial towards a deeper understanding of chiral spin texture control in +ferrimagnetic materials.",2304.13698v2 +2011-02-22,Frustration-Induced Ferrimagnetism in S=1/2 Heisenberg Spin Chain,"The ground-state properties of the S=1/2 frustrated Heisenberg spin chain +with interactions up to fourth nearest neighbors are investigated by the +exact-diagonalization method and density matrix renormalization group method. +Our numerical calculations clarify that the ferrimagnetic state is realized in +the ground state in spite of the fact that a multi-sublattice structure in the +shape of the system is absent. We find that there are two types of +ferrimagnetic phases: one is the well-known ferrimagnetic phase of the +Lieb-Mattis type and the other is the nontrivial ferrimagnetic phase that is +different from that of the Lieb-Mattis type. Our results suggest that a +multi-sublattice structure of the shape is not necessarily required for the +occurrence of ferrimagnetism.",1102.4414v1 +2011-12-07,Magnetization and spin gap in two-dimensional organic ferrimagnet BIPNNBNO,"A magnetization process in two-dimensional ferrimagnet BIPNNBNO is analyzed. +The compound consists of ferrimagnetic (1,1/2) chains coupled by two sorts of +antiferromagnetic interactions. Whereas a behavior of the magnetization curve +in higher magnetic fields can be understood within a process for the separate +ferrimagnetic chain, an appearance of the singlet plateau at lower fields is an +example of non-Lieb-Mattis type ferrimagnetism. By using the exact +diagonalization technique for a finite clusters of sizes 4x8 and 4x10 we show +that the interchain frustration coupling plays an essential role in +stabilization of the singlet phase. These results are complemented by an +analysis of four cylindrically coupled ferrimagnetic (1,1/2) chains via an +abelian bosonization technique and an effective theory based on the XXZ +spin-1/2 Heisenberg model when the interchain interactions are sufficiently +weak/strong, respectively.",1112.1646v1 +2015-03-02,Frustrated mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice,"Mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice with +sublattices A, B and C are studied for two spin value distributions $(S_{\rm +A},S_{\rm B},S_{\rm C})=(1/2,1/2,1)$ and $(1/2,1,1)$ by Monte Carlo +simulations. The non-bipartite character of the lattice induces geometrical +frustration in both systems, which leads to the critical behavior rather +different from their ferromagnetic counterparts. We confirm second-order phase +transitions belonging to the standard Ising universality class occurring at +higher temperatures, however, in both models these change at tricritical points +(TCP) to first-order transitions at lower temperatures. In the model +$(1/2,1/2,1)$, TCP occurs on the boundary between paramagnetic and +ferrimagnetic $(\pm 1/2,\pm 1/2,\mp 1)$ phases. The boundary between two +ferrimagnetic phases $(\pm 1/2,\pm 1/2,\mp 1)$ and $(\pm 1/2,\mp 1/2,0)$ at +lower temperatures is always first order and it is joined by a line of +second-order phase transitions between the paramagnetic and the ferrimagnetic +$(\pm 1/2,\mp 1/2,0)$ phases at a critical endpoint. The tricritical behavior +is also confirmed in the model $(1/2,1,1)$ on the boundary between the +paramagnetic and ferrimagnetic $(0,\pm 1,\mp 1)$ phases.",1503.00589v2 +2015-05-04,Spiral ferrimagnetic phases in the two-dimensional Hubbard model,"We address the possibility of spiral ferrimagnetic phases in the mean-field +phase diagram of the two-dimensional (2D) Hubbard model. For intermediate +values of the interaction $U$ ($6 \lesssim U/t \lesssim 11$) and doping $n$, a +spiral ferrimagnetic phase is the most stable phase in the $(n,U)$ phase +diagram. Higher values of $U$ lead to a non-spiral ferrimagnetic phase. If +phase separation is allowed and the chemical potential $\mu$ replaces the +doping $n$ as the independent variable, the $(\mu,U)$ phase diagram displays, +in a considerable region, a spiral (for $6 \lesssim U/t \lesssim 11$) and +non-spiral (for higher values of $U$) ferrimagnetic phase with fixed particle +density, $n=0.5$, reflecting the opening of an energy gap in the mean-field +quasi-particle bands.",1505.00583v1 +2019-05-06,Ground State Phases of Distorted $S=1$ Diamond Chains,"The ground states of distorted $S=1$ diamond chains are investigated for two +types of distortion called type A and B [J. Phys. Soc. Jpn. 79 (2010) 114703]. +For the type A distortion, Haldane phases with and without spontaneous +translational symmetry breakdown are present for large values of parameter +$\lambda$ that parametrize the strength of frustration. For small $\lambda$, +the Haldane phase and two quantized ferrimagnetic phases in the undistorted +chain remain stable even for strong distortion. In contrast, for the type B +distortion, the quantized ferrimagnetic phases with and without spontaneous +translational symmetry breakdown are present for large $\lambda$. The partial +ferrimagnetic phases emerge between them. For small $\lambda$, two quantized +ferrimagnetic phases remain and the partial ferrimagnetic phases also emerge +between them. The Haldane phase between the two kinds of ferrimagnetic phases +turns into a topologically trivial double Haldane phase for strong distortion.",1905.02117v2 +2019-11-01,Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys,"Skyrmions can be stabilized in magnetic systems with broken inversion +symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions +(DMI). Further, compensation of magnetic moments in ferrimagnetic materials can +significantly reduce magnetic dipolar interactions, which tend to favor large +skyrmions. Tuning DMI is essential to control skyrmion properties, with +symmetry breaking at interfaces offering the greatest flexibility. However, in +contrast to the ferromagnet case, few studies have investigated interfacial DMI +in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic +CoGd films by Brillouin light scattering. We demonstrate the ability to control +DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic +layer thickness. The DMI thickness dependence confirms its interfacial nature. +In addition, magnetic force microscopy reveals the ability to tune DMI in a +range that stabilizes sub-100 nm skyrmions at room temperature in zero field. +Our work opens new paths for controlling interfacial DMI in ferrimagnets to +nucleate and manipulate skyrmions.",1911.00607v1 +2021-04-30,Current-Induced Magnetization Control in Insulating Ferrimagnetic Garnets,"The research into insulating ferrimagnetic garnets has gained enormous +momentum in the past decade. This is partly due to the improvement in the +techniques to grow high-quality ultrathin films with desirable properties and +the advances in understanding the spin transport within the ferrimagnetic +garnets and through their interfaces with conducting materials. In recent +years, we have seen remarkable progress in controlling the magnetization state +of ferrimagnetic garnets by electrical means in suitable heterostructures and +device architectures. These advances have readily placed ferrimagnetic garnets +in a favorable position for the future development of insulating spintronic +concepts. The purpose of this article is to review recent experimental results +of the current-induced magnetization control and associated phenomena in +ferrimagnetic garnets, as well as to discuss future directions in this rapidly +evolving area of spintronics.",2104.14819v1 +2021-09-01,Epitaxial Integration of a Perpendicularly Magnetized Ferrimagnetic Metal on a Ferroelectric oxide for Electric-Field Control,"Ferrimagnets, which contain the advantages of both ferromagnets (detectable +moments) and antiferromagnets (ultrafast spin dynamics), have recently +attracted great attention. Here we report the optimization of epitaxial growth +of a tetragonal perpendicularly magnetized ferrimagnet Mn2Ga on MgO. Electrical +transport, magnetic properties and the anomalous Hall effect (AHE) were +systematically studied. Furthermore, we successfully integrated high-quality +epitaxial ferrimagnetic Mn2Ga thin films onto ferroelectric PMN-PT single +crystals with a MgO buffer layer. It was found that the AHE of such a +ferrimagnet can be effectively modulated by a small electric field over a large +temperature range in a nonvolatile manner. This work thus demonstrates the +great potential of ferrimagnets for developing high-density and low-power +spintronic devices.",2109.00169v1 +2021-11-23,Dynamics of ferrimagnetic skyrmionium driven by spin-orbit torque,"Magnetic skyrmionium is a skyrmion-like spin texture with nanoscale size and +high mobility. It is a topologically trivial but dynamically stable structure, +which can be used as a non-volatile information carrier for next-generation +spintronic storage and computing devices. Here, we study the dynamics of a +skyrmionium driven by the spin torque in a ferrimagnetic nanotrack. It is found +that the direction of motion is jointly determined by the internal +configuration of a skyrmionium and the spin polarization vector. Besides, the +deformation of a skyrmionium induced by the intrinsic skyrmion Hall effect +depends on both the magnitude of the driving force and the net angular +momentum. The ferrimagnetic skyrmionium is most robust at the angular momentum +compensation point, whose dynamics is quite similar to the skyrmionium in +antiferromagnet. The skyrmion Hall effect is perfectly prohibited, where it is +possible to observe the position of the skyrmionium by measuring the +magnetization. Furthermore, the current-induced dynamics of a ferrimagnetic +skyrmionium is compared with that of a ferromagnetic and antiferromagnetic +skyrmionium. We also make a comparison between the motion of a ferrimagnetic +skyrmionium and a skyrmion. Our results will open a new field of ferrimagnetic +skyrmioniums for future development of ferrimagnetic spintronics devices.",2111.11603v1 +2022-07-21,Unusual ferrimagnetism in CaFe2O4,"Incomplete cancellation of collinear antiparallel spins gives rise to +ferrimagnetism. Even if the oppositely polarized spins are owing to the equal +number of a single magnetic element having the same valence state, in +principle, a ferrimagnetic state can still arise from the crystallographic +inequivalence of the host ions. However, experimental identification of such a +state as ferrimagnetic is not straightforward because of the tiny magnitude +expected for M and the requirement for a sophisticated technique to +differentiate similar magnetic sites. We report a synchrotron-based resonant +x-ray investigation at the Fe L2,3 edges on an epitaxial film of CaFe2O4, which +exhibits two magnetic phases with similar energies. We find that while one +phase of CaFe2O4 is antiferromagnetic, the other one is ferrimagnetic with an +antiparallel arrangement of an equal number of spins between two distinct +crystallographic sites with very similar local coordination environments. Our +results further indicate two distinct origins of an overall minute M; one is +intrinsic, from distinct Fe3+ sites, and the other one is extrinsic, arising +from defective Fe2+ likely forming weakly-coupled ferrimagnetic clusters. These +two origins are uncorrelated and have very different coercive fields. Hence, +this work provides a direct experimental demonstration of ferrimagnetism solely +due to crystallographic inequivalence of the Fe3+ as the origin of the weak M +of CaFe2O4.",2207.10775v1 +2000-08-10,Thermal properties of ferrimagnetic systems,"The heat capacity of some ferrimagnets has additional structures like a +shoulder in the Schottky-like peak, or emergence of a second peak when an +external magnetic field is applied. It is shown here that as long as spin +wave-spin wave interactions are ignored in a ferrimagnet, the ferromagnetic and +antiferromagnetic elementary excitation spectra give rise to two independent +heat capacity peaks, one enveloped by the other, which add up to give the peak +for the total system. Taking this into account helps understand the additional +structures in the peaks. Moreover, the classification of ferrimagnets into +predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is +shown to be validated by studying them under additional influences like +dimerization and frustration. Because these two are shown to influence the +ferromagnetic and antiferromagnetic dispersion relations - and hence the +quantities like heat capacity and magnetic susceptibility - by different +amounts, the characterisation of ferrimagnetic systems ($1,1/2$), ($3/2,1$) and +($3/2,1/2$) is brought out more clearly. Both these influences enhance +antiferromagnetic character.",0008167v1 +2000-11-22,Collective excitations in ferrimagnetic Heisenberg ladders,"We study ground-state properties and the low-lying excitations of Heisenberg +spin ladders composed of two ferrimagnetic chains with alternating site spins +$(S_1>S_2)$ by using the bosonic Dyson-Maleev formalism and Lanczos numerical +techniques. The emphasis is on properties of the ferrimagnetic phase which is +stable for antiferromagnetic interchain couplings $J_{\perp}\geq 0$. There are +two basic implications of the underlying lattice structure: (i) the spin-wave +excitations form folded acoustic and optical branches in the extended Brillouin +zone and (ii) the ground state parameters (such as the on-site magnetizations +and spin-stiffness constant) show a crossover behavior in the weak-coupling +region $0 Js$. We then extend our approach to a system of interacting ferrimagnetic +molecules. For one dimensional nearest neighbor interaction we have observed +that the correlation of more than two neighboring sites is negligible at +moderate and high temperature behavior. Thus the results of a single molecule +can be applied to the chain of interacting molecules for temperatures greater +than classical energy scale, i.e $T>JS_1s_2$. Finally we will discuss the +effect of spin inhomogeneity on the accuracy of this method.",0409293v1 +2006-10-24,Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation,"The ground state properties of the high spin Heisenberg chains with +alternating single site anisotropy are investigated by means of the numerical +exact daigonaization and DMRG method. It is found that the ferrimagnetic state +appears between the Haldane phase and period doubled N\'eel phase for the +integer spin chains. On the other hand, the transition from the +Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for +the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous +magnetization varies continuously with the modulation amplitude of the single +site anisotropy. Eventually, the magnetization is locked to fractional values +of the saturated magnetization. These fractional values satisfy the +Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to +reveal the physical nature of each state. In contrast to the case of +frustration induced ferrimagnetism, no incommensurate magnetic superstructure +is found.",0610660v1 +2010-02-24,Magnetic Structure of CaBaCo4O7: Lifting of Geometrical Frustration towards Ferrimagnetism,"CaBaCo4O7 represents a new class of ferrimagnets whose structure is built up +of CoO4 tetrahedra only, similarly to other members LnBaCo4O7 of the 114 +series, forming an alternate stacking of kagome and triangular layers. Neutron +powder diffraction reveals, that this compound exhibits the largest distortion +within the 114 series, characterized by a strong buckling of the kagome layers. +Differently from all other members it shows charge ordering, with Co2+ sitting +on two sites (Co2, Co3) and mixed valent cobalt Co3+/Co2+L sitting on two other +sites (Co1, Co4). The unique ferrimagnetic structure of this cobaltite at 4 K +can be described as the assemblage of ferrimagnetic triple chains (Co1 Co2 Co3) +running perpendicular to the kagome layers, ferromagnetically coupled within +the layers, and antiferromagnetically coupled with a fourth cobalt species Co4. +The lifting of the geometrical frustration towards ferrimagnetism, which +appears in spite of the triangular topology of the cobalt lattice, is explained +by the very large structural distortion, charge ordering phenomena and large +cobalt valence compared to other LnBaCo4O7 oxides.",1002.4544v1 +2016-07-13,"Breakdown of a Magnetization Plateau in Ferrimagnetic Mixed Spin-(1/2,S) Heisenberg Chains Due to a Quantum Phase Transition Towards the Luttinger Spin Liquid","Magnetization curves of the ferrimagnetic mixed spin-(1/2,S) Heisenberg +chains are calculated with the help of density-matrix renormalization group +method for several quantum spin numbers S=1, 3/2, 2 and 5/2. It is shown that +the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains exhibit irrespective of +the spin value S exactly one intermediate magnetization plateau, which can be +identified with the gapped Lieb-Mattis ferrimagnetic ground state. The +magnetization plateau due to the Lieb-Mattis ferrimagnetism breaks down at a +quantum phase transition towards the Luttinger spin liquid, which is +characterized by a continuous change of the magnetization with the magnetic +field until another quantum critical point is reached at the saturation field.",1607.03617v1 +2017-03-24,Anomalous current-induced spin torques in ferrimagnets near compensation,"While current-induced spin-orbit torques (SOTs) have been extensively studied +in ferromagnets and antiferromagnets, ferrimagnets have been less studied. Here +we report the presence of enhanced spin-orbit torques resulting from negative +exchange interaction in ferrimagnets. The effective field and switching +efficiency increase substantially as CoGd approaches its compensation point, +giving rise to 9 times larger spin-orbit torques compared to that of +non-compensated one. The macrospin modelling results also support efficient +spin-orbit torques in a ferrimagnet. Our results suggest that ferrimagnets near +compensation can be a new route for spin-orbit torque applications due to their +high thermal stability and easy current-induced switching assisted by negative +exchange interaction.",1703.08263v1 +2016-12-19,Completely compensated ferrimagnetism and sublattice spin crossing in the half-metallic Heusler compound Mn1.5FeV0.5Al,"The Slater-Pauling rule states that L21 Heusler compounds with 24 valence +electrons do never exhibit a total spin magnetic moment. In case of strongly +localized magnetic moments at one of the atoms (here Mn) they will exhibit a +fully compensated half-metallic ferrimagnetic state instead, in particular, +when symmetry does not allow for antiferromagnetic order. With aid of magnetic +and anomalous Hall effect measurements it is experimentally demonstrated that +Mn1.5V0.5FeAl follows such a scenario. The ferrimagnetic state is tuned by the +composition. A small residual magnetization, that arises due to a slight +mismatch of the magnetic moments in the different sublattices results in a +pronounced change of the temperature dependence of the ferrimagnet. A +compensation point is confirmed by observation of magnetic reversal and sign +change of the anomalous Hall effect. Theoretical models are presented that +correlate the electronic structure and the compensation mechanisms of the +different half-metallic ferrimagnetic states in the Mn-V-Fe-Al Heusler system.",1612.06300v1 +2018-10-01,Stabilizing Mechanism for Bose-Einstein Condensation of Interacting Magnons in Ferrimagnets and Ferromagnets,"We propose a stabilizing mechanism for the Bose-Einstein condensation (BEC) +of interacting magnons in ferrimagnets and ferromagnets. By studying the +effects of the magnon-magnon interaction on the stability of the magnon BEC in +a ferrimagnet and two ferromagnets, we show that the magnon BEC remains stable +even in the presence of the magnon-magnon interaction in the ferrimagnet and +ferromagnet with a sublattice structure, whereas it becomes unstable in the +ferromagnet without a sublattice structure. This indicates that the existence +of a sublattice structure is the key to stabilizing the BEC of interacting +magnons, and the difference between the spin alignments of a ferrimagnet and a +ferromagnet is irrelevant. Our result can resolve a contradiction between +experiment and theory in the magnon BEC of yttrium iron garnet. Our theoretical +framework may provide a starting point for understanding the physics of the +magnon BEC including the interaction effects.",1810.00584v2 +2019-07-10,Temperature dependence of magnetic resonance in ferrimagnetic GdFeCo alloys,"We provide a macroscopic theory and experimental results for magnetic +resonances of antiferromagnetically-coupled ferrimagnets. Our theory, which +interpolates the dynamics of antiferromagnets and ferromagnets smoothly, can +describe ferrimagnetic resonances across the angular momentum compensation +point. We also present experimental results for spin-torque induced +ferrimagnetic resonance at several temperatures. The spectral analysis based on +our theory reveals that the Gilbert damping parameter, which has been +considered to be strongly temperature dependent, is insensitive to temperature. +We envision that our work will facilitate further investigation of +ferrimagnetic dynamics by providing a theoretical framework suitable for a +broad range of temperatures.",1907.04540v1 +2018-12-03,"Mn2V0.5Co0.5Z (Z= Ga, Al) Heusler alloys: Fully compensated ferrimagnets with high Tc and compensation temperature","High TC fully compensated ferrimagnets are potential candidates for spin +transfer torque based spintronic devices. We report the structural and magnetic +properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is +Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent +alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value +around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly +fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and +ribbon form respectively. For Mn2V0.5Co0.5Al this turned out to be 0.04 and +0.08 muB per f.u. In Contrast to the bulk sample's Neel P type ferrimagnetic +behaviour, ribbon samples exhibit Neel N type ferrimagnetic characteristic with +a high compensation temperature of 420 K for Ga alloy and 275 K for Al alloy. +The observed TC values are more than 640 K for all samples. The differences in +the magnetic properties of arc melted and melt spun alloys indicates that even +a slight variation in stoichiometry and sample preparation method can influence +the physical properties of a compensated system.",1812.00714v1 +2021-07-16,Influence of inter-sublattice coupling on the terahertz nutation spin dynamics in antiferromagnets,"Spin nutation resonance has been well-explored in one-sublattice +ferromagnets. Here, we investigate the spin nutation in two-sublattice +antiferromagnets as well as, for comparison, ferrimagnets with inter-and +intra-sublattice nutation coupling. In particular, we derive the susceptibility +of the two-sublattice magnetic system in response to an applied external +magnetic field. To this end, the antiferromagnetic and ferrimagnetic (sub-THz) +precession and THz nutation resonance frequencies are calculated. Our results +show that the precession resonance frequencies and effective damping decrease +with intra-sublattice nutation coupling, while they increase with inter +-sublattice nutation in an antiferromagnet. However, we find that the THz +nutation resonance frequencies decrease with both the intra-and +inter-sublattice nutation couplings. For ferrimagnets, conversely, we calculate +two nutation modes with distinct frequencies, unlike antiferromagnets. The +exchange-like precession resonance frequency of ferrimagnets decreases with +intra-sublattice nutation coupling and increases with inter-sublattice nutation +coupling, like antiferromagnets, but the ferromagnetic-like precession +frequency of ferrimagnets is practically invariant to the intra and +inter-sublattice nutation couplings.",2107.07939v2 +2021-11-16,Ultrathin ferrimagnetic GdFeCo films with very low damping,"Ferromagnetic materials dominate as the magnetically active element in +spintronic devices, but come with drawbacks such as large stray fields, and low +operational frequencies. Compensated ferrimagnets provide an alternative as +they combine the ultrafast magnetization dynamics of antiferromagnets with a +ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets +in spintronic devices their advantageous properties must be retained also in +ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x +thin films in the thickness range t = 2-20 nm were grown on high resistance +Si(100) substrates and studied using broadband ferromagnetic resonance +measurements at room temperature. By tuning their stoichiometry, a nearly +compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films +for the first time, with an effective magnetization of Meff = 0.02 T and a low +effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the +lowest values reported so far in 30 nm films. These results show great promise +for the development of ultrafast and energy efficient ferrimagnetic spintronic +devices.",2111.08768v1 +2023-07-02,"Giant coercivity, resistivity upturn, and anomalous Hall effect in ferrimagnetic FeTb","Despite the blooming interest, the transition-metal rare-earth ferrimagnets +have not been comprehensively understood in terms of their coercivity and +transport properties. Here, we report a systematic study of the magnetic and +transport properties of ferrimagnetic FeTb alloy by varying the layer thickness +and temperature. The FeTb is tuned from the Tb-dominated regime to the +Fe-dominated regime via the layer thickness, without varying the composition. +The coercivity closely follows the $1/\cos\theta_H$ scaling (where $\theta_H$ +is the polar angle of the external magnetic field) and increases +quasi-exponentially upon cooling (exceeding 90 kOe at low temperatures), +revealing that the nature of the coercivity is the thermally-assisted domain +wall depinning field. The resistivity exhibits a quasi-linear upturn upon +cooling possibly due to thermal vibrations of the structure factor of the +amorphous alloy. The existing scaling laws of the anomalous Hall effect in the +literature break down for the amorphous FeTb that are either Fe- or +Tb-dominated. These findings should advance the understanding of the +transition-metal-rare-earth ferrimagnets and the associated ferrimagnetic +phenomena in spintronics.",2307.00475v1 +2023-12-27,Sublattice-selective inverse Faraday effect in ferrimagnetic rare-earth iron garnet,"We performed time-resolved pump--probe measurements using rare-earth iron +garnet \ce{Gd3/2Yb1/2BiFe5O12} as a two-sublattice ferrimagnet. We measured the +initial phases of the magnetic resonance modes below and above the +magnetization compensation temperature to clarify the sublattice selectivity of +the inverse Faraday effect in ferrimagnets. A comparison of the time evolution +of magnetization estimated using the equations of motion revealed that the +inverse Faraday effect occurring in ferrimagnetic materials has sublattice +selectivity. This is in striking contrast to antiferromagnets, in which the +inverse Faraday effect acts on each sublattice identically. The initial phase +analysis can be applied to other ferrimagnets with compensation temperatures.",2312.16553v1 +2024-02-07,Quantum Theory of Spin-Transfer and Spin-Pumping in Collinear Antiferromagnets and Ferrimagnets,"Antiferromagnets are promising candidates as active components in spintronic +applications. They share features with ferrimagnets in that opposing spin +orientations exist in two or more sublattices. Spin transfer torque and spin +pumping are essential ingredients in antiferromagnetic and ferrimagnet +spintronics. This paper develops an out-of-equilibrium quantum theory of the +spin dynamics of collinear magnets containing many spins coupled to normal +metal reservoirs. At equilibrium, the spins are parallel or antiparallel to the +easy axis. The theory, therefore, covers collinear antiferromagnets and +ferrimagnets. We focus on the resulting semi-classical spin dynamics. The +dissipation in the spin dynamics is enhanced due to spin-pumping. Spin +accumulations in the normal metals induce deterministic spin-transfer torques +on the magnet. Additionally, each electron's discrete spin angular momentum +causes stochastic fluctuating torques on the antiferromagnet or ferrimagnet. We +derive these fluctuating torques. The fluctuation-dissipation theorem holds at +high temperatures, including the effects of spin-pumping. At low temperatures, +we derive shot noise contributions to the fluctuations.",2402.04719v1 +1995-09-13,Numerical Study of a Mixed Ising Ferrimagnetic System,"We present a study of a classical ferrimagnetic model on a square lattice in +which the two interpenetrating square sublattices have spins one-half and one. +This model is relevant for understanding bimetallic molecular ferrimagnets that +are currently being synthesized by several experimental groups. We perform +exact ground-state calculations for the model and employ Monte Carlo and +numerical transfer-matrix techniques to obtain the finite-temperature phase +diagram for both the transition and compensation temperatures. When only +nearest-neighbor interactions are included, our nonperturbative results +indicate no compensation point or tricritical point at finite temperature, +which contradicts earlier results obtained with mean-field analysis.",9509076v1 +1997-12-01,Spin-wave series for quantum one-dimensional ferrimagnets,"Second-order spin-wave expansions are used to compute the ground-state energy +and sublattice magnetizations of the quantum one-dimensional Heisenberg +ferrimagnet with nearest-neighbor antiferromagnetic interactions and two types +of alternating sublattice spins $S_1>S_2$. It is found that in the extreme +quantum cases $(S_1,S_2)=(1,1/2)$, $(3/2,1)$, and $(3/2,1/2)$, the estimates +for the ground-state energy and sublattice magnetizations differ less than +0.03% for the energy and 0.2% for the sublattice magnetizations from the +recently published density matrix renormalization group numerical calculations. + The reported results strongly suggest that the quantum Heisenberg +ferrimagnetic chains give another example of a low-dimensional quantum spin +system where the spin-wave approach demonstrates a surprising efficiency.",9712014v1 +1999-10-07,Phase diagram of ferrimagnetic ladders with bond-alternation,"We study the phase diagram of a 2-leg bond-alternation spin-(1/2, 1) ladder +for two different configurations using a quantum renormalization group +approach. Although d-dimensional ferrimagnets show gapless behavior, we will +explicitly show that the effect of the spin mixing and the bond-alternation can +open the possibility for observing an energy gap. We show that the gapless +phases of such systems can be equivalent to the 1-dimensional half-integer +antiferroamgnets, besides the gapless ferrimagnetic phases. We therefore +propose a phase transition between these two gapless phases that can be seen in +the parameter space.",9910103v1 +2000-01-31,Magnon dispersions in quantum Heisenberg ferrimagnetic chains at zero temperature,"Within the Dyson-Maleev boson formalism, we study the zero-temperature magnon +dispersions in a family of one-dimensional quantum Heisenberg ferrimagnets +composed of two different spins $(S_1,S_2)$ in the elementary cell. It is shown +that the spin-wave theory can produce precise quantitative results for the +low-energy excitations. The spin-stiffness constant $\rho_s$ and the optical +magnon gap $\Delta$ of different $(S_1,S_2)$ ferrimagnetic systems are +calculated, respectively, to second and third order in the quasiparticle +interaction. The spin-wave results are compared with available numerical +estimates.",0001441v1 +2000-07-26,First- and second-order transitions of the escape rate in ferrimagnetic or antiferromagnetic particles,"Quantum-classical escape-rate transition has been studied for two general +forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles. +It is found that the range of the first-order transition is greatly reduced as +the system becomes ferrimagnetic and there is no first-order transition in +almost compensated antiferromagnetic particles. These features can be tested +experimentally in nanomagnets like molecular magnets.",0007406v1 +2005-12-24,Modified spin-wave theory of nuclear magnetic relaxation in one-dimensional quantum ferrimagnets: Three-magnon versus Raman processes,"Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is +studied by means of a modified spin-wave theory. Calculating beyond the +first-order mechanism, where a nuclear spin directly interacts with spin waves +through the hyperfine coupling, we demonstrate that the +exchange-scattering-enhanced three-magnon nuclear relaxation may generally +predominate over the Raman one with increasing temperature and decreasing +field. Recent proton spin-lattice relaxation-time (T_1_) measurements on the +ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O suggest +that the major contribution to 1/T_1_ be made by the three-magnon scattering.",0512629v1 +2006-07-25,Quantum Hall Ferrimagnetism in lateral quantum dot molecules,"We demonstrate the existance of ferrimagnetic and ferromagnetic phases in a +spin phase diagram of coupled lateral quantum dot molecules in the quantum Hall +regime. The spin phase diagram is determined from Hartree-Fock Configuration +Interaction method as a function of electron numbers N, magnetic field B, +Zeeman energy, and tunneling barrier height. The quantum Hall ferrimagnetic +phase corresponds to spatially imbalanced spin droplets resulting from strong +inter-dot coupling of identical dots. The quantum Hall ferromagnetic phases +correspond to ferromagnetic coupling of spin polarization at filling factors +between $\nu=2$ and $\nu=1$.",0607638v1 +1995-07-19,On behaviour of critical lines near ferrimagnetic phase in Higgs-Yukawa systems,"We calculate within a mean-field approximation the slopes of the critical +lines near the point of appearing the ferrimagnetic phase for the U(1) systems +in the weak coupling regime. It is demonstrated that the slope of one of the +critical line is continuous, while change of the slope of the other depends +strongly on the number of the fermion flavours. We also find that in the +ferrimagnetic phase near such a point the magnetization and the staggered +magnetization align orthogonally to each other.",9507019v1 +2006-04-13,Thermal Entanglement in Ferrimagnetic Chains,"A formula to evaluate the entanglement in an one-dimensional ferrimagnetic +system is derived. Based on the formula, we find that the thermal entanglement +in a small size spin-1/2 and spin-s ferrimagnetic chain is rather robust +against temperature, and the threshold temperature may be arbitrarily high when +s is sufficiently large. This intriguing result answers unambiguously a +fundamental question: ``can entanglement and quantum behavior in physical +systems survive at arbitrary high temperatures?""",0604099v1 +2008-08-28,Magnetoelectric coupling in the cubic ferrimagnet Cu2OSeO3,"We have investigated the magnetoelectric coupling in the lone pair containing +piezoelectric ferrimagnet Cu2OSeO3. Significant magnetocapacitance develops in +the magnetically ordered state (TC = 60 K). We find critical behavior near TC +and a divergence near the metamagnetic transition at 500 Oe. High-resolution +X-ray and neutron powder diffraction measurements show that Cu2OSeO3 is +metrically cubic down to 10 K but that the ferrimagnetic ordering reduces the +symmetry to rhombohedral R3. The metric cubic lattice dimensions exclude a +magnetoelectric coupling mechanism involving spontaneous lattice strain, and +this is unique among magnetoelectric and multiferroic materials.",0808.3955v1 +2008-10-22,"Study of the mixed Ising spins (1/2,3/2) in a random crystal field","We study the magnetic properties of a mixed Ising ferrimagnetic system, in +which the two interacting sublattices have spins $\sigma$, $(\pm 1/2)$ and +spins $S$, $(\pm 3/2,\pm 1/2)$ in the presence of a random crystal field, with +the mean field approach. The obtained results show the existence of some +interesting phenomena, such as the appearance of a new ferrimagnetic phase +namely the partly ferrimagnetic phase $(m_{\sigma}=\frac{-1}{2},m_S=+1)$ and +consequently the existence of three topologically different types of phase +diagrams. The effect of increasing the exchange interaction parameter $J$, at +very low temperature is investigated. The transitions shown in these phase +diagrams are in good agreement with those obtained in the ground state case.",0810.4128v1 +2010-04-26,Andreev reflection in ferrimagnetic CoFe2O4/SrRuO3 spin filters,"We have performed point contact spectroscopy measurements on a sample +constituted by a metallic ferromagnetic oxide (SrRuO_3) bottom electrode and a +tunnel ferrimagnetic (CoFe_2O_4) barrier. Andreev reflection is observed across +the tunnel barrier. From the comparison of Andreev reflection in SrRuO3 and +across the CoFe_2O_4 barrier we infer that the ferrimagnetic barrier has a spin +filter efficiency not larger than +13%. The observation of a moderate and +positive spin filtering is discussed in the context of the microstructure of +the barriers and symmetry-related spin filtering effects.",1004.4631v1 +2011-04-20,Magnetic properties of the ferrimagnetic cobaltite CaBaCo4O7,"The magnetic properties of the ferrimagnetic cobaltite CaBaCo$_4$O$_7$ are +systematically investigated. We find that the susceptibility exhibits a +downward deviation below $\sim$ 360 K, suggesting the occurrence of short range +magnetic correlations at temperature well above $T_C$. The effective moment is +determined to be 4.5 $\mu_B$/f.u, which is consistent with that expected for +the Co$^{2+}$/Co$^{3+}$ high spin species. Using a criterion given by Banerjee +[Phys. Lett. \textbf{12}, 16 (1964)], we demonstrate that the paramagnetic to +ferrimagnetic transition in CaBaCo$_4$O$_7$ has a first order character.",1104.4032v1 +2012-07-17,Ultrafast dynamical path for the switching of a ferrimagnet after femtosecond heating,"Ultrafast laser-induced magnetic switching in rare earth, transition metal +ferrimagnetic alloys has recently been reported to occur by ultrafast heating +alone. Using atomistic simulations and a ferrimagnetic Landau-Lifshitz-Bloch +formalism, we demonstrate that for switching to occur it is necessary that +angular momentum is transferred from the longitudinal to transverse +magnetization components. This dynamical path leads to magnetization switching +and subsequent ultrafast precession caused by the inter-sublattice exchange +field on the nanoscale.",1207.4092v2 +2012-10-24,Dirac half-metal in a triangular ferrimagnet,"An idea is proposed for realizing a fully spin-polarized Dirac semimetal in +frustrated itinerant magnets. We show that itinerant electrons on a triangular +lattice exhibit the Dirac cone dispersion with half-metallic behavior in the +presence of a three-sublattice ferrimagnetic order. The Dirac nodes have the +same structure as those of graphene. By variational calculation and Monte Carlo +simulation, we demonstrate that the ferrimagnetic order with the Dirac node +spontaneously emerges in a simple Kondo lattice model with Ising anisotropy. +The realization will be beneficial for spintronics as a candidate for +spin-current generator.",1210.6700v1 +2012-12-25,Magnetization process in the exactly solved spin-1/2 Ising-Heisenberg model on decorated Bethe lattices,"The spin-1/2 Ising-Heisenberg model on diamond-like decorated Bethe lattices +is exactly solved in the presence of the longitudinal magnetic field by +combining the decoration-iteration mapping transformation with the method of +exact recursion relations. In particular, the ground state and low-temperature +magnetization process of the ferrimagnetic version of the considered model is +investigated in detail. Three different magnetization scenarios with up to two +consecutive fractional magnetization plateaus were found, whereas the +intermediate magnetization plateau may either correspond to the classical +ferrimagnetic spin arrangement and/or the field-induced quantum ferrimagnetic +spin ordering without any classical counterpart.",1212.6032v1 +2016-02-06,Lieb-Mattis ferrimagnetism in diluted magnetic semiconductors,"We show the possibility of long-range ferrimagnetic ordering with a +saturation magnetisation of the order of 1 Bohr magneton per spin for +arbitrarily low concentration of magnetic impurities in semiconductors, +provided that the impurities form a superstructure satisfying the conditions of +the Lieb-Mattis theorem. Explicit examples of such superstructures are given +for the wurtzite lattice, and the temperature of ferrimagnetic transition is +estimated from a high-temperature expansion. Exact diagonalization studies show +that small fragments of the structure exhibit enhanced magnetic response and +isotropic superparamagnetism at low temperatures. A quantum transition in a +high magnetic field is considered and similar superstructures in cubic +semiconductors are discussed as well.",1602.02239v1 +2019-05-29,Spin wave propagation in ferrimagnetic $Gd_{x}Co_{1-x}$,"Recent advances in antiferromagnetic spin dynamics using rare-earth (RE) and +transition-metal (TM) ferrimagnets have attracted much interest for spintronic +devices with a high speed and density. In this study, the spin wave properties +in the magnetostatic backward volume mode and surface mode in RE-TM +ferrimagnetic $Gd_{x}Co_{1-x}$ films with various composition x are +investigated using spin wave spectroscopy. The obtained group velocity and +attenuation length are well explained by the ferromagnet-based spin wave theory +when the composition of $Gd_{x}Co_{1-x}$ is far from the compensation point.",1905.12771v1 +2011-11-15,Frustration-Induced Ferrimagnetism in Heisenberg Spin Chains,"We study ground-state properties of the Heisenberg frustrated spin chain with +interactions up to fourth nearest neighbors by the exact-diagonalization method +and the density matrix renormalization group method. We find that +ferrimagnetism is realized not only in the case of S=1/2 but also S=1 despite +that there is only a single spin site in each unit cell determined from the +shape of the Hamiltonian. Our numerical results suggest that a +""multi-sublattice structure"" is not required for the occurrence of +ferrimagnetism in quantum spin systems with isotropic interactions.",1111.3430v1 +2019-09-19,Magnetization dynamics of the compensated ferrimagnet $Mn_{2}Ru_{x}Ga$,"Here we study both static and time-resolved dynamic magnetic properties of +the compensated ferrimagnet from room temperature down to 10K, thus crossing +the magnetic compensation temperature $T_{M}$. The behaviour is analysed with a +model of a simple collinear ferrimagnet with uniaxial anisotropy and +site-specific gyromagnetic ratios. We find a maximum zero-applied-field +resonance frequency of $\sim$160GHz and a low intrinsic Gilbert damping +$\alpha$$\sim$0.02, making it a very attractive candidate for various +spintronic applications.",1909.09085v1 +2021-01-18,Quantum fluctuation effects on the ordered Moments in a two dimensional frustrated ferrimagnet,"We propose a novel two-dimensional (2D)frustrated quantum spin-1/2 +anisotropic Heisenberg model with alternating ferromagnetic and +antiferromagnetic magnetic chains along one direction and antiferromagnetic +interactions along the other. The (mean-field) ground state is ferrimagnetic in +certain range of the interaction space. Spin-wave theory analysis of the +reduction of ordered moments at inequivalent spin sites and the instability of +the spin waves suggest a quantum phase transition which has the characteristics +of both the frustrated two-dimensional antiferromagnetic S=1/2 ($J_1, J_2$) +model and 1D S$_1$=1, S$_2$=1/2 quantum ferrimagnetic model.",2101.07300v1 +2019-08-19,Amorphous Ferrimagnets: an Ideal Host for Ultra-Small Skyrmions at Room Temperature,"Recently, magnetic skyrmion has emerged as an active topic of fundamental +study and applications in magnetic materials research. Magnetic skyrmions are +vortex-like spin excitations with topological protection and therefore are more +robust to pinning compared with magnetic domain walls. We employ atomistic +simulations to create room-temperature ultra-small Neel skyrmions in amorphous +ferrimagnet. The fast propagation and low-dissipation dynamics of ultra-small +ferrimagnetic skyrmions make them attractive for utilization as an alternative +to domain walls in spin-based memory and logic devices.",1908.07003v2 +2022-07-30,On field-driven domain wall motion in compensated ferrimagnetic nanowires,"The fascinating high-speed field-driven domain wall (DW) motion along +ferrimagnetic nanowires near the angular momentum compensation point (AMCP) is +solved based on the generic ferrimagnetic dynamics. The physics of the absences +of precessional torque and infinite high Walker breakdown field at the AMCP is +proved under general conditions. Based on the energy conservation principle, an +almost exact DW velocity formula, valid beyond the Walker breakdown field, is +obtained. Our results agree with all existing experiments and simulations. This +theory provides useful guidances to DW manipulation.",2208.00179v1 +2023-07-28,Analysis of magneto-optical Kerr spectra of ferrimagnetic Mn$_4$N,"Simulations of magneto-optical Kerr effect in biaxially strained Mn$_4$N are +performed using density functional theory and linear response theory. We +consider three ferrimagnetic phases, two collinear and one noncollinear, which +have been corroborated separately by earlier studies. The simulated spectra are +compared to magneto-optical data available in recent literature. A collinear +ferrimagnetic phase with a small saturation magentization, a large +perpendicular anisotropy, and Curie temperature above 700~K is found to be +consistent with the measured spectra. We hypothesise that an admixture of the +noncollinear phase, which could explain the lower than predicted net moment and +magnetic anisotropy observed experimentally, is also present.",2307.15246v1 +2001-05-05,"Spin, charge and orbital ordering in ferrimagnetic insulator YBaMn$_2$O$_5$","The oxygen-deficient (double) perovskite YBaMn$_2$O$_5$, containing +corner-linked MnO$_5$ square pyramids, is found to exhibit ferrimagnetic +ordering in its ground state. In the present work we report +generalized-gradient-corrected, relativistic first-principles full-potential +density-functional calculations performed on YBaMn$_2$O$_5$ in the nonmagnetic, +ferromagnetic and ferrimagnetic states. The charge, orbital and spin orderings +are explained with site-, angular momentum- and orbital-projected density of +states, charge-density plots, electronic structure and total energy studies. +YBaMn$_2$O$_5$ is found to stabilize in a G-type ferrimagnetic state in +accordance with experimental results. The experimentally observed insulating +behavior appears only when we include ferrimagnetic ordering in our +calculation. We observed significant optical anisotropy in this material +originating from the combined effect of ferrimagnetic ordering and crystal +field splitting. In order to gain knowledge about the presence of different +valence states for Mn in YBaMn$_2$O$_5$ we have calculated $K$-edge x-ray +absorption near-edge spectra for the Mn and O atoms. The presence of the +different valence states for Mn is clearly established from the x-ray +absorption near-edge spectra, hyperfine field parameters and the magnetic +properties study. Among the experimentally proposed structures, the recently +reported description based on $P$4/$nmm$ is found to represent the stable +structure.",0105117v1 +2017-03-22,Fast domain wall motion induced by antiferromagnetic spin dynamics at the angular momentum compensation temperature of ferrimagnets,"Antiferromagnetic spintronics is an emerging research field which aims to +utilize antiferromagnets as core elements in spintronic devices. A central +motivation toward this direction is that antiferromagnetic spin dynamics is +expected to be much faster than ferromagnetic counterpart because +antiferromagnets have higher resonance frequencies than ferromagnets. Recent +theories indeed predicted faster dynamics of antiferromagnetic domain walls +(DWs) than ferromagnetic DWs. However, experimental investigations of +antiferromagnetic spin dynamics have remained unexplored mainly because of the +immunity of antiferromagnets to magnetic fields. Furthermore, this immunity +makes field-driven antiferromagnetic DW motion impossible despite rich physics +of field-driven DW dynamics as proven in ferromagnetic DW studies. Here we show +that fast field-driven antiferromagnetic spin dynamics is realized in +ferrimagnets at the angular momentum compensation point TA. Using rare-earth +3d-transition metal ferrimagnetic compounds where net magnetic moment is +nonzero at TA, the field-driven DW mobility remarkably enhances up to 20 km/sT. +The collective coordinate approach generalized for ferrimagnets and atomistic +spin model simulations show that this remarkable enhancement is a consequence +of antiferromagnetic spin dynamics at TA. Our finding allows us to investigate +the physics of antiferromagnetic spin dynamics and highlights the importance of +tuning of the angular momentum compensation point of ferrimagnets, which could +be a key towards ferrimagnetic spintronics.",1703.07515v1 +2020-01-22,The dynamics of a domain wall in ferrimagnets driven by spin-transfer torque,"The spin-transfer-torque-driven (STT-driven) dynamics of a domain wall in an +easy-axis rare-earth transition-metal ferrimagnet is investigated theoretically +and numerically in the vicinity of the angular momentum compensation point +$T_A$, where the net spin density vanishes. The particular focus is given on +the unusual interaction of the antiferromagnetic dynamics of a ferrimagnetic +domain wall and the adiabatic component of STT, which is absent in +antiferromagnets but exists in the ferrimagnets due to the dominant coupling of +conduction electrons to transition-metal spins. Specifically, we first show +that the STT-induced domain-wall velocity changes its sign across $T_A$ due to +the sign change of the net spin density, giving rise to a phenomenon unique to +ferrimagnets that can be used to characterize $T_A$ electrically. It is also +shown that the frequency of the STT-induced domain-wall precession exhibits its +maximum at $T_A$ and it can approach the spin-wave gap at sufficiently high +currents. Lastly, we report a numerical observation that, as the current +density increases, the domain-wall velocity starts to deviate from the +linear-response result, calling for a more comprehensive theory for the +domain-wall dynamics in ferrimagnets driven by a strong current.",2001.08037v1 +2020-04-23,Temperature-dependent Magnetic Transitions in CoCrPt-Ru-CoCrPt Synthetic Ferrimagnets,"The magnetic orientations and switching fields of a CoCrPt-Ru-CoCrPt +synthetic ferrimagnet with perpendicular magnetic anisotropy have been studied +in the temperature range from 2 K to 300 K. It was found that two sets of +magnetic transitions occur in the CoCrPt-Ru-CoCrPt ferrimagnet across this +temperature range. The first set exhibits three magnetic transitions in the 50 +K - 370 K range, whereas the second involves only two transitions in the 2 K +and 50 K range. The observed magnetic hysteresis curves of the synthetic +ferrimagnet are explained using the energy diagram technique framework +pioneered by Koplak et al. [1] which accurately describes the competition +between interlayer exchange coupling energy, Zeeman energy, and anisotropy +energy in the system. In this work we expand the framework to include synthetic +ferrimagnets (SFMs) comprising higher perpendicular magnetic anisotropy +materials and large (4X) interlayer exchange coupling energies which are +promising for the development of ultrafast (ps) magnetic switching free layers +in MTJ structures. Furthermore, we apply the analysis to predict SFM magnetic +hysteresis curves in a temperature regime that includes temperature extrema +that a synthetic ferrimagnet would be expected to reliably operate at, were it +to be utilized as a free layer in a memory or sensor spintronic device.",2004.11406v2 +2003-01-30,"The Mixed Spin S=(1/2,1) XXZ Ferrimagnet at Zero Temperature","Linked cluster series expansions about the Ising limit are used to study +ground state preperties, viz. ground state energy, magnetization and excitation +spectra, for mixed spin S=(1/2,1) quantum ferrimagnets on simple bipartite +lattices in 1, 2, and 3-dimensions. Results are compared to second-order spin +wave theory and, in general, excellent agreement is obtained.",0301580v1 +2003-09-30,Recent Progress of the Low-Dimensional Spin-Wave Theory,"A modified spin-wave theory is developed and applied to low-dimensional +quantum magnets. Double-peaked specific heat for one-dimensional ferrimagnets, +nuclear spin-lattice relaxation in ferrimagnetic chains and clusters, and +thermal behavior of Haldane-gap antiferromagnets are described within the +scheme. Mentioning other bosonic and fermionic representations as well, we +demonstrate that spin waves are still effective in low dimensions.",0310004v1 +2004-12-15,Nuclear Magnetic Relaxation in the Ferrimagnetic Chain Compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O: Three-Magnon Scattering?,"Recent proton spin-lattice relaxation-time (T_1_) measurements on the +ferrimagnetic chain compound NiCu(C_7_H_6_N_2_O_6_)(H_2_O)_3_2H_2_O are +explained by an elaborately modified spin-wave theory. We give a strong +evidence of the major contribution to 1/T_1_ being made by the three-magnon +scattering rather than the Raman one.",0412389v1 +2005-03-02,Quasi-One-Dimensional Quantum Ferrimagnets,"We present an exact diagonalization study of the half-filled Hubbard model on +bipartite quasi-one-dimensional lattices. In particular, we emphasize the +dependence of the ferrimagnetic ground state properties, and its associated +magnetic excitations, on the Coulomb repulsion U.",0503058v1 +2010-06-29,Magnetostatics of synthetic ferrimagnet elements,"We calculate the magnetostatic energy of synthetic ferrimagnet (SyF) +elements, consisting of two thin ferromagnetic layers coupled +antiferromagnetically through RKKY coupling. We calculate exact formulas as +well as approximate yet accurate ones, which can be used to easily derive +energy barriers and anisotropy fields of SyF. These can be used to evaluate +coercivity, thermal stability and other useful quantities.",1006.5531v2 +2012-08-31,Magnetic symmetry of the plain domain walls in ferro- and ferrimagnets,"Magnetic symmetry of all possible plane domain walls in ferro- and +ferrimagnets is considered. Magnetic symmetry classes of non 180 degree +(including 0 degree) domain walls are obtained. The domain walls degeneracy is +investigated. The symmetry classification is applied for research of all +possible plane domain walls in crystals of the hexoctahedral crystallographic +class.",1209.0003v1 +2018-04-16,Unidirectional Loop Metamaterials (ULM) as Magnetless Artificial Ferrimagnetic Materials: Principles and Applications,"This paper presents an overview of Unidirectional Loop Metamaterial (ULM) +structures and applications. Mimicking electron spin precession in ferrites +using loops with unidirectional loads (typically transistors), the ULM exhibits +all the fundamental properties of ferrite materials, and represents the only +existing magnetless ferrimagnetic medium. We present here an extended +explanation of ULM physics and unified description of its component and system +applications.",1804.08719v1 +1998-07-27,Magnetic Properties of a Quantum Ferrimagnet: NiCu(pba)(D_2O)_3 . 2D_2O,"We report the results of magnetic measurements on a powder sample of +NiCu(pba)(D_2O)_3 \cdot 2D_2O$ (pba=1,3-propylenebis(oxamato)) which is one of +the prototypical examples of an $S$=1/2 and 1 ferrimagnetic chain. +Susceptibility($\chi$) shows a monotonous increase with decreasing temperature +(T) and reaches a maximum at about 7 K. In the plot of $\chi T$ versus $T$, the +experimental data exhibit a broad minimum and are fit to the $\chi T$ curve +calculated for the ferrimagnetic Heisenberg chain composed of S=1/2 and 1. From +this fit, we have evaluated the nearest-neighbor exchange constant $J/k_B=121 +K$, the g-values of Ni$^{2+}$ and Cu$^{2+}$, $g_{Ni}$=2.22 and $g_{Cu}$=2.09, +respectively. Applied external field dependence of $\chi T$ at low temperatures +is reproduced fairly well by the calculation for the same ferrimagnetic model.",9807348v1 +2000-01-01,Characterization of ferrimagnetic Heisenberg chains according to the constituent spins,"The low-energy structure and the thermodynamic properties of ferrimagnetic +Heisenberg chains of alternating spins $S$ and $s$ are investigated by the use +of numerical tools as well as the spin-wave theory. The elementary excitations +are calculated through an efficient quantum Monte Carlo technique featuring +imaginary-time correlation functions and are characterized in terms of +interacting spin waves. The thermal behavior is analyzed with particular +emphasis on its ferromagnetic and antiferromagnetic dual aspect. The extensive +numerical and analytic calculations lead to the classification of the +one-dimensional ferrimagnetic behavior according to the constituent spins: the +ferromagnetic ($S>2s$), antiferromagnetic ($S<2s$), and balanced ($S=2s$) +ferrimagnetism.",0001004v1 +2001-02-22,Low-Temperature Properties of Quasi-One-Dimensional Molecule-Based Ferromagnets,"Quantum and thermal behaviors of low-dimensional mixed-spin systems are +investigated with particular emphasis on the design of molecule-based +ferromagnets. One can obtain a molecular ferromagnet by assembling molecular +bricks so as to construct a low-dimensional system with a magnetic ground state +and then coupling the chains or the layers again in a ferromagnetic fashion. +Two of thus-constructed quasi-one-dimensional bimetallic compounds are +qualitatively viewed within the spin-wave treatment, one of which successfully +grows into a bulk magnet, while the other of which ends in a singlet ground +state. Then, concentrating on the ferrimagnetic arrangement on a two-leg ladder +which is well indicative of general coupled-chain ferrimagnets, we develop the +spin-wave theory and fully reveal its low-energy structure. We inquire further +into the ferromagnetic aspect of the ferrimagnetic ladder numerically +calculating the sublattice magnetization and the magnetic susceptibility. There +exists a moderate coupling strength between the chains in order to obtain the +most ferromagnetic ferrimagnet.",0102417v2 +2004-01-24,Bosonic representation of one-dimensional Heisenberg ferrimagnets,"The energy structure and the thermodynamics of ferrimagnetic Heisenberg +chains of alternating spins S and s are described in terms of the Schwinger +bosons and modified spin waves. In the Schwinger representation, we average the +local constraints on the bosons and diagonalize the Hamiltonian at the +Hartree-Fock level. In the Holstein-Primakoff representation, we optimize the +free energy in two different ways introducing an additional constraint on the +staggered magnetization. A new modified spin-wave scheme, which employs a +Lagrange multiplier keeping the native energy structure free from temperature +and thus differs from the original Takahashi Scheme, is particularly stressed +as an excellent language to interpret one-dimensional quantum ferrimagnetism. +Other types of one-dimensional ferrimagnets and the antiferromagnetic limit S=s +are also mentioned.",0401476v1 +2006-08-26,Ferrimagnetic States in S=1/2 Frustrated Heisenberg Chains with Period 3 Exchange Modulation,"Ground state properties of the S=1/2 frustrated Heisenberg chain with period +3 exchange modulation are investigated using the numerical diagonalization and +DMRG method. It is known that this model has a magnetization plateau at 1/3 of +the saturation magnetization M_s. On the other hand, the ground state is +ferrimagnetic even in the absence of frustration if one of the nearest +neighbour bond is ferromagnetic and others are antiferromagnetic. In the +present work, we show that this ferrimagnetic state continues to the region in +which all bonds are antiferromagnetic if frustration is strong. This state +further continues to the above mentioned 1/3-plateau state. In between, we also +find the noncollinear ferrimagnetic phase in which the spontaneous +magnetization is finite but less than M_s/3. The intuitive interpretation for +the phase diagram is given and the physical properties of these phases are +discussed.",0608582v1 +2011-01-19,Mott transition and ferrimagnetism in the Hubbard model on the anisotropic kagomé lattice,"Mott transition and ferrimagnetism are studied in the Hubbard model on the +anisotropic kagom\'e lattice using the variational cluster approximation and +the phase diagram at zero temperature and half-filling is analyzed. The +ferrimagnetic phase rapidly grows as the geometric frustration is relaxed, and +the Mott insulator phase disappears in moderately frustrated region, showing +that the ferrimagnetic fluctuations stemming from the relaxation of the +geometric frustration is enhanced by the electron correlations. In metallic +phase, heavy fermion behavior is observed and mass enhancement factor is +computed. Enhancement of effective spatial anisotropy by the electron +correlations is also confirmed in moderately frustrated region, and its effect +on heavy fermion behavior is examined.",1101.3645v3 +2013-10-18,Ultrafast thermally induced magnetic switching in synthetic ferrimagnets,"Synthetic ferrimagnets are composite magnetic structures formed from two or +more anti- ferromagnetically coupled magnetic sublattices with different +magnetic moments. Here we report on atomistic spin simulations of the +laser-induced magnetization dynamics on such synthetic ferrimag- nets, and +demonstrate that the application of ultrashort laser pulses leads to +sub-picoscond magnetization dynamics and all-optical switching in a similar +manner as in ferrimagnetic alloys. Moreover, we present the essential material +properties for successful laser-induced switching, demonstrating the +feasibility of using a synthetic ferrimagnet as a high density magnetic storage +element without the need of a write field.",1310.5170v2 +2014-09-30,Predicting a Ferrimagnetic Phase of Zn2FeOsO6 with Strong Magnetoelectric Coupling,"Multiferroic materials, in which ferroelectric and magnetic ordering coexist, +are of fundamental interest for the development of novel memory devices that +allow for electrical writing and non-destructive magnetic readout operation. +The great challenge is to create room temperature multiferroic materials with +strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic) orderings. +BiFeO3 has been the most heavily investigated single-phase multiferroic to date +due to the coexistence of its magnetic order and ferroelectric order at room +temperature. However, there is no net magnetic moment in the cycloidal +(antiferromagnetic-like) magnetic state of bulk BiFeO3, which severely limits +its realistic applications in electric field controlled spintronic devices. +Here, we predict that double perovskite Zn2FeOsO6 is a new multiferroic with +properties superior to BiFeO3. First, there are strong ferroelectricity and +strong ferrimagnetism at room temperature in Zn2FeOsO6. Second, the easy-plane +of the spontaneous magnetization can be switched by an external electric field, +evidencing the strong magnetoelectric coupling existing in this system. Our +results suggest that ferrimagnetic 3d-5d double perovskite may therefore be +used to achieve voltage control of magnetism in future spintronic devices.",1409.8430v2 +2016-10-08,Perpendicularly magnetized CoFeB multilayers with tunable interlayer exchange for synthetic ferrimagnets,"A study of the multilayer system MgO/CoFeB(1.1nm)/Ta($t$)/CoFeB(0.8nm)/MgO is +presented, where the two CoFeB layers are separated by a Ta interlayer of +varying thickness $t$. The magnetization properties deduced from complementary +techniques such as superconducting quantum interference magnetometry, +ferromagnetic resonance frequency measurements and Brillouin light scattering +spectroscopy can be tuned by changing the Ta thickness between $t$=0.25 nm, 0.5 +nm and 0.75 nm. For $t$=0.5 nm, a ferromagnetic coupling is observed, whereas +for t=0.75 nm, the antiferromagnetic coupling needed to construct a synthetic +ferrimagnet is realized. In the later case, the shape of magnetic domain walls +between two ferrimagnetic alignments or between a ferro- and a ferrimagnetic +alignment is very different. This behavior can be interpreted as a result of +the change in dipolar as well as interlayer exchange energy and domain wall +pinning, which is an important conclusion for the realization of data storage +devices based on synthetic ferri- and antiferromagnets.",1610.02550v1 +2017-02-08,Self-Focusing Skyrmion Racetracks in Ferrimagnets,"We theoretically study the dynamics of ferrimagnetic skyrmions in +inhomogeneous metallic films close to the angular momentum compensation point. +In particular, it is shown that the line of the vanishing angular momentum can +be utilized as a self-focusing racetrack for skyrmions. To that end, we begin +by deriving the equations of motion for the dynamics of collinear ferrimagnets +in the presence of a charge current. The obtained equations of motion reduce to +those of ferromagnets and antiferromagnets at two special limits. In the +collective coordinate approach, a skyrmion behaves as a massive charged +particle moving in a viscous medium subjected to a magnetic field. Analogous to +the snake orbits of electrons in a nonuniform magnetic field, we show that a +ferrimagnet with the nonuniform angular momentum density can exhibit snake +trajectories of skyrmions, which can be utilized as racetracks for skyrmions.",1702.02554v1 +2018-11-13,X-ray magnetic linear dichroism as a probe for non-collinear magnetic state in ferrimagnetic single layer exchange bias systems,"Ferrimagnetic alloys are extensively studied for their unique magnetic +properties leading to possible applications in perpendicular magnetic +recording, due to their deterministic ultrafast switching and heat assisted +magnetic recording capabilities. On a prototype ferrimagnetic alloy we +demonstrate fascinating properties that occur close to a critical temperature +where the magnetization is vanishing, just as in an antiferromagnet. From the +X-ray magnetic circular dichroism measurements, an anomalous 'wing shape' +hysteresis loop is observed slightly above the compensation temperature. This +bears the characteristics of an intrinsic exchange bias effect, referred to as +atomic exchange bias. We further exploit the X-ray magnetic linear dichroism +(XMLD) contrast for probing non-collinear states which allows us to +discriminate between two main reversal mechanisms, namely perpendicular domain +wall formation versus spin-flop transition. Ultimately, we analyze the +elemental magnetic moments for the surface and the bulk parts, separately, +which allows to identify in the phase diagram the temperature window where this +effect takes place. Moreover, we suggests that this effect is a general +phenomenon in ferrimagnetic thin films which may also contribue to the +understanding of the mechanism behind the all optical switching effect.",1811.05362v1 +2020-07-22,Nuclear Magnetic Relaxation Time near Compensation Temperature in Ferrimagnetic Insulator,"The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is +calculated by a Raman process of hyperfine interaction with a meanfield +approximation. It is found that the 1/$T_1$ on one site rapidly increases near +the compensation temperature $T_0$, whereas that on another site does not +increase up to Curie temperature $T_c$. This is due to that the band width of +soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$ +below $T_c$ is found also in another type ferrimagnet, which shows hump +structure in the temperature dependence of magnetization instead of +compensation. Also in this case, we find the rapid increase of 1/$T_1$ below +$T_c$, even though the magnetization does not show the compensation. Such a +coexistence of soft and hard magnons will lead to remarkable properties of +ferrimagnet.",2007.11214v3 +2010-05-04,Competition between Ferrimagnetism and Magnetic Frustration in Zinc Substituted YBaFe4O7,"The substitution of zinc for iron in YBaFe4O7 has allowed the oxide series +YBaFe4-xZnxO7, with 0.40 < x < 1.50, belonging to the ""114"" structural family +to be synthesized. These oxides crystallize in the hexagonal symmetry (P63mc), +as opposed to the cubic symmetry (F-43m) of YBaFe4O7. Importantly, the d.c. +magnetization shows that the zinc substitution induces ferrimagnetism, in +contrast to the spin glass behaviour of YBaFe4O7. Moreover, a.c. susceptibility +measurements demonstrate that concomitantly these oxides exhibit a spin glass +or a cluster glass behaviour, which increases at the expense of ferrimagnetism, +as the zinc content is increased. This competition between ferrimagnetism and +magnetic frustration is interpreted in terms of lifting of the geometric +frustration, inducing the magnetic ordering, and of cationic disordering, which +favours the glassy state.",1005.0480v1 +2017-06-02,Coherent Terahertz Spin-Wave Emission Associated with Ferrimagnetic Domain Wall Dynamics,"We theoretically study the dynamics of ferrimagnetic domain walls in the +presence of Dzyaloshinskii-Moriya interaction. We find that an application of a +DC magnetic field can induce terahertz spin-wave emission by driving +ferrimagnetic domain walls, which is not possible for ferromagnetic or +antiferromagnetic domain walls. Dzyaloshinskii-Moriya interaction is shown to +facilitate the teraherz spin-wave emission in wide ranges of net angular +momentum by increasing the Walkerbreakdown field. Moreover, we show that +spin-orbit torque combined with Dzyaloshinskii-Moriya interaction also drives a +fast ferrimagnetic domain wall motion with emitting terahertz spin-waves in +wide ranges of net angular momentum.",1706.00549v1 +2019-07-18,Electric bias-controlled switching of magnetization of ferrimagnetically coupled Mn delta-layers in a GaAs-AlGaAs quantum well,"We suggest a model of synthetic ferrimagnetic semiconductor structure based +on GaAs-AlGaAs quantum well doped by two Mn delta-layers. The coupling between +the delta-layers is mediated by extra holes, and can be switched between ferro- +and antiferromagnetic one by gating the structure. A proper choice of Mn +concentrations in the delta-layers and of local degree of disorder enables +fabrication of a ferrimagnetic structure supporting ultrafast switching of +magnetization by short pulses of electric bias without an external magnetic +field. The switching mechanism in the structure relies on kinetic spin exchange +between the two delta-layers which is mediated by exchange scattering of +electric-pulse heated holes by magnetic ions within the layers. Owing to +specific interplay between characteristics of the exchange scattering, spin +decay times, and the heat withdraw in the suggested synthetic ferrimagnetic +semiconductor, the necessary parameters of electric-bias pulse are within the +technologically accessible range, and do not contradict typical thermal +kinetics of semiconductor structures.",1907.07997v2 +2019-09-25,Stability and Absence of a Tower of States in Ferrimagnets,"Antiferromagnets and ferromagnets are archetypes of the two distinct (type-A +and type-B) ways of spontaneously breaking a continuous symmetry. Although +type-B Nambu--Goldstone modes arise in various systems, the ferromagnet was +considered pathological due to the stability and symmetry-breaking nature of +its exact ground state. However, here we show that symmetry-breaking in +ferrimagnets closely resembles the ferromagnet. In particular, there is an +extensive ground state degeneracy, there is no Anderson tower of states, and +the maximally polarized ground state is thermodynamically stable. Our results +are derived analytically for the Lieb--Mattis ferrimagnet and numerically for +the Heisenberg ferrimagnet. We argue that these properties are generic for +type-B symmetry-broken systems, where the order parameter operator is a +symmetry generator.",1909.11381v1 +2019-10-03,Current driven domain wall dynamics in ferrimagnetic strips explained by means of a two interacting sublattices model,"The current-driven domain wall dynamics along ferrimagnetic systems are here +theoretically analyzed as a function of the temperature by means of +micromagnetic simulations and a one dimensional model. Contrarily to +conventional effective approaches, our model takes into account the two coupled +ferromagnetic sublattices forming the ferrimagnetic system. Although the model +is suitable for systems with asymmetric exchange interaction and spin-orbit +coupling effects due to adjacent heavy metal layers, we here focus our +attention on the case of single-layer ferrimagnetic strips where domain walls +adopt achiral Bloch configurations at rest. Such domain walls can be driven by +either out-of-plane fields or spin transfer torques upon bulk current +injection. Our results indicate that the domain wall velocity is optimized at +the angular compensation temperature for both field-driven and current-driven +cases. Our advanced models allow us to infer that the precession of the +internal domain wall moments is suppressed at such compensation temperature, +and they will be useful to interpret state-of-the art experiments on these +systems.",1910.01405v2 +2020-01-19,Dephasing of Transverse Spin Current in Ferrimagnetic Alloys,"It has been predicted that transverse spin current can propagate coherently +(without dephasing) over a long distance in antiferromagnetically ordered +metals. Here, we estimate the dephasing length of transverse spin current in +ferrimagnetic CoGd alloys by spin pumping measurements across the compensation +point. A modified drift-diffusion model, which accounts for spin-current +transmission through the ferrimagnet, reveals that the dephasing length is +about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals. +This finding suggests that antiferromagnetic order can mitigate spin dephasing +-- in a manner analogous to spin echo rephasing for nuclear and qubit spin +systems -- even in structurally disordered alloys at room temperature. We also +find evidence that transverse spin current interacts more strongly with the Co +sublattice than the Gd sublattice. Our results provide fundamental insights +into the interplay between spin current and antiferromagnetic order, which are +crucial for engineering spin torque effects in ferrimagnetic and +antiferromagnetic metals.",2001.06918v5 +2017-05-03,Synthetic ferrimagnet spin transfer torque oscillator: model and non-linear properties,"The non-linear parameters of spin-torque oscillators based on a synthetic +ferrimagnet free layer (two coupled layers) are computed. The analytical +expressions are compared to macrospin simulations in the case of a synthetic +ferrimagnet excited by a current spin-polarized by an external fixed layer. It +is shown that, of the two linear modes, acoustic and optical, only one is +excited at a time, and therefore the self-sustained oscillations are similar to +the dynamics of a single layer. However, the non-linear parameters values can +be controlled by the parameters of the synthetic ferrimagnet. With a strong +coupling between the two layers and asymmetric layers (different thicknesses), +it is demonstrated that the non-linear frequency shift can be reduced, which +results in the reduction of the linewidth of the power spectral density. For a +particular applied field, the non-linear parameter can even vanish; this +corresponds to a transition between a red-shift and a blue-shift frequency +dependence on the current and a linewidth reduction to the linear linewidth +value.",1705.01335v1 +2017-05-13,"Partial Ferrimagnetism in S=1/2 Heisenberg Ladders with a Ferromagnetic Leg, an Antiferromagnetic Leg, and Antiferromagnetic Rungs","Ground-state and finite-temperature properties of $S=1/2$ Heisenberg ladders +with a ferromagnetic leg, an antiferromagnetic leg, and antiferromagnetic rungs +are studied. It is shown that a partial ferrimagnetic phase extends over a wide +parameter range in the ground state. The numerical results are supported by an +analytical calculation based on a mapping onto the nonlinear $\sigma$ model and +a perturbation calculation from the strong-rung limit. It is shown that the +partial ferrimagnetic state is a spontaneously magnetized Tomonaga--Luttinger +liquid with incommensurate magnetic correlation, which is confirmed by a DMRG +calculation. The finite-temperature magnetic susceptibility is calculated using +the thermal pure quantum state method. It is suggested that the susceptibility +diverges as $T^{-2}$ in the ferrimagnetic phases as in the case of +ferromagnetic Heisenberg chains.",1705.04836v2 +2017-05-29,Distinct domain-wall motion between creep and flow regimes near the angular momentum compensation temperature of ferrimagnet,"We investigate a magnetic domain-wall (DW) motion in two dynamic regimes, +creep and flow regimes, near the angular momentum compensation temperature +(T_A) of ferrimagnet. In the flow regime, the DW speed shows sharp increase at +T_A due to the emergence of antiferromagnetic DW dynamics. In the creep regime, +however, the DW speed exhibits a monotonic increase with increasing the +temperature. This result suggests that, in the creep regime, the thermal +activation process governs the DW dynamics even near T_A. Our result +unambiguously shows the distinct behavior of ferrimagnetic DW motion depending +on the dynamic regime, which is important for emerging ferrimagnet-based +spintronic applications.",1705.10062v1 +2018-06-04,Current-induced domain wall motion in compensated ferrimagnet,"Due to the difficulty in detecting and manipulating magnetic states of +antiferromagnetic materials, studying their switching dynamics using electrical +methods remains a challenging task. In this work, by employing heavy metal/rare +earth-transition metal alloy bilayers, we experimentally studied +current-induced domain wall dynamics in an antiferromagnetically coupled +system. We show that the current-induced domain wall mobility reaches a maximum +close to the angular momentum compensation. With experiment and modelling, we +further reveal the internal structures of domain walls and the underlying +mechanisms for their fast motion. We show that the chirality of the +ferrimagnetic domain walls remains the same across the compensation points, +suggesting that spin orientations of specific sublattices rather than net +magnetization determine Dzyaloshinskii-Moriya interaction in heavy +metal/ferrimagnet bilayers. The high current-induced domain wall mobility and +the robust domain wall chirality in compensated ferrimagnetic material opens +new opportunities for high-speed spintronic devices.",1806.01167v1 +2018-07-06,Spin-torque-induced magnetization dynamics in ferrimagnets based on Landau-Lifshitz-Bloch Equation,"A theoretical model based on the Landau-Lifshitz-Bloch equation is developed +to study the spin-torque effect in ferrimagnets. Experimental findings, such as +the temperature dependence, the peak in spin torque, and the angular-momentum +compensation, can be well captured. In contrast to the ferromagnet system, the +switching trajectory in ferrimagnets is found to be precession free. The two +sublattices are not always collinear, which produces large exchange field +affecting the magnetization dynamics. The study of material composition shows +the existence of an oscillation region at intermediate current density, induced +by the nondeterministic switching. Compared to the Landau-Lifshitz-Gilbert +model, our developed model based on the Landau-Lifshitz-Bloch equation enables +the systematic study of spin-torque effect and the evaluation of +ferrimagnet-based devices.",1807.02445v1 +2018-08-17,Laser-induced antiferromagnetic-like resonance in amorphous ferrimagnets,"The magnetization dynamics for ferrimagnets at the angular momentum +compensation temperature T_A is believed to be analogous to that for +antiferromagnets. We investigated the pulsed-laser-induced magnetization +dynamics in amorphous rare-earth transition-metal ferrimagnet films with a T_A +just above room temperature. For a low pulse fluence, the magnetization +precession frequency decreases as the applied magnetic field increases, whereas +for a higher pulse fluence, it increases as the applied field increases. The +result was well explained by the left-handed and right-handed precession modes +of the antiferromagnetic-like resonance at temperatures below and above T_A, +respectively, and the data were in agreement with the theoretical simulation. +The study demonstrated the experimental route to achieving antiferromagnetic +resonance in ferrimagnets using a pulsed laser.",1808.05707v1 +2018-08-20,Tunable Magnonic Thermal Hall Effect in Skyrmion Crystal Phases of Ferrimagnets,"We theoretically study the thermal Hall effect by magnons in skyrmion crystal +phases of ferrimagnets in the vicinity of the angular momentum compensation +point (CP). To this end, we start by deriving the equation of motion for +magnons in the background of an arbitrary equilibrium spin texture, which gives +rise to the fictitious electromagnetic field for magnons. As the net spin +density varies, the resultant equation of motion interpolates between the +relativistic Klein-Gordon equation at CP and the nonrelativistic +Schr{\""o}dinger-like equation away from it. In skyrmion crystal phases, the +right- and the left-circularly polarized magnons with respect to the order +parameter are shown to form the Landau levels separately within the uniform +skyrmion-density approximation. For an experimental proposal, we predict that +the magnonic thermal Hall conductivity changes its sign when the ferrimagnet is +tuned across CP, providing a way to control heat flux in spin-caloritronic +devices on the one hand and a feasible way to detect CP of ferrimagnets on the +other hand.",1808.06690v1 +2019-03-11,High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets,"Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in +the equilibrium and ultrafast magnetic properties of the ferrimagnetic +rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the +magnetization compensation temperature, each of the magnetizations of the +antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis +loops. Contrary to state-of-the-art theory, which explains such loops by sample +inhomogeneities, here we show that they are an intrinsic property of the +rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and +have a non-zero orbital momentum in the ground state and, therefore, a large +magnetic anisotropy, we are able to reproduce the experimentally observed +behavior in equilibrium. The same theory is also able to describe the +experimentally observed critical slowdown of the spin dynamics in the vicinity +of the magnetization compensation temperature, emphasizing the role played by +the orbital momentum in static and ultrafast magnetism of ferrimagnets.",1903.04293v1 +2019-08-18,Anomalous magnetic behavior and complex magnetic structure of proximate LaCrO3 LaFeO3 system,"We investigated complex magnetic properties of multifunctional LaCrO3-LaFeO3 +system. The magnetic measurements substantiate the presence of competing +complex magnetic ordering against temperature, showing paramagnetic to +ferrimagnetic transition at 300 K, followed by antiferromagnetic (AFM) +transition near 250 K superimposed on ferrimagnetic phase. The onset of weak +ferrimagnetic ordering is attributed to the competing complex interaction +between two AFM LaCrO3-LaFeO3 sublattices. The low-temperature AFM ordering is +also substantiated by temperature-dependent Raman measurements, where the +intensity ratio of 700 cm-1 Raman active mode showed the clear enhancement with +lowering the temperature. The non-saturating nature of magnetic moments in +LaCrO3-LaFeO6 suggests the predominating AFM ordering in conjunction with +ferrimagnetic ordering between 250 K to 300 K up to 5 T magnetic field. A +complex magnetic structure of LaCrO3-LaFeO3 is constructed, emphasizing the +metastable magnetic phase near room temperature and low temperature +antiferromagnetic state.",1908.06450v1 +2019-11-25,Identification of ferrimagnetic orbitals preventing spinel degradation by charge ordering in Li$_x$Mn$_2$O$_4$,"Spinel Li$_x$Mn$_2$O$_4$ is a key cathode material that is used extensively +in commercial Li-ion batteries. A challenge with this material has been that +the capacity of the battery fades with cycling, an effect that can be traced to +the presence of an anti-ferromagnetic insulator phase in the fully lithiated +LiMn$_2$O$_4$ (LMO) and the associated charge disproportionation that drives +distortions of the MnO$_6$ octahedra. Here, by combining x-ray magnetic Compton +scattering experiments with parallel first-principles computations, we show +that the anti-ferromagnetic phase of LMO is surrounded by a robust +ferrimagnetic metallic phase, which becomes stable when even a small amount of +Li is removed from or added to the charge-ordered LMO. In this surprising +ferrimagnetic state, charge-ordering and octahedral distortions are found to be +strongly suppressed. We identify the nature of the ferrimagnetic orbitals +involved through theoretical and experimental analyses of the magnetic Compton +scattering spectra.",1911.11183v1 +2020-05-02,Optically driven ultrafast magnetic order transitions in two-dimensional ferrimagnets,"Laser-induced switching and manipulation of the spins in magnetic materials +are of great interest to revolutionize future magnetic storage technology and +spintronics with fastest speed and least power dissipative. Inspired by the +recent discovery of intrinsic two-dimensional (2D) magnets, which provide +unique platform to explore the new phenomenon for light-control magnetism in +the 2D limit, we propose to realize light can efficiently tune magnetic +properties of 2D ferrimagnets in early time. Here, using the 2D ferrimagnetic +MXenes as prototype systems, our real-time density functional theory (TDDFT) +simulation show that laser pulses can directly induce ultrafast spin-selective +charge transfer between two magnetic sublattices on a few femtoseconds, and +further generate dramatic changes in the magnetic structure of these MXenes, +including a magnetic order transition from ferrimagnetic (FiM) to transient +ferromagnetic (FM). The microscopic mechanism underpinning this ultrafast +switching of magnetic order in MXenes is governed by optically induced +inter-site spin transfer (OISTR) effect, which theoretically enables the +ultrafast direct optical manipulation of the magnetic state in MXenes-based +materials. Our results open new opportunities to optically manipulate the spin +in 2D magnets.",2005.00871v1 +2020-05-18,Noncollinear Magnetic Modulation of Weyl Nodes in Ferrimagnetic Mn$_3$Ga,"The tetragonal ferrimagnetic Mn$_3$Ga exhibits a wide range of intriguing +magnetic properties. Here, we report the emergence of topologically nontrivial +nodal lines in the absence of spin orbit coupling (SOC) which are protected by +both mirror and $C_{4z}$ rotational symmetries. In the presence of SOC we +demonstrate that the doubly degenerate nontrivial crossing points evolve into +$C_{4z}$-protected Weyl nodes with chiral charge of $\pm$2. Furthermore, we +have considered the experimentally reported noncollinear ferrimagnetic +structure, where the magnetic moment of the Mn$_I$ atom (on the Mn-Ga plane) is +tilted by an angle $\theta$ with respect to the crystallographic $c$ axis. The +evolution of the Weyl nodes with $\theta$ reveals that the double Weyl nodes +split into a pair of charge-1 Weyl nodes whose separation can be tuned by the +magnetic orientation in the noncollinear ferrimagnetic structure.",2005.08914v3 +2021-03-06,Anomalies in the dynamics of ferrimagnets near the angular momentum compensation point,"In this paper, we elaborate analytical theory of domain wall dynamics close +to the angular momentum compensation point based on non-linear dynamic +equations derived from the effective Lagrangian of a ferrimagnet. Analysis of +the precession angle and domain wall velocity oscillations in post Walker +regime in a ferrimagnet is performed. In the framework of the proposed model, +we explore dynamic processes in the Walker and post Walker regimes. We show +that although spin oscillations quench the dynamics of domain walls near the +Walker breakdown field, a further increase of the driving magnetic field +increases domain wall speed and mobility. An anomalous behavior of domain wall +dynamic properties near the angular momentum compensation point in ferrimagnets +is discussed.",2103.04105v1 +2021-04-06,Landau-Lifshitz-Bloch equation for ferrimagnets with higher-order interaction,"We present a micromagnetic formulation for modeling the magnetization +dynamics and thermal equilibrium in ferrimagnetic materials at low and elevated +temperatures. The formulation is based on a mean field approximation (MFA). In +this formulation, the ferrimagnet is described micromagnetically by two coupled +sublattices with corresponding interactions, including inter- and +intra-sublattice micromagnetic exchange as well as four-spin interactions +described as an inter-sublattice molecular field with a cubic dependence of the +magnetization. The MFA is used to derive a Landau Lifshitz Bloch type equation +for ferrimagnetic material, including cases with a ferromagnetic - +antiferromagnetic phase transitions. For validation, the results obtained via +the presented model are compared with recent experimental data for phase +transitions in FeRh.",2104.02198v3 +2021-09-25,Phase transitions in rare-earth ferrimagnets with surface anisotropy near the magnetization compensation point,"We report of a theoretical model for calculating the H-T phase diagrams of a +rare-earth ferrimagnet, taking into account anisotropies originated by both +magnetization sublattices' and by the surface. The possibility of an exchange +spring formation due to surface anisotropy is considered. This situation is +realized in heterostructures containing a ferrimagnet and a heavy metal. We +derive the stability lose lines of the collinear phase from the free energy of +the two sublattice ferrimagnet. We numerical calculate the magnetic phase +diagrams for the cases when the magnetic field applied along and perpendecular +to the easy axis. We demonstrate that tricritical point down at the low field +range due to surface anisotropy effect. Moreover, the line of the first order +phase transition between angular and collinear phases reduces due to surface +anisotropy. In the case when magnetic field is applied perpendicular to the +easy axis we show the possibility of the first order phase transition between +two collinear phases in contrast to the phase diagram without surface +anisotropy.",2109.12377v2 +2021-11-11,Kondo effect in Lieb's ferrimagnetic system on the T-shaped bipartite lattice,"The minimal ferrimagnetism by Lieb's theorem emerges on the T-shaped +bipartite lattice composed of four sites, which can be realized experimentally, +just as Nagaoka ferromagnetism has been demonstrated experimentally using a +quartet quantum-dot(J.P.Dehollain et al., Nature 579, 528 (2020).). In this +paper, the Kondo effect on this ferrimagnetism is theoretically studied. The +magnetic moment $S=1$ is screened in two steps by the Kondo effect and the +series conductance $g_{s}$ is strongly suppressed to $g_{s}\simeq 0$, while the +parallel conductance $g_{p}$ has the maximum value $g_{p}\simeq 4e^{2}/h$. The +robustness of these properties against a parameter change toward reducing the +Lieb's ferrimagnetism is also discussed, showing the scenarios for entanglement +of the degrees of freedom toward the ground state.",2111.06045v3 +2021-12-14,"Ground State, Magnetization Process and Bipartite Quantum Entanglement of a Spin-1/2 Ising-Heisenberg Model on Planar Lattices of Interconnected Trigonal Bipyramids","The ground state, magnetization scenario and the local bipartite quantum +entanglement of a mixed spin-$1/2$ Ising--Heisenberg model in a magnetic field +on planar lattices formed by identical corner-sharing bipyramidal plaquettes is +examined by combining the exact analytical concept of generalized +decoration-iteration mapping transformations with Monte Carlo simulations +utilizing the Metropolis algorithm. The ground-state phase diagram of the model +involves six different phases, namely, the standard ferrimagnetic phase, fully +saturated phase, two unique quantum ferrimagnetic phases, and two +macroscopically degenerate quantum ferrimagnetic phases with two chiral degrees +of freedom of the Heisenberg triangular clusters. The diversity of ground-state +spin arrangement is manifested themselves in seven different magnetization +scenarios with one, two or three fractional plateaus whose values are +determined by the number of corner-sharing plaquettes. The low-temperature +values of the concurrence demonstrate that the bipartite quantum entanglement +of the Heisenberg spins in quantum ferrimagnetic phases is field independent, +but twice as strong if the Heisenberg spin arrangement is unique as it is +two-fold degenerate.",2112.07233v1 +2022-01-22,Universal criteria for single femtosecond pulse ultrafast magnetization switching in ferrimagnets,"Single-pulse switching has been experimentally demonstrated in ferrimagnetic +GdFeCo and Mn$_2$Ru$_x$Ga alloys. Complete understanding of single-pulse +switching is missing due to the lack of an established theory accurately +describing the transition to the non-equilibrium reversal path induced by +femtosecond laser photo-excitation. In this work we present general macroscopic +theory for the magnetization dynamics of ferrimagnetic materials upon +femtosecond laser excitation. Our theory reproduces quantitatively all stages +of the switching process observed in experiments. We directly compare our +theory to computer simulations using atomistic spin dynamics methods for both +GdFeCo and Mn$_2$Ru$_x$Ga alloys. We provide explicit expressions for the +magnetization relaxation rates in terms of microscopic parameters which allows +us to propose universal criteria for switching in ferrimagnets.",2201.09067v1 +2022-04-25,Ultrafast racetrack based on compensated Co/Gd-based synthetic ferrimagnet with all-optical switching,"Spin-orbitronics and single pulse all-optical switching (AOS) of +magnetization are two major successes of the rapidly advancing field of +nanomagnetism in recent years, with high potential for enabling novel, fast and +energy-efficient memory and logic platforms. Fast current-induced domain wall +motion (CIDWM) and single shot AOS have been individually demonstrated in +different ferrimagnetic alloys. However, the stringent requirement for their +composition control makes these alloys challenging materials for wafer-scale +production. Here, we simultaneously demonstrate fast CIDWM and energy efficient +AOS in a synthetic ferrimagnetic system based on multilayered [Co/Gd/Co/Gd]. We +firstly show that AOS is present in its full composition range. We find that +current-driven domain wall velocities over 2000 m/s at room temperature, +achieved by compensating the total angular momentum through layer thickness +tuning. Furthermore, analytical modeling of the CIDWM reveals that Joule +heating needs to be treated transiently to properly describe the CIDWM for our +sub-ns current pulses. Our studies establish [Co/Gd]-based synthetic +ferrimagnets to be a unique materials platform for domain wall devices with +access to ultrafast single pulse AOS.",2204.11595v1 +2022-10-25,Ultrafast Switching in Synthetic Antiferromagnet with Bilayer Rare-Earth Transition-Metal Ferrimagnets,"In spintronics, it is important to be able to manipulate magnetization +rapidly and reliably. Several methods can control magnetization, such as by +applying current pulses or magnetic fields. An applied current can reverse +magnetization with nanosecond speed through the spin torque effect. For faster +switching, subpicosecond switching with femtoseconds laser pulse has been +achieved in amorphous rare-earth transition-metal ferrimagnets. In this study, +we employed atomistic simulations to investigate ultrafast switching in a +synthetic antiferromagnet with bilayer amorphous FeGd ferrimagnets. Using a +two-temperature model, we demonstrated ultrafast switching in this synthetic +antiferromagnet without external magnetic fields. Furthermore, we showed that +if we initially stabilize a skyrmion in this heterostructure, the ultrafast +laser can switch the skyrmion state using the same mechanism. Furthermore, this +bilayer design allows the control of each ferrimagnetic layer individually and +opens the possibility for a magnetic tunnel junction.",2210.14119v1 +2022-11-28,Anomalous Nernst effect in compensated ferrimagnetic CoxGd1-x films,"The anomalous Nernst effect (ANE) is one of the most intriguing +thermoelectric phenomena which has attracted growing interest both for its +underlying physics and potential applications. Typically, a large ANE response +is observed in magnets with pronounced magnetizations or nontrivial Berry +curvature. Here, we report a significant ANE signal in compensated +ferrimagnetic CoxGd1-x alloy films, which exhibit vanishingly small +magnetization. In particular, we found that the polarity of ANE signal is +dominated by the magnetization orientation of the transition metal Co +sublattices, rather than the net magnetization of CoxGd1-x films. This +observation is not expected from the conventional understanding of ANE but is +analogous to the anomalous Hall effect in compensated ferrimagnets. We +attribute the origin of ANE and its Co-dominant property to the Co-dominant +Berry curvature. Our work could trigger a more comprehensive understanding of +ANE and may be useful for building energy-harvesting devices by employing ANE +in compensated ferrimagnets.",2211.15074v1 +2023-02-06,Observation of Coherently Coupled Cation Spin Dynamics in an Insulating Ferrimagnetic Oxide,"Many technologically useful magnetic oxides are ferrimagnetic insulators, +which consist of chemically distinct cations. Here, we examine the spin +dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite +(Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave +excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance +to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice +sites. Our results show that the precessing cation moments retain a rigid, +collinear configuration to within $\approx$2$^\circ$. Moreover, the effective +spin relaxation is identical to within $<$10% for all magnetic cations in the +ferrite. We thus validate the oft-assumed ``ferromagnetic-like'' dynamics in +resonantly driven ferrimagnetic oxides, where the magnetic moments from +different cations precess as a coherent, collective magnetization.",2302.03100v1 +2023-03-28,Analysis of ultrafast magnetization switching dynamics in exchange-coupled ferromagnet-ferrimagnet heterostructures,"Magnetization switching in ferromagnets has so far been limited to the +current-induced spin-orbit-torque effects. Recent observation of +helicity-independent all-optical magnetization switching in exchange-coupled +ferromagnet ferrimagnet heterostructures expanded the range and applicability +of such ultrafast heat-driven magnetization switching. Here we report the +element-resolved switching dynamics of such an exchange-coupled system, using a +modified microscopic three-temperature model. We have studied the effect of i) +the Curie temperature of the ferromagnet, ii) ferrimagnet composition, iii) the +long-range RKKY exchange-coupling strength, and iv) the absorbed optical energy +on the element-specific time-resolved magnetization dynamics. The phase-space +of magnetization illustrates how the RKKY coupling strength and the absorbed +optical energy influence the switching time. Our analysis demonstrates that the +threshold switching energy depends on the composition of the ferrimagnet and +the switching time depends on the Curie temperature of the ferromagnet as well +as RKKY coupling strength. This simulation anticipates new insights into +developing faster and more energy-efficient spintronics devices.",2303.16294v1 +2023-04-27,"Room Temperature Ferrimagnetism, Magnetodielectric and Exchange Bias Effect in CoFeRhO$_4$","Geometrically frustrated structures combined with competing exchange +interactions that have different magnitudes are known ingredients for achieving +exotic properties. Herein, we studied detailed structural, magnetic, thermal +(specific heat), magneto-dielectric, and magnetic exchange bias properties of a +mixed 3d - 4d spinel oxide with composition CoFeRhO$_4$. Detailed +magnetization, heat capacity, and neutron powder diffraction studies (NPD) +highlight long-range ferrimagnetic ordering with an onset at 355 K. The +magnetic structure is established using a ferrimagnetic model (collinear-type) +that has a propagation vector k = 0, 0, 0. The magneto-dielectric effect +appears below the magnetic ordering temperature, and the exchange bias (EB) +effect is observed in field cooled (FC) conditions below 355 K. The +magneto-dielectric coupling in CoFeRhO$_4$ originates due to the frustration in +the structure, collinear ferrimagnetic ordering, and uncompensated magnetic +moments. The unidirectional anisotropy resulting from the uncompensated +magnetic moments causes the room-temperature exchange bias effect. Remarkably, +the appearance of technologically important properties (ferromagnetism, +magnetodielectric effect, and EB) at room temperature in CoFeRhO$_4$ indicates +its potential use in sensors or spintronics.",2304.13983v1 +2023-05-04,Effective rectification of THz electromagnetic fields in a ferrimagnetic iron garnet,"It is found that single-cycle THz electromagnetic fields efficiently excite a +GHz spin resonance mode in ferrimagnetic Tm$_3$Fe$_5$O$_{12}$, despite the near +absence of GHz spectral components in the exciting THz pulse. By analyzing how +the efficiency of excitation depends on the orientation and strength of the THz +electric field, we show that it can be explained in terms of the nonlinear THz +inverse Cotton-Mouton effect. Here, the THz electric field gets effectively +rectified and acts on the ferrimagnetic spins as a uni-polar effective magnetic +field pulse. This interpretation is confirmed by a theoretical model based on +the phenomenological analysis of the effective magnetic field, combined with +the equations of motion derived from the effective Lagrangian for a +ferrimagnet. Moreover, by using the outcome of two-dimensional THz +spectroscopy, we conjecture a quantum-mechanical interpretation of the observed +effect in terms of stimulated Raman scattering of THz photons by the +crystal-field split f-f electronic transitions of Tm$^{3+}$.",2305.02971v1 +2023-07-25,Lattice structure dependence of laser-induced ultrafast magnetization switching in ferrimagnets,"The experimental discovery of single-pulse ultrafast magnetization switching +in ferrimagnetic alloys, such as GdFeCo and MnRuGa, opened the door to a +promising route toward faster and more energy efficient data storage. A recent +semi-phenomenological theory has proposed that a fast, laser-induced +demagnetization below a threshold value puts the system into a dynamical regime +where angular momentum transfer between sublattices dominates. Notably, this +threshold scales inversely proportional to the number of exchange-coupled +nearest neighbours considered in the model, which in the simplest case is +directly linked to the underlying lattice structure. In this work, we study the +role of the lattice structure on the laser-induced ultrafast magnetization +switching in ferrimagnets by complementing the phenomenological theory with +atomistic spin dynamics computer simulations. We consider a spin model of the +ferrimagnetic GdFeCo alloy with increasing number of exchange-coupled +neighbours. Within this model, we demonstrate that the laser-induced +magnetization dynamics and switching depends on the lattice structure. Further, +we determine that the critical laser energy for switching reduces for +decreasing number of exchange-coupled neighbours.",2307.13522v1 +2023-09-16,Antiferromagnetic to Ferrimagnetic Phase Transition and Possible Phase Coexistence in Polar Magnets (Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$,"In the present work, magnetic properties of single crystal +(Fe$_{1-x}$Mn$_x$)$_2$Mo$_3$O$_8$ ($00.3$. Meanwhile, sizeable electric polarization of spin origin is +commonly observed in all samples, no matter what the magnetic state is. For the +samples hosting a ferrimagnetic state, square-like magnetic hysteresis loops +are revealed, while the remnant magnetization and coercive field can be tuned +drastically by simply varying the Mn-content or temperature. Possible +coexistence of the antiferromagnetic and ferrimagnetic phases is proposed to be +responsible for the remarkable modulation of magnetic properties in the +samples.",2309.08990v1 +2024-03-12,Ferrimagnetic Heusler tunnel junctions with fast spin-transfer torque switching enabled by low magnetization,"Magnetic random access memory that uses magnetic tunnel junction memory cells +is a high performance, non-volatile memory technology that goes beyond +traditional charge-based memories. Today its speed is limited by the high +magnetization of the memory storage layer. Here we show that fast and highly +reliable switching is possible using a very low magnetization ferrimagnetic +Heusler alloy, Mn3Ge. Moreover, the tunneling magnetoresistance is the highest +yet achieved for a ferrimagnetic material at ambient temperature. Furthermore, +the devices were prepared on technologically relevant amorphous substrates +using a novel combination of a nitride seed layer and a chemical templating +layer. These results show a clear path to the lowering of switching currents +using ferrimagnetic Heusler materials and, therefore, to the scaling of high +performance magnetic random access memories beyond those nodes possible with +ferromagnetic devices.",2403.08112v1 +2017-07-16,Competing magnetic and spin gap-less semiconducting behaviour in fully compensated ferrimagnet CrVTiAl: Theory and Experiment,"We report the structural, magnetic and transport properties of +polycrystalline CrVTiAl alloy along with first principles calculations. It +crystallizes in the LiMgPdSn type structure with lattice parameter 6.14 \AA\ at +room temperature. Absence of (111) peak along with the presence of a weak (200) +peak indicates the antisite disorder of Al with Cr and V atoms. The +magnetization measurements reveal a ferrimagnetic transition near 710 K and a +coercive field of 100 Oe at 3 K. Very low moment and coercive field indicate +fully compensated ferrimagnetism in the alloy. Temperature coefficient of +resistivity is found to be negative, indicating a characteristic of +semiconducting nature. Absence of exponential dependence of resistivity on +temperature indicates a gapless/spin-gapless semiconducting behaviour. +Electronic and magnetic properties of CrVTiAl for three possible +crystallograpic configurations are studied theoretically. All the three +configurations are found to be different forms of semiconductors. Ground state +configuration is a fully compensated ferrimagnet with band gaps 0.58 eV and +0.30 eV for up and down spin bands respectively. The next higher energy +configuration is also ferrimagnetic, but has spin-gapless semiconducting +nature. The highest energy configuration corresponds to a non-magnetic gapless +semiconductor. The energy differences among these configurations are quite +small ($<$ 1 $\mathrm{mRy/atom}$) which hints that at finite temperatures, the +alloy exists in a disordered phase, which is a mixture of the three +configurations. By taking into account the theoretical and the experimental +findings, we conclude that CrVTiAl is a fully compensated ferrimagnet with +predominantly spin gap-less semiconductor nature.",1707.04854v1 +2010-06-10,NMR study on the stability of the magnetic ground state in MnCr${}_2$O${}_4$,"The canting angles and fluctuation of the magnetic ion spins of spinel oxide +MnCr${}_2$O${}_4$ were studied by nuclear magnetic resonance (NMR) at low +temperatures, which has a collinear ferrimagnetic order below $T_C$ and a +ferrimagnetic spiral order below $T_s < T_C$. Contrary to previous reports, +only one spin canting angle of Cr ions was observed. The spin canting angles of +Mn and Cr ions in the ferrimagnetic spiral obtained at a liquid-He temperature +were $43\,^{\circ}$ and $110\,^{\circ}$, respectively. The nuclear spin-spin +relaxation was determined by the Suhl-Nakamura interaction at low temperatures +but the relaxation rate $T_2^{-1}$ increases rapidly as the temperature +approaches $T_s$. This indicates that the fluctuation of the spiral component +becomes faster as the temperature increases but not fast enough to leave an +averaged hyperfine field to nuclei in the time scale of nuclear spin precession +in the ferrimagnetic phase, which is on the order of $10^{-8}$ s. The spiral +volume fraction measured for various temperatures reveals that the collinear +and the spiral ferrimagnetic phases are mixed below the transition temperature +of the spiral order. The temperature hysteresis in the volume fraction implies +that this transition has first-order characteristics.",1006.1983v1 +2016-07-29,"A rock-salt type Li-based oxide, Li3Ni2RuO6, exhibiting a chaotic ferrimagnetism with cluster spin-glass dynamics and thermally frozen charge carriers","The area of research to discover new Li containing materials and to +understand their physical properties has been of constant interest due to +applications potential for rechargeable batteries. Here, we present the results +of magnetic investigations on a Li compound, Li3Ni2RuO6, which was believed to +be a ferrimagnet below 80K. While our neutron diffraction (ND) and isothermal +magnetization (M) data support ferrimagnetism, more detailed magnetic studies +establish that this ferrimagnetic phase exhibits some features similar to +spin-glasses. In addition, we find another broad magnetic anomaly around 40-55 +K in magnetic susceptibility, attributable to cluster spin-glass phenomenon. +Gradual dominance of cluster spin-glass dynamics with a decrease of temperature +(T) and the apparent spread in freezing temperature suggest that the +ferrimagnetism of this compound is a chaotic one. The absence of a unique +freezing temperature for a crystalline material is interesting. In addition, +pyroelectric current data reveals a feature in the range 40-50 K, attributable +to thermally stimulated depolarization current. We hope this finding motivates +future work to explore whether there is any intriguing correlation of such a +feature with spin-glass dynamics. We attribute these magnetic and electric +dipole anomalies to the crystallographic disorder intrinsic to this compound.",1607.08689v1 +2017-10-07,Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation,"To gain control over magnetic order on ultrafast time scales, a fundamental +understanding of the way electron spins interact with the surrounding crystal +lattice is required. However, measurement and analysis even of basic collective +processes such as spin-phonon equilibration have remained challenging. Here, we +directly probe the flow of energy and angular momentum in the model insulating +ferrimagnet yttrium iron garnet. Following ultrafast resonant lattice +excitation, we observe that magnetic order reduces on distinct time scales of 1 +ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis and +simulations show that the two dynamics directly reflect two stages of +spin-lattice equilibration. On the 1-ps scale, spins and phonons reach +quasi-equilibrium in terms of energy through phonon-induced modulation of the +exchange interaction. This mechanism leads to identical demagnetization of the +ferrimagnet's two spin-sublattices and a novel ferrimagnetic state of increased +temperature yet unchanged total magnetization. Finally, on the much slower, +100-ns scale, the excess of spin angular momentum is released to the crystal +lattice, resulting in full equilibrium. Our findings are relevant for all +insulating ferrimagnets and indicate that spin manipulation by phonons, +including the spin Seebeck effect, can be extended to antiferromagnets and into +the terahertz frequency range.",1710.02700v2 +2019-09-30,Disorder-induced ferrimagnetism in sputtered Mn$_{x}$CoGe thin films,"Investigations into the magnetic properties of sputtered Mn$_{x}$CoGe films +in the range $0.8 \leq x \leq 2.5$ uncovered ferrimagnetic order, unlike the +ferromagnetic order reported in bulk samples. These films formed hexagonal +Ni$_{2}$In-type structures when annealed at temperatures below 600$^{\circ}$C. +While the Curie temperatures of the films are comparable to those of hexagonal +bulk MnCoGe, there is a reduction in the magnetization of the Mn$_{x}$CoGe +films relative to bulk MnCoGe, and a magnetization compensation point is +observed in the $x<1$ samples. To understand the behavior, we calculated the +magnetic moments of Mn-antisite defects in MnCoGe with density-function theory +(DFT) calculations. Models constructed from the calculation suggest that films +become ferrimagnetic due to the presence of Mn on the Co and Ge sites. In the +$x<1$ samples, these defects arose from the disorder in the films, whereas for +$x>1$, the excess Mn was driven onto the antisites. Mean field modeling of the +temperature dependence of the magnetization provides additional evidence for +ferrimagnetism. Our mean field and DFT models provide a description of how the +variation in film defects with composition will transition the magnetic +behavior from a compensated (V-type) to an uncompensated (Q-type) ferrimagnet.",1910.00124v3 +2020-12-18,Rare-earth-free ferrimagnetic Mn4N sub-20 nm thin films as high-temperature spintronic material,"Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane) +magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and +Mn4N, were predicted to be favorable for hosting small Neel skyrmions for room +temperature applications. Due to the exponential decay of interfacial +Dzyaloshinskii-Moriya interaction (DMI) and the limited range of +spin-orbit-torques, which can be used to drive skyrmion motion, the thickness +of the ferrimagnetic layer has to be small, preferably under 20 nm. While there +are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic +thin films fabricated by sputter deposition, to date rare-earth-free sub-20 nm +Mn4N films with PMA have only been reported to be achieved by molecular beam +epitaxy, which is not suitable for massive production. Here we report the +successful thermal growth of sub-20 nm Mn4N films with PMA at 400-450 {\deg}C +substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films +were achieved by reducing the surface roughness of MgO substrate through a +high-temperature vacuum annealing process. The optimal films showed low +saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7 +Merg/cc), and a remanent magnetization to saturation magnetization ratio +(Mr/Ms) near 1 at room temperature. Preliminary ab-initio density functional +theory (DFT) calculations have confirmed the ferrimagnetic ground state of Mn4N +grown on MgO. The magnetic properties, along with the high thermal stability of +Mn4N thin films in comparison with RE-TM thin films, provide the platform for +future studies of practical skyrmion-based spintronic materials.",2012.10493v1 +2017-05-25,Fast Vortex Oscillations in a Ferrimagnetic Disk near the Angular Momentum Compensation Point,"We theoretically study the oscillatory dynamics of a vortex core in a +ferrimagnetic disk near its angular momentum compensation point, where the spin +density vanishes but the magnetization is finite. Due to the finite +magnetostatic energy, a ferrimagnetic disk of suitable geometry can support a +vortex as a ground state similar to a ferromagnetic disk. In the vicinity of +the angular momentum compensation point, the dynamics of the vortex resemble +those of an antiferromagnetic vortex, which is described by equations of motion +analogous to Newton's second law for the motion of particles. Owing to the +antiferromagnetic nature of the dynamics, the vortex oscillation frequency can +be an order of magnitude larger than the frequency of a ferromagnetic vortex, +amounting to tens of GHz in common transition-metal based alloys. We show that +the frequency can be controlled either by applying an external field or by +changing the temperature. In particular, the latter property allows us to +detect the angular momentum compensation temperature, at which the lowest +eigenfrequency attains its maximum, by performing FMR measurements on the +vortex disk. Our work proposes a ferrimagnetic vortex disk as a tunable source +of fast magnetic oscillations and a useful platform to study the properties of +ferrimagnets.",1705.09049v2 +2020-09-25,Temperature dependence of the damping parameter in the ferrimagnet Gd$_3$Fe$_5$O$_{12}$,"The damping parameter ${\alpha}_{\text{FM}}$ in ferrimagnets defined +according to the conventional practice for ferromagnets is known to be strongly +temperature dependent and diverge at the angular momentum compensation +temperature, where the net angular momentum vanishes. However, recent +theoretical and experimental developments on ferrimagnetic metals suggest that +the damping parameter can be defined in such a way, which we denote by +${\alpha}_{\text{FiM}}$, that it is free of the diverging anomaly at the +angular momentum compensation point and is little dependent on temperature. To +further understand the temperature dependence of the damping parameter in +ferrimagnets, we analyze several data sets from literature for a ferrimagnetic +insulator, gadolinium iron garnet, by using the two different definitions of +the damping parameter. Using two methods to estimate the individual sublattice +magnetizations, which yield results consistent with each other, we found that +in all the used data sets, the damping parameter ${\alpha}_{\text{FiM}}$ does +not increase at the angular compensation temperature and shows no anomaly +whereas the conventionally defined ${\alpha}_{\text{FM}}$ is strongly dependent +on the temperature.",2009.12073v2 +2022-01-11,Effect of a Gaussian random external magnetic field with spatio temporal variation on compensation in Ising spin-1/2 trilayered square ferrimagnets,"In this work, an extensive Metropolis Monte Carlo simulation is performed to +investigate the steady-state magnetic and thermodynamic behaviour of a +trilayered spin-1/2 Ising ferrimagnet with square monolayers, driven by +external Gaussian random magnetic field with certain spatio-temporal +variations. Such thin ferrimagnetic systems exhibit compensation phenomenon and +thus are potentially interesting candidates for several technological +applications. Here, two distinct theoretical atoms, A and B, make up the ABA +and AAB types of configurations in which the like atoms (A-A and B-B) +ferromagnetically interact and the unlike atoms (A-B) interact +antiferromagnetically. Depending upon the strength of the spatio-temporally +varying Gaussian random field, the compensation and critical points shift and +steady-state magnetic behaviours change between the different distinct types of +ferrimagnetic behaviours. The compensation phenomenon even vanishes after +crossing a finite threshold of the standard deviation of the magnetic field for +particular choices of the other controlling parameters. Consequently, in the +Hamiltonian parameter space of both configurations, islands of ferrimagnetic +phase without compensation appear within the phase area with compensation of +field-free case. The areas of such islands grow with an increasing standard +deviation of the external field, $\sigma$, obeying the scaling relation: +$f(\sigma, A(\sigma))=\sigma^{-b}A(\sigma)$ with $b_{ABA}=1.913\pm 0.137$ and +$b_{AAB}=1.625\pm 0.066$ . These values of exponents match within the +statistical interval with those obtained with the uniform random magnetic +field.",2201.03883v4 +2022-03-29,Realistic micromagnetic description of all-optical ultrafast switching processes in ferrimagnetic alloys,"Both helicity-independent and helicity-dependent all-optical switching +processes driven by single ultrashort laser pulse have been experimentally +demonstrated in ferrimagnetic alloys as GdFeCo. Although the switching has been +previously reproduced by atomistic simulations, the lack of a robust +micromagnetic framework for ferrimagnets limits the predictions to small +nano-systems, whereas the experiments are usually performed with lasers and +samples of tens of micrometers. Here we develop a micromagnetic model based on +the extended Landau-Lifshitz-Bloch equation, which is firstly validated by +directly reproducing atomistic results for small samples and uniform laser +heating. After that, the model is used to study ultrafast single shot +all-optical switching in ferrimagnetic alloys under realistic conditions. We +find that the helicity-independent switching under a linearly polarized laser +pulse is a pure thermal phenomenon, in which the size of inverted area directly +correlates with the maximum electron temperature in the sample. On the other +hand, the analysis of the helicity-dependent processes under circular polarized +pulses in ferrimagnetic alloys with different composition indicates qualitative +differences between the results predicted by the magnetic circular dichroism +and the ones from inverse Faraday effect. Based on these predictions, we +propose experiments that would allow to resolve the controversy over the +physical phenomenon that underlies these helicity-dependent all optical +processes.",2203.15460v1 +2022-05-28,Helicity-independent all-optical switching of magnetization in ferrimagnetic alloys,"We review and discuss the process of single-shot helicity-independent +all-optical switching of magnetization by which a single suitably-ultrafast +excitation, under the right conditions, toggles magnetization from one stable +state to another. For almost a decade, this phenomenon was only consistently +observed in specific rare-earth-transition-metal ferrimagnetic alloys of +GdFeCo, but breakthrough experiments in recent years have revealed that the +same behavior can be achieved in a wide range of multi-sublattice magnets +including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co +synthetic ferrimagnets, and the rare-earth-free Heusler alloy Mn$_2$Ru$_x$Ga. +Aiming to resolve the conditions that allow switching, a series of experiments +have shown that the process in the ferrimagnetic alloys GdFeCo and +Mn$_2$Ru$_x$Ga is highly sensitive to the pulse duration, starting temperature +and the alloy composition. We argue here that the switching displayed by these +two very different ferrimagnetic alloys can be generally understood within a +single phenomenological framework describing the flow of angular momentum +between the constituent sublattices and from the sublattices to the +environment. The conditions that facilitate switching stem from the properties +of these channels of angular momentum flow in combination with the size of the +angular momentum reservoirs. We conclude with providing an outlook in this +vibrant research field, with emphasis on the outstanding open questions +pertaining to the underlying physics along with noting the advances in +exploiting this switching process in technological applications.",2205.14342v1 +2022-11-22,Spatially Nonuniform Oscillations in Ferrimagnets Based on an Atomistic Model,"The ferrimagnets, such as GdxFeCo(1-x), can produce ultrafast magnetic +switching and oscillation due to the strong exchange field. The two-sublattices +macrospin model has been widely used to explain the experimental results. +However, it fails in describing the spatial nonuniform magnetic dynamics which +gives rises to many important phenomenons such as the domain walls and +skyrmions. Here we develop the two-dimensional atomistic model and provide a +torque analysis method to study the ferrimagnetic oscillation. Under the +spin-transfer torque, the magnetization oscillates in the exchange mode or the +flipped exchange mode. When the Gd composition is increased, the exchange mode +firstly disappears, and then appears again as the magnetization compensation +point is reached. We show that these results can only be explained by analyzing +the spatial distribution of magnetization and effective fields. In particular, +when the sample is small, a spatial nonuniform oscillation is also observed in +the square film. Our work reveals the importance of spatial magnetic +distributions in understanding the ferrimagnetic dynamics. The method developed +in this paper provides an important tool to gain a deeper understanding of +ferrimagnets and antiferromagnets. The observed ultrafast dynamics can also +stimulate the development of THz oscillators.",2211.12247v1 +2022-11-30,Unconventional spin dynamics in the non-collinear phase of a ferrimagnet,"Ferrimagnets containing several partially compensated magnetic sublattices +are considered the most promising materials for all-optical data storage and +for ultrafast communications based on spin waves. There are two magnetic phases +of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics +in ferrimagnets has been studied mostly in the collinear state without paying +much attention to the kind of the magnetic phase. Here we investigate laser +induced ultrafast spin dynamics in a rare-earth iron garnet film in the +noncollinear phase as well. We identify a crucial influence of the magnetic +phase on the excited spin modes which allowed us to discover several prominent +effects previously overlooked. In particular, the non-collinearity makes the +quasi-antiferromagnetic mode sensitive to the external magnetic field and +brings its frequency close to the frequency of the quasiferromagnetic mode. The +latter maximizes near the magnetization compensation point and vanishes towards +the collinear phase. Spectacularly, at the phase transition the +quasiferromagnetic mode becomes soft and its amplitude significantly increases +reaching 7{\deg}. This opens new opportunities for the ultrafast control of +spins in ferrimagnets for nonthermal data storage and data processing.",2212.00085v2 +2023-03-27,Strain effects on magnetic compensation and spin reorientation transition of Co/Gd synthetic ferrimagnets,"Synthetic ferrimagnets are an attractive materials class for spintronics as +they provide access to all-optical switching of magnetization and, at the same +time, allow for ultrafast domain wall motion at angular momentum compensation. +In this work, we systematically study the effects of strain on the +perpendicular magnetic anisotropy and magnetization compensation of Co/Gd and +Co/Gd/Co/Gd synthetic ferrimagnets. Firstly, the spin reorientation transition +of a bilayer system is investigated in wedge type samples, where we report an +increase in the perpendicular magnetic anisotropy in the presence of in-plane +strain. Using a model for magnetostatics and spin reorientation transition in +this type of system, we confirm that the observed changes in anisotropy field +are mainly due to the Co magnetoelastic anisotropy. Secondly, the magnetization +compensation of a quadlayer is studied. We find that magnetization compensation +of this synthetic ferrimagnetic system is not altered by external strain. This +confirms the resilience of this material system against strain that may be +induced during the integration process, making Co/Gd ferrimagnets suitable +candidates for spintronics applications.",2303.15191v4 +2023-12-12,Dzyaloshinskii-Moriya interaction inducing weak ferromagnetism in centrosymmetric altermagnets and weak ferrimagnetism in noncentrosymmetric altermagnets,"The Dzyaloshinskii-Moriya interaction (DMI) has explained successfully the +weak ferromagnetism in some centrosymmetric antiferromagnets. However, in the +last years, it was generally claimed that the DMI is not effective in +centrosymmetric systems. We reconciled these views by separating the +conventional antiferromagnets and altermagnets. Altermagnets represent +collinear antiferromagnetic compounds with spin-up and spin-down sublattices +connected only by mirror and roto-translational symmetries. Consequently, the +system shows even-parity wave spin order in the k-space lifting the Kramer's +degeneracy in the non-relativistic band structure. We emphasize that the DMI +can create weak ferromagnetism in centrosymmetric altermagnets while it is not +effective in centrosymmetric conventional antiferromagnets. Additionally, DMI +can create weak ferromagnetism or weak ferrimagnetism in noncentrosymmetric +altermagnets. Once the spin-orbit coupling is included in an altermagnetic +system without time-reversal symmetry, the components of spin moments of the +two sublattices along the Neel vector are antiparallel but the other two spin +components orthogonal to the N\'eel vector can be either parallel or +antiparallel for centrosymetric systems. For noncentrosymmetric systems, we can +have different bands showing parallel or antiparallel spin components resulting +in weak ferrimagnetism. We can divide the altermagnetic compounds into classes +based on the weak ferromagnetism or weak ferrimagnetism properties. The weak +ferromagnetism and weak ferrimagnetism induced by DMI is a property exclusively +of the altermagnets, not present in either ferromagnets or conventional +antiferromagnets so we propose that altermagnets should be classified based on +this property.",2312.07678v2 +2019-11-13,Unveiling domain wall dynamics of ferrimagnets in thermal magnon currents: competition of angular momentum transfer and entropic torque,"Control of magnetic domain wall motion holds promise for efficient +manipulation and transfer of magnetically stored information. Thermal magnon +currents, generated by temperature gradients, can be used to move magnetic +textures, from domain walls, to magnetic vortices and skyrmions. In the last +years, theoretical studies have centered in ferro- and antiferromagnetic spin +structures, where domain walls always move towards the hotter end of the +thermal gradient. Here we perform numerical studies using atomistic spin +dynamics simulations and complementary analytical calculations to derive an +equation of motion for the domain wall velocity. We demonstrate that in +ferrimagnets, domain wall motion under thermal magnon currents shows a much +richer dynamics. Below the Walker breakdown, we find that the temperature +gradient always pulls the domain wall towards the hot end by minimizating its +free energy, in agreement with the observations for ferro- and antiferromagnets +in the same regime. Above Walker breakdown, the ferrimagnetic domain wall can +show the opposite, counterintuitive behavior of moving towards the cold end. We +show that in this case, the motion to the hotter or the colder ends is driven +by angular momentum transfer and therefore strongly related to the angular +momentum compensation temperature, a unique property of ferrimagnets where the +intrinsic angular momentum of the ferrimagnet is zero while the sublattice +angular momentum remains finite. In particular, we find that below the +compensation temperature the wall moves towards the cold end, whereas above it, +towards the hot end. Moreover, we find that for ferrimagnets, there is a torque +compensation temperature at which the domain wall dynamics shows similar +characteristics to antiferromagnets, that is, quasi-inertia-free motion and the +absence of Walker breakdown.",1911.05393v1 +1997-01-10,Macroscopic Quantum Coherence in Ferrimagnets,"We study macroscopic quantum coherence (MQC) in small ferrimagnets. Through +semi-classical calculations we show that even a small uncompensated moment has +a drastic effect on MQC. In particular, there is a rapid crossover to a regime +where the MQC tunnel splitting is equal to that obtained for a ferromagnet, +even though the system is still an antiferromagnet for all other aspects. We +calculate this tunnel splitting via instanton methods and compare it with +numerical evaluations. As an application we re-examine the experimental +evidence for MQC in ferritin and show that even though the uncompensated moment +of ferritin is small it greatly modifies the MQC behavior. We also discuss the +implications of our results for MQC in molecular magnets.",9701070v1 +1997-10-27,Thermodynamic Properties of Heisenberg Ferrimagnetic Spin Chains: Ferromagnetic-Antiferromagnetic Crossover,"We study thermodynamic properties of the one-dimensional Heisenberg +ferrimagnet with antiferromagnetically exchange-coupled two kinds of spins 1 +and 1/2. The specific heat and the magnetic susceptibility are calculated +employing a modified spin-wave theory as well as a quantum Monte Carlo method. +The specific heat is in proportion to $T^{1/2}$ at low enough temperatures but +shows a Schottky-like peak at mid temperatures. The susceptibility diverges as +$T^{-2}$. We reveal that at low temperatures the model is regarded as a +ferromagnet, while at mid temperatures it behaves like a gapped +antiferromagnet.",9710291v2 +1997-12-26,Quantum Tunneling in Ferrimagnetic Nanoparticles Coupled to a Spin Bath: An Effective Hamiltonian,"An effective Hamiltonian, describing quantum tunneling in ferrimagnetic +nanoparticles which includes interactions between the electronic spins of +nanoparticle and microscopic environmental spins (like nuclear spins or +paramagnetic impurities), is obtained. Two limiting cases, describing tunneling +in antiferromagnetic and ferromagnetic regimes are considered, and criterion +for the transition between the two regimes is found. The validity of analytic +results is verified by the exact diagonalization method.",9712302v1 +1998-05-28,"Thermodynamics of the (1,1/2) Ferrimagnet in Finite Magnetic Fields","We investigate the specific heat and magnetisation of a ferrimagnet with gS=1 +and S=1/2 spins in a finite magnetic field using the transfer matrix DMRG down +to T=0.025J. Ferromagnetic gapless and antiferromagnetic gapped excitations for +H=0 lead to rich thermodynamics for H > 0. While the specific heat is +characterized by a generic double peak structure, magnetisation reveals two +critical fields, Hc1=1.76(1) and Hc2=3.00(1) with square-root behaviour in the +T=0 magnetisation. Simple analytical arguments allow to understand these +experimentally accessible findings.",9805376v1 +1998-06-28,Combination of Ferromagnetic and Antiferromagnetic Features in Heisenberg Ferrimagnets,"We investigate the thermodynamic properties of Heisenberg ferrimagnetic +mixed-spin chains both numerically and analytically with particular emphasis on +the combination of ferromagnetic and antiferromagnetic features. Employing a +new density-matrix renormalization-group technique as well as a quantum Monte +Carlo method, we reveal the overall thermal behavior: At very low temperatures, +the specific heat and the magnetic susceptibility times temperature behave like +$T^{1/2}$ and $T^{-1}$, respectively, whereas at intermediate temperatures, +they exhibit a Schottky-like peak and a minimum, respectively. Developing the +modified spin-wave theory, we complement the numerical findings and give a +precise estimate of the low-temperature behavior.",9806344v1 +1998-10-09,Low-Energy Structure of Heisenberg Ferrimagnetic Spin Chains,"Static and dynamic structure factors of Heisenberg ferrimagnetic spin chains +are numerically investigated. There exist two distinct branches of elementary +excitations, which exhibit ferromagnetic and antiferromagnetic aspects. The +ferromagnetic feature is smeared out with the increase of temperature, whereas +the antiferromagnetic one persists up to higher temperatures. The scattering +intensity is remarkably large at lower boundaries of the ferromagnetic and +antiferromagnetic spectra. All these observations are consistent with the +ferromagnetic-to-antiferromagnetic crossover in the thermal behavior which has +recently been reported.",9810113v1 +1999-01-24,Half-Metallic Ferrimagnetism in Mn_2VAl,"We show that Mn_2VAl is a compound for which the generalized gradient +approximation (GGA) to the exchange-correlation functional in density +functional theory makes a qualitative change in predicted behavior compared to +the usual local density approximation (LDA). Application of GGA leads to +prediction of Mn_2VAl being a half-metallic ferrimagnet, with the minority +channel being the conducting one. The electronic and magnetic structure is +analyzed and contrasted with the isostructural enhanced semimetal Fe_2VAl.",9901253v2 +1999-12-18,Nuclear spin relaxation in ordered bimetallic chain compounds,"A theoretical interpretation is given to recent proton spin relaxation-time +(T_1) measurements on NiCu(C_7H_6N_2O_6)(H_2O)_3$\cdot$2H_2O, which is an ideal +one-dimensional ferrimagnetic Heisenberg model system of alternating spins 1 +and 1/2. The relaxation rate T_1^{-1} is formulated in temrs of the spin-wave +theory and is evaluated by the use of a quantum Monte Carlo method. +Calculations of the temperature and applied-field (H) dependences of T_1^{-1} +are in total agreement with the experimental findings. T_1 behaves as +$T_1^{-1}\propto H^{-1/2}$, which turns out an indirect observation of the +quadratic dispersion relations dominating the low-energy physics of quantum +ferrimagnets.",9912340v1 +2000-05-15,Multi-plateau magnetization curves of one-dimensional Heisenberg ferrimagnets,"Ground-state magnetization curves of ferrimagnetic Heisenberg chains of +alternating spins $S$ and $s$ are numerically investigated. Calculating several +cases of $(S,s)$, we conclude that the spin-$(S,s)$ chain generally exhibits +$2s$ magnetization plateaux even at the most symmetric point. In the double- or +more-plateau structure, the initial plateau is generated on a classical basis, +whereas the higher ones are based on a quantum mechanism.",0005248v1 +2002-10-14,Phase diagram and influence of defects in the double perovskites,"The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo +O_6 is analyzed, with and without disorder due to antisites. In addition to an +homogeneous half metallic ferrimagnetic phase in the absence of doping and +disorder, we find antiferromagnetic phases at large dopings, and other +ferrimagnetic phases with lower saturation magnetization, in the presence of +disorder.",0210303v2 +2002-10-29,Dynamical Mean Field Theory of Double Perovskite Ferrimagnets,"The dynamical mean field method is used to analyze the magnetic transition +temperature and optical conductivity of a model for the ferrimagnetic double +perovskites such as $Sr_2FeMoO_6$. The calculated transition temperatures and +optical conductivities are found to depend sensitively on the band structure. +For parameters consistent with local spin density approximation band +calculations, the computed transition temperatures are lower than observed, and +in particular decrease dramatically as band filling is increased, in +contradiction to experiment. Band parameters which would increase the +transition temperature are identified.",0210627v1 +2003-04-15,Shape and surface anisotropy effects on the hysteresis of ferrimagnetic nanoparticles,"We present the results of Monte Carlo simulations of a model of a single +maghemite ferrimagnetic nanoparticle with the aim to clarify the role played by +the increased anisotropy at the surface and by the shape (spherical or +elliptical) of the particle on the magnetization processes at low temperatures. +The formation of hedgehog-like structures for high enough surface anisotropy is +responsible for a change in the reversal mechanism of the particles.",0304330v1 +2004-04-10,Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes,"Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is +studied by means of a modified spin-wave theory. We consider the second-order +process, where a nuclear spin flip induces virtual spin waves which are then +scattered thermally via the four-magnon exchange interaction, as well as the +first-order process, where a nuclear spin directly interacts with spin waves +via the hyperfine interaction. We point out a possibility of the three-magnon +relaxation process predominating over the Raman one and suggest model +experiments.",0404243v2 +2005-06-27,Spin-lattice coupling in the ferrimagnetic semiconductor FeCr2S4 probed by surface acoustic waves,"Using surface acoustic waves, the elastomagnetic coupling could be studied in +thin single crystalline plates of the ferrimagnetic semiconductor FeCr2S4 by +measuring the attenuation and the frequency tracking in the temperature range +4.2 K to 200 K. The data clearly display the anomalies found in low-field +magnetization measurements.",0506702v1 +2005-07-20,Persistent spin current in mesoscopic ferrimagnetic spin ring,"Using a semiclassical approach, we study the persistent magnetization current +of a mesoscopic ferrimagnetic ring in a nonuniform magnetic field. At zero +temperature, there exists persistent spin current because of the quantum +fluctuation of magnons, similar to the case of an antiferromagnetic spin ring. +At low temperature, the current shows activation behavior because of the +field-induced gap. At higher temperature, the magnitude of the spin current is +proportional to temperature T, similar to the reported result of a +ferromagnetic spin ring.",0507467v2 +2006-03-13,Phase transitions in random magnetic bilayer,"The influence of random interlayer exchange on the phase states of the +simplest magnetic heterostructure consisting of two ferromagnetic Ising layers +with large interaction radius is studied. It is shown that such system can +exist in three magnetic phases: ferromagnetic, antiferromagnetic and +ferrimagnetic. The possible phase diagrams and temperature dependencies of +thermodynamic parameters are described. The regions of existence of the +magnetic phases in external magnetic field are determined at zero temperature.",0603347v3 +2006-05-06,Evidence for multimagnon-mediated nuclear spin relaxation in the intertwining double-cain ferrimagnet $Ca_3 Cu_3 (PO_4)_4$,"The nuclear spin-lattice relaxation time $T_1$ of $^{31}P$ nuclei in the +title compound is measured for the first time and interpreted in terms of a +modified spin-wave theory. We establish a novel scenario for one-dimensional +ferrimagnetic spin dynamics -- it is three-magnon processes enhanced by +exchange scattering, rather than Raman processes, that make the major +contribution to $1/T_1$.",0605157v2 +2006-09-12,Phase diagram of frustrated mixed-spin ladders in the strong-coupling limit,"We study the ground-state properties of frustrated Heisenberg ferrimagnetic +ladders with antiferromagnetic exchange interactions and two types of +alternating sublattice spins. In the limit of strong rung couplings, we show +that the mixed spin-1/2 and spin-1 ladders can be systematically mapped onto a +spin-1/2 Heisenberg model with additional next-nearest-neighbor exchanges. The +system is either in a ferrimagnetic state or in a critical spin-liquid state +depending on the competition between the spin exchanges along the legs and the +diagonal exchanges.",0609269v2 +1995-03-07,On ferrimagnetic phases in chiral Yukawa models,"We discuss the phase structure of chiral Yukawa models in the mean-field +approximation. In particular, we examine under which conditions a ferrimagnetic +phase appears, by calculating the slopes of possible second order phase +transition lines near a critical point. Our results contrast with some +statements which appeared in the literature recently.",9503006v1 +2007-06-06,Peculiar Ferrimagnetism Associated with Charge Order in Layered Perovskite GdBaMn2O5,"The magnetic properties of GdBaMn_{2}O_{5.0}, which exhibits charge ordering, +are studied from 2 to 400 K using single crystals. In a small magnetic field +applied along the easy axis, the magnetization M shows a temperature-induced +reversal which is sometimes found in ferrimagnets. In a large magnetic field, +on the other hand, a sharp change in the slope of M(T) coming from an unusual +turnabout of the magnetization of the Mn sublattices is observed. Those +observations are essentially explained by a molecular field theory which +highlights the role of delicate magnetic interactions between Gd^{3+} ions and +the antiferromagnetically coupled Mn^{2+}/Mn^{3+} sublattices.",0706.0749v1 +2007-07-14,"Martensitic transition, ferrimagnetism and Fermi surface nesting in Mn_2NiGa","The electronic structure of Mn_2NiGa has been studied using density +functional theory and photoemission spectroscopy. The lower temperature +tetragonal martensitic phase with c/a= 1.25 is more stable compared to the +higher temperature austenitic phase. Mn_2NiGa is ferrimagnetic in both phases. +The calculated valence band spectrum, the optimized lattice constants and the +magnetic moments are in good agreement with experiment. The majority-spin Fermi +surface (FS) expands in the martensitic phase, while the minority-spin FS +shrinks. FS nesting indicates occurrence of phonon softening and modulation in +the martensitic phase.",0707.2133v2 +2008-08-28,Inhomogeneous ferrimagnetic-like behavior in Gd2/3Ca1/3MnO3 single crystals,"We present a study of the magnetic properties of Gd2/3Ca1/3MnO3 single +crystals at low temperatures. We show that this material behave as an +inhomogeneous ferrimagnet. In addition to small saturation magnetization at 5 +K, we have found history dependent effects in the magnetization and the +presence of exchange bias. These features are compatible with microscopic phase +separation in the clean Gd2/3Ca1/3MnO3 system studied.",0808.3922v1 +2008-12-19,Origin of the Ising Ferrimagnetism and Spin-Charge Coupling in LuFe2O4,"The spin ordering and spin-charge coupling in LuFe2O4 were investigated on +the basis of density functional calculations and Monte Carlo simulations. The +2:1 ferrimagnetism arises from the strong antiferromagnetic intra-sheet +Fe3+-Fe3+ and Fe3+ -Fe2+ as well as some substantial antiferromagnetic +Fe2+-Fe3+ inter-sheet spin exchange interactions. The giant magnetocapacitance +at room temperature and the enhanced electric polarization at 240 K of LuFe2O4 +are explained by the strong spin-charge coupling.",0812.3897v1 +2009-02-18,Majority-spin non-quasiparticle states in half-metallic ferrimagnet Mn$_2$VAl,"The density of non-quasiparticle states in the ferrimagnetic full-Heuslers +Mn$_2$VAl alloy is calculated from first principles upon appropriate inclusion +of correlations. In contrast to most half-metallic compounds, this material +displays an energy gap in the majority-spin spectrum. For this situation, +non-quasiparticle states are located below the Fermi level, and should be +detectable by spin-polarized photoemission. This opens a new way to study +many-body effects in spintronic-related materials.",0902.3109v1 +2009-03-11,Ferrimagnetic-like surface resonance from hybrid metamaterial slab,"We show that a hybrid metamaterial slab comprising of an one-dimensional +array of two different types of cavities exhibits ferrimagnetic-like surface +resonances which can be used to realize interesting phenomena such as directive +emission as a consequence of strong angle-dependent reflection phase and the +selective coupling of a Gaussian incident beam into a higher order diffractive +channel, giving rise to the phenomenon of negative reflection and +retro-directive backtracking. The findings are verified by experiments in the +microwave regime.",0903.1907v2 +2009-07-08,Magnetic hysteresis in a molecular Ising ferrimagnet: Glauber dynamics approach,"Motivated by recent experimental results reporting giant coercive fields in +Co(II)-based molecular magnets we present a theory of hysteresis phenomena +based on the Glauber stochastic dynamics. Unusual form of hysteresis loops is +similar to those of found in Co-based quasi-one-dimensional ferrimagnet CoPhOMe +at low temperatures. Temperature dependence of the coercive field has a +characteristic form with an inflection that may serve as an indicator of the +Glauber dynamics in real compounds. A relevance of the model for other Co-based +molecular magnets is discussed.",0907.1348v1 +2009-09-11,Spin models of quasi-1D quantum ferrimagnets with competing interactions,"We present a brief survey of the recent theoretical work related to generic +Heisenberg spin models describing quasi-one-dimensional quantum ferrimagnets. +The emphasis is on quantum chains and ladders with strong competing +interactions, such as the frustrated $J_1-J_2$ chain with alternating (1,1/2) +spins, the spin-1/2 diamond chain with four-spin cyclic couplings, and some +generic types of mixed-spin ladders with geometric frustration. As a rule, +discussed models exhibit rich quantum phase diagrams and provide some +interesting examples of one-dimensional magnetic-paramagnetic quantum phase +transitions. A number of open problems in the reviewed research area are +discussed.",0909.2182v1 +2009-10-13,"Monte Carlo Study of Mixed-Spin S=(1/2,1) Ising Ferrimagnets","We investigate Ising ferrimagnets on square and simple-cubic lattices with +exchange couplings between spins of values S=1/2 and S=1 on neighbouring sites +and an additional single-site anisotropy term on the S=1 sites. Based mainly on +a careful and comprehensive Monte Carlo study, we conclude that there is no +tricritical point in the two--dimensional case, in contradiction to mean-field +predictions and recent series results. However, evidence for a tricritical +point is found in the three-dimensional case. In addition, a line of +compensation points is found for the simple-cubic, but not for the square +lattice.",0910.2377v1 +2010-10-23,High spin polarization in epitaxial films of ferrimagnetic Mn3Ga,"Ferrimagnetic Mn3Ga exhibits a unique combination of low saturation +magnetization (Ms = 0.11 MA m-1) and high perpendicular anisotropy with a +uniaxial anisotropy constant of Ku = 0.89 MJ m-3. Epitaxial c-axis films +exhibit spin polarization as high as 58%, measured using point contact Andreev +reflection. These epitaxial films will be able to support thermally stable +sub-10 nm bits for spin transfer torque memories.",1010.4872v1 +2010-12-23,On the derivation of the magnetocaloric properties in ferrimagnetic spinel Mn3O4,"Large magnetocaloric effect has been observed in Mn3O4 around its +ferrimagnetic transition at TN = 42.75 K. Field-induced isothermal entropy +changes (\DeltaS) were derived from both magnetic and calorimetric techniques. +The maximum |\DeltaS| and adiabatic temperature change ({\Delta}Tad) at TN are +11 J kg-1 K-1 and 1.9 K, respectively, for a magnetic field change of 20 kOe. +Moreover, it is found that the complex magnetic phase transitions taking place +below TN produce additional -but smaller- features on \DeltaS(T).",1012.5161v1 +2011-09-08,Mixed Ising ferrimagnets with next-nearest neighbour couplings on square lattices,"We study Ising ferrimagnets on square lattices with antiferromagnetic +exchange couplings between spins of values S=1/2 and S=1 on neighbouring sites, +couplings between S=1 spins at next--nearest neighbour sites of the lattice, +and a single--site anisotropy term for the S=1 spins. Using mainly ground state +considerations and extensive Monte Carlo simulations, we investigate various +aspects of the phase diagram, including compensation points, critical +properties, and temperature dependent anomalies. In contrast to previous +belief, the next--nearest neighbour couplings, when being of antiferromagnetic +type, may lead to compensation points.",1109.1709v1 +2013-05-14,Ferrimagnetic Spin Wave Resonance and Superconductivity in Carbon Nanotubes,"The phenomenon of ferrimagnetic spin wave resonance [uncompensated +antiferromagnetic spin wave resonance] has been detected for the first time. It +has been observed in carbon nanotubes, produced by high energy ion beam +modification of diamond single crystals in $\ <{100}\ >$ direction. +Peculiarities of spin wave resonance observed allow to insist on the formation +in given nanotubes of $s^+$ superconductivity at room temperature, coexisting +with uncompensated antiferromagnetic ordering.",1305.3256v1 +2013-10-30,Geometrical origin of ferrimagnetism and superparamagnetism in Fe-based double perovskite multiferroics,"We show that a superstructure of antiferromagnetically interacting Fe$^{3+}$ +($S=5/2$) ions in double perovskites AFe$_{1/2}$M$_{1/2}$O$_{3}$ exhibits a +ferrimagnetic ordering below $T_{fe} \approx 5.6J_1$ ($J_1/k_B \sim 50$~K), +which is close to room temperature. Small clusters of the same structure +exhibit a superparamagnetic behavior at $T \lesssim T_{fe}$. The possibility of +formation of such clusters explains the room-temperature (superpara)magnetism +in 3$d$-metal based oxides.",1310.8079v2 +2014-01-13,Room-Temperature Ferrimagnet with Frustrated Antiferroelectricity: Promising Candidate Toward Multiple State Memory,"On the basis of first-principles calculations we show that the M-type +hexaferrite BaFe12O19 exhibits frustrated antiferroelectricity associated with +its trigonal bipyramidal Fe3+ sites. The ferroelectric (FE) state of BaFe12O19, +reachable by applying an external electric field to the antiferroelectric (AFE) +state, can be made stable at room temperature by appropriate element +substitution or strain engineering. Thus M-type hexaferrite, as a new type of +multiferoic with coexistence of antiferroelectricity and ferrimagnetism, +provide a basis for studying the phenomenon of frustrated antiferroelectricity +and realizing multiple state memory devices.",1401.2747v1 +2014-10-21,Magnetic switching dynamics in a ferrimagnetic two sub-lattice model including ultrafast exchange scattering,"We study the heat-induced magnetization dynamics in a toy model of a +ferrimagnetic alloy, which includes localized spins antiferromagnetically +coupled to an itinerant carrier system with a Stoner gap. We determine the +one-particle spin-density matrix including exchange scattering between +localized and itinerant bands as well as scattering with phonons. While a +transient ferromagnetic-like state can always be achieved by a sufficiently +strong excitation, this transient ferromagnetic-like state only leads to +magnetization switching for model parameters that also yield a compensation +point in the equilibrium M(T) curve.",1410.5745v2 +2016-09-07,Magnetodielectric and spin-lattice coupling in quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$,"We have studied magnetodielectric and spin-lattice coupling in +CoNb$_{2}$O$_{6}$ single crystals. Magnetostriction and magnetodielectric +experiments are performed at temperatures in and above antifferomagnetic phase +of quasi 1D Ising spin chain CoNb$_{2}$O$_{6}$. Field induced magnetic +transitions are clearly reflected in magnetodielectric measurement as well as +magnetostriction measurement also. Two sharp anomalies are found around the +critical fields of antiferromagnetic to ferrimagnetic transition and +ferrimagnetic to saturated paramagnetic transition in both magnetodielectric +and magnetostriction experiments. High field anomaly is more pronounced for +magnetodielectric response and magnetostriction also. So, in CoNb$_{2}$O$_{6}$, +spins are strongly coupled with lattice as well as charges also.",1609.02048v1 +2017-03-15,Modeling ultrafast all-optical switching in synthetic ferrimagnets,"Based on numerical simulations, we demonstrate thermally induced magnetic +switching in synthetic ferrimagnets composed of multilayers of rare-earth and +transition metals. Our findings show that deterministic magnetization reversal +occurs above a certain threshold temperature if the ratio of transition metal +atoms to rare-earth atoms is sufficiently large. Surprisingly, the total +thickness of the multilayer system has little effect on the occurence of +switching. We further provide a simple argument to explain the temperature +dependence of the reversal process.",1703.05220v1 +2018-11-16,Ferrimagnetic organelles in multicellular organisms,"In this paper, it was revealed by means of methods of atomic force microscopy +and magnetic force microscopy that the biogenic magnetic nanoparticles are +localized in the form of chains in the walls of the capillaries of animals and +the walls of the conducting tissue of plants and fungi. The biogenic magnetic +nanoparticles are part of the transport system in multicellular organisms. In +this connection, a new idea of function of biogenic magnetic nanoparticles is +discussed in the paper that the chains of biogenic magnetic nanoparticles +represent a ferrimagnetic organelles of a specific purpose.",1811.06717v1 +2013-08-01,Exchange relaxation as the mechanism of ultrafast spin reorientation in two-sublattice ferrimagnets,"In the exchange approximation, an exact solution is obtained for the +sublattice magnetizations evolution in a two-sublattice ferrimagnet. Nonlinear +regimes of spin dynamics are found that include both the longitudinal and +precessional evolution of the sublattice magnetizations, with the account taken +of the exchange relaxation. In particular, those regimes describe the spin +switching observed in the GdFeCo alloy under the influence of a femtosecond +laser pulse.",1308.0203v1 +2014-03-03,CaBaCo$_4$O$_7$ : A ferrimagnetic pyroelectric,"Magneto-electric coupling in pyroelectric CaBaCo$_4$O$_7$ is investigated +using ab-intio calculations and Landau theory. The former shows that +exchange-striction is strong enough to produce a giant change in electric +polarization upon ferrimagnetic ordering, comparable to the experimentally +determined value of ~17 mC/m$^2$ . Furthermore, Landau theory demonstrates that +magneto-elastic coupling in CaBaCo$_4$O$_7$ is responsible for the strong +magneto-electric coupling appearing close to the magnetic phase transition.",1403.0614v1 +2017-04-17,Strain-magneto-optics of a magnetostrictive ferrimagnet CoFe2O4,"We experimentally demonstrate that in magnetostrictive ferrimagnetic single +crystal of CoFe2O4 there is clear correlation between magnetostriction and +magnetoreflection of unpolarized light in the infrared range. The influence of +magnetic field on specular reflection is likely to be indirect: application of +a magnetic field results in strong strain and deformation of the crystal +lattice, which leads to the change in electron energy structure and hence +reflection spectrum.",1704.04890v1 +2012-01-10,Direct observation of magnetic phase coexistence and magnetization reversal in a Gd$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin film,"We have investigated the ferrimagnetic domain structure in a +Gd$_{0.67}$Ca$_{0.33}$MnO$_{3}$ thin film using magnetic force microscopy. We +observe clear signs of phase separation, with magnetic islands embedded in a +non-magnetic matrix. We also directly visualize the reversal of magnetization +of ferrimagnetic domains as a function of temperature and attribute it to a +change in the balance of magnetization of anti-aligned Mn and Gd sublattices.",1201.2144v1 +2014-06-07,Interface-dependent magnetotransport properties for thin Pt films on ferrimagnetic Y3Fe5O12,"We have studied magnetoresistance and Hall effects for 1.8-nm-thick Pt films +grown on a ferrimagnetic insulator Y3Fe5O12 in a wide temperature (0.46-300 K) +and magnetic-field (-15-15 T) region. In the low-temperature regime where +quantum corrections to conductivity are observed, weak antilocalization +behavior observed in Pt films is critically suppressed when the film is +attached to Y3Fe5O12. Hall resistance in the Pt film is also affected by +Y3Fe5O12, and it exhibits logarithmic temperature dependence in a broad +temperature range. The magnetotransport properties in the high-field range are +significantly influenced by the interface between Pt and Y3Fe5O12.",1406.1859v1 +2017-12-13,Theoretical Proposal for Determining Angular Momentum Compensation in Ferrimagnets,"This work demonstrates that the magnetization and angular momentum +compensation temperature (TMC and TAMC) in ferrimagnets (FiM) can be +unambiguously determined by performing two sets of temperature dependent +current switching, with the symmetry reverses at TMC and TAMC, respectively. A +theoretical model based on the modified Landau-Lifshitz-Bloch equation is +developed to systematically study the spin torque effect under different +temperatures, and numerical simulations are performed to corroborate our +proposal. Furthermore, we demonstrate that the recently reported linear +relation between TAMC and TMC can be explained using the Curie-Weiss theory.",1712.04624v1 +2017-12-15,Effect of the Canting of Local Anisotropy Axes on Ground-State Properties of a Ferrimagnetic Chain with Regularly Alternating Ising and Heisenberg Spins,"The effect of the canting of local anisotropy axes on the ground-state phase +diagram and magnetization of a ferrimagnetic chain with regularly alternating +Ising and Heisenberg spins is exactly examined in an arbitrarily oriented +magnetic field. It is shown that individual contributions of Ising and +Heisenberg spins to the total magnetization basically depend on the spatial +orientation of the magnetic field and the canting angle between two different +local anisotropy axes of the Ising spins.",1712.05622v1 +2018-10-01,Trimers of MnO6 octahedra and ferrimagnetism of Ba4NbMn3O12,"Ba4NbMn3O12 is reported, synthesized by a solid state method in air. The +crystal structure, determined by performing refinements on room temperature +powder X-ray diffraction data by the Rietveld method, consists of Mn3O12 +trimers in the configuration of three face-sharing MnO6 octahedra, with the +trimers arranged in triangular planes. An effective moment of 4.82 {\mu}B/f.u +is observed and competing antiferromagnetic and ferromagnetic interactions +between Mn ions are inferred from the Weiss temperature of -4 K and the +ferrimagnetic ordering transition of approximately 42 K. Ba4NbMn3O12 is a +semiconductor with a transport activation energy of 0.37 eV.",1810.00763v1 +2019-07-03,Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the form of AB$_p$C$_{1-p}$,"Dynamic magnetic features of a mixed ferro-ferrimagnetic ternary alloy in the +form of AB$_p$C$_{1-p}$, especially. The effect of Hamiltonian parameters on +the dynamic magnetic features of the system are investigated. For this aim, an +AB$_p$C$_{1-p}$ ternary alloy system was simulated within the mean-field +approximation based on a Glauber type stochastic dynamic and for simplicity, A, +B and C ions as SA = 1/2, SB = 1 and SC = 3/2, were chosen respectively. It was +found that in our dynamic system the critical temperature was always dependent +on the concentration ratio of the ternary alloy.",1907.01850v1 +2021-01-14,Anomalous Hall effect in weak-itinerant ferrimagnet FeCr$_2$Te$_4$,"We carried out a comprehensive study of electronic transport, thermal and +thermodynamic properties in FeCr$_2$Te$_4$ single crystals. It exhibits +bad-metallic behavior and anomalous Hall effect (AHE) below a weak-itinerant +paramagentic-to-ferrimagnetic transition $T_c$ $\sim$ 123 K. The linear scaling +between the anomalous Hall resistivity $\rho_{xy}$ and the longitudinal +resistivity $\rho_{xx}$ implies that the AHE in FeCr$_2$Te$_4$ is most likely +dominated by extrinsic skew-scattering mechanism rather than intrinsic KL or +extrinsic side-jump mechanism, which is supported by our Berry phase +calculations.",2101.05831v1 +2021-05-13,Thermal instability in a ferrimagnetic resonator strongly coupled to a loop-gap microwave cavity,"We study nonlinear response of a ferrimagnetic sphere resonator (FSR) +strongly coupled to a microwave loop gap resonator (LGR). The measured response +in the regime of weak nonlinearity allows the extraction of the FSR Kerr +coefficient and its cubic damping rate. We find that there is a certain range +of driving parameters in which the system exhibits instability. In that range, +self-sustained modulation of the reflected power off the system is generated. +The instability is attributed to absorption-induced heating of the FSR above +its Curie temperature.",2105.06102v2 +2021-10-23,Optical interface for a hybrid magnon-photon resonator,"We study optical detection of magnetic resonance of a ferrimagnetic sphere +resonator, which is strongly coupled to a microwave loop gap resonator. Optical +fibers are employed for coupling the sphere resonator with light in the telecom +band. We find that magnetic resonance can be optically detected in the region +of anti-crossing between the loop gap and the ferrimagnetic resonances. By +measuring the response time of the optical detection we rule out the +possibility that microwave induced heating is responsible for the optical +detectability.",2110.13644v1 +2023-04-27,Effective Tight-Binding Model of Compensated Ferrimagnetic Weyl Semimetal with Spontaneous Orbital Magnetization,"The effective tight-binding model with compensated ferrimagnetic +inverse-Heusler lattice Ti$_{2}$MnAl, candidate material of magnetic Weyl +semimetal, is proposed. The energy spectrum near the Fermi level, the +configurations of the Weyl points, and the anomalous Hall conductivity are +calculated. We found that the orbital magnetization is finite, while the total +spin magnetization vanishes, at the energy of the Weyl points. The magnetic +moments at each site are correlated with the orbital magnetization, and can be +controlled by the external magnetic field.",2304.14009v1 +2023-12-19,Evidence for coexistence of spin-glass and ferrimagnetic phases in BaFe12O19 due to basal plane freezing,"We present here the results of low-temperature magnetization and X-ray +magnetic circular dichroism studies on single crystals of BaFe12O19 which +reveal for the first time the emergence of a spin glass phase, in coexistence +with the long-range ordered ferrimagnetic phase, due to the freezing of the +basal plane spin component.",2312.11990v1 +2005-10-30,Lattice expansion and non-collinear to collinear ferrimagnetic order in MnCr$_2$O$_4$ nanoparticle,"We report magnetic behaviour of MnCr$_2$O$_4$, which belongs to a special +class of spinel, known as chromite. Bulk MnCr$_2$O$_4$ shows a sequence of +magnetic states, which follows paramagnetic (PM) to collinear ferrimagnetic +(FM) state below T$_C$ $\sim$ 45 K and collinear FM state to non-collinear FM +state below T$_S$ $\sim$ 18 K. The non-collinear spin structure has been +modified on decreasing the particle size, and magnetic transition at T$_S$ +decreases in nanoparticle samples. However, ferrimagnetic order is still +dominating in nanoparticles, except the observation of superparamagnetic like +blocking and decrease of spontaneous magnetization for nanoparticle. This may, +according to the core-shell model of ferrimagnetic nanoparticle, be the surface +disorder effect of nanoparticle. The system also show the increase of T$_C$ in +nanoparticle samples, which is not consistent with the core-shell model. The +analysis of the M(T) data, applying spin wave theory, has shown an unusual +Bloch exponent value 3.35 for bulk MnCr$_2$O$_4$, which decreases and +approaches to 1.5, a typical value for any standard ferromagnet, with +decreasing the particle size. MnCr$_2$O$_4$ has shown a few more unusual +behaviour. For example, lattice expansion in nanoparticle samples. The present +work demonstrates the correlation between a systematic increase of lattice +parameter and the gradual decrease of B site non-collinear spin structure in +the light of magnetism of MnCr$_2$O$_4$ nanoparticles.",0510814v1 +2011-07-26,Magnetic Behaviour of Disordered Ising Ferrimagnet in High Magnetic Field,"The magnetic behaviour of a disordered ferrimagnetic system Ap B1-p where +both A and B represent the magnetic atoms with respective spin SA = 1/2 and SB += 1 in presence of high magnetic field is treated theoretically.Assuming the +magnetic interaction can be described through Ising Hamiltonian the approximate +free energy is obtained using the cluster-variational method. The field +dependence of the magnetization is then obtained for different concentration p +and exchange parameters (JAA, JBB and JAB). For p = 0.5,the magnetization M in +ferrimagnetic state and in absence of compensation temperature Tcm vanishes at +TC.Field induced reversal of M is found at switching temperature TS (0K$, are calculated. The $T\chi_{uni}$ has a +minimum at intermediate temperatures and the spin correlation length behaves as +$T^{-1}$ at low temperatures. These qualitatively agree with the numerical +results and the difference is small at low temperatures.",9904291v2 +1999-12-13,Simulated nuclear spin-lattice relaxation in Heisenberg ferrimagnets: Indirect observation of quadratic dispersion relations,"In response to recent proton spin relaxation-time measurements on +NiCu(pba)(H$_2$O)$_3$$\cdot$2H$_2$O with ${pba}=1,3{-propylenebis(oxamato)}$, +which is an excellent one-dimensional ferrimagnetic Heisenberg model system of +spin-$(1,{1/2})$, we study the Raman relaxation process in spin-$(S,s)$ quantum +ferrimagnets on the assumption of predominantly dipolar hyperfine interactions +between protons and magnetic ions. The relaxation time $T_1$ is formulated +within the spin-wave theory and is estimated as a function of temperature and +an applied field $H$ by a quantum Monte Carlo method. The low-temperature +behavior of the relaxation rate $T_1^{-1}$ qualitatively varies with $(S,s)$, +while $T_1^{-1}$ is almost proportional to $H^{-1/2}$ due to the characteristic +dispersion relations.",9912211v1 +2000-03-24,Magnetic Behavior of a Mixed Ising Ferrimagnetic Model in an Oscillating Magnetic Field,"The magnetic behavior of a mixed Ising ferrimagnetic system on a square +lattice, in which the two interpenetrating square sublattices have spins +- 1/2 +and spins +-1,0, in the presence of an oscillating magnetic field has been +studied with Monte Carlo techniques. The model includes nearest and +next-nearest neighbor interactions, a crystal field and the oscillating +external field. By studying the hysteretic response of this model to an +oscillating field we found that it qualitatively reproduces the increasing of +the coercive field at the compensation temperature observed in real +ferrimagnets, a crucial feature for magneto-optical applications. This behavior +is basically independent of the frequency of the field and the size of the +system. The magnetic response of the system is related to a dynamical +transition from a paramagnetic to a ferromagnetic phase and to the different +temperature dependence of the relaxation times of both sublattices.",0003403v1 +2000-08-10,Combined effect of frustration and dimerization in ferrimagnetic chains and square lattice,"Within the zero-temperature linear spin-wave theory we have investigated the +effect of frustration and dimerization of a Heisenberg system with alternating +spins $s_{1}$ and $s_{2}$ on one- and two-dimensional lattices. The combined +effect most visibly appears in the elementary excitation spectra. In contrast +to the ground state energy that decreases with dimerization and increases with +frustration, the excitation energies are shown to be suppressed in energy by +both dimerization and frustration. The threshold value of frustration that +signals a transition from a classical ferrimagnetic state to a spiral state, +decreases with dimerization, showing that dimerization further helps in the +phase transition. The correlation length and sublattice magnetization decrease +with both dimerization and frustration indicating the destruction of the +long-range classical ferrimagnetic. The linear spin wave theory shows that in +the case of a square lattice, dimerization initially opposes the +frustration-led transition to a spiral magnetic state, but then higher +magnitudes of lattice deformation facilitate the transition. It also shows that +the transition to spiral state is inhibited in a square lattice beyond a +certain value of dimerization.",0008165v1 +2000-11-15,A Mechanism for Ferrimagnetism and Incommensurability in One-Dimensional Systems,"A mechanism for ferrimagnetism in + (1+1)-dimensions is discussed. The ferrimagnetism is cased by interactions +described by operators with non-zero conformal spin. Such interactions appear +in such problems as the problem of tunneling between Luttinger liquids and the +problem of frustrated spin ladder. I present exact solutions for a +representative class of models containing such interactions together with a +simple mean field analysis. It is shown that the interactions (i) dynamically +generate static oscillations with a wave vector dependent on the coupling +constant, (ii) give rise to a finite magnetic moment at $T = 0$ accompanied by +the soft mode with a non-relativistic ({\it ferromagnetic}) dispersion $E \sim +k^2$, (iii) generate massive (roton) modes.",0011268v4 +2001-01-12,Superfluid-spiral state of quantum ferrimagnets in magnetic field,"We study the phase diagram of one-dimensional quantum ferrimagnets by using a +numerical exact diagonalization of a finite size system along with a +field-theoretical non-linear $\sigma$ model of the quantum ferrimagnets at zero +temperature and its effective description in the presence of the external +magnetic field in terms of the quantum XY-model. The low- and the high-field +phases correspond respectively to the classical N\'eel and the fully polarized +ferromagnetic states where in the intermediate magnetic field ($h_{c1} < h < +h_{c2}$), it is an XXZ+h model with easy plane anisotropy, which possess the +spiral (superfluid) states that carry the dissipationless spin-supercurrent. We +derive the critical exponents, and then will study the stability of the XY +spiral state against these spin-supercurrents and the hard axis fluctuations. +We will show a first order phase transition from the easy plane spiral state to +a saturated ferromagnetic state occurs at $h=h_{c2}$ if the spin-supercurrent +reaches to its critical value.",0101194v1 +2001-09-03,Tunnel splitting and quantum phase interference in biaxial ferrimagnetic particles at excited states,"The tunneling splitting in biaxial ferrimagnetic particles at excited states +with an explicit calculation of the prefactor of exponent is obtained in terms +of periodic instantons which are responsible for tunneling at excited states +and is shown as a function of magnetic field applied along an arbitrary +direction in the plane of hard and medium axes. Using complex time +path-integral we demonstrate the oscillation of tunnel splitting with respect +to the magnitude and the direction of the magnetic field due to the quantum +phase interference of two tunneling paths of opposite windings . The +oscillation is gradually smeared and in the end the tunnel splitting +monotonously increases with the magnitude of the magnetic field when the +direction of the magnetic field tends to the medium axis. The oscillation +behavior is similar to the recent experimental observation with Fe$_8$ +molecular clusters. A candidate of possible experiments to observe the effect +of quantum phase interference in the ferrimagnetic particles is proposed.",0109016v1 +2002-08-29,"Microscopic model, spin wave theory and competing orders in the double perovskites","We present a microscopic theory of carrier-induced ferrimagnetism in metallic +double perovskite compounds such as ${\rm Sr}_{2}{\rm FeMoO}_{6}$ and ${\rm +Sr}_{2}{\rm FeReO}_{6}$ which have recently attracted intense interest for +their possible applications to magnetotransport devices. The theory is based on +an effective ""Kondo-like"" Hamiltonian treated here within the large-$S$ +expansion. We find that depending on the value of the carrier density the +ground state is either a ferrimagnet or a layered antiferromagnet. The +ferrimagnetic state has a robust half-metallic electronic structure. The +transition to antiferromagnetic phase is first order accompanied with the +regime of phase separation. We study spin wave spectrum including quantum +corrections and find strongly enhanced quantum effects in the vicinity of +zero-temperature phase transition.",0208586v3 +2003-09-29,Novel Electronic States in Graphene Ribbons -Competing Spin and Charge Orders-,"In a nanographene ring with zigzag edges, the spin-polarized state and the +charge-polarized state are stabilized by the on-site and the nearest neighbor +Coulomb repulsions, U and V, respectively, within the extended Hubbard model +under the mean field approximation. In a Moebius strip of the nanographene with +a zigzag edge, U stabilizes two magnetic states, the domain wall state and the +helical state. Both states have ferrimagnetic spins localized along the zigzag +edge while the former connects the opposite ferrimagnetic orders resulting in a +magnetic frustration forced by the topology and the latter rotates the +ferrimagnetic spins uniformly to circumvent the frustration. The helical state +is lower in energy than the domain wall state. On the other hand, V stabilizes +another domain wall state connecting the opposite charge orders.",0309636v1 +2004-04-06,Dilute ferrimagnetic semiconductors in Fe-substituted spinel ZnGa$_2$O$_4$,"Solid solutions of nominal composition +[ZnGa$_2$O$_4$]$_{1-x}$[Fe$_3$O$_4$]$_x$, of the semiconducting spinel +ZnGa$_2$O$_4$ with the ferrimagnetic spinel Fe$_3$O$_4$ have been prepared with +$x$ = 0.05, 0.10, and 0.15. All samples show evidence for long-range magnetic +ordering with ferromagnetic hysteresis at low temperatures. Magnetization as a +function of field for the $x$ = 0.15 sample is S-shaped at temperatures as high +as 200 K. M\""ossbauer spectroscopy on the $x$ = 0.15 sample confirms the +presence of Fe$^{3+}$, and spontaneous magnetization at 4.2 K. The magnetic +behavior is obtained without greatly affecting the semiconducting properties of +the host; diffuse reflectance optical spectroscopy indicates that Fe +substitution up to $x$ = 0.15 does not affect the position of the band edge +absorption. These promising results motivate the possibility of dilute +ferrimagnetic semiconductors which do not require carrier mediation of the +magnetic moment.",0404147v2 +2005-12-15,"Search for half-metallic ferrimagnetism in V-based Heusler alloys Mn$_2$VZ (Z$=$Al, Ga, In, Si, Ge, Sn)","Using a state-of-the-art full-potential electronic structure method within +the local spin density approximation, we study the electronic and magnetic +structure of Mn$_2$V-based full Heusler alloys: Mn$_2$VZ (Z=Al, Ga, In, Si, Ge, +and Sn). We show that small expansion of the calculated theoretical equilibrium +lattice constants restores the half-metallic ferrimagnetism in these compounds. +Moreover a small degree of disorder between the V and Z atoms, although iduces +some states within the gap, it preserves the Slater-Pauling behaviour of the +spin magnetic moments and the alloys keep a high degree of spin-polarisation at +the Fermi level opening the way for a half-metallic compensated ferrimagnet.",0512361v1 +2006-01-22,Thermodynamic properties of the ferrimagnetic spin chains in the presence of a magnetic field,"We have implemented three approaches to describe the thermodynamic properties +of ferrimagnetic ($S=5/2, s=2$) spin chains. The application of cumulant +expansion has been generalized to the ferrimagnetic chain in the presence of an +external magnetic field. Using cumulants, we have obtained the field dependent +effective Hamiltonian in terms of the classical variables up to the second +order of quantum corrections. Thermodynamic functions, the internal energy, the +specific heat and the magnetic susceptibility are obtained from the effective +Hamiltonian. We have also examined the modified spin wave theory to derive the +same physical properties. Finally, we have studied our model using quantum +Monte Carlo simulation to obtain accurate results. The comparison of the above +results and also the high temperature series expansion shows that cumulant +expansion gives good results for moderate and high temperature regions while +the modified spin wave theory is good for low temperatures. Moreover, the +convergence regions of the cumulant expansion and the modified spin wave theory +overlap each other which propose these two as a set of complement methods to +get the thermodynamic properties of spin models.",0601494v1 +2006-03-10,Dielectric anomalies and spiral magnetic order in CoCr2O4,"We have investigated the structural, magnetic, thermodynamic, and dielectric +properties of polycrystalline CoCr$_2$O$_4$, an insulating spinel exhibiting +both ferrimagnetic and spiral magnetic structures. Below $T_c$ = 94 K the +sample develops long-range ferrimagnetic order, and we attribute a sharp phase +transition at $T_N$ $\approx$ 25 K with the onset of long-range spiral magnetic +order. Neutron measurements confirm that while the structure remains cubic at +80 K and at 11 K; there is complex magnetic ordering by 11 K. Density +functional theory supports the view of a ferrimagnetic semiconductor with +magnetic interactions consistent with non-collinear ordering. Capacitance +measurements on CoCr$_2$O$_4$, show a sharp decrease in the dielectric constant +at $T_N$, but also an anomaly showing thermal hysteresis falling between +approximately $T$ = 50 K and $T$ = 57 K. We tentatively attribute the +appearance of this higher temperature dielectric anomaly to the development of +\textit{short-range} spiral magnetic order, and discuss these results in the +context of utilizing dielectric spectroscopy to investigate non-collinear +short-range magnetic structures.",0603307v1 +2007-02-19,Defects-driven appearance of half-metallic ferrimagnetism in Co-Mn--based Heusler alloys,"Half-metallic ferromagnetic full-Heusler alloys containing Co and Mn, having +the formula Co$_2$MnZ where Z a sp element, are among the most studied Heusler +alloys due to their stable ferromagnetism and the high Curie temperatures which +they present. Using state-of-the-art electronic structure calculations we show +that when Mn atoms migrate to sites occupied in the perfect alloys by Co, these +Mn atoms have spin moments antiparallel to the other transition metal atoms. +The ferrimagnetic compounds, which result from this procedure, keep the +half-metallic character of the parent compounds and the large +exchange-splitting of the Mn impurities atoms only marginally affects the width +of the gap in the minority-spin band. The case of [Co$_{1-x}$Mn$_x$]$_2$MnSi is +of particular interest since Mn$_3$Si is known to crystallize in the Heusler +$L2_1$ lattice structure of Co$_2$MnZ compounds. Robust half-metallic +ferrimagnets are highly desirable for realistic applications since they lead to +smaller energy losses due to the lower external magnetic fields created with +respect to their ferromagnetic counterparts.",0702437v1 +2007-03-02,"Ab-initio design of half-metallic fully-compensated ferrimagnets: the case of Cr$_2$MnZ (Z= P, As, Sb, Bi) compounds","Electronic structure calculations from first-principles are employed to +design some new half-metallic fully-compensated ferrimagnets (or as they are +widely known half-metallic antiferromagnets) susceptible of finding +applications in spintronics. Cr$_2$MnZ (Z= P, As, Sb, Bi) compounds have 24 +valence electrons per unit cell and calculations show that their total spin +moment is approximately zero for a wide range of lattice constants in agreement +with the Slater-Pauling behavior for ideal half-metals. Simultaneously, the +spin magnetic moments of Cr and Mn atoms are antiparallel and the compounds are +ferrimagnets. Mean-field approximation is employed to estimate their Curie +temperature, which exceeds room temperature for the alloy with Sb. Our findings +suggest that Cr$_2$MnSb is the compound of choice for further experimental +investigations. Contrary to the alloys mentioned above half-metallic +antiferromagnetism is unstable in the case of the Cr$_2$FeZ (Z= Si, Ge, Sn) +alloys.",0703078v1 +2007-11-07,"Low-energy structure of the intertwining double-chain ferrimagnets A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb)","Motivated by the homometallic intertwining double-chain ferrimagnets +A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb), we investigate the low-energy structure of +their model Hamiltonian H=\sum_n_[J_1_(S_{n :1}_+S_{n :3}_) ++J_2_(S_{n+1:1}+S_{n-1:3}_)]\cdotS_{n:2}_, where S_{n:l}_ stands for the +Cu^{2+}^ ion spin labeled l in the nth trimer unit, with particular emphasis on +the range of bond alternation 01$ decreases +approaching one, and above some critical value of the exchange constant there +is only one phase $T_N = T^*$, and the magnetization-temperature curve has the +typical Curie-Weiss profile. When the intra-exchange constant of sublattice +with stronger intra-exchange interaction increases the $Ne\grave{e}l$ +temperature increases while $T^*$ remains unchanged. Finally, when the magnetic +order of the sublattice with smaller magnetic order decreases, $T^*$ decreases. +The theoretical predictions are utilize to interpret the experimentally +measured magnetization-temperature curves.",0905.1036v1 +2009-09-01,Magnetism in Re-based ferrimagnetic double perovskites,"We have investigated spin and orbital magnetic moments of the Re 5d ion in +the double perovskites A2FeReO6 (A = Ba, Sr, Ca) by X-ray magnetic circular +dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds an +unusually large negative spin and positive orbital magnetic moment at the Re +atoms was detected. The presence of a finite spin magnetic moment in a +'non-magnetic' double perovskite as observed in the double perovskite Sr2ScReO6 +proves that Re has also a small, but finite intrinsic magnetic moment. We +further show for the examples of Ba and Ca that the usually neglected alkaline +earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic +double perovskites.",0909.0209v1 +2010-11-10,"Ab initio prediction of ferrimagnetism, exchange interactions and Curie temperatures in Mn2TiZ Heusler compounds","The Heusler compounds Mn$_2$TiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are +of large interest due to their potential ferrimagnetic properties and high spin +polarization. Here, we present calculations of the structural and magnetic +properties of these materials. Their magnetic moment follows the Slater-Pauling +rule $m = N_V - 24$. None of them is actually a perfect half-metallic +ferrimagnet, but some exhibit more than 90% spin polarization and Curie +temperatures well above room temperature. The exchange interactions are +complex, direct and indirect exchange contributions are identified. The Curie +temperature scales with the total magnetic moment, and it has a positive +pressure dependence. The role of the Z element is investigated: it influences +the properties of the compounds mainly via its valence electron number and its +atomic radius, which determines the lattice parameter. Based on these results, +Mn$_2$TiSi, Mn$_2$TiGe, and Mn$_2$TiSn are proposed as candidates for +spintronic applications.",1011.2486v1 +2011-01-31,Ferrimagnetism and disorder in epitaxial Mn(2-x)Co(x)VAl thin films,"The quaternary full Heusler compound Mn(2-x)Co(x)VAl with x = 1 is predicted +to be a half-metallic antiferromagnet. Thin films of the quaternary compounds +with x = 0...2 were prepared by DC and RF magnetron co-sputtering on heated MgO +(001) substrates. The magnetic structure was examined by x-ray magnetic +circular dichroism and the chemical disorder was characterized by x-ray +diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn2VAl (x = 0). +For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to +Mn. The observed reduced magnetic moments are interpreted with the help of band +structure calculations in the coherent potential approximation. Mn2VAl is very +sensitive to disorder involving Mn, because nearest-neighbor Mn atoms couple +anti-ferromagnetically. Co2VAl has B2 order and has reduced magnetization. In +the cases with x >= 0.9 conventional ferromagnetism was observed, closely +related to the atomic disorder in these compounds.",1101.5994v1 +2011-03-15,Oxygen hyperstoichiometric hexagonal ferrite CaBaFe4O7+δ(δ \approx 0.14) : coexistence of ferrimagnetism and spin glass behavior,"An oxygen hyperstoichiometric ferrite CaBaFe4O7+\delta (\delta \approx 0.14) +has been synthesized using ""soft"" reduction of CaBaFe4O8. Like the oxygen +stoichiometric ferrimagnet CaBaFe4O7, this oxide also keeps the hexagonal +symmetry (space group: P63mc), and exhibits the same high Curie temperature of +270 K. However, the introduction of extra oxygen into the system weakens the +ferrimagnetic interaction significantly at the cost of increased magnetic +frustration at low temperature. Moreover, this canonical spin glass (Tg ~ 166 +K) exhibits an intriguing cross-over from de Almeida-Thouless type to +Gabay-Toulouse type critical line in the field temperature plane above a +certain field strength, which can be identified as the anisotropy field. Domain +wall pinning is also observed below 110 K. These results are interpreted on the +basis of cationic disordering on the iron sites.",1103.2939v1 +2011-09-13,Interplay between non equilibrium and equilibrium spin torque using synthetic ferrimagnets,"We discuss the current induced magnetization dynamics of spin valves F0|N|SyF +where the free layer is a synthetic ferrimagnet SyF made of two ferromagnetic +layers F1 and F2 coupled by RKKY exchange coupling. In the interesting +situation where the magnetic moment of the outer layer F2 dominates the +magnetization of the ferrimagnet, we find that the sign of the effective spin +torque exerted on the free middle layer F1 is controlled by the strength of the +RKKY coupling: for weak coupling one recovers the usual situation where spin +torque tends to, say, anti-align the magnetization of F1 with respect to the +pinned layer F0. However for large coupling the situation is reversed and the +spin torque tends to align F1 with respect to F0. Careful numerical simulations +in the intermediate coupling regime reveal that the competition between these +two incompatible limits leads generically to spin torque oscillator (STO) +behavior. The STO is found in the absence of magnetic field, with very +significant amplitude of oscillations and frequencies up to 50 GHz or higher.",1109.2705v2 +2012-02-28,"Gallium Substituted ""114"" YBaFe4O7: From a ferrimagnetic cluster glass to a cationic disordered spin glass","The study of the ferrites YBaFe4-xGaxO7 shows that the substitution of Ga for +Fe in YBaFe4O7 stabilizes the hexagonal symmetry for 0.40 < x < 0.70, at the +expense of the cubic one. Using combined measurements of a. c. and d. c. +magnetization, we establish that Ga substitution for Fe in YBaFe4O7 leads to an +evolution from a geometrically frustrated spin glass (for x = 0) to a cationic +disorder induced spin glass (x = 0.70). We also find an intermediate narrow +range of doping where the samples are clearly phase separated having small +ferrimagnetic clusters embedded in a spin glass matrix. The origin of the +ferrimagnetic clusters lies in the change in symmetry of the samples from cubic +to hexagonal (and a consequent lifting of the geometrical frustration) as a +result of Ga doping. We also show the presence of exchange bias and domain wall +pinning in these samples. The cause of both these effects can be traced back to +the inherent phase separation present in the samples.",1202.6166v1 +2012-06-28,The Landau-Lifshitz-Bloch equation for ferrimagnetic materials,"We derive the Landau-Lifshitz-Bloch (LLB) equation for a two-component +magnetic system valid up to the Curie temperature. As an example, we consider +disordered GdFeCo ferrimagnet where the ultrafast optically induced +magnetization switching under the action of heat alone has been recently +reported. The two-component LLB equation contains the longitudinal relaxation +terms responding to the exchange fields from the proper and the neighboring +sublattices. We show that the sign of the longitudinal relaxation rate at high +temperatures can change depending on the dynamical magnetization value and a +dynamical polarisation of one material by another can occur. We discuss the +differences between the LLB and the Baryakhtar equation, recently used to +explain the ultrafast switching in ferrimagnets. The two-component LLB equation +forms basis for the largescale micromagnetic modeling of nanostructures at high +temperatures and ultrashort timescales.",1206.6672v1 +2012-09-18,Nontrivial ferrimagnetism of the Heisenberg model on the Union Jack strip lattice,"We study the ground-state properties of the S=1/2 antiferromagnetic +Heisenberg model on the Union Jack strip lattice by using the +exact-diagonalization and density matrix renormalization group methods. We +confirm a region of the intermediate-magnetization state between the Neel-like +spin liquid state and the conventional ferrimagnetic state of Lieb-Mattis type. +In the intermediate-state, we find that the spontaneous magnetization changes +gradually with respect to the strength of the inner interaction. In addition, +the local magnetization clearly shows an incommensurate modulation with +long-distance periodicity in the intermediate-magnetization state. These +characteristic behaviors lead to the conclusion that the +intermediate-magnetization state is the non-Lieb-Mattis ferrimagnetic one. We +also discuss the relationship between the ground-state properties of the S=1/2 +antiferromagnetic Heisenberg model on the original Union Jack lattice and those +on our strip lattice.",1209.3965v1 +2013-02-22,Gigantic magnetic field polarization and magnetoelectric coupling in a ferrimagnetic oxide CaBaCo4O7,"The single crystal study of CaBaCo4O7, a non collinear ferrimagnet (TC=64K), +with a polar orthorhombic space group (Pbn21) between 4 K and 293 K, shows the +appearance below TC of a large electric polarization along its c axis, reaching +17mC.m-2 at 10K. At 62.5K, a magnetic field driven giant variation of +polarization, P(9T)-P(0T)=8mC.m-2, is observed. Moreover, the present +magnetoelectric measurements, are fully consistent with the m'm2' magnetic +point group, strongly supporting that this oxide is also ferrotoroidic. This +ferrimagnetic oxide, which belongs to the '114' structural family, opens an +avenue for the search of new magnetoelectrics.",1302.5541v2 +2013-03-06,Change in the Magnetic Domain Alignment Process at the Onset of a Frustrated Magnetic State in Ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 Double Perovskite,"We have performed a combined study of magnetization hysteresis loops and time +dependence of the magnetization in a broad temperature range for the +ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 double perovskite. This material has a +ferrimagnetic order transition at ~100 K and at lower temperatures (~ 20 K) +shows the signature of a frustrated state due to the presence of two competing +magnetic exchange interactions. The temperature dependence of the coercive +field shows an important upturn below the point where the frustrated state sets +in. The use of the magnetization vs. applied magnetic field hysteresis data, +together with the magnetization vs. time data provides a unique opportunity to +distinguish between different scenarios for the low temperature regime. From +our analysis, a strong domain wall pinning results the best scenario for the +low temperature regime. For temperatures larger than 20K the adequate scenario +seems to correspond to a weak domain wall pinning.",1303.1372v1 +2013-05-14,Electromagnon in ferrimagnetic eps-Fe2O3 nanograin ceramics,"Electromagnons are known from multiferroics as spin waves excited by the +electric component of electromagnetic radiation. We report the discovery of an +excitation in the far-infrared spectra of eps-Fe2O3 which we attribute to an +electromagnon appearing below 110 K, where the ferrimagnetic structure becomes +incommensurately modulated. Inelastic neutron scattering shows that the +electromagnon energy corresponds to that of a magnon from the Brillouin zone +boundary. Dielectric measurements did not reveal any sign of ferroelectricity +in eps-Fe2O3 down to 10 K, despite its acentric crystal structure. This shows +that the activation of an electromagnon requires, in addition to the polar +ferrimagnetic structure, a modulation of the magnetic structure. We demonstrate +that a combination of inelastic neutron scattering with infrared and / or +terahertz spectroscopies allows detecting electromagnons in ceramics, where no +crystal-orientation analysis of THz and infrared spectra is possible.",1305.3064v3 +2013-10-07,Ferrimagnetic Slater Insulator Phase of the Sn/Ge(111) Surface,"We have performed the semilocal and hybrid density-functional theory (DFT) +studies of the Sn/Ge(111) surface to identify the origin of the observed +insulating ${\sqrt{3}}{\times}{\sqrt{3}}$ phase below ${\sim}$30 K. Contrasting +with the semilocal DFT calculation predicting a metallic 3${\times}$3 ground +state, the hybrid DFT calculation including van der Waals interactions shows +that the insulating ferrimagnetic structure with ${\sqrt{3}}{\times}{\sqrt{3}}$ +structural symmetry is energetically favored over the metallic 3${\times}$3 +structure. It is revealed that the correction of self-interaction error with a +hybrid exchange-correlation functional gives rise to a band-gap opening induced +by a ferrimagnetic order. The results manifest that the observed insulating +phase is attributed to the Slater mechanism via itinerant magnetic order rather +than the hitherto accepted Mott-Hubbard mechanism via electron correlations.",1310.1782v1 +2013-12-20,Effects of the spin-orbital coupling on the vacancy-induced magnetism on the honeycomb lattice,"The local magnetism induced by vacancies in the presence of the spin-orbital +interaction is investigated based on the half-filled Kane-Mele-Hubbard model on +the honeycomb lattice. Using the self-consistent mean-field theory, we find +that the spin-orbital coupling will enhance the localization of the spin +moments near a single vacancy. We further study the magnetic structures along +the zigzag edges formed by a chain of vacancies. We find that the spin-orbital +coupling tends to suppress the counter-polarized ferrimagnetic order on the +upper and lower edges, because of the open of the spin-orbital gap. As a +result, in the case of the balance number of sublattices, it will suppress +completely this kind of ferrimagnetic order. But, for the imbalance case, a +ferrimagnetic order along both edges exists because additional zero modes will +not be affected by the spin-orbital coupling.",1312.5809v1 +2015-04-17,Model for the FC and ZFC Ferrimagnetic Spinel,"There are two methods of preparation of ferrimagnetic spinel. If, during the +preparation, an external magnetic field as high as 300 O\""{e} is applied upon +cooling the material is named field-cooled (FC). If the applied field is about +1O\""{e} the material is zero-field cooled (ZFC). To explore the magnetic and +thermodynamic properties of these materials we consider two-sublattice spin +system, defined on the bcc lattice, with spin-$s^A$ operators $\bf{S_{i}^A}$ at +the sublattice $A$ site and spin-$s^B$ operators $\bf{S_{i}^B}$ at the +sublattice $B$ site, where $s^A>s^B$. The subtle point is the exchange between +sublattice A and B spins, which is antiferromanetic. Applying magnetic field +along the sublattice A magnetization, during preparation of the material, one +compensates the Zeeman splitting, due to the exchange, of sublattice B +electrons. This effectively leads to a decrease of the $s^B$ spin. We consider +a model with $s^B$ varying parameter which accounts for the applied, during the +preparation, magnetic field. + It is shown that the model agrees well with the observed +magnetization-temperature curves of zero field cooled (ZFC) and non-zero field +cooled (FC) spinel ferrimagnetic spinel and explains the anomalous temperature +dependence of the specific heat.",1504.04547v1 +2015-10-23,Laser-induced THz magnetization precession for a tetragonal Heusler-like nearly compensated ferrimagnet,"Laser-induced magnetization precessional dynamics was investigated in +epitaxial films of Mn$_3$Ge, which is a tetragonal Heusler-like nearly +compensated ferrimagnet. The ferromagnetic resonance (FMR) mode was observed, +the precession frequency for which exceeded 0.5 THz and originated from the +large magnetic anisotropy field of approximately 200 kOe for this ferrimagnet. +The effective damping constant was approximately 0.03. The corresponding +effective Landau-Lifshitz constant of approximately 60 Mrad/s and is comparable +to those of the similar Mn-Ga materials. The physical mechanisms for the +Gilbert damping and for the laser-induced excitation of the FMR mode were also +discussed in terms of the spin-orbit-induced damping and the laser-induced +ultrafast modulation of the magnetic anisotropy, respectively.",1510.06793v1 +2015-11-06,Coupled Cluster Treatment of the Alternating Bond Diamond Chain,"By the analytical coupled cluster method (CCM), we study both the ground +state and lowest-lying excited-state properties of the alternating bond diamond +chain. The numerical exact diagonalization (ED) method is also applied to the +chain to verify the accuracy of CCM results. The ED results show that the +ground-state phase diagram contains two exact spin cluster solid ground states, +namely, the tetramer-dimer (TD) state and dimer state, and the ferrimagnetic +long-range-ordered state. We prove that the two exact spin cluster solid ground +states can both be formed by CCM. Moreover, the exact spin gap in the TD state +can be obtained by CCM. In the ferrimagnetic region, we find that the CCM +results for some physical quantities, such as the ground-state energy, the +sublattice magnetizations, and the antiferromagnetic gap, are comparable to the +results obtained by numerical methods. The critical line dividing the TD state +from the ferrimagnetic state is also given by CCM and is in perfect agreement +with that determined by the ED method.",1511.01985v1 +2016-07-14,Room temperature polarization in the ferrimagnetic Ga2-xFexO3 ceramics,"The effect of the Fe-Ga ratio on the magnetic and electric properties of the +multiferroic Ga2-xFexO3 compound has been studied in order to determine the +composition range exhibiting magnetic and electric orders coexistence and their +critical temperatures. A magnetoelectric phase diagram, showing the evolution +of both the Neel magnetic ordering temperature and the electric ordering +temperature, versus the iron content has been established for x values between +0.9 and 1.4. While the ferrimagnetic Neel temperature increases with the iron +content, the electric ordering temperature shows an opposite trend. The +electric polarization has been found to exist far above room temperature for +the x value of 1.1 composition which shows the highest observed electric +ordering temperature of approx. 580K. The compounds with x values of 1.3 and +1.4 are ferrimagnetic-electric relaxors with both properties coexisting at room +temperature.",1607.04312v1 +2016-07-21,Ferrimagnetism in delta chain with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider analytically and numerically an anisotropic spin-$\frac{1}{2}$ +delta-chain (sawtooth chain) in which exchange interactions between apical and +basal spins are ferromagnetic and those between basal spins are +antiferromagnetic. In the limit of strong anisotropy of exchange interactions +this model can be considered as the Ising delta chain with macroscopic +degenerate ground state perturbed by transverse quantum fluctuations. These +perturbations lift the ground state degeneracy and the model reduces to the +basal XXZ spin chain in the magnetic field induced by static apical spins. We +show that the ground state of such model is ferrimagnetic. The excitations of +the model are formed by ferrimagnetic domains separated by domain walls with a +finite energy. At low temperatures the system is effectively divided into two +independent subsystems, the apical subsystem described by the Ising +spin-$\frac{1}{2}$ chain and the basal subsystem described by the XXZ chain +with infinite $zz$ interactions.",1607.06200v1 +2016-09-19,Switching ferromagnetic spins by an ultrafast laser pulse: Emergence of giant optical spin-orbit torque,"Faster magnetic recording technology is indispensable to massive data storage +and big data sciences. {All-optical spin switching offers a possible solution}, +but at present it is limited to a handful of expensive and complex rare-earth +ferrimagnets. The spin switching in more abundant ferromagnets may +significantly expand the scope of all-optical spin switching. Here by studying +40,000 ferromagnetic spins, we show that it is the optical spin-orbit torque +that determines the course of spin switching in both ferromagnets and +ferrimagnets. Spin switching occurs only if the effective spin angular momentum +of each constituent in an alloy exceeds a critical value. Because of the strong +exchange coupling, the spin switches much faster in ferromagnets than +weakly-coupled ferrimagnets. This establishes a paradigm for all-optical spin +switching. The resultant magnetic field (65 T) is so big that it will +significantly reduce high current in spintronics, thus representing the +beginning of photospintronics.",1609.05855v1 +2016-10-28,Spin-Orbit Torque Efficiency in Compensated Ferrimagnetic Cobalt-Terbium Alloys,"Despite the potential advantages of information storage in +antiferromagnetically coupled materials, it remains unclear whether one can +control the magnetic moment orientation efficiently because of the cancelled +magnetic moment. Here, we report spin-orbit torque induced magnetization +switching of ferrimagnetic Co1-xTbx films with perpendicular magnetic +anisotropy. Current induced switching is demonstrated in all of the studied +film compositions, including those near the magnetization compensation point. +The spin-orbit torque induced effective field is further quantified in the +domain wall motion regime. A divergent behavior that scales with the inverse of +magnetic moment is confirmed close to the compensation point, which is +consistent with angular momentum conservation. Moreover, we also quantify the +Dzyaloshinskii-Moriya interaction energy in the Ta/Co1-xTbx system and we find +that the energy density increases as a function of the Tb concentration. The +demonstrated spin-orbit torque switching, in combination with the fast magnetic +dynamics and minimal net magnetization of ferrimagnetic alloys, promises +spintronic devices that are faster and with higher density than traditional +ferromagnetic systems.",1610.09200v1 +2019-05-09,Bidirectional spin-wave-driven domain wall motion in antiferromagnetically coupled ferrimagnets,"We investigate ferrimagnetic domain wall dynamics induced by circularly +polarized spin waves theoretically and numerically. We find that the direction +of domain wall motion depends on both the circular polarization of spin waves +and the sign of net spin density of ferrimagnet. Below the angular momentum +compensation point, left- (right-) circularly polarized spin waves push a +domain wall towards (away from) the spin-wave source. Above the angular +momentum compensation point, on the other hand, the direction of domain wall +motion is reversed. This bidirectional motion originates from the fact that the +sign of spin-wave-induced magnonic torque depends on the circular polarization +and the subsequent response of the domain wall to the magnonic torque is +governed by the net spin density. Our finding provides a way to utilize a spin +wave as a versatile driving force for bidirectional domain wall motion.",1905.03521v1 +2020-07-14,Three-dimensional Ising Ferrimagnetism of Cr-Fe-Cr trimers in FeCr2Te4,"We carried out a comprehensive study of magnetic critical behavior in single +crystals of ternary chalcogenide FeCr$_2$Te$_4$ that undergoes a ferrimagnetic +transition below $T_c$ $\sim$ 123 K. Detailed critical behavior analysis and +scaled magnetic entropy change indicate a second-order ferrimagentic +transition. Critical exponents $\beta = 0.30(1)$ with $T_c = 122.4(5)$ K, +$\gamma = 1.22(1)$ with $T_c = 122.8(1)$ K, and $\delta = 4.24(2)$ at $T_c$ +$\sim$ 123 K suggest that the spins approach three-dimensional Ising ($\beta$ = +0.325, $\gamma$ = 1.24, and $\delta$ = 4.82) model coupled with the attractive +long-range interactions between spins that decay as $J(r)\approx r^{-4.88}$. +Our results suggest that the ferrimagnetism in FeCr$_2$Te$_4$ is due to +itinerant ferromagnetism among the antiferromagnetically coupled Cr-Fe-Cr +trimers.",2007.06805v2 +2010-05-28,Haldane Phases and Ferrimagnetic Phases with Spontaneous Translational Symmetry Breakdown in Distorted Mixed Diamond Chains with Spins 1 and 1/2,"The ground states of two types of distorted mixed diamond chains with spins 1 +and 1/2 are investigated using exact diagonalization, DMRG, and mapping onto +low-energy effective models. In the undistorted case, the ground state consists +of an array of independent spin-1 clusters separated by singlet dimers. The +lattice distortion induces an effective interaction between cluster spins. When +this effective interaction is antiferromagnetic, several Haldane phases appear +with or without spontaneous translational symmetry breakdown (STSB). The +transition between the Haldane phase without STSB and that with $(n+1)$-fold +STSB ($n$ = 1, 2, and 3) belongs to the same universality class as the +$(n+1)$-clock model. In contrast, when the effective interaction is +ferromagnetic, the quantized and partial ferrimagnetic phases appear with or +without STSB. An effective low-energy theory for the partial ferrimagnetic +phase is presented.",1005.5297v2 +2018-05-08,Spin-Hall and Anisotropic Magnetoresistance in Ferrimagnetic Co-Gd / Pt layers,"We present the Co-Gd composition dependence of the spin-Hall +magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for +ferrimagnetic Co100-xGdx / Pt bilayers. With Gd concentration x, its magnetic +moment increasingly competes with the Co moment in the net magnetization. We +find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign +from positive to negative with increasing x, vanishing near the magnetization +compensation. On the other hand, the SMR does not vary significantly even where +the AMR vanishes. These experimental results indicate that very different +scattering mechanisms are responsible for AMR and SMR. We discuss a possible +origin for the alloy composition dependence.",1805.02827v2 +2018-05-27,Prediction of new multiferroic and magnetoelectric material Fe3Se4,"Nowdays, multiferroic materials with magnetoelectric coupling have many +real-world applications in the fields of novel memory devices. It is +challenging is to create multiferroic materials with strongly coupled +ferroelectric and ferrimagnetic orderings at room temperature. The single +crystal of ferric selenide (Fe3Se4) shows type-II multiferroic due to the +coexistence of ferroelectric as well as magnetic ordering at room temperature. +We have investigated the lattice instability, electronic structure, +ferroelectric, ferrimagnetic ordering and transport properties of ferroelectric +metal Fe3Se4. The density of states shows considerable hybridization of Fe-3d +and Se-4p states near the Fermi level confirming its metallic behavior. The +magnetic moments of Fe cations follow a type-II ferrimagnetic and ferroelectric +ordering with a calculated total magnetic moment of 4.25 per unit cell +(Fe6Se8). The strong covalent bonding nature of Fe-Se leads to its +ferroelectric properties. In addition, the symmetry analysis suggests that +tilting of Fe sub-lattice with 3d-t2g orbital ordering is due to the +Jahn-Teller (JT) distortion. This study provides further insight in the +development of spintronics related technology using multiferroic materials.",1805.10607v1 +2008-07-25,Frustration-induced quantum phase transitions in a quasi-one-dimensional ferrimagnet: Hard-core boson map and the Ton ks-Girardeau limit,"We provide evidence of a superfluid-insulator transition (SIT) of magnons in +a quasi-one-dimensional quantum ferrimagnet with {\it isotropic} competing +antiferromagnetic spin interactions. This SIT occurs between two distinct +ferrimagnetic phases due to the frustration-induced closing of the gap to a +magnon excitation. It thus causes a coherent superposition of singlet and +triplet states at lattice unit cells and a power-law decay on the staggered +spin correlation function along the transverse direction to the spontaneous +magnetization. A hard-core boson map suggests that asymptotically close to the +SIT the magnons attain the Tonks-Girardeau limit. The quantized nature of the +condensed singlets is observed before a first-order transition to a singlet +magnetic spiral phase accompanied by critical antiferromagnetic ordering. In +the limit of strong frustration, the system undergoes a decoupling transition +to an isolated gapped two-leg ladder and a critical single linear chain.",0807.4153v1 +2016-08-19,Competing Exchange Interactions in the Multiferroic and Ferrimagnetic CaBaCo$_4$O$_7$,"Competing exchange interactions can produce complex magnetic states together +with spin-induced electric polarizations. With competing interactions on +alternating triangular and kagome layers, the swedenborgite CBO may have one of +the largest measured spin-induced polarizations of about 1700 nC/cm$^2$ below +its ferrimagnetic transition temperature at 70 K. Powder neutron-diffraction +data, magnetization measurements, and spin-wave resonance frequencies in the +THz range reveal that the complex spin order of multiferroic CBO can be +described as a triangular array of c-axis chains ferrimagnetically coupled to +each other in the ab plane. Magnetostriction on bonds that couple those chains +produces the large spin-induced polarization of CBO.",1608.05628v3 +2017-06-20,"Magnetic signatures of quantum critical points of the ferrimagnetic mixed spin-(1/2, S) Heisenberg chains at finite temperatures","Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains +are examined using quantum Monte Carlo simulations for two different quantum +spin numbers S = 1 and 3/2. The calculated magnetization curves at finite +temperatures are confronted with zero-temperature magnetization data obtained +within density-matrix renormalization group method, which imply an existence of +two quantum critical points determining a breakdown of the gapped Lieb-Mattis +ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. +While a square-root behavior of the magnetization accompanying each quantum +critical point is gradually smoothed upon rising temperature, the +susceptibility and isothermal entropy change data provide a stronger evidence +of the quantum critical points at finite temperatures through marked local +maxima and minima, respectively.",1706.06379v1 +2017-06-21,Spin pumping and shot noise in ferrimagnets: bridging ferro- and antiferromagnets,"A combination of novel technological and fundamental physics prospects has +sparked a huge interest in pure spin transport in magnets, starting with +ferromagnets and spreading to antiferro- and ferrimagnets. We present a +theoretical study of spin transport across a ferrimagnet$|$non-magnetic +conductor interface, when a magnetic eigenmode is driven into a coherent state. +The obtained spin current expression includes intra- as well as +cross-sublattice terms, both of which are essential for a quantitative +understanding of spin-pumping. The dc current is found to be sensitive to the +asymmetry in interfacial coupling between the two sublattice magnetizations and +the mobile electrons, especially for antiferromagnets. We further find that the +concomitant shot noise provides a useful tool for probing the quasiparticle +spin and interfacial coupling.",1706.07118v2 +2017-07-06,Switching from pyroelectric to ferroelectric order in Ni doped CaBaCo4O7,"We report ferroelectric ordering in Ni substituted CaBaCo4O7. Magnetization +showed ferrimagnetic transition at 60 K and an additional transition is found ~ +82 K, further, enhanced antiferromagnetic interactions and decrease in +saturation magnetization are noticed with Ni substitution. The dielectric and +pyroelectric measurements illustrate a strong coupling between spin and charge +degrees of freedom; ferroelectric behavior is confirmed with enhanced ordering +temperature (~82 K) and saturation polarization (250 muC/m2. Neutron +diffraction has revealed an increase in c-lattice parameter in Ni sample and +all the Co/Ni moments are reoriented in a- direction; evidently a non-collinear +ferrimagnetic to collinear ferrimagnetic spin order is observed. The coupling +between the triangular and Kagome layers weakens and leads to up-up-down-down +AFM ordering in the Kagoma layer. This can be viewed as a 2D-collinear layer +with unequal bond distances and most likely responsible for the switching of +electric polarization.",1707.01712v1 +2017-12-28,Charge ordering and ferrimagnetism in the strongly correlated $β$-V$_2$PO$_5$ single crystal,"A combined study of transport, thermodynamic, neutron diffraction, nuclear +magnetic resonance measurements and first principles calculation were performed +for $\beta$-V$_2$PO$_5$ single crystal. It was shown to be a semiconductor with +a band gap of 0.48 eV, undergoing a charge ordering (unusual V$^{2+}$ and +V$^{3+}$) phase transition accompanied by a tetragonal to monoclinic structural +distortion at 610 K and a paramagnetic to ferrimagnetic phase transition at 128 +K with a propagation vector of $\textbf{k} = 0$. The easy axis is in the +monoclinic $ac$ plane pointing 47(9)$^\circ$ away from the monoclinic $a$ axis. +This collinear ferrimagnetic structure and anisotropic isothermal magnetization +measurements suggest weak magnetic anisotropy in this compound. The first +principles calculations indicate that the intra-chain interactions in the +face-sharing VO$_6$ chains dominate the magnetic hamiltonian and identify the +$\Gamma_5^+$ normal mode of the lattice vibration to be responsible for the +charge ordering and thus the structural phase transition.",1712.09973v1 +2019-06-21,Magnetic domains without domain walls: a unique effect of He+ ion bombardment in ferrimagnetic Co/Tb multilayers,"We show that it is possible to engineer magnetic multi-domain configurations +without domain walls in a prototypical rare earth/transition metal ferrimagnet +using keV He+ ion bombardment. We additionally shown that these patterns +display a particularly stable magnetic configuration due to a deep minimum in +the free energy of the system which is caused by flux closure and the +corresponding reduction of the magnetostatic part of the total free energy. +This is possible because light-ion bombardment differently affects an elements +relative contribution to the effective properties of the ferrimagnet. The +impact of bombardment is stronger for rare earth elements. Therefore, it is +possible to influence the relative contributions of the two magnetic subsystems +in a controlled manner. The selection of material system and the use of +light-ion bombardment open a route to engineer domain patterns in continuous +magnetic films much smaller than what is currently considered possible.",1906.09318v1 +2019-09-12,Single pulse all-optical toggle switching of magnetization without Gd: The example of Mn2RuxGa,"Energy-efficient control of magnetization without the help of a magnetic +field is a key goal of spintronics. Purely heat-induced single-pulse +all-optical toggle switching has been demonstrated, but so far only in Gd based +amorphous ferrimagnet films. In this work, we demonstrate toggle switching in +the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have +two crystallographically-inequivalent Mn sublattices. Moreover, we observe the +switching at room temperature in samples that are immune to external magnetic +fields in excess of 1 T, provided they exhibit compensation above room +temperature. Observations of the effect in compensated ferrimagnets without Gd +challenges our understanding of all-optical switching. The dynamic behavior +indicates that Mn2RuxGa switches in 2 ps or less. Our findings widen the basis +for fast optical switching of magnetization and break new ground for engineered +materials that can be used for nonvolatile ultrafast switches using ultrashort +pulses of light.",1909.05809v2 +2019-09-12,Magnetostrictively induced stationary entanglement between two microwave fields,"We present a scheme to entangle two microwave fields by using the nonlinear +magnetostrictive interaction in a ferrimagnet. The magnetostrictive interaction +enables the coupling between a magnon mode (spin wave) and a mechanical mode in +the ferrimagnet, and the magnon mode simultaneously couples to two microwave +cavity fields via the magnetic dipole interaction. The magnon-phonon coupling +is enhanced by directly driving the ferrimagnet with a strong red-detuned +microwave field, and the driving photons are scattered onto two sidebands +induced by the mechanical motion. We show that two cavity fields can be +prepared in a stationary entangled state if they are respectively resonant with +two mechanical sidebands. The present scheme illustrates a new mechanism for +creating entangled states of optical fields, and enables potential applications +in quantum information science and quantum tasks that require entangled +microwave fields.",1909.05936v3 +2020-01-03,Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1-xCoxGa Heusler alloys,"Neutron diffraction and ab initio studies were carried out on Mn2V1-xCoxGa +(x=0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high TC fully +compensated ferrimagnetic characteristic for x=0.5. A combined analysis of +neutron diffraction and ab initio calculations revealed the crystal structure +and magnetic configuration which could not be determined from the X-ray +diffraction and magnetic measurements. As reported earlier, Rietveld refinement +of neutron diffraction data confirmed L21 structure for Mn2VGa and Xa structure +for Mn2CoGa. The alloys with x=0.25 and 0.5 possess L21 structure with Mn(C)-Co +disorder. As the Co concentration reaches 0.75, a structural transition has +been observed from disordered L21 to disordered Xa. Detailed ab initio studies +also confirmed this structural transition. The reason for the magnetic moment +compensation in Mn2(V1-xCox)Ga was identified to be different from that of the +earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of +neutron diffraction and ab initio studies, it is identified that the disordered +L21 structure with antiparallel coupling between the ferromagnetically aligned +magnetic moments of (Mn(A)-Mn(C)) and (V-Co) atom pairs enables the +compensation in Mn2V1-xCoxGa.",2001.00707v1 +2020-01-23,Magnetization plateaus and bipartite entanglement of an exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain,"Spin-1/2 orthogonal-dimer chain composed of regularly alternating Ising and +Heisenberg dimers is exactly solved in a presence of the magnetic field by the +transfer-matrix method. It is shown that the ground-state phase diagram +involves in total six different phases. Besides the ferromagnetic phase with +fully polarized spins one encounters the singlet antiferromagnetic and +modulated antiferromagnetic phases manifested in zero-temperature magnetization +curves as zero magnetization plateau, the frustrated ferrimagnetic and singlet +ferrimagnetic phases causing existence of an intermediate one-half +magnetization plateau, and finally, the intriguing modulated ferrimagnetic +phase with a translationally broken symmetry leading to an unconventional +one-quarter magnetization plateau. The quantum character of individual ground +states is quantified via the concurrence, which measures a strength of the +bipartite entanglement within the pure and mixed states of the Heisenberg +dimers at zero as well as nonzero temperatures. The parameter region, where the +bipartite entanglement may be in contrast to general expectations reinforced +upon increasing of temperature and/or magnetic field, is elucidated.",2001.08701v2 +2020-12-01,Magnon hybridization in ferrimagnetic heterostructures,"We study magnon hybridization in a ferrimagnetic heterostructure consisting +of ultrathin gadolinium iron garnet and yttrium iron garnet layers and show the +localized and extended spatial profiles of the magnon modes with different +polarizations. These modes are expected to have distinct thermal excitation +properties in the presence of a temperature gradient across the +heterostructure. From a quantitative analysis of their consequences on +longitudinal spin Seebeck effect, we predict an observable shift of the +sign-changing temperature with respect to the one previously observed in +gadolinium iron garnet. Moreover, the sign-changing point of spin Seebeck +signal is found to be tunable by YIG thickness. Our results suggest the +necessity of taking into account the temperature difference between the magnon +modes in ferrimagnetic heterostructures.",2012.00576v1 +2020-12-12,Ultra-fast Double Pulse All-Optical Re-switching of a Ferrimagnet,"All-optical re-switching has been investigated in the half-metallic Heusler +ferrimagnet Mn2Ru0.9Ga, where Mn atoms occupy two inequivalent sites in the +XA-type structure. The effect of a second 200 fs 800 nm pump pulse that follows +a first pulse, when both are above the threshold for switching, is studied as a +function of t12, the time between them. The aims are to identify the physical +mechanisms involved and to determine the minimum time needed for re-switching. +The time trajectory of the switching process on a plot of sublattice angular +momentum, S4a vs S4c, is in three stages; When t < 0.1 ps, the sublattice +moments are rapidly disordered, but not destroyed, while conserving net angular +momentum via optical spin-wave excitations. This leads to transient parallel +alignment of the residual Mn spins in the first quadrant. The net angular +momentum associated with the majority sublattice then flips in about 2 ps, and +a fully-reversed ferrimagnetic state is then established via the spin-lattice +interaction, which allows re-switching provided t12 > 10 ps.",2012.06823v1 +2021-01-10,Tuning Dzyaloshinskii-Moriya Interaction in Ferrimagnetic GdCo: A First Principles Approach,"We present a systematic analysis of our ability to tune chiral +Dzyaloshinskii-Moriya Interactions (DMI) in compensated ferrimagnetic +Pt/GdCo/Pt1-xWx trilayers by cap layer composition. Using first principles +calculations, we show that the DMI increases rapidly for only ~ 10% W and +saturates thereafter, in agreement with experiments. The calculated DMI shows a +spread in values around the experimental mean, depending on the atomic +configuration of the cap layer interface. The saturation is attributed to the +vanishing of spin orbit coupling energy at the cap layer and the simultaneous +constancy at the bottom interface. Additionally, we predict the DMI in +Pt/GdCo/X (X=Ta, W, Ir) and find that W in the cap layer favors a higher DMI +than Ta and Ir that can be attributed to the difference in d-band alignment +around the Fermi level. Our results open up exciting combinatorial +possibilities for controlling the DMI in ferrimagnets towards nucleating and +manipulating ultrasmall high-speed skyrmions.",2101.03449v1 +2017-05-08,Non-local magnon transport in the compensated ferrimagnet GdIG,"We study the diffusive transport of magnons through the compensated +ferrimagnetic insulator Gd3Fe5O12 (GdIG). The magnons are injected and detected +electrically in a non-local measurement configuration via two parallel Pt +strips deposited on top of the ferrimagnet. GdIG exhibits a rich magnon +spectrum, with several thermally populated magnon bands at room temperature. We +observe a strong temperature and field dependence of the non-local voltage in +the detector strip. Just below the magnetization compensation temperature we +find that the increasing magnetic field causes an unexpected enhancement of the +non-local signal. A comparison with GdIG spin wave spectra obtained from +atomistic modeling indicates that the thermal magnon population is important +for understanding the non-local voltage signal.",1705.02871v1 +2017-11-15,Octahedral tilt independent magnetism in confined GdTiO$_3$ films,"Polarized neutron reflectometry measurements are presented exploring the +evolution of ferrimagnetism in GdTiO$_3$ films as they are confined between +SrTiO$_3$ layers of variable thicknesses. As GdTiO$_3$ films approach the thin +layer limit and are confined within a substantially thicker SrTiO$_3$ matrix, +the TiO$_6$ octahedral tilts endemic to GdTiO$_3$ coherently relax toward the +undistorted, cubic phase of SrTiO$_3$. Our measurements reveal that the +ferrimagnetic state within the GdTiO$_3$ layers survives as the TiO$_6$ +octahedral tilts in the GdTiO$_3$ layers are suppressed. Furthermore, our data +suggest that a magnetic dead layer develops within the GdTiO$_3$ layer at each +GdTiO$_3$/ SrTiO$_3$ interface. The ferrimagnetic moment inherent to the core +GdTiO$_3$ layers is negligibly (in models with dead layers) or only weakly (in +models without dead layers) impacted as the octahedral tilt angles are +suppressed by more than 50$\%$ and the $t_{2g}$ bandwidth is dramatically +renormalized.",1711.05808v1 +2018-03-01,Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets,"Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism, +is often explained in terms of ferromagnets. However, the best performing +permanent magnets based on rare earths and transition metals (RE-TM) are in +fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show +how a naive calculation of the magnetocrystalline anisotropy of the classic +RE-TM ferrimagnet GdCo$_5$ gives numbers which are too large at 0 K and exhibit +the wrong temperature dependence. We solve this problem by introducing a +first-principles approach to calculate temperature-dependent magnetization vs. +field (FPMVB) curves, mirroring the experiments actually used to determine the +anisotropy. We pair our calculations with measurements on a recently-grown +single crystal of GdCo$_5$, and find excellent agreement. The FPMVB approach +demonstrates a new level of sophistication in the use of first-principles +calculations to understand RE-TM magnets.",1803.00235v1 +2018-06-13,Low magnetic damping of ferrimagnetic GdFeCo alloys,"We investigate the Gilbert damping parameter for rare earth (RE)-transition +metal (TM) ferrimagnets over a wide temperature range. Extracted from the +field-driven magnetic domain-wall mobility, the Gilbert damping parameter was +as low as 0.0072 and was almost constant across the angular momentum +compensation temperature, starkly contrasting previous predictions that the +Gilbert damping parameter should diverge at the angular momentum compensation +temperature due to vanishing total angular momentum. Thus, magnetic damping of +RE-TM ferrimagnets is not related to the total angular momentum but is +dominated by electron scattering at the Fermi level where the TM has a dominant +damping role.",1806.04881v1 +2018-06-17,Skyrmion Formation Induced by Antiferromagnetic-enhanced Interfacial Dzyaloshinskii Moriya Interaction,"Ne\'el skyrmions originate from interfacial Dzyaloshinskii Moriya interaction +(DMI). Recent studies have explored using ferromagnet to host Ne\'el skyrmions +for device applications. However, challenges remain to reduce the size of +skyrmion to near 10 nm. Amorphous rare-earth-transitional-metal ferrimagnets +are attractive alternative materials to obtain ultrasmall skyrmions at room +temperature. Their intrinsic perpendicular magnetic anisotropy and tunable +magnetization provides a favorable environment for skyrmion stability. In this +work, we employ atomistic stochastic Landau-Liftshitz-Gilbert (LLG) algorithm +to investigate skyrmions in GdFe within the interfacial DMI model. Despite the +rapid decay of DMI away from the interface, small skyrmions of near 10 nm are +found in thick ~ 5 nm amorphous GdFe film at 300K. We have also considered +three scenarios for the sign of DMI between Gd-Fe pair. It is revealed that +antiferromagnetic coupling in the ferrimagnet plays an important role in +enhancing the effect of interfacial DMI and to stabilize skyrmion. These +results show that ferrimagnets and antiferromagnets with intrinsic +antiferromagnetic couplings are appealing materials to host small skyrmions at +room temperature, which is crucial to improve density and energy efficiency in +skyrmion based devices.",1806.06334v1 +2018-06-20,Magneto-optic Kerr effect in a spin-polarized zero-moment ferrimagnet,"The magneto-optical Kerr effect (MOKE) is often assumed to be proportional to +the magnetisation of a magnetically ordered metallic sample; in metallic +ferrimagnets with chemically distinct sublattices, such as rare-earth +transition-metal alloys, it depends on the difference between the sublattice +contributions. Here we show that in a highly spin polarized, fully compensated +ferrimagnet, where the sublattices are chemically similar, MOKE is observed +even when the net moment is strictly zero. We analyse the spectral ellipsometry +and MOKE of Mn 2 Ru x Ga, and show that this behaviour is due to a highly +spin-polarized conduction band dominated by one of the two manganese +sublattices which creates helicity-dependent reflectivity determined by a broad +Drude tail. Our findings open new prospects for studying spin dynamics in the +infra-red.",1806.07719v2 +2018-07-18,Controlled anisotropic dynamics of tightly bound skyrmions in a synthetic ferrimagnet due to skyrmion-deformation mediated by induced uniaxial in-plane anisotropy,"We study speed and skew deflection-angle dependence on skyrmion deformations +of a tightly bound two-skyrmion state in a synthetic ferrimagnet. We condsider +here, an in-plane uniaxial magnetocrystalline anisotropy-term in order to +induce lateral shape distortions and an overall size modulation of the +skyrmions due to a reduction of the effective out-of-plane anisotropy, thus +affecting the skyrmion speed, skew-deflection and inducing anisotropy in these +quantities with respect to the driving current-angle. Because of frustrated +dipolar interactions in a synthetic ferrimagnet, sizeable skyrmion deformations +can be induced with relatively small induced anisotropy constants and thus a +wide range of tuneability can be achieved. We also show analytically, that a +consequence of the skyrmion deformation can, under certain conditions cause a +skyrmion deflection with respect to driving-current angles, unrelated to the +topological charge. Results are analyzed by a combination of micromagnetic +simulations and a compound particle description within the Thiele-formalism +from which an over-all mobility tensor is constructed. This work offers an +additional path towards in-situ tuning of skyrmion dynamics.",1807.06884v2 +2018-08-13,Application of two-sublattice bilinearly coupled Heisenberg model to the description of certain ferrimagnetic materials,"We study phenomenologically on the basis of two bilinearly coupled Heisen- +berg models the phase diagram of some ferrimagnetic substances. Calculations +are performed with the help of Landau energy obtained through applying the +Hubbard-Stratonovich transformation to the initial microscopic Heisenberg +Hamiltonian. The phase transitions within the model are of second order with +the emergence of a compensation point at lower temperatures for some values of +parameters of the system. The main phase is a two-sublattice collinear +ferrimagnet but also a metastable non-collinear phase is present within the +exchange approximation presented here. The numerical results give a detailed +description of temperature dependence of magnetization on the strength of in- +tersublattice interaction and the difference between the effective exchanges of +two ferromagnetically ordered sublattices.",1808.04326v1 +2019-01-10,Ultrafast magnetization dynamics in uniaxial ferrimagnets with compensation point. GdFeCo,"We derive an effective Lagrangian in the quasi-antiferromagnetic +approximation that allows to describe the magnetization dynamics for uniaxial +f-d (rare-earth - transition metal) ferrimagnet near the magnetization +compensation point in the presence of external magnetic field. We perform +calculations for the parameters of GdFeCo, a metallic ferrimagnet with +compensation point that is one of the most promising materials in ultrafast +magnetism. Using the developed approach, we find the torque that acts on the +magnetization due to ultrafast demagnetization pulse that can be caused either +by ultrashort laser or electrical current pulse. We show that the torque is +non-zero only in the non-collinear magnetic phase that can be acquired by +applying external magnetic field to the material. The coherent response of +magnetization dynamics amplitude and its timescale exhibits critical behavior +near certain values of the magnetic field corresponding to a spin-flop like +phase transition. Understanding the underlying mechanisms for these effects +opens the way to efficient control of the amplitude and the timescales of the +spin dynamics, which is one of the central problems in the field of ultrafast +magnetism.",1901.03072v2 +2019-01-28,"Structural, magnetic, and electrical properties of collinear antiferromagnetic heteroepitaxy cubic Mn$_3$Ga thin films","Although a cubic phase of Mn$_3$Ga with an antiferromagnetic order has been +theoretically predicted, it has not been experimentally verified in a bulk or +film form. Here, we report the structural, magnetic, and electrical properties +of antiferromagnetic cubic Mn$_3$Ga (C-Mn$_3$Ga) thin films, in comparison with +ferrimagnetic tetragonal Mn$_3$Ga (T-Mn3Ga). The structural analyses reveal +that C-Mn$_3$Ga is hetero-epitaxially grown on MgO substrate with the +Cu$_3$Au-type cubic structure, which transforms to T-Mn$_3$Ga as the RF +sputtering power increases. The magnetic and magnetotransport data show the +antiferromagnetic transition at T$_N$ = 400 K for C-Mn$_3$Ga and the +ferrimagnetic transition at T$_C$ = 820 K for T-Mn$_3$Ga. Furthermore, we find +that the antiferromagnetic C-Mn$_3$Ga exhibits a higher electrical resistivity +than the ferrimagnetic T-Mn$_3$Ga, which can be understood by spin-dependent +scattering mechanism.",1901.09524v1 +2019-03-01,Entangling two magnon modes via magnetostrictive interaction,"We present a scheme to entangle two magnon modes in a cavity magnomechanical +system. The two magnon modes are embodied by collective motions of a large +number of spins in two macroscopic ferrimagnets, and couple to a single +microwave cavity mode via magnetic dipole interaction. We show that by +activating the nonlinear magnetostrictive interaction in one ferrimagnet, +realized by driving the magnon mode with a strong red-detuned microwave field, +the two magnon modes can be prepared in an entangled state. The entanglement is +achieved by exploiting the nonlinear magnon-phonon coupling and the linear +magnon-cavity coupling, and is in the steady state and robust against +temperature. The entangled magnon modes in two massive ferrimagnets represent +genuinely macroscopic quantum states, and may find applications in the study of +macroscopic quantum mechanics and quantum information processing based on +magnonics.",1903.00221v2 +2019-03-11,Exchange-enhanced Ultrastrong Magnon-Magnon Coupling in a Compensated Ferrimagnet,"The ultrastrong coupling of (quasi-)particles has gained considerable +attention due to its application potential and richness of the underlying +physics. Coupling phenomena arising due to electromagnetic interactions are +well explored. In magnetically ordered systems, the quantum-mechanical +exchange-interaction should furthermore enable a fundamentally different +coupling mechanism. Here, we report the observation of ultrastrong intralayer +exchange-enhanced magnon-magnon coupling in a compensated ferrimagnet. We +experimentally study the spin dynamics in a gadolinium iron garnet single +crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic +compensation temperature, we observe ultrastrong coupling of clockwise and +anticlockwise magnon modes. The magnon-magnon coupling strength reaches more +than 30% of the mode frequency and can be tuned by varying the direction of the +external magnetic field. We theoretically explain the observed phenomenon in +terms of an exchange-enhanced mode-coupling mediated by a weak cubic +anisotropy.",1903.04330v2 +2019-04-26,Blueprint for deterministic all-optical switching of magnetization,"We resolve a significant controversy about how to understand and engineer +single-shot all-optical switching of magnetization in ferrimagnets using femto- +or picosecond-long heat pulses. By realistically modelling a generic +ferrimagnet as two coupled macrospins, we comprehensively show that the net +magnetization can be reversed via different pathways, using a heat pulse with +duration spanning all relevant timescales within the non-adiabatic limit. This +conceptual understanding is fully validated by experiments studying the +material and optical limits at which the switching process in GdFeCo alloys +loses its reliability. Our interpretation and results constitute a blueprint +for understanding how deterministic all-optical switching can be achieved in +alternative ferrimagnets using short thermal pulses.",1904.11977v1 +2019-11-06,Enhancement of domain-wall mobility detected by NMR at the angular momentum compensation temperature,"The angular momentum compensation temperature $T_{\rm A}$ of ferrimagnets has +attracted much attention because of high-speed magnetic dynamics near $T_{\rm +A}$. We show that NMR can be used to investigate domain wall dynamics near +$T_{\rm A}$ in ferrimagnets. We performed $^{57}$Fe-NMR measurements on the +ferrimagnet Ho$_3$Fe$_5$O$_{12}$ with $T_{\rm A} = 245$ K. In a multi-domain +state, the NMR signal is enhanced by domain wall motion. We found that the NMR +signal enhancement shows a maximum at $T_{\rm A}$ in the multi-domain state. +The NMR signal enhancement occurs due to increasing domain-wall mobility toward +$T_{\rm A}$. We develop the NMR signal enhancement model involves domain-wall +mobility. Our study shows that NMR in multi-domain state is a powerful tool to +determine $T_{\rm A}$, even from a powder sample and it expands the possibility +of searching for angular momentum-compensated materials.",1911.02207v3 +2020-05-20,Frequency mixing in a ferrimagnetic sphere resonator,"Frequency mixing in ferrimagnetic resonators based on yttrium and calcium +vanadium iron garnets (YIG and CVBIG) is employed for studying their nonlinear +interactions. The ferrimagnetic Kittel mode is driven by applying a pump tone +at a frequency close to resonance. We explore two nonlinear frequency mixing +configurations. In the first one, mixing between a transverse pump tone and an +added longitudinal weak signal is explored, and the experimental results are +compared with the predictions of the Landau-Zener-Stuckelberg model. In the +second one, intermodulation measurements are employed by mixing pump and signal +tones both in the transverse direction for studying a bifurcation between a +stable spiral and a stable node attractors. Our results are applicable for +developing sensitive signal receivers with high gain for both the radio +frequency and the microwave bands.",2005.09864v1 +2020-08-03,Observation of compact ferrimagnetic skyrmions in DyCo$_3$ film,"Owing to the experimental discovery of magnetic skyrmions stabilized by the +Dzyaloshinskii-Moriya and/or dipolar interactions in thin films, there is a +recent upsurge of interest in magnetic skyrmions with antiferromagnetic spins +in order to overcome the fundamental limitations inherent with skyrmions in +ferromagnetic materials. Here, we report on the observation of compact +ferrimagnetic skyrmions for the class of amorphous alloys consisting of 4f +rare-earth and 3d transition-metal elements with perpendicular magnetic +anisotropy, using a DyCo$_3$ film, that are identified by combining x-ray +magnetic scattering, scanning transmission x-ray microscopy, and Hall transport +technique. These skyrmions, with antiparallel aligned Dy and Co magnetic +moments and a characteristic core radius of about 40~nm, are formed during the +nucleation and annihilation of the magnetic maze-like domain pattern exhibiting +a topological Hall effect contribution. Our findings provide a promising route +for fundamental research in the field of ferrimagnetic/antiferromagnetic +spintronics towards practical applications.",2008.00725v1 +2020-10-13,Effects of spin-orbit torque on the ferromagnetic and exchange spin wave modes in ferrimagnetic CoGd alloy,"We use micro-focus Brillouin light scattering spectroscopy to study the +effects of spin-orbit torque on thermal spin waves in almost angular-momentum +compensated ferrimagnetic CoGd alloy films. The spin-orbit torque is produced +by the electric current flowing in the Pt layer adjacent to CoGd. Both the +ferromagnetic and the exchange modes are detected in our measurements. The +intensity and the linewidth of the ferromagnetic mode are modified by the +spin-orbit torque. In contrast, the properties of the exchange mode are +unaffected by the spin-orbit torque. We also find that the frequencies and the +linewidths of both modes are significantly modified by Joule heating, due to +the strong temperature dependence of the magnetic properties of CoGd in the +vicinity of angular momentum compensation point. Our results provide insight +into the mechanisms that can enable the implementation of sub-THz magnetic +nano-oscillators based on ferrimagnetic materials, as well as related effects +in antiferromagnets.",2010.06615v1 +2020-11-03,An attempt to simulate laser-induced all-optical spin switching in a crystalline ferrimagnet,"Interest in all-optical spin switching (AOS) is growing rapidly. The recent +discovery of AOS in Mn$_2$RuGa provides a much needed clean case of crystalline +ferrimagnets for theoretical simulations. Here, we attempt to simulate it using +the state-of-the-art first-principles method combined with the Heisenberg +exchange model. We first compute the spin moments at two inequivalent manganese +sites and then feed them into our model Hamiltonian. We employ an ultrafast +laser pulse to switch the spins. We find that there is a similar optimal laser +field amplitude to switch spins. However, we find that the exchange interaction +has a significant effect on the system switchability. Weakening the exchange +interaction could make the system unswitchable. This provides a crucial insight +into the switching mechanism in ferrimagnets.",2011.02001v1 +2021-02-01,Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets,"Measurements of the transverse Hall resistance are widely used to investigate +electron transport, magnetization phenomena, and topological quantum states. +Owing to the difficulty of probing transient changes of the transverse +resistance, the vast majority of Hall effect experiments are carried out in +stationary conditions using either dc or ac currents. Here we present an +approach to perform time-resolved measurements of the transient Hall resistance +during current-pulse injection with sub-nanosecond temporal resolution. We +apply this technique to investigate in real-time the magnetization reversal +caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall +effect measurements show that the current-induced switching of GdFeCo is widely +distributed in time and characterized by significant activation delays, which +limit the total switching speed despite the high domain-wall velocity typical +of ferrimagnets. Our method applies to a broad range of current-induced +phenomena and can be combined with non-electrical excitations to perform +pump-probe Hall effect measurements.",2102.00716v1 +2021-02-03,Infinite Series of Ferrimagnetic Phases Emergent from the Gapless Spin Liquid Phase of Mixed Diamond Chains,"The ground-state phases of mixed diamond chains with ($S, \tau^{(1)}, +\tau^{(2)})=(1/2,1/2,1)$, where $S$ is the magnitude of vertex spins, and +$\tau^{(1)}$ and $\tau^{(2)}$ are those of apical spins, are investigated. The +apical spins $\tau^{(1)}$ and $\tau^{(2)}$ are connected with each other by an +exchange coupling $\lambda$. Other exchange couplings are set equal to unity. +This model has an infinite number of local conservation laws. For large +$\lambda$, the ground state is equivalent to that of the uniform spin $1/2$ +chain. Hence, the ground state is a gapless spin liquid. For $\lambda \leq 0$, +the ground state is a Lieb-Mattis ferrimagnetic phase with spontaneous +magnetization $m_{\rm sp}=1$ per unit cell. For intermediate $\lambda$, we find +a series of ferrimagnetic phases with $m_{\rm sp}=1/p$ where $p$ takes positive +integer values. The phases with $p \geq 2$ are accompanied by the spontaneous +breakdown of the $p$-fold translational symmetry. It is suggested that the +phase with arbitrarily large $p$, namely infinitesimal spontaneous +magnetization, is allowed as $\lambda$ approaches the transition point to the +gapless spin liquid phase.",2102.02116v2 +2021-02-22,"The role of density-dependent magnon hopping and magnon-magnon repulsion in ferrimagnetic spin-(1/2, $S$) chains in a magnetic field","We compare the ground-state features of alternating ferrimagnetic chains +$(1/2, S)$ with $S=1,3/2,2,5/2$ in a magnetic field and the corresponding +Holstein-Primakoff bosonic models up to order $\sqrt{s/S}$, with $s=1/2$, +considering the fully polarized magnetization as the boson vacuum. {The +single-particle Hamiltonian is a Rice-Mele model with uniform hopping and +modified boundaries, while the interactions have a correlated +(density-dependent) hopping term and magnon-magnon repulsion.} The +magnon-magnon repulsion increases the many-magnon energy and the +density-dependent hopping decreases the kinetic energy. We use density matrix +renormalization group calculations to investigate the effects of these two +interaction terms in the bosonic model{, and display the quantitative agreement +between the results from the spin model and the full bosonic approximation. In +particular, we verify the good accordance in the behavior of the edge states, +associated with the ferrimagnetic plateau, from the spin and from the bosonic +models. Furthermore, we show that the boundary magnon density strongly depends +on the interactions and particle statistics.",2102.11143v1 +2021-03-03,THz Field-induced Spin Dynamics in Ferrimagnetic Iron Garnets,"THz magnetization dynamics is excited in ferrimagnetic thulium iron garnet +with a picosecond, single-cycle magnetic field pulse and seen as a +high-frequency modulation of the magneto-optical Faraday effect. Data analysis +combined with numerical modelling and evaluation of the effective Lagrangian +allow us to conclude that the dynamics corresponds to the exchange mode excited +by Zeeman interaction of the THz field with the antiferromagnetically coupled +spins. We argue that THz-pump IR-probe experiments on ferrimagnets offer a +unique tool for quantitative studies of dynamics and mechanisms to control +antiferromagnetically coupled spins.",2103.02449v1 +2021-03-19,Domain wall dynamics of ferrimagnets induced by spin-current near the angular momentum compensation temperature,"We report on a theoretical study of the spin-current excited dynamics of +domain walls (DWs) in ferrimagnets in the vicinity of the angular momentum +compensation point. Effective Lagrangian and nonlinear dynamic equations are +derived for a two-sublattice ferrimagnet taking into account both spin-torques +and external magnetic field. The dynamics of the DW before and after the Walker +breakdown is calculated for any direction of the spin current polarization. It +is shown that for the in-plane polarization of the spin current, the DW +mobility reaches a maximum near the temperature of the angular momentum +compensation. For the out-of-plane spin polarization, in contrast, a spin +current with the densities below the Walker breakdown does not excite the +dynamics of the DW. After overcoming the Walker breakdown, the domain wall +velocity increases linearly with increasing the current density. In this +spin-current polarization configuration the possibility of a gigahertz +oscillation dynamics of the quasi-antiferromagnetic vector under the action of +a damping-like torque in the angular momentum compensation point is +demonstrated. Possible structures for experimental demonstration of the +considered effects are discussed.",2103.10711v1 +2021-06-18,Atomistic spin model of single pulse toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys,"Single femtosecond pulse toggle switching of ferrimagnetic alloys is an +essential building block for ultrafast spintronics. Very different +element-specific demagnetization dynamics is believed to be a hard limit for +switching in ferrimagnets. This suggests that ferrimagnets composed of two ions +of different nature, such as rare earth transition metal alloys, are necessary +for switching. However, experimental observation of toggle switching in +Mn$_2$Ru$_x$Ga Heusler alloys, has contested this limit since Mn ions are of +the same nature. To shed some light into this question, we present an atomistic +spin model for the simulation of single pulse toggle switching of +Mn$_2$Ru$_x$Ga. The magnetic parameters entering in our model are extracted +from previous experimental observations. We show that our model is able to +quantitatively reproduce measured magnetization dynamics of single pulse toggle +switching. We demonstrate that differently to previous understanding toggle +switching in Mn$_2$Ru$_x$Ga is possible even when both Mn sublattices +demagnetization at very similar rate.",2106.10111v2 +2021-10-27,Low temperature competing magnetic energy scales in the topological ferrimagnet TbMn6Sn6,"TbMn6Sn6 is a metallic ferrimagnet displaying signatures of both topological +electrons and topological magnons arising from ferromagnetism and spin-orbit +coupling within its Mn kagome layers. Inelastic neutron scattering measurements +find strong ferromagnetic (FM) interactions within the Mn kagome layer and +reveal a magnetic bandwidth of ~230 meV. The low-energy magnetic excitations +are characterized by strong FM Mn-Mn and antiferromagnetic (AFM) Mn-Tb +interlayer magnetic couplings. We observe weaker, competing long-range FM and +AFM Mn-Mn interlayer interactions similar to those driving helical magnetism in +the YMn6Sn6 system. Combined with density-functional theory calculations, we +find that competing Mn-Mn interlayer magnetic interactions occur in all RMn6Sn6 +compounds with R= Y, Gd-Lu, resulting in magnetic instabilities and tunability +when Mn-R interactions are weak. In the case of TbMn6Sn6, strong AFM Mn-Tb +coupling ensures a highly stable three-dimensional ferrimagnetic network.",2110.14713v2 +2022-01-11,Nonreciprocal dynamics of ferrimagnetic bimerons,"Magnetic bimerons are topologically nontrivial spin textures in in-plane +easy-axis magnets, which can be used as particle-like information carriers. +Here, we report a theoretical study on the nonreciprocal dynamics of +asymmetrical ferrimagnetic (FiM) bimerons induced by spin currents. The FiM +bimerons have the ability to move at a speed of kilometers per second and do +not show the skyrmion Hall effect at the angular momentum compensation point. +Our micromagnetic simulations and analytical results demonstrate that spin +currents are able to induce the nonreciprocal transport and a drift motion of +the FiM bimeron even if the system is at the angular momentum compensation +point. By analyzing the current-induced effective fields, we find that the +nonreciprocal transport is attributed to the asymmetry of the bimeron +structure. Our results are useful for understanding the physics of bimerons in +ferrimagnets and may provide guidelines for building bimeron-based spintronic +devices.",2201.03781v1 +2022-03-17,Rare-earth-free noncollinear metallic ferrimagnets Mn4-xZxN with compensation at room temperature,"Compensated ferrimagnets, like antiferromagnets, show no net magnetization +but their transport and magneto-optic properties resemble those of +ferromagnets, thereby creating opportunities for applications in high-frequency +spintronics and low-energy loss communications. Here we study the modification +the noncollinear ferrimagnetic spin structure of Mn4N by a variety of metallic +substitutions Z (Z = Cu - Ge and Ag - Sn) to achieve compensation at room +temperature. The noncollinear frustrated 2.35 Bohr magneton moments of Mn on 3c +sites of the (111) kagome planes tilt about 20 degree out-of-plane in Mn4N and +are easily influenced by the substitutions on 1a sites, leading to different +efficiency of compensation in Mn4-xZxN that increases gradually from group 11 +(Cu, Ag) to group 14 (Ge, Sn) with increasing number of valance electrons. +Elements from the 5th period are more efficient for compensation than those +from the 4th period due to lattice expansion. The manganese site moments are +determined by Z, orbital hybridization, charge transfer and the tilt angle, +analyzed by constrained density functional theory. The Ga compound with +compensation at room temperature for x = 0.26 is recommended for high-frequency +spintronic applications.",2203.09641v1 +2022-04-04,Towards high all-optical data writing rates in synthetic ferrimagnets,"Although all-optical magnetization switching with fs laser pulses has +garnered much technological interest, the ultimate data rates achievable have +scarcely been investigated. Recently it has been shown that after a switching +event in a GdCo alloy, a second laser pulse arriving 7 ps later can +consistently switch the magnetization. However, it is as of yet unknown whether +the same holds in layered ferrimagnetic systems, which hold much promise for +applications. In this work we investigate the minimum time delay required +between two subsequent switching events in synthetic ferrimagnetic Co/Gd +bilayers using two fs laser pulses. We experimentally demonstrate that the +minimum time delay needed for consistent switching can be as low as 10 ps. +Moreover, we demonstrate the importance of engineering heat diffusion away from +the magnetic material, as well as control over the laser pulse power. This +behavior is reproduced using modelling, where we find that the second switch +can occur even when the magnetization is not fully recovered. We further +confirm that heat diffusion is a critical factor in reducing the time delay for +the second switch, while also confirming a critical dependence on laser power.",2204.01459v1 +2022-05-06,Interband magnon drag in ferrimagnetic insulators,"We propose a new drag phenomenon, an interband magnon drag, and report on +interaction effects and multiband effects in magnon transport of ferrimagnetic +insulators. We study a spin-Seebeck coefficient $S_{\textrm{m}}$, a magnon +conductivity $\sigma_{\textrm{m}}$, and a magnon thermal conductivity +$\kappa_{\textrm{m}}$ of interacting magnons for a minimal model of +ferrimagnetic insulators using a $1/S$ expansion of the Holstein-Primakoff +method, the linear-response theory, and a method of Green's functions. We show +that the interband magnon drag enhances $\sigma_{\textrm{m}}$ and reduces +$\kappa_{\textrm{m}}$, whereas its total effects on $S_{\textrm{m}}$ are small. +This drag results from the interband momentum transfer induced by the +magnon-magnon interactions. We also show that the higher-energy band magnons +contribute to $S_{\textrm{m}}$, $\sigma_{\textrm{m}}$, and +$\kappa_{\textrm{m}}$ even for temperatures smaller than the energy difference +between the two bands.",2205.03058v1 +2022-06-27,Bridging atomistic spin dynamics methods and phenomenological models of single pulse ultrafast switching in ferrimagnets,"We bridge an essential knowledge gap on the understanding of all-optical +ultrafast switching in ferrimagnets; namely, the connection between atomistic +spin dynamics methods and macroscopic phenomenological models. All-optical +switching of the magnetization occurs after the application of a single +femtosecond laser pulse to specific ferrimagnetic compounds. This strong +excitation puts the involved degrees of freedom, electrons, lattice and spins +out-of-equilibrium between each other. Atomistic spin models have +quantitatively described all-optical switching in a wide range of experimental +conditions, while having failed to provide a simple picture of the switching +process. Phenomenological models are able to qualitatively describe the +dynamics of the switching process. However, a unified theoretical framework is +missing that describes the element-specific spin dynamics as atomistic spin +models with the simplicity of phenomenology. Here, we bridge this gap and +present an element-specific macrospin dynamical model which fully agrees with +atomistic spin dynamics simulations and symmetry considerations of the +phenomenological models.",2206.13593v1 +2022-09-21,Effect of Co Substitution on Ferrimagnetic Heusler compound Mn3Ga,"Effect of Co substitution on Mn$_3$Ga is investigated using first-principles +study for structural and magnetic properties. Without Co, ferrimagnetic Heusler +compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co +concentration (x) Mn$_3$Ga prefers tetragonal (cubic) phase when x \leq 0.5 (x +\geq 0.5). Ferrimagnetism is robust regardless of x in both phases. While +magnetic moments of two Mn do not vary significantly with x, Co magnetic moment +in two phases exhibit different behaviors, leading to distinct features in +total magnetic moment (M_{tot}). When x \leq 0.5, in tetragonal phase, Co +magnetic moment is vanishingly small, resulting in a decrease of M_{tot} with +x. In contrast, when x \geq 0.5, in cubic phase, Co magnetic moment is roughly +1$\mu_B$, which is responsible for an increase of Mtot. Electronic structure is +analyzed with partial density of states for various x. To elucidate the +counterintuitively small Co moment, the magnetic exchange interaction is +investigated where exchange coefficient between Co and Mn is much smaller in x +\leq 0.5 case than x \geq 0.5 one.",2209.10216v1 +2022-09-23,Magnetostatics of Room Temperature Compensated Co/Gd/Co/Gd-based Synthetic Ferrimagnets,"Flexibility for interface engineering, and access to all-optical switching of +the magnetization, make synthetic ferrimagnets an interesting candidate for +advanced opto-spintronic devices. Moreover, due to their layered structure and +disordered interfaces they also bear promise for the emerging field of graded +magnetic materials. The fastest and most efficient spin-orbit torque driven +manipulation of the magnetic order in this material system generally takes +place at compensation. Here, we present a systematic experimental and modeling +study of the conditions for magnetization compensation and perpendicular +magnetic anisotropy in the synthetic ferrimagnetic Co/Gd/Co/Gd system. A model +based on partial intermixing at the Co/Gd interfaces of this system has been +developed which explains the experiments well, and provides a new tool to +understand its magnetic characteristics. More specifically, this work provides +new insight in the decay of the Co proximity-induced magnetization in the Gd, +and the role the capping layer plays in the Gd magnetization.",2209.11562v1 +2022-10-04,Local density of states as a probe for tunneling magnetoresistance effect: application to ferrimagnetic tunnel junctions,"We investigate the tunneling magnetoresistance (TMR) effect using the lattice +models which describe the magnetic tunnel junctions (MTJ). First, taking a +conventional ferromagnetic MTJ as an example, we show that the product of the +local density of states (LDOS) at the center of the barrier traces the TMR +effect qualitatively. The LDOS inside the barrier has the information on the +electrodes and the electron tunneling through the barrier, which enables us to +easily evaluate the tunneling conductance more precisely than the conventional +Julliere's picture. We then apply this method to the MTJs with collinear +ferrimagnets and antiferromagnets. We find that the TMR effect in the +ferrimagnetic and antiferromagnetic MTJs changes depending on the interfacial +magnetic structures originating from the sublattice structure, which can also +be captured by the LDOS. Our findings will reduce the computational cost for +the qualitative evaluation of the TMR effect, and be useful for a broader +search for the materials which work as the TMR devices showing high +performance.",2210.01441v1 +2022-10-20,Strong variation of spin-orbit torques with relative spin relaxation rates in ferrimagnets,"Spin-orbit torques (SOTs) have been widely understood as an interfacial +transfer of spin that is independent of the bulk properties of the magnetic +layer. Here, we report that SOTs acting on ferrimagnetic FexTb1-x layers +decrease and vanish upon approaching the magnetic compensation point because +the rate of spin transfer to the magnetization becomes slower than the rate of +spin relaxation into the crystal lattice due to spin-orbit scattering. These +results indicate that the relative rates of competing spin relaxation processes +within magnetic layers play a critical role in determining the strength of +SOTs, which provides a unified understanding for the diverse and even seemingly +puzzling SOT phenomena in ferromagnetic and compensated systems. Our work +indicates that spin-orbit scattering within the magnet should be minimized for +efficient SOT devices. We also find that the interfacial spin-mixing +conductance of interfaces of ferrimagnetic alloys (such as FexTb1-x) is as +large as that of 3d ferromagnets and insensitive to the degree of magnetic +compensation.",2210.11042v1 +2022-12-06,Dynamics of hybrid magnetic skyrmion driven by spin-orbit torque in ferrimagnets,"Magnetic skyrmions are magnetic textures with topological protection, which +are expected to be information carriers in future spintronic devices. In this +work, we propose a scheme to implement hybrid magnetic skyrmions (HMS) in +ferrimagnets, and we study theoretically and numerically the dynamics of the +HMS driven by spin-orbit torque. It is revealed that the skyrmion Hall effect +depends on the skyrmion helicity and the net angular momentum ({\delta}s), +allowing the effective modulation of the HMS motion through tuning +Dzyaloshinskii-Moriya interaction and {\delta}s. Thus, the Hall effect can be +suppressed through selecting suitable materials to better control the HMS +motion. Moreover, Magnus force for finite {\delta}s suppresses the transverse +motion and enhances the longitudinal propagation, resulting in the HMS dynamics +in ferrimagnets faster than that in antiferromagnets.",2212.02807v1 +2023-03-21,Unveiling the magnetic structure and phase transition of Cr$_2$CoAl using neutron diffraction,"We report the detailed analysis of temperature dependent neutron diffraction +pattern of the Cr$_2$CoAl inverse Heusler alloy and unveil the magnetic +structure up to the phase transition as well as its fully compensated +ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using +the space group I$\bar4${\it m}2 confirm the inverse tetragonal structure over +the large temperature range from 100~K to 900~K. The refinement of the magnetic +phase considering the wave vector $k=$ (0, 0, 0) reveals the ferrimagnetic +nature of the sample below 730$\pm$5~K. This transition temperature is obtained +from empirical power law fitting of the variation in the ordered net magnetic +moment and intensity of (110) peak as a function of temperature. The spin +configuration of the microscopic magnetic structure suggests the nearly fully +compensated ferrimagnetic behavior where the magnetic moments of Cr2 are +antiparallel with respect to the Cr1, and Co moments. Moreover, the observed +anomaly in the thermal expansion and lattice parameters at 730$\pm$5~K suggest +that the distortion in crystal structure may play an important role in the +magnetic phase transition.",2303.11869v1 +2023-03-26,Strong lateral exchange coupling and current-induced switching in single-layer ferrimagnetic films with patterned compensation temperature,"Strong, adjustable magnetic couplings are of great importance to all devices +based on magnetic materials. Controlling the coupling between adjacent regions +of a single magnetic layer, however, is challenging. In this work, we +demonstrate strong exchange-based coupling between arbitrarily shaped regions +of a single ferrimagnetic layer. This is achieved by spatially patterning the +compensation temperature of the ferrimagnet by either oxidation or He+ +irradiation. The coupling originates at the lateral interface between regions +with different compensation temperature and scales inversely with their width. +We show that this coupling generates large lateral exchange coupling fields and +we demonstrate its application to control the switching of magnetically +compensated dots with an electric current.",2303.14809v1 +2023-07-10,Reversal of the skyrmion topological deflection across ferrimagnetic angular momentum compensation,"Due to their non-trivial topology, skyrmions describe deflected trajectories, +which hinders their straight propagation in nanotracks and can lead to their +annihilation at the track edges. This deflection is caused by a gyrotropic +force proportional to the topological charge and the angular momentum density +of the host film. In this article we present clear evidence of the reversal of +the topological deflection angle of skyrmions with the sign of angular momentum +density. We measured the skyrmion trajectories across the angular momentum +compensation temperature (TAC) in GdCo thin films, a rare earth/transition +metal ferrimagnetic alloy. The sample composition was used to engineer the +skyrmion stability below and above the TAC. A refined comparison of their +dynamical properties evidenced a reversal of the skyrmions deflection angle +with the total angular momentum density. This reversal is a clear demonstration +of the possibility of tuning the skyrmion deflection angle in ferrimagnetic +materials and paves the way for deflection-free skyrmion devices.",2307.04669v2 +2023-08-23,Magnetic analogue of liquid-gas phase transition of water: case study of a spin-1/2 Ising-Heisenberg model on a diamond-decorated square lattice,"The spin-1/2 Ising-Heisenberg model on a diamond-decorated square lattice +exhibits an intriguing temperature-driven phase transition in a magnetic field +between a classical ferrimagnetic phase and a quantum monomer-dimer phase. A +generalized decoration-iteration transformation accurately maps the considered +model to an effective spin-1/2 Ising model on a square lattice with +temperature-dependent effective interactions and field, whereby the effective +field vanishes at the phase boundary separating the classical ferrimagnetic +phase from the quantum monomer-dimer phase. Typical features of the +magnetization, magnetic susceptibility and specific heat in the vicinity of +discontinuous and continuous thermal phase transitions between the classical +ferrimagnetic phase and the quantum monomer-dimer phase are elucidated.",2308.12410v1 +2023-08-31,Tunable magnetic domains in ferrimagnetic MnSb$_2$Te$_4$,"Highly tunable properties make Mn(Bi,Sb)$_2$Te$_4$ a rich playground for +exploring the interplay between band topology and magnetism: On one end, +MnBi$_2$Te$_4$ is an antiferromagnetic topological insulator, while the +magnetic structure of MnSb$_2$Te$_4$ (MST) can be tuned between +antiferromagnetic and ferrimagnetic. Motivated to control electronic properties +through real-space magnetic textures, we use magnetic force microscopy (MFM) to +image the domains of ferrimagnetic MST. We find that magnetic field tunes +between stripe and bubble domain morphologies, raising the possibility of +topological spin textures. Moreover, we combine in situ transport with domain +manipulation and imaging to both write MST device properties and directly +measure the scaling of the Hall response with domain area. This work +demonstrates measurement of the local anomalous Hall response using MFM, and +opens the door to reconfigurable domain-based devices in the M(B,S)T family.",2308.16806v1 +2023-09-05,Strong and nearly 100$\%$ spin-polarized second-harmonic generation from ferrimagnet Mn$_{2}$RuGa,"Second-harmonic generation (SHG) has emerged as a promising tool for +detecting electronic and magnetic structures in noncentrosymmetric materials, +but 100$\%$ spin-polarized SHG has not been reported. In this work, we +demonstrate nearly 100$\%$ spin-polarized SHG from half-metallic ferrimagnet +Mn$_{2}$RuGa. A band gap in the spin-down channel suppresses SHG, so the +spin-up channel contributes nearly all the signal, as large as 3614 pm/V about +10 times larger than that of GaAs. In the spin-up channel, $\chi_{xyz}^{(2)}$ +is dominated by the large intraband current in three highly dispersed bands +near the Fermi level. With the spin-orbit coupling (SOC), the reduced magnetic +point group allows additional SHG components, where the interband contribution +is enhanced. Our finding is important as it predicts a large and complete +spin-polarized SHG in a all-optical spin switching ferrimagnet. This opens the +door for future applications.",2309.01965v1 +2023-09-28,Magnetism and magnetocaloric properties of Co$_{1-x}$Mn$_x$Cr$_2$O$_4$,"Co$_{1-x}$Mn$_x$Cr$_2$O$_4$ crystallizes as a normal spinel in the cubic $Fd +\overline{3}m$ space group, and the end members have been reported to display a +region of collinear ferrimagnetism as well as a low-temperature spin-spiral +state with variable coherence lengths from 3 nm to 10 nm in polycrystalline +samples. Here, we present the synthesis of the entire solid solution, and data +showing that the ferrimagnetic ordering temperature as well as the spin-spiral +lock-in temperature are tunable with the Co/Mn ratio. The peak magnetocaloric +entropy change was determined to be $\Delta S_M$ = -5.63 J kg$^{-1}$ K$^{-1}$ +in an applied magnetic field change of $\Delta H$ = 0 T to 5 T for the Mn +end-member at the ferrimagnetic ordering temperature. Using density functional +theory (DFT), we explore the shortcomings of the magnetic deformation proxy to +identify trends in $\Delta S_M$ across composition in this spinel system, and +explore future extensions of theory to address these discrepancies.",2309.16168v1 +2023-11-13,Magnetoresistive detection of perpendicular switching in a magnetic insulator,"Spintronics offers promising routes for efficient memory, logic, and +computing technologies. The central challenge in spintronics is electrically +manipulating and detecting magnetic states in devices. The electrical control +of magnetization via spin-orbit torques is effective in both conducting and +insulating magnetic layers. However, the electrical readout of magnetization in +the latter is inherently difficult, limiting its use in practical applications. +Here, we demonstrate magnetoresistive detection of perpendicular magnetization +reversal in an electrically insulating ferrimagnet, terbium iron garnet (TbIG). +To do so, we use TbIG|Cu|TbCo, where TbCo is a conducting ferrimagnet and +serves as the reference layer, and Cu is a nonmagnetic spacer. Current +injection through Cu|TbCo allows us to detect the magnetization reversal of +TbIG with a simple resistance readout during an external magnetic field sweep. +By examining the effect of measurement temperature, TbCo composition, and Cu +thickness on the sign and amplitude of the magnetoresistance, we conclude that +the spin-dependent electron scattering at the TbIG|Cu interface is the +underlying cause. Technologically-feasible magnetoresistive detection of +perpendicular switching in a ferrimagnetic garnet is a breakthrough, as it +opens broad avenues for novel insulating spintronic devices and concepts.",2311.07350v1 +2023-12-08,Convergent finite element methods for antiferromagnetic and ferrimagnetic materials,"We consider the numerical approximation of a continuum model of +antiferromagnetic and ferrimagnetic materials. The state of the material is +described in terms of two unit-length vector fields, which can be interpreted +as the magnetizations averaging the spins of two sublattices. For the static +setting, which requires the solution of a constrained energy minimization +problem, we introduce a discretization based on first-order finite elements and +prove its $\Gamma$-convergence. Then, we propose and analyze two iterative +algorithms for the computation of low-energy stationary points. The algorithms +are obtained from (semi-)implicit time discretizations of gradient flows of the +energy. Finally, we extend the algorithms to the dynamic setting, which +consists of a nonlinear system of two Landau-Lifshitz-Gilbert equations solved +by the two fields, and we prove unconditional stability and convergence of the +finite element approximations toward a weak solution of the problem. Numerical +experiments assess the performance of the algorithms and demonstrate their +applicability for the simulation of physical processes involving +antiferromagnetic and ferrimagnetic materials.",2312.04939v1 +2023-12-21,Altermagnetic ferroelectric LiFe2F6 and spin-triplet excitonic insulator phase,"Altermagnetism is a new magnetic phase with k-dependent spin polarization and +may exist in an insulating state with a high N\'eel temperature. This provides +a new opportunity to obtain both spin and electric polarization in one +material. Here, based on symmetry analysis and the first-principles electronic +structures calculations, we predict that LiFe2F6 is a d-wave altermagnetic and +charge-ordering-mediated ferroelectric material. Moreover, the LiFe2F6 +transforms into a ferrimagnetic and ferroelectric phase with strong +magnetoelectric coupling under biaxial compressive strain. Interestingly, the +spins of the valence band and the conduction band are opposite in ferrimagnetic +LiFe2F6, which facilitates a simultaneous spin-triplet excitonic insulator +phase. More importantly, the spin-triplet excitons with spin 1 and -1 can be +switched by electric fields in ferrimagnetic LiFe2F6 due to strong +magnetoelectric coupling. Due to the abundance of novel physical properties, +LiFe2F6 will certainly attract a wide range of theoretical and experimental +interest.",2312.13911v1 +2024-01-16,Spin Waves in Ferrimagnets near the Angular Magnetization Compensation Temperature: A Micromagnetic Study,"Spin wave propagation along a ferrimagnetic strip with out-of-plane +magnetization is studied by means of micromagnetic simulations. The +ferrimagnetic material is considered as formed by two antiferromagnetically +coupled sublattices. Two critical temperatures can be defined for such systems: +that of magnetization compensation and that of angular momentum compensation, +both different due to distinct Land\'e factors for each sub-lattice. Spin waves +in the strip are excited by a spin current injected at one of its edges. The +obtained dispersion diagrams show exchange-dominated forward volume spin waves. +For a given excitation frequency, N\'eel vector describes highly eccentric +orbits, the eccentricity depending on temperature, whose semi-major axis are +oriented differently at distinct locations on the FiM strip.",2401.08235v1 +2024-01-24,Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation,"Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide +multilayer strips is investigated using systematic micromagnetic simulations +which account for spin-orbit coupling phenomena. Domain wall velocity and +characteristic relaxation times are studied as functions of the geometry, +curvature and width of the strip, at and out of the angular momentum +compensation. Results show that domain walls can propagate faster and without a +significant distortion in such strips in contrast to their ferromagnetic +counterparts. Using an artificial system based on a straight strip with an +equivalent current density distribution, we can discern its influence on the +wall terminal velocity, as part of a more general geometrical influence due to +the curved shape. Curved and narrow ferrimagnetic strips are promising +candidates for designing high speed and fast response spintronic circuitry +based on current-driven domain wall motion.",2401.13617v1 +2024-03-11,Magnon bands and transverse transport in a proposed two-dimensional $Cu_2F_5$ ferrimagnet,"The copper fluoride $Cu_2F_5$ is a proposed stable compound that can be seen +as a layered magnetic lattice of $S=1$ and $S=1/2$ sites, corresponding to +copper ions. Intending to cast light on the transport properties of +ferrimagnetic magnons, we use the linear spin wave approach to study the magnon +band structure of the 2D lattice in a ferrimagnetic off-plane order, as well as +the transverse transport of magnons in the crystal bulk. That transverse +(Hall-like) transport can be induced by a magnetic field or temperature +gradient, and within the linear response theory is generated by the Berry +curvature of the eigenstates. As in most of the cases for magnons, the Berry +curvature here is related to Dzyaloshinskii-Moriya interactions between +next-near-neighbors. The band structure of the system is non-degenerate and the +transport coefficients are non-null. We also determine the condition for two +transport coefficients to change sign in response to temperature.",2403.07169v1 +2018-10-24,Long spin coherence length and bulk-like spin-orbit torque in ferrimagnetic multilayers,"Ferromagnetic spintronics has been a main focus as it offers non-volatile +memory and logic applications through current-induced spin-transfer torques. +Enabling wider applications of such magnetic devices requires a lower switching +current for a smaller cell while keeping the thermal stability of magnetic +cells for non-volatility. As the cell size reduces, however, it becomes +extremely difficult to meet this requirement with ferromagnets because +spin-transfer torque for ferromagnets is a surface torque due to rapid spin +dephasing, leading to the 1/ferromagnet-thickness dependence of the spin-torque +efficiency. Requirement of a larger switching current for a thicker and thus +more thermally stable ferromagnetic cell is the fundamental obstacle for +high-density non-volatile applications with ferromagnets. Theories predicted +that antiferromagnets have a long spin coherence length due to the staggered +spin order on an atomic scale, thereby resolving the above fundamental +limitation. Despite several spin-torque experiments on antiferromagnets and +ferrimagnetic alloys, this prediction has remained unexplored. Here we report a +long spin coherence length and associated bulk-like-torque characteristic in an +antiferromagnetically coupled ferrimagnetic multilayer. We find that a +transverse spin current can pass through > 10 nm-thick ferrimagnetic Co/Tb +multilayers whereas it is entirely absorbed by 1 nm-thick ferromagnetic Co/Ni +multilayer. We also find that the switching efficiency of Co/Tb multilayers +partially reflects a bulk-like-torque characteristic as it increases with the +ferrimagnet-thickness up to 8 nm and then decreases, in clear contrast to +1/thickness-dependence of Co/Ni multilayers. Our results on +antiferromagnetically coupled systems will invigorate researches towards +energy-efficient spintronic technologies.",1810.10404v1 +2020-09-12,Ferrimagnetic States of Na-K Alloy Clusters in Zeolite Low-Silica X,"In zeolite low-silica X (LSX), beta-cages with the inside diameter of approx +7 AA{} are arrayed in a diamond structure. Among them, supercages with the +inside diameter of approx 13 AA{} are formed and arrayed in a diamond structure +by the sharing of windows with the inside diameter of approx 8 AA{}. The +chemical formula of zeolite LSX used in the present study is given by +Na$_{x}$K$_{12-x}$Al$_{12}$Si$_{12}$O$_{48}$ per supercage (or beta-cage), +where Na$_{x}$K$_{12-x}$ and Al$_{12}$Si$_{12}$O$_{48}$ are the exchangeable +cations of zeolite LSX and the aluminosilicate framework, respectively. Na-K +alloy clusters are incorporated in these cages by the loading of guest K metal +at $n$K atoms per supercage (or beta-cage). A N'eel's N-type ferrimagnetism has +been observed at $n = 7.8$ for $x = 4$. In the present paper, optical, magnetic +and electrical properties are studied in detail mainly for $x = 4$. +Ferrimagnetic properties are observed at $6.5 < n < 8.5$. At the same time, the +Curie constant suddenly increases. An optical reflection band of beta-cage +clusters at 2.8 eV is observed at $n > 6.5$ in accordance with the sudden +increase in the Curie constant. An electrical resistivity indicates metallic +values at $n$ gtrapprox 6, because a metallic state is realized in the energy +band of supercage clusters. The ferrimagnetism is explained by the +antiferromagnetic interaction between the magnetic sublattice of itinerant +electron ferromagnetism at supercage clusters and that of localized moments at +beta-cage clusters. The electrical resistivity in ferrimagnetic samples at $n = +8.2$ for $x = 4$ increases extraordinarily at very low temperatures, such as +approx $10^6$ times larger than the value at higher temperatures. Observed +anomalies in the electrical resistivity resembles the Kondo insulator, but +itinerant electrons of narrow energy band of supercage clusters are +ferromagnetic.",2009.05742v1 +2022-05-16,Ferrimagnetism in stable non-metal covalent organic framework,"We synthesized a pure organic non-metal crystalline covalent organic +framework TAPA-BTD-COF by bottom-up Schiff base chemical reaction. And this +imine-based COF is stable in aerobic condition and room-temperature. We +discovered that this TAPA-BTD-COF exhibited strong magneticity in 300 K +generating magnetic hysteresis loop in M-H characterization and giant chimol up +to 0.028. And we further conducted zero-field cooling and field-cooling +measurement of M-T curves. The as-synthesized materials showed a large chi/mol +up to 0.028 in 300 K and increasing to 0.037 in 4.0 K with 200 Oe measurement +field. The TAPA-BTD-COF 1/chimol~T curve supported its ferrimagnetism, with an +intrinsic delta temperature as -33.03 K by extrapolating the 1/chimol~T curve. +From the continuously increasing slope of 1/chimol~T, we consider that this +TAPA-BTD-COF belongs to ferrimagnetic other than antiferromagnetic materials. +And the large chimol value 0.028 at 300 K and 0.037 at 4.0 K also supported +this, since common antiferromagnetic materials possess chimol in the range of +10-5 to 10-3 as weak magnetics other than strong magnetic materials such as +ferrimagnetics and ferromagnetics. Since this material is purely non-metal +organic polymer, the possibility of d-block and f-block metal with +unpaired-electron induced magnetism can be excluded. Besides, since the COF +does not involve free-radical monomer in the processes of synthesis, we can +also exclude the origin of free-radical induced magnetism. According to recent +emerging flat-band strong correlated exotic electron property, this +unconventional phenomenon may relate to n-type doping on the flat-band locating +in the CBM, thus generating highly-localized electron with infinite effective +mass and exhibiting strong correlation, which accounts for this non-trivial +strong and stable ferrimagneticity at room-temperature and aerobic atmospheric +conditions.",2205.07541v1 +1999-08-10,Existence of Saturated Ferromagnetic and Spiral States in 1D Lieb-Ferrimagnetic Models away from Half-Filling,"In order to study conditions for the appearance of ferromagnetism in a wide +filling region, we investigate numerically three types of one-dimensional +Lieb-ferrimagnetic Hubbard models: a periodic diamond (PD) chain, a periodic +alternately-attached leg (PAAL) chain and an open diamond (OD) chain. All of +these models have a flat band (or equivalently, degenerate single-electron +eigenvalues). The PD and OD chains commonly have a local-loop structure. +Nagaoka's theorem holds only in the PD chain. At half-filling, it have been +rigorously proven that all of these models are ferrimagnet. Away from +half-filling, however, quite different magnetic properties are found. In the +fillings 1/3< rho_e <1/2, the ground state of the PD chain for a +infinitely-large U is the extended ferromagnetic state, that is, the saturated +ferromagnetic state or the spiral state for odd or even number of electrons, +respectively. In the PAAL chain, on the other hand, there is no magnetic order. +Thus, the flat band is found to be not a sufficient condition of the extended +ferromagnetic state. We find, moreover, that the saturated ferromagnetism +appears in the OD chain, although the Nagaoka theorem does not hold on this +chain. This indicates that the local-loop structure plays an important role on +the appearance of the extended ferromagnetic state.",9908144v1 +2005-05-04,From Finite-Size and Surface Effects to Glassy Behaviour in Ferrimagnetic Nanoparticles,"This chapter is aimed at studying the anomalous magnetic properties (glassy +behaviour) observed at low temperatures in nanoparticles of ferrimagnetic +oxides. This topic is discussed both from numerical results and experimental +data. Ferrimagnetic fine particles show most of the features of glassy systems +due to the random distribution of anisotropy axis, interparticle interactions +and surface effects. Experiments have shown that the hysteresis loops display +high closure fields with high values of the differential susceptibility. Low +magnetisation as compared to bulk, shifted loops after field-cooling, highfield +irreversibilities between zero-field and field cooling processes and ageing +phenomena in the time-dependence of the magnetisation, are also observed. This +phenomenology indicates the existence of some kind of freezing phenomenon +arising from a complex hierarchy of the energy levels, whose origin is +currently under discussion. Two models have been proposed to account for it: i) +the existence of a spin-glass state at the surface of the particle which is +coupled to the particle core through an exchange field; and ii) the collective +behaviour induced by interparticle interactions. In real systems, both +contributions simultaneously occur, being difficult to distinguish their +effects. In contrast, numerical simulations allow us to build a model just +containing the essential ingredients to study solely one of two phenomena.",0505112v1 +2007-11-19,Probing phase coexistence and stabilization of the spin-ordered ferrimagnetic state by Calcium addition in the YBa_{1-x}Ca_{x}Co_{2}O_{5.5} layered cobaltites using neutron diffraction,"In this article we study the effects of a partial substitution of Ba with the +smaller cation Ca in the layered cobaltites YBaCo_2O_{5+\delta} for \delta +\approx 0.5. Neutron thermodiffractograms are reported for the compounds +YBa_{0.95}Ca_{0.05}Co_2O_{5.5} (x_{Ca}=0.05) and YBa_{0.90}Ca_{0.10}Co_2O_{5.5} +(x_{Ca}=0.10) in the temperature range 20 K \leq T \leq 300 K, as well as high +resolution neutron diffraction experiments at selected temperatures for the +samples x_{Ca}=0.05, x_{Ca}=0.10 and the parent compound x_{Ca}=0. We have +found the magnetic properties to be strongly affected by the cationic +substitution. Although the ""122"" perovskite structure seems unaffected by Ca +addition, the magnetic arrangements of Co ions are drastically modified: the +antiferromagnetic (AFM) long-range order is destroyed, and a ferrimagnetic +phase with spin state order is stabilized below T \sim 290 K. For the sample +with x_{Ca}=0.05 a fraction of AFM phase coexists with the ferrimagnetic one +below T \sim 190 K, whereas for x_{Ca}=0.10 the AFM order is completely lost. +The systematic refinement of the whole series has allowed for a better +understanding of the observed low-temperature diffraction patterns of the +parent compound, YBaCo_2O_{5.5}, which had not yet been clarified. A two-phase +scenario is proposed for the x_{Ca}=0 compound which is compatible with the +phase coexistence observed in the x_{Ca}=0.05 sample.",0711.3002v1 +2008-09-15,Kinetics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic model,"We present a study, within a mean-field approach, of the kinetics of a mixed +ferrimagnetic model on a square lattice in which two interpenetrating square +sublattices have spins that can take two values, $\sigma=\pm1/2$, alternated +with spins that can take the four values, $S=\pm3/2, \pm1/2$. We use the +Glauber-type stochastic dynamics to describe the time evolution of the system +with a crystal-field interaction in the presence of a time-dependent +oscillating external magnetic field. The nature (continuous and discontinuous) +of transition is characterized by studying the thermal behaviors of average +order parameters in a period. The dynamic phase transition points are obtained +and the phase diagrams are presented in the reduced magnetic field amplitude +$(h)$ and reduced temperature $(T)$ plane, and in the reduced temperature and +interaction parameter planes, namely in the $(h, T)$ and $(d, T)$ planes, $d$ +is the reduced crystal-field interaction. The phase diagrams always exhibit a +tricritical point in $(h, T)$ plane, but do not exhibit in the $(d, T)$ plane +for low values of $h$. The dynamic multicritical point or dynamic critical end +point exist in the $(d, T)$ plane for low values of $h$. Moreover, phase +diagrams contain paramagnetic $(p)$, ferromagnetic $(f)$, ferrimagnetic $(i)$ +phases, two coexistence or mixed phase regions, $(f+p)$ and $(i+p)$, that +strongly depend on interaction parameters.",0809.2450v1 +2011-03-10,"Phase diagram of the XXZ ferrimagnetic spin-(1/2, 1) chain in the presence of transverse magnetic field","We investigate the phase diagram of an anisotropic ferrimagnet spin-(1/2, 1) +in the presence of a non-commuting (transverse) magnetic field. We find a +magnetization plateau for the isotropic case while there is no plateau for the +anisotropic ferrimagnet. The magnetization plateau can appear only when the +Hamiltonian has the U(1) symmetry in the presence of the magnetic field. The +anisotropic model is driven by the magnetic field from the N\'{e}el phase for +low fields to the spin-flop phase for intermediate fields and then to the +paramagnetic phase for high fields. We find the quantum critical points and +their dependence on the anisotropy of the aforementioned field-induced quantum +phase transitions. The spin-flop phase corresponds to the spontaneous breaking +of Z2 symmetry. We use the numerical density matrix renormalization group and +analytic spin wave theory to find the phase diagram of the model. The energy +gap, sublattice magnetization, and total magnetization parallel and +perpendicular to the magnetic field are also calculated. The elementary +excitation spectrums of the model are obtained via the spin wave theory in the +three different regimes depending on the strength of the magnetic field.",1103.1967v2 +2011-04-13,Optimized Effective Potential Model for the Double Perovskites Sr2-xYxVMoO6 and Sr2-xYxVTcO6,"In attempt to explore half-metallic properties of the double perovskites +Sr2-xYxVMoO6 and Sr2-xYxVTcO6, we construct an effective low-energy model, +which describes the behavior of the t2g-states of these compounds. All +parameters of such model are derived rigorously on the basis of +first-principles electronic structure calculations. In order to solve this +model we employ the optimized effective potential method and treat the +correlation interactions in the random phase approximation. Although +correlation interactions considerably reduce the intraatomic exchange splitting +in comparison with the Hartree-Fock method, this splitting still substantially +exceeds the typical values obtained in the local-spin-density approximation +(LSDA), which alters many predictions based on the LSDA. Our main results are +summarized as follows: (i) all ferromagnetic states are expected to be +half-metallic. However, their energies are generally higher than those of the +ferrimagnetic ordering between V- and Mo/Tc-sites (except Sr2VMoO6); (ii) all +ferrimagnetic states are metallic (except fully insulating Y2VTcO6) and no +half-metallic antiferromagnetism has been found; (iii) moreover, many of the +ferrimagnetic structures appear to be unstable with respect to the spin-spiral +alignment. Thus, the true magnetic ground state of the most of these systems is +expected to be more complex. In addition, we discuss several methodological +issues related to the nonuniqueness of the effective potential for the magnetic +half-metallic and insulating states.",1104.2399v1 +2011-10-21,Exchange-spring behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite,"In this work we report a study of the magnetic behavior of ferrimagnetic +oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 +nanocomposites. The latter compound is a good system to study hard +ferrimagnet/soft ferromagnet exchange coupling. Two steps were used to +synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposites: (i) first preparation +of CoFe2O4 nanoparticles using the a simple hydrothermal method and (ii) second +reduction reaction of cobalt ferrite nanoparticles using activated charcoal in +inert atmosphere and high temperature. The phase structures, particle sizes, +morphology, and magnetic properties of CoFe2O4 nanoparticles have been +investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), +transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) +with applied field up to 3.0 kOe at room temperature and 50K. The mean diameter +of CoFe2O4 particles is about 16 nm. Mossbauer spectra reveal two sites for +Fe3+. One site is related to Fe in an octahedral coordination and the other one +to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal +structure of CoFe2O4. TEM measurements of nanocomposite show the formation of a +thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles +increase to about 100 nm. The magnetization of nanocomposite showed hysteresis +loop that is characteristic of the exchange spring systems. A maximum energy +product (BH)max of 1.22 MGOe was achieved at room temperature for CoFe2O4/CoFe2 +nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 +precursor. The exchange-spring interaction and the enhancement of product +(BH)max in nanocomposite CoFe2O4/CoFe2 have been discussed.",1110.4905v1 +2012-06-28,Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field,"The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg +spins in an arbitrarily oriented magnetic field is exactly solved using the +spin-rotation transformation and the transfer-matrix method. It is shown that +the low-temperature magnetization process depends basically on a spatial +orientation of the magnetic field. A sharp stepwise magnetization curve with a +marked intermediate plateau, which emerges for the magnetic field applied along +the easy-axis direction of the Ising spins, becomes smoother and the +intermediate plateau shrinks if the external field is tilted from the easy-axis +direction. The magnetization curve of a polycrystalline system is also +calculated by performing powder averaging of the derived magnetization formula. +The proposed spin-chain model brings an insight into high-field magnetization +data of 3d-4f bimetallic polymeric compound Dy(NO_3)(DMSO)_2Cu(opba)(DMSO)_2, +which provides an interesting experimental realization of the ferrimagnetic +chain composed of two different but regularly alternating spin-1/2 magnetic +ions Dy^{3+} and Cu^{2+} that are reasonably approximated by the notion of +Ising and Heisenberg spins, respectively.",1206.6656v2 +2013-11-25,A study of crossover from 3D ferrimagnetic Bulk $NiCr_{2}O_{4}$ compound into 2D spin-glass like nanophase,"In this report, the magnetic behaviour of $NiCr_{2}O_{4}$ bulk and +nanoparticle samples under different applied magnetic field has been +investigated extensively. Nanoparticles of $NiCr_{2}O_{4}$ were obtained by +mechanical milling of polycrystalline powder prepared by polyol method. FC-ZFC +measurement of bulk at different applied magnetic field has revealed the +existence of a ferrimagnetic transition around 66K followed by an +antiferromagnetic transition close to 30K. However, its nano counterpart has +shown remarkable change in magnetic properties - a suppression of ferrimagnetic +transition accompanied by strengthening low temperature magnetic phase and +observation of a new transition at 90K ($T_P$), which is weakly magnetic in +nature. The frequency dependent ac susceptibility data of nanoparticle have +been fitted to the well known de Almedia-Thouless equation and a $H^{2/3}$ +dependence of the low temperature peak is observed with a resulting zero field +freezing temperature ($T_f^0$) equal to 10.1K. Further, the dynamical behaviour +near freezing temperature has been analysed in terms of critical behaviour and +the obtained fitted parameters values being as $\tau_0$(relaxation time +constant) = $3.6 X 10^{-6}s$, $T_f^0=8.7$K and $z\nu = 11.1$. Moreover, +Vogel-Fulcher law has been used to understand the nature of freezing transition +and the parameter after fitting are obtained as $E_a/k_B = 58.9$K, $\tau_0 = +5.22 \times 10^{-8}$ and $T_0 = 8.03$K. Finally, the spin-glass phase is +concluded. Moreover, in contrast to bulk, the $H^{2/3}$ dependence of freezing +temperature of nanoparticle sample (75h) does support the 2D surface like spin +glass nature.",1311.6269v1 +2014-01-07,Complex magnetic behavior of the sawtooth Fe chains in Rb$_{2}$Fe$_{2}$O(AsO$_{4}$)$_{2}$,"Results of magnetic field and temperature dependent neutron diffraction and +magnetization measurements on oxy-arsenate Rb$_{2}$Fe$_{2}$O(AsO$_{4}$)$_{2}$ +are reported. The crystal structure of this compound contains +pseudo-one-dimensional [Fe$_{2}$O$_{6}$]$^\infty$ sawtooth-like chains, formed +by corner sharing isosceles triangles of $Fe^{3+}$ ions occupying two +nonequivalent crystallographic sites. The chains extend infinitely along the +crystallographic $b$-axis and are structurally confined from one another via +diamagnetic (AsO$_{4}$)$^{3-}$ units along the $a$-axis, and Rb$^+$ cations +along the $c$-axis direction. Neutron diffraction measurements indicate the +onset of a long range antiferromagnetic order below approximately 25 K. The +magnetic structure consists of ferrimagnetic chains which are +antiferromagnetically coupled with each other. Within each chain, one of the +two Fe sites carries a moment which lies along the \emph{b}-axis, while the +second site bears a canted moment in the opposite direction. Externally applied +magnetic field induces a transition to a ferrimagnetic state, in which the +coupling between the sawtooth chains becomes ferromagnetic. Magnetization +measurements performed on optically-aligned single crystals reveal evidence for +an uncompensated magnetization at low magnetic fields that could emerge from to +a phase-segregated state with ferrimagnetic inclusions or from +antiferromagnetic domain walls. The observed magnetic states and the +competition between them is expected to arise from strongly frustrated +interactions within the sawtooth chains and relatively weak coupling between +them.",1401.1539v1 +2014-12-01,Coexistence of superconductivity and magnetism in spin-fermion model of ferrimagnetic spinel in an external magnetic field,"A two-sublattice spin-fermion model of ferrimagnetic spinel, with spin-$1/2$ +itinerant electrons at the sublattice $A$ site and spin-$s$ localized electrons +at the sublattice $B$ site is considered. The exchange between itinerant and +localized electrons is antiferromanetic. As a result the external magnetic +field, applied along the magnetization of the localized electrons, compensates +the Zeeman splitting due to the spin-fermion exchange and magnon-fermion +interaction induces spin anti-parallel p-wave superconductivity which coexists +with magnetism. We have obtained five characteristic values of the applied +field (in units of energy) $H_{cr1}$ $\beta_{crit}$. The results show that +$\phi(\beta,T = 0)$ tracks the transition in the form of a cusp maximum at +$\beta_{crit}$. + While both phases show frustration, the obtained magnetic structures reveal +that the frustration originates in different bonds for the two phases. The +frustration and ferrimagnetic order get quenched by selective exchange +coupling, and lead to robust antiferromagnetic ordering for $x$ = 1/6 and 1/3. +From mean-field calculations, we determine the temperature-dependent +sub-lattice magnetizations for $x$ = $0, 1/6$ and $1/3$. The calculated results +are discussed in relation to known experimental results for trivalent +Bi$_2$Fe$_4$O$_9$ and mixed valent BiFe$_2$O$_{4.63}$. The study identifies the +role of frustration effects, the ratio $\beta$ and selective exchange coupling +for stabilizing ferrimagnetic versus anti-ferromagnetic order in the Cairo +pentagonal lattice.",1412.6944v1 +2015-06-08,"Geometric, electronic and magnetic structure of Fe$_{x}$O$_{y}^{+}$ clusters","Correlation between geometry, electronic structure and magnetism of solids is +both intriguing and elusive. This is particularly strongly manifested in small +clusters, where a vast number of unusual structures appear. Here, we employ +density functional theory in combination with a genetic search algorithm, +GGA$+U$ and a hybrid functional to determine the structure of gas phase +Fe$_{x}$O$_{y}^{+/0}$ clusters. For Fe$_{x}$O$_{y}$ cation clusters we also +calculate the corresponding vibration spectra and compare them with +experiments. We successfully identify Fe$_{3}$O$_{4}^{+}$, Fe$_{4}$O$_{5}^{+}$, +Fe$_{4}$O$_{6}^{+}$, Fe$_{5}$O$_{7}^{+}$ and propose structures for +Fe$_{6}$O$_{8}^{+}$. Within the triangular geometric structure of +Fe$_{3}$O$_{4}^{+}$ a non-collinear, ferrimagnetic and ferromagnetic state are +comparable in energy. Fe$_{4}$O$_{5}^{+}$ and Fe$_{4}$O$_{6}^{+}$ are +ferrimagnetic with a residual magnetic moment of 1~\muB{} due to ionization. +Fe$_{5}$O$_{7}^{+}$ is ferrimagnetic due to the odd number of Fe atoms. We +compare the electronic structure with bulk magnetite and find +Fe$_{4}$O$_{5}^{+}$, Fe$_{4}$O$_{6}^{+}$, Fe$_{6}$O$_{8}^{+}$ to be mixed +valence clusters. In contrast, in Fe$_{3}$O$_{4}^{+}$ and Fe$_{5}$O$_{7}^{+}$ +all Fe are found to be trivalent.",1506.02532v2 +2015-06-22,Exchange scattering as the driving force for ultrafast all-optical and bias-controlled reversal in ferrimagnetic metallic structures,"Experimentally observed ultrafast all-optical magnetization reversal in +ferrimagnetic metals and heterostructures based on antiferromagnetically +coupled ferromagnetic $d-$ and $f-$metallic layers relies on intricate energy +and angular momentum flow between electrons, phonons and spins. Here we treat +the problem of angular momentum transfer in the course of ultrafast +laser-induced dynamics in a ferrimagnetic metallic system using microscopical +approach based on the system of rate equations. We show that the magnetization +reversal is supported by a coupling of $d-$ and $f-$ subsystems to delocalized +$s-$ or $p-$ electrons. The latter can transfer spin between the two subsystems +in an incoherent way owing to the $(s;p)-(d;f)$ exchange scattering. Since the +effect of the external excitation in this process is reduced to the transient +heating of the mobile electron subsystem, we also discuss possibility to +trigger the magnetization reversal by applying a voltage bias pulse to +antiferromagnetically coupled metallic ferromagnetic layers embedded in point +contact or tunneling structures. We argue that such devices allow controlling +reversal with high accuracy. We also suggest to use the anomalous Hall effect +to register the reversal, thus playing a role of reading probes.",1506.06585v3 +2015-06-23,Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias,"The discovery of materials with improved functionality can be accelerated by +rational material design. Heusler compounds with tunable magnetic sublattices +allow to implement this concept to achieve novel magnetic properties. Here, we +have designed a family of Heusler alloys with a compensated ferrimagnetic +state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant +exchange bias (EB) of more than 3 T and a similarly large coercivity are +established. The large exchange anisotropy originates from the exchange +interaction between the compensated host and ferrimagnetic clusters that arise +from intrinsic anti-site disorder. We demonstrate the applicability of our +design concept on a second material, Mn-Fe-Ga, with a magnetic transition above +room temperature, exemplifying the universality of the concept and the +feasibility of room-temperature applications. Our study points to a new +direction for novel magneto-electronic devices. At the same time it suggests a +new route for realizing rare-earth free exchange-biased hard magnets, where the +second quadrant magnetization can be stabilized by the exchange bias.",1506.07028v1 +2015-10-17,Ferrimagnetic nanostructures for magnetic memory bits,"Increasing the magnetic data recording density requires reducing the size of +the individual memory elements of a recording layer as well as employing +magnetic materials with temperature-dependent functionalities. Therefore, it is +predicted that the near future of magnetic data storage technology involves a +combination of energy-assisted recording on nanometer-scale magnetic media. We +present the potential of heat-assisted magnetic recording on a patterned +sample; a ferrimagnetic alloy composed of a rare earth and a transition metal, +DyCo$_5$, which is grown on a hexagonal-ordered nanohole array membrane. The +magnetization of the antidot array sample is out-of-plane oriented at room +temperature and rotates towards in-plane upon heating above its +spin-reorientation temperature (T$_R$) of ~350 K, just above room temperature. +Upon cooling back to room temperature (below T$_R$), we observe a well-defined +and unexpected in-plane magnetic domain configuration modulating with ~45 nm. +We discuss the underlying mechanisms giving rise to this behavior by comparing +the magnetic properties of the patterned sample with the ones of its extended +thin film counterpart. Our results pave the way for novel applications of +ferrimagnetic antidot arrays of superior functionality in magnetic nano-devices +near room temperature.",1510.05087v1 +2017-02-13,"Lieb and hole-doped ferrimagnetism, spiral, resonating valence-bond states, and phase separation in large-U $AB_{2}$ Hubbard chains","The ground state (GS) properties of the quasi-one-dimensional $AB_2$ Hubbard +model are investigated taking the effects of charge and spin quantum +fluctuations on equal footing. In the strong-coupling regime, we derive a +low-energy Lagrangian suitable to describe the ferrimagnetic phase at half +filling and the phases in the hole-doped regime. At half filling, a +perturbative spin-wave analysis allows us to find the GS energy, sublattice +magnetizations, and Lieb total spin per unit cell of the effective quantum +Heisenberg model, in very good agreement with previous results. In the +challenging hole doping regime away from half filling, we derive the +corresponding $t\textrm{-}J$ Hamiltonian. Under the assumption that charge and +spin quantum correlations are decoupled, the evolution of the second-order +spin-wave modes in the doped regime unveils the occurrence of spatially +modulated spin structures and the emergence of phase separation in the presence +of resonating-valence-bond states. We also calculate the doping-dependent GS +energy and total spin per unit cell, in which case it is shown that the spiral +ferrimagnetic order collapses at a critical hole concentration. Notably, our +analytical results in the doped regime are in very good agreement with density +matrix renormalization group studies, where our assumption of spin-charge +decoupling is numerically supported by the formation of charge-density waves in +anti-phase with the modulation of the magnetic structure.",1702.03609v4 +2017-03-24,Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal YbFeO3,"The magnetic interaction between rare-earth and Fe ions in hexagonal +rare-earth ferrites (h-REFeO3), may amplify the weak ferromagnetic moment on +Fe, making these materials more appealing as multiferroics. To elucidate the +interaction strength between the rare-earth and Fe ions as well as the magnetic +moment of the rare-earth ions, element specific magnetic characterization is +needed. Using X-ray magnetic circular dichroism, we have studied the +ferrimagnetism in h-YbFeO3 by measuring the magnetization of Fe and Yb +separately. The results directly show anti-alignment of magnetization of Yb and +Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about +17 kOe. The magnetic moment of Yb is about 1.6 \muB at low-temperature, +significantly reduced compared with the 4.5 \muB moment of a free Yb3+. In +addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable +enhancement compared with that in h-LuFeO3. These findings directly demonstrate +that ferrimagnetic order exists in h-YbFeO3; they also account for the +enhancement of magnetization and the reduction of coercivity in h-YbFeO3 +compared with those in h-LuFeO3 at low temperature, suggesting an important +role for the rare-earth ions in tuning the multiferroic properties of h-REFeO3.",1703.08482v2 +2018-02-12,Canted ferrimagnetism and giant coercivity in the non-stoichiometric double perovskite La2Ni1.19Os0.81O6,"The non-stoichiometric double perovskite oxide La2Ni1.19Os0.81O6 was +synthesized by solid state reaction and its crystal and magnetic structures +were investigated by powder x-ray and neutron diffraction. La2Ni1.19Os0.81O6 +crystallizes in the monoclinic double perovskite structure (general formula +A2BB'O6) with space group P21/n, where the B site is fully occupied by Ni and +the B' site by 19 % Ni and 81 % Os atoms. Using x-ray absorption spectroscopy +an Os4.5+ oxidation state was established, suggesting presence of about 50 % +paramagnetic Os5+ (5d3, S = 3/2) and 50 % non-magnetic Os4+ (5d4, Jeff = 0) +ions at the B' sites. Magnetization and neutron diffraction measurements on +La2Ni1.19Os0.81O6 provide evidence for a ferrimagnetic transition at 125 K. The +analysis of the neutron data suggests a canted ferrimagnetic spin structure +with collinear Ni2+ spin chains extending along the c axis but a non-collinear +spin alignment within the ab plane. The magnetization curve of +La2Ni1.19Os0.81O6 features a hysteresis with a very high coercive field, HC = +41 kOe, at T = 5 K, which is explained in terms of large magnetocrystalline +anisotropy due to the presence of Os ions together with atomic disorder. Our +results are encouraging to search for rare earth free hard magnets in the class +of double perovskite oxides.",1802.03874v1 +2013-08-16,Theory of metallic double perovskites with spin orbit coupling and strong correlations; application to ferrimagnetic Ba2FeReO6,"We consider a model of the double perovskite Ba2FeReO6, a room temperature +ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in +the background of Fe moments stabilized by Hund's coupling. We show that for +such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are +essential in driving a half-metallic ground state. Incorporating both strong +spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure +consistent with ab initio calculations. Using our model, we find a large spin +polarization at the Fermi level, and obtain a semi-quantitative understanding +of the saturation magnetization of Ba2FeReO6, as well as X-ray magnetic +circular dichroism data indicating a significant orbital magnetization. Based +on the orbital populations obtained in our theory, we predict a specific doping +dependence to the tetragonal distortion accompanying ferrimagnetic order. +Finally, the combination of a net magnetization and spin-orbit interactions is +shown to induce Weyl nodes in the band structure, and we predict a significant +intrinsic anomalous Hall effect in hole-doped Ba2FeReO6. The uncovered +interplay of strong correlations and spin-orbit coupling lends partial support +to our previous work, which used a local moment description to capture the spin +wave dispersion found in neutron scattering measurements. Our work is of broad +interest for understanding metallic 4d-based and 5d-based double perovskites +which are of fundamental interest and of possible relevance to spintronic +applications.",1308.3701v2 +2017-04-25,A variety of elastic anomalies in orbital-active nearly-itinerant cobalt vanadate spinel,"We perform ultrasound velocity measurements on a single crystal of +nearly-metallic spinel Co$_{1.21}$V$_{1.79}$O$_4$ which exhibits a +ferrimagnetic phase transition at $T_C \sim$ 165 K. The experiments reveal a +variety of elastic anomalies in not only the paramagnetic phase above $T_C$ but +also the ferrimagnetic phase below $T_C$, which should be driven by the +nearly-itinerant character of the orbitally-degenerate V 3$d$ electrons. In the +paramagnetic phase above $T_C$, the elastic moduli exhibit +elastic-mode-dependent unusual temperature variations, suggesting the existence +of a dynamic spin-cluster state. Furthermore, above $T_C$, the sensitive +magnetic-field response of the elastic moduli suggests that, with the negative +magnetoresistance, the magnetic-field-enhanced nearly-itinerant character of +the V 3$d$ electrons emerges from the spin-cluster state. This should be +triggered by the inter-V-site interactions acting on the orbitally-degenerate +3$d$ electrons. In the ferrimagnetic phase below $T_C$, the elastic moduli +exhibit distinct anomalies at $T_1\sim$ 95 K and $T_2\sim$ 50 K, with a sign +change of the magnetoresistance at $T_1$ (positive below $T_1$) and an +enhancement of the positive magnetoresistance below $T_2$, respectively. These +observations below $T_C$ suggest the successive occurrence of an orbital glassy +order at $T_1$ and a structural phase transition at $T_2$, where the rather +localized character of the V 3$d$ electrons evolves below $T_1$ and is further +enhanced below $T_2$.",1704.07537v2 +2012-01-17,Weak ferrimagnetism and multiple magnetization reversal in α-Cr3(PO4)2,"The chromium(II) orthophosphate {\alpha}-Cr3(PO4)2 is a weak ferrimagnet with +the Curie temperature TC = 29 K confirmed by a \lambda-type peak in specific +heat. Dominant antiferromagnetic interactions in this system are characterized +by the Weiss temperature {\Theta} = - 96 K, indicating an intermediate +frustration ratio |{\Theta}|/TC ~ 3. In its magnetically ordered states +{\alpha}-Cr3(PO4)2 exhibits a remarkable sequence of temperature-induced +magnetization reversals sensitive to the protocol of measurements, i.e. either +field-cooled or zero-field-cooled regimes. The reduction of the effective +magnetic moment 4.5 {\mu}B/Cr2+, as compared to the spin-only moment 4.9 +{\mu}B/Cr2+, cannot be ascribed to the occurence of the low-spin state in any +crystallographic site of the Jahn-Teller active 3d4 Cr2+ ions. X-ray absorption +spectra at the K-edge indicate divalent chromium and unravel the high-spin +state of these ions at the L2,3-edges. Weak ferrimagnetism and multiple +magnetization reversal phenomena seen in this compound could be ascribed to +incomplete cancellation and distortion of partial spontaneous magnetization +functions of Cr2+ in its six crystallographically inequivalent positions.",1201.3465v1 +2019-07-01,Robust Formation of Ultrasmall Room-Temperature Neél Skyrmions in Amorphous Ferrimagnets from Atomistic Simulations,"Ne\'el skyrmions originate from interfacial Dzyaloshinskii Moriya interaction +(DMI). Recent studies have explored using thin-film ferromagnets and +ferrimagnets to host Ne\'el skyrmions for spintronic applications. However, it +is unclear if ultrasmall (10 nm or less) skyrmions can ever be stabilized at +room temperature for practical use in high density parallel racetrack memories. +While thicker films can improve stability, DMI decays rapidly away from the +interface. As such, spins far away from the interface would experience +near-zero DMI, raising question on whether or not unrealistically large DMI is +needed to stabilize skyrmions, and whether skyrmions will also collapse away +from the interface. To address these questions, we have employed atomistic +stochastic Landau-Lifshitz-Gilbert simulations to investigate skyrmions in +amorphous ferrimagnetic GdCo. It is revealed that a significant reduction in +DMI below that of Pt is sufficient to stabilize ultrasmall skyrmions even in +films as thick as 15 nm. Moreover, skyrmions are found to retain a uniform +columnar shape across the film thickness despite the decaying DMI. Our results +show that increasing thickness and reducing DMI in GdCo can further reduce the +size of skyrmions at room temperature, which is crucial to improve the density +and energy efficiency in skyrmion based devices.",1907.00647v1 +2020-01-08,Non-equilibrium spin dynamics in the temperature and magnetic field dependence of magnetization curves of ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ and its composite with BaTiO$_3$,"A comparative study of the non-equilibrium magnetic phenomena (magnetic +blocking, memory, exchange bias and aging effect) has been presented for +ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with +non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have +confirmed coexistence of CFO and BTO structures in composite, but magnetic spin +dynamics have been remarkably modified. The blocking phenomenon of +ferrimagnetic domains below the room temperature has been studied by different +modes of (zero field cooled and field cooled) magnetic measurements in +collaboration with magnetic fields ON and OFF modes and time dependent +magnetization. The applications of unconventional protocols during time +dependent magnetization measurement at different stages of the temperature and +field dependence of the magnetization curves have been useful to reveal the +non-equilibrium dynamics of magnetic spin order. The applying of off-field +relaxation experiments has made possible to tune the magnetic state and +coercivity of the systems. The role of interfacial coupling between magnetic +and non-magnetic particles has been understood on different magnetic phenomena +(meta-stable magnetic state, exchange bias and memory effect) by comparing the +experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its +composite with BaTiO$_3$ particles.",2001.02602v2 +2020-04-22,Magnetic correlations in polycrystalline $\mathrm{Tb_{0.15}Co_{0.85}}$,"We investigated a polycrystalline sample of the ferrimagnetic compound +$\mathrm{Tb_{0.15}Co_{0.85}}$ by magnetometry and small-angle neutron +scattering (SANS). The magnetization curve at 300 K is characteristic for soft +ferrimagnets but at 5 K the hysteresis indicates the existence of magnetic +domains. The magnetic SANS signal suggests that at 300 K the Tb and Co moments +are correlated over large volumes within the micrometer-sized grains with +correlation lengths > 100 nm. At 5 K, however, the magnetic SANS analysis +reveals a reduced correlation length of around 4.5 nm, which indicates the +formation of narrow magnetic domains within the ferrimagnet with one dimension +being in the nm range. We attribute the observed changes of the domain +structure to the temperature-dependence of the magnetic properties of the Tb +sublattice.",2004.10475v2 +2020-12-29,Spin-polarized imaging of strongly interacting fermions in the ferrimagnetic state of Weyl candidate CeBi,"CeBi has an intricate magnetic phase diagram whose fully-polarized state has +recently been suggested as a Weyl semimetal, though the role of $f$ states in +promoting strong interactions has remained elusive. Here we focus on the +less-studied, but also time-reversal symmetry-breaking ferrimagnetic phase of +CeBi, where our density functional theory (DFT) calculations predict additional +Weyl nodes near the Fermi level $E_\mathrm{F}$. We use spin-polarized scanning +tunneling microscopy and spectroscopy to image the surface ferrimagnetic order +on the itinerant Bi $p$ states, indicating their orbital hybridization with +localized Ce $f$ states. We observe suppression of this spin-polarized +signature at $E_\mathrm{F}$, coincident with a Fano line shape in the +conductance spectra, suggesting the Bi $p$ states partially Kondo screen the +$f$ magnetic moments, and this $p-f$ hybridization causes strong Fermi-level +band renormalization. The $p$ band flattening is supported by our quasiparticle +interference (QPI) measurements, which also show band splitting in agreement +with DFT, painting a consistent picture of a strongly interacting magnetic Weyl +semimetal.",2012.14911v2 +2021-01-15,Tunable spin-flop transition in artificial ferrimagnets,"Spin-flop transition (SFT) consists in a jump-like reversal of +antiferromagnetic magnetic moments into a non-collinear state when the magnetic +field increases above the critical value. Potentially the SFT can be utilized +in many applications of a rapidly developing antiferromagnetic spintronics. +However, the difficulty of using them in conventional antiferromagnets lies in +(a) too large switching magnetic fields (b) the need for presence of a magnetic +anisotropy, and (c) requirement to apply magnetic field along the correspondent +anisotropy axis. In this work we propose to use artificial ferrimagnets in +which the spin-flop transition occurs without anisotropy and the transition +field can be lowered by adjusting exchange coupling in the structure. This is +proved by experiment on artificial Fe-Gd ferrimagnets where usage of Pd spacers +allowed us to suppress the transition field by two orders of magnitude.",2101.06155v2 +2017-05-18,Magnetic vortex nucleation/annihilation in artificial-ferrimagnet microdisks,"The topological nature of magnetic-vortex state gives rise to peculiar +magnetization reversal observed in magnetic microdisks. Interestingly, +magnetostatic and exchange energies which drive this reversal can be +effectively controlled in artificial ferrimagnet heterostructures composed of +rare-earth and transition metals. 25x[Py(t)/Gd(t)] (t=1 or 2 nm) superlattices +demonstrate a pronounced change of the magnetization and exchange stiffness in +a 10-300 K temperature range as well as very small magnetic anisotropy. Due to +these properties, the magnetization of cylindrical microdisks composed of these +artificial ferrimagnets can be transformed from the vortex to +uniformly-magnetized states in a permanent magnetic field by changing the +temperature. We explored the behavior of magnetization in 1.5-micrometer +25x[Py(t)/Gd(t)] (t=1 or 2 nm) disks at different temperatures and magnetic +fields and observed that due to the energy barrier separating vortex and +uniformly-magnetized states, the vortex nucleation and annihilation occur at +different temperatures. This causes the temperature dependences of the Py/Gd +disks magnetization to demonstrate unique hysteretic behavior in a narrow +temperature range. It was discovered that for the 25x[Py(2 nm)/Gd(2 nm)] +microdisks the vortex can be metastable at a certain temperature range.",1705.06398v1 +2017-11-29,Thermal contribution to the spin-orbit torque in metallic/ferrimagnetic systems,"We report a systematic study of current-induced perpendicular magnetization +switching in W/Co$_{x}$Tb$_{1-x}$/Al thin films with strong perpendicular +magnetic anisotropy. Various Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys with +different magnetic compensation temperatures are presented. The systems are +characterized using MOKE, SQUID and anomalous Hall resistance at different +cryostat temperature ranging from 10 K to 350 K. The current-switching +experiments are performed in the spin-orbit torque geometry where the current +pulses are injected in plane and the magnetization reversal is detected by +measuring the Hall resistance. The full reversal magnetization has been +observed in all samples. Some experimental results could only be explained by +the strong sample heating effect during the current pulses injection. We have +found that, for a given composition $x$ and switching polarity, the devices +always reach the same temperature $\textit{T}_{switch}(x)$ before switching +independently of the cryostat temperature. $\textit{T}_{switch}$ seems to scale +with the Curie temperature of the Co$_{x}$Tb$_{1-x}$ ferrimagnetic alloys. This +explains the evolution of the critical current (and critical current density) +as a function of the alloy concentration. Future application could take +advantages of this heating effect which allows reducing the in-plane external +field. Unexpected double magnetization switching has been observed when the +heat generated by the current allows crosses the compensation temperature.",1711.10790v1 +2018-08-28,Magnetic field - temperature phase diagram of ferrimagnetic alternating chains: spin-wave theory from a fully polarized vacuum,"Quantum critical (QC) phenomena can be accessed by studying quantum magnets +under an applied magnetic field ($B$). The QC points are located at the +endpoints of magnetization plateaus and separate gapped and gapless phases. In +one dimension, the low-energy excitations of the gapless phase form a Luttinger +liquid (LL), and crossover lines bound insulating (plateau) and LL regimes, as +well as the QC regime. Alternating ferrimagnetic chains have a spontaneous +magnetization at $T=0$ and gapped excitations at zero field. Besides the +plateau at the fully polarized (FP) magnetization; due to the gap, there is +another magnetization plateau at the ferrimagnetic (FRI) magnetization. We +develop spin-wave theories to study the thermal properties of these chains +under an applied magnetic field: one from the FRI classical state, and other +from the FP state, comparing their results with quantum Monte Carlo data. We +deepen the theory from the FP state, obtaining the crossover lines in the $T$ +vs. $B$ low-$T$ phase diagram. In particular, from local extreme points in the +susceptibility and magnetization curves, we identify the crossover between an +LL regime formed by excitations from the FRI state to another built from +excitations of the FP state. These two LL regimes are bounded by an asymmetric +dome-like crossover line, as observed in the phase diagram of other quantum +magnets under an applied magnetic field.",1808.09240v1 +2019-03-11,Giant spin-orbit torque in a single ferrimagnetic metal layer,"Antiferromagnets and compensated ferrimagnets offer opportunities to +investigate spin dynamics in the 'terahertz gap' because their resonance modes +lie in the 0.3 THz to 3 THz range. Despite some inherent advantages when +compared to ferromagnets, these materials have not been extensively studied due +to difficulties in exciting and detecting the high-frequency spin dynamics, +especially in thin films. Here we show that spin-obit torque in a single layer +of the highly spin-polarized compensated ferrimagnet Mn2RuxGa is remarkably +efficient at generating spin-orbit fields \mu_0H_eff, which approach 0.1x10-10 +T m2/A in the low-current density limit -- almost a thousand times the Oersted +field, and one to two orders of magnitude greater than the effective fields in +heavy metal/ferromagnet bilayers. From an analysis of the harmonic Hall effect +which takes account of the thermal contributions from the anomalous Nernst +effect, we show that the antidamping component of the spin-orbit torque is +sufficient to sustain self-oscillation. Our study demonstrates that spin +electronics has the potential to underpin energy-frugal, chip-based solutions +to the problem of ultra high-speed information transfer.",1903.04432v3 +2019-03-25,Octahedral tilting and emergence of ferrimagnetism in cobalt-ruthenium based double perovskites,"Rare earth based cobalt-ruthenium double perovskites A$_2$CoRuO$_6$ (A = La, +Pr, Nd and Sm) were synthesized and investigated for their structural and +magnetic properties. All the compounds crystallize in the monoclinic $P2_1/n$ +structure with the indication of antisite disorder between Co and Ru sites. +While, La compound is already reported to have an antiferromagnetic state below +27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below $T_c$ = 46, +55 and 78 K respectively. Field dependent magnetization data indicate prominent +hysteresis loop below $T_c$ in the samples containing magnetic rare-earth ions, +however magnetization does not saturate even at the highest applied fields. Our +structural analysis indicates strong distortion in the Co-O-Ru bond angle, as +La$^{3+}$ is replaced by smaller rare-earth ions such as Pr$^{3+}$, Nd$^{3+}$ +and Sm$^{3+}$. The observed ferrimagnetism is possibly associated with the +enhanced antiferromagnetic superexchange interaction in the Co-O-Ru pathway due +to bond bending. The Pr, Nd and Sm samples also show small magnetocaloric +effect with Nd sample showing highest value of magnitude $\sim$ 3 +Jkg$^{-1}$K$^{-1}$ at 50 kOe. The change in entropy below 20 K is found to be +positive in the Sm sample as compared to the negative value in the Nd +counterpart.",1903.10271v1 +2019-03-27,Investigation of Room Temperature Ferroelectricity and Ferrimagnetism in Multiferroic AlxFe2-xO3 Epitaxial Thin Films,"Multiferroic materials open up the possibility to design novel functionality +in electronic devices, with low energy consumption. However, there are very few +materials that show multiferroicity at room temperature, which is essential to +be practically useful. AlxFe2-xO3 (x-AFO) thin films, belonging to the k-Al2O3 +family are interesting because they show room temperature ferrimagnetism and +have a polar crystal structure. However, it is difficult to realise its +ferroelectric properties at room temperature, due to low resistivity of the +films. In this work, we have deposited x-AFO (0.5 <= x <= 1) epitaxial thin +films with low leakage, on SrTiO3<111> substrates by Pulsed Laser Deposition. +Magnetic measurements confirmed room temperature ferrimagnetism of the films, +however the Curie temperature was found to be influenced by deposition +conditions. First principle calculations suggested that ferroelectric domain +switching occurs through shearing of in-plane oxygen layers, and predicted a +high polarization value of 24 uC/cm2. However, actual ferroelectric +measurements showed the polarization to be two order less. Presence of multiple +in-plane domains which oppose polarization switching of adjacent domains, was +found to be the cause for the small observed polarization. Comparing dielectric +relaxation studies and ferroelectric characterization showed that +oxygen-vacancy defects assist domain wall motion, which in turn facilitates +polarization switching.",1903.11422v1 +2019-08-20,"Peculiarities in pseudo-transitions of a mixed spin-$(1/2,1)$ Ising-Heisenberg double-tetrahedral chain in an external magnetic field","Recently, it has been rigorously verified that several one-dimensional (1D) +spin models may exhibit a peculiar pseudo-transition accompanied with anomalous +response of thermodynamic quantities in a close vicinity of pseudo-critical +temperature. In the present work we will introduce and exactly solve a mixed +spin-(1/2,1) Ising-Heisenberg double-tetrahedral chain in an external magnetic +field as another particular example of 1D lattice-statistical model with +short-range interactions that displays a pseudo-transition of this type. The +investigated model exhibits at zero temperature three ferrimagnetic phases, +three frustrated phases, and one saturated paramagnetic phase. The ground-state +phase diagram involves five unusual interfaces (phase boundaries), at which the +residual entropy per site equals to a larger entropy of one of two coexisting +phases. Four such interfaces are between a non-degenerate ferrimagnetic phase +and a macroscopically degenerate frustrated phase, while one interface is +between two non-degenerate ferrimagnetic phases. Though thermal excitations +typically destroy all fingerprints of zero-temperature phase transitions of 1D +lattice-statistical models with short-range forces, the mixed spin-(1/2,1) +Ising-Heisenberg double-tetrahedral chain is quite robust with respect to +thermal excitations and it displays peculiar pseudo-transitions close to all +five aforementioned interfaces.",1908.07286v2 +2019-11-13,Variety of order-by-disorder phases in the asymmetric $J_1-J_2$ zigzag ladder: From the delta chain to the $J_1-J_2$ chain,"We study an asymmetric $J_1$-$J_2$ zigzag ladder consisting of two different +spin-$\frac{1}{2}$ antiferromagnetic (AFM; $J_2$, $\gamma J_2>0$) Heisenberg +legs coupled by zigzag-shaped ferromagnetic (FM; $J_1<0$) inter-leg +interaction. On the basis of density-matrix renormalization group based +calculations the ground-state phase diagram is obtained as functions of +$\gamma$ and $J_2/|J_1|$. It contains four kinds of frustration-induced ordered +phases except a trivial FM phase. Two of the ordered phases are valence bond +solid (VBS) with spin-singlet dimerization, which is a rather conventional +order by disorder. Still, it is interesting to note that the VBS states possess +an Affleck-Kennedy-Lieb-Tasaki-type topological hidden order. The remaining two +phases are ferrimagnetic orders, each of which is distinguished by commensurate +or incommensurate spin-spin correlation. It is striking that the ferrimagnetic +orders are not associated with geometrical symmetry breaking; instead, the +global spin-rotation symmetry is broken. In other words, the system lowers its +energy via the FM inter-leg interaction by polarizing both of the AFM +Heisenberg legs. This is a rare type of order by disorder. Besides, the +incommensurate ferrimagnetic state appears as a consequence of the competition +between a polarization and a critical Tomonaga-Luttinger-liquid behavior in the +AFM Heisenberg legs.",1911.05270v3 +2020-03-10,Room-temperature ferrimagnetism of anti-site-disordered Ca2MnOsO6,"Room-temperature ferrimagnetism was discovered for the anti-site-disordered +perovskite Ca2MnOsO6 with Tc = 305 K. Ca2MnOsO6 crystallizes into an +orthorhombic structure with a space group of Pnma, in which Mn and Os share the +oxygen-coordinated-octahedral site at an equal ratio without a noticeable +ordered arrangement. The material is electrically semiconducting with +variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the +trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic +circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are +aligned antiferromagnetically, thereby classifying the material as a +ferrimagnet which is in accordance with band structure calculations. It is +intriguing that the magnetic signal of the Os is very weak, and that the +observed total magnetic moment is primarily due to the Mn. The Tc = 305 K is +the second highest in the material category of so-called disordered +ferromagnets such as CaRu1-xMnxO3, SrRu1-xCrxO3, and CaIr1-xMnxO3, and hence, +may support the development of spintronic oxides with relaxed requirements +concerning the anti-site disorder of the magnetic ions.",2003.04608v1 +2020-03-17,Electrical generation and detection of terahertz signal based on spin-wave emission from ferrimagnets,"Terahertz (THz) signals, mainly generated by photonic or electronic +approaches, are being sought for various applications, whereas the development +of magnetic source might be a necessary step to harness the magnetic nature of +electromagnetic radiation. We show that the relativistic effect on the +current-driven domain-wall motion induces THz spin-wave emission in +ferrimagnets. The required current density increases dramatically in materials +with strong exchange interaction and rapidly exceeds 1012 A m-2, leading to the +device breakdown and thus the lack of experimental evidence. By translating the +collective magnetization oscillations into voltage signals, we propose a +three-terminal device for the electrical detection of THz spin wave. Through +material engineering, wide frequency range from 264 GHz to 1.1 THz and uniform +continuous signals with improved output power can be obtained. As a reverse +effect, the spin wave generated in this system is able to move ferrimagnetic +domain wall. Our work provides guidelines for the experimental verification of +THz spin wave, and could stimulate the design of THz spintronic oscillators for +wideband applications as well as the all-magnon spintronic devices.",2003.07750v1 +2020-06-22,Insights into nature of a magnetization plateau of 3$d$-4$f$ coordination polymer [Dy$_2$Cu$_2$]$_n$ from a spin-1/2 Ising-Heisenberg orthogonal-dimer chain,"The ground state and magnetization process of an exactly solved spin-$1/2$ +Ising-Heisenberg orthogonal-dimer chain with two different gyromagnetic factors +of the Ising and Heisenberg spins are investigated in detail. It is shown that +the investigated quantum spin chain exhibits up to seven possible ground states +depending on a mutual interplay of the magnetic field, intra- and inter-dimer +coupling constants. More specifically, the frustrated and modulated quantum +antiferromagnetic phases are responsible in zero-temperature magnetization +curves for a zero magnetization plateau. The intermediate 1/11- and +5/11-plateaus emerge due to the frustrated and modulated quantum ferrimagnetic +phases, while the intermediate 9/11- and 10/11-plateaus can be attributed to +the quantum and classical ferrimagnetic phases. It is conjectured that the +magnetization plateau experimentally observed in a high-field magnetization +curve of 3$d$-4$f$ heterobimetallic coordination polymer +[\{Dy(hfac)$_2$(CH$_3$OH)\}$_2$\{Cu(dmg)(Hdmg)\}$_2$]$_n$ (H$_2$dmg $=$ +dimethylglyoxime; Hhfac $=$ 1,1,1,5,5,5-hexafluoropentane-2,4-dione) could be +attributed to the classical and quantum ferrimagnetic phases.",2006.12553v3 +2020-09-21,Unusual effects of magnetic dilution in the ferrimagnetic columnar ordered $\mathrm{Sm_2MnMnMn_{4-x}Ti_xO_{12}}$ perovskites,"Powder neutron diffraction experiments have been employed to establish the +effects of site-selective magnetic dilution in the Sm2MnMnMn4-x Tix O12 A-site +columnar ordered quadruple perovskite manganites (x = 1, x = 2 and x = 3). We +show that in all three compositions the Mn ions adopt a collinear ferrimagnetic +structure below 27 K, 62 K and 34 K, respectively. An unexpected increase in +the ordering temperature was observed between the x = 1 and x = 2 samples, +which indicates a considerable departure from mean field behaviour. This result +is corroborated by large reductions in the theoretical ground state magnetic +moments observed across the series, which indicate the presence of spin +fluctuations and or disorder. We show that long range magnetic order in the x = +3 sample, which occurs below the percolation threshold for B-B exchange, can +only be understood to arise if magnetic order in Sm2MnMnMn4-xTixO12 is mediated +via both A-B and B-B exchange, hence confirming the importance of A-B exchange +interactions in these materials. Finally we show that site-selective magnetic +dilution enables the tuning of a ferrimagnetic compensation point and the +introduction of temperature-induced magnetization reversal.",2009.10005v1 +2020-09-21,Magneto-Elastic Coupling to Coherent Acoustic Phonon Modes in Ferrimagnetic Insulator GdTiO$_3$,"In this work we investigate single crystal GdTiO$_{3}$, a promising candidate +material for Floquet engineering and magnetic control, using ultrafast optical +pump-probe reflectivity and magneto-optical Kerr spectroscopy. GdTiO${}_{3}$ is +a Mott-Hubbard insulator with a ferrimagnetic and orbitally ordered ground +state (\textit{T${}_{C}$} = 32 K). We observe multiple signatures of the +magnetic phase transition in the photoinduced reflectivity signal, in response +to above band-gap 660 nm excitation. Magnetic dynamics measured via Kerr +spectroscopy reveal optical perturbation of the ferrimagnetic order on +spin-lattice coupling timescales, highlighting the competition between the +Gd${}^{3+}$ and Ti${}^{3+}$ magnetic sub-lattices. Furthermore, a strong +coherent oscillation is present in the reflection and Kerr dynamics, +attributable to an acoustic strain wave launched by the pump pulse. The +amplitude of this acoustic mode is highly dependent on the magnetic order of +the system, growing sharply in magnitude at \textit{T${}_{C}$}, indicative of +strong magneto-elastic coupling. The driving mechanism, involving +strain-induced modification of the magnetic exchange interaction, implies an +indirect method of coupling light to the magnetic degrees of freedom and +emphasizes the potential of GdTiO${}_{3}$ as a tunable quantum material.",2009.10222v1 +2021-02-26,Direct imaging of chiral domain walls and Néel-type skyrmionium in ferrimagnetic alloys,"The evolution of chiral spin structures is studied in ferrimagnet +Ta/Ir/Fe/GdFeCo/Pt multilayers as a function of temperature using scanning +electron microscopy with polarization analysis (SEMPA). The GdFeCo ferrimagnet +exhibits pure right-hand N\'eel-type domain wall (DW) spin textures over a +large temperature range. This indicates the presence of a negative +Dzyaloshinskii-Moriya interaction (DMI) that can originate from both the top +Fe/Pt and the Co/Pt interfaces. From measurements of the DW width, as well as +complementary magnetic characterization, the exchange stiffness as a function +of temperature is ascertained. The exchange stiffness is surprisingly mostly +constant, which is explained by theoretical predictions. Beyond single +skyrmions, we find by direct imaging a pure N\'eel-type skyrmionium, which due +to the absence of a skyrmion Hall angle is a promising topological spin +structure to enable high impact potential applications in the next generation +of spintronic devices.",2102.13502v2 +2021-12-19,Pressure-induced charge orders and their coupling to magnetism in hexagonal multiferroic LuFe2O4,"Hexagonal LuFe2O4 is a promising charge-order (CO) driven multiferroic +material with high charge and spin ordering temperatures. The coexisting charge +and spin orders on Fe3+/Fe2+ sites result in novel magnetoelectric behaviors, +but the coupling mechanism between the charge and spin orders remains elusive. +Here, by tuning external pressure, we reveal three correlated spin-charge +ordered phases in LuFe2O4: i) a centrosymmetric incommensurate +three-dimensional CO with ferrimagnetism, ii) a non-centrosymmetric +incommensurate quasi-two-dimensional CO with ferrimagnetism, and iii) a +centrosymmetric commensurate CO with antiferromagnetism. Experimental in-situ +single-crystal X-ray diffraction and X-ray magnetic circular dichroism +measurements combined with density functional theory calculations suggest that +the charge density redistribution caused by pressure-induced compression in the +frustrated double-layer [Fe2O4] cluster is responsible for the correlated +spin-charge phase transitions. The pressure-enhanced effective Coulomb +interactions among Fe-Fe bonds drive the frustrated (1/3, 1/3) CO to a less +frustrated (1/4, 1/4) CO, which induces the ferrimagnetic to antiferromagnetic +transition. Our results not only elucidate the coupling mechanism among charge, +spin and lattice degrees of freedom in LuFe2O4 but also provide a new way to +tune the spin-charge orders in a highly controlled manner.",2112.10036v1 +2022-02-06,Enhancing Perpendicular Magnetic Anisotropy in Garnet Ferrimagnet by Interfacing with Few-Layer WTe2,"Engineering magnetic anisotropy in a ferro- or ferrimagnetic (FM) thin film +is crucial in spintronic device. One way to modify the magnetic anisotropy is +through the surface of the FM thin film. Here, we report the emergence of a +perpendicular magnetic anisotropy (PMA) induced by interfacial interactions in +a heterostructure comprised of a garnet ferrimagnet, Y3Fe5O12 (YIG), and the +low-symmetry, high spin orbit coupling (SOC) transition metal dichalcogenide, +WTe2. At the same time, we also observed an enhancement in Gilbert damping in +the WTe2 covered YIG area. Both the magnitude of interface-induced PMA and the +Gilbert damping enhancement have no observable WTe2 thickness dependence down +to single quadruple-layer, indicating that the interfacial interaction plays a +critical role. The ability of WTe2 to enhance the PMA in FM thin film, combined +with its previously reported capability to generate out-of-plane damping like +spin torque, makes it desirable for magnetic memory applications.",2202.02834v1 +2022-04-20,Ferrimagnet GdFeCo characterization for spin-orbitronics: large field-like and damping-like torques,"Spintronics is showing promising results in the search for new materials and +effects to reduce energy consumption in information technology. Among these +materials, ferrimagnets are of special interest, since they can produce large +spin currents that trigger the magnetization dynamics of adjacent layers or +even their own magnetization. Here, we present a study of the generation of +spin current by GdFeCo in a GdFeCo/Cu/NiFe trilayer where the FeCo sublattice +magnetization is dominant at room temperature. Magnetic properties such as the +saturation magnetization are deduced from magnetometry measurements while +damping constant is estimated from spin-torque ferromagnetic resonance +(ST-FMR). We show that the overall damping-like (DL) and field-like (FL) +effective fields as well as the associated spin Hall angles can be reliably +obtained by performing the dependence of ST-FMR by an added dc current. The sum +of the spin Hall angles for both the spin Hall effect (SHE) and the spin +anomalous Hall effect (SAHE) symmetries are: $\theta_{DL}^{SAHE} + +\theta_{DL}^{SHE}=-0.15 \pm 0.05$ and $\theta_{FL}^{SAHE} + +\theta_{FL}^{SHE}=0.026 \pm 0.005$. From the symmetry of ST-FMR signals we find +that $\theta_{DL}^{SHE}$ is positive and dominated by the negative +$\theta_{DL}^{SAHE}$. The present study paves the way for tuning the different +symmetries in spin conversion in highly efficient ferrimagnetic systems.",2204.09776v1 +2022-05-27,Magnonic Casimir Effect in Ferrimagnets,"Quantum fluctuations are the key concepts of quantum mechanics. Quantum +fluctuations of quantum fields induce a zero-point energy shift under spatial +boundary conditions. This quantum phenomenon, called the Casimir effect, has +been attracting much attention beyond the hierarchy of energy scales, ranging +from elementary particle physics to condensed matter physics together with +photonics. However, the application of the Casimir effect to spintronics has +not yet been investigated enough, particularly to ferrimagnetic thin films, +although yttrium iron garnet (YIG) is one of the best platforms for +spintronics. Here we fill this gap. Using the lattice field theory, we +investigate the Casimir effect induced by quantum fields for magnons in +insulating magnets and find that the magnonic Casimir effect can arise not only +in antiferromagnets but also in ferrimagnets including YIG thin films. Our +result suggests that YIG, the key ingredient of magnon-based spintronics, can +serve also as a promising platform for manipulating and utilizing Casimir +effects, called Casimir engineering. Microfabrication technology can control +the thickness of thin films and realize the manipulation of the magnonic +Casimir effect. Thus, we pave the way for magnonic Casimir engineering.",2205.13802v3 +2022-05-28,Magnetic collapse in Fe$_3$Se$_4$ under high pressure,"Electronic structure and magnetic properties of Fe$_3$Se$_4$ are calculated +using the density functional approach. Due to the metallic properties, magnetic +moments of the iron atoms in two nonequivalent positions in the unit cell are +different from ionic values for Fe$^{3+}$ and Fe$^{2+}$ and are equal to +$M_1=2.071 \mu_B$ and $M_2=-2.042 \mu_B$, making the system ferrimagnetic. The +total magnetic moment for the unit cell is $2.135 \mu_B$. Under isotropic +compression, the total magnetic moment decreases non-monotonically and +correlates with the non-monotonic dependence of the density of states at the +Fermi level $N(E_F)$. For 7% compression, the magnetic order changes from the +ferrimagnetic to the ferromagnetic. At 14% compression, the magnetic order +disappears and the total magnetic moment becomes zero, leaving the system in a +paramagnetic state. This compression corresponds to the pressure of 114 GPa. +The magnetic ordering changes faster upon application of an isotropic external +pressure due to the sizeable anisotropy of the chemical bondings in +Fe$_3$Se$_4$. The ferrimagnetic and paramagnetic states occur under pressures +of 5.0 and 8.0 GPa, respectively. The system remains in the metallic state for +all values of compression.",2205.14346v2 +2022-07-21,First-principles insights into all-optical spin switching in the half-metallic Heusler ferrimagnet Mn$_2$RuGa,"All-optical spin switching (AOS) represents a new frontier in magnetic +storage technology -- spin manipulation without a magnetic field, -- but its +underlying working principle is not well understood. Many AOS ferrimagnets such +as GdFeCo are amorphous and renders the high-level first-principles study +unfeasible. The crystalline half-metallic Heusler Mn$_2$RuGa presents an +opportunity. Here we carry out hitherto the comprehensive density functional +investigation into the material properties of Mn$_2$RuGa, and introduce two +concepts - the spin anchor site and the optical active site - as two pillars +for AOS in ferrimagnets. In Mn$_2$RuGa, Mn$(4a)$ serves as the spin anchor +site, whose band structure is below the Fermi level and has a strong spin +moment, while Mn$(4c)$ is the optical active site whose band crosses the Fermi +level. Our magneto-optical Kerr spectrum and band structure calculation jointly +reveal that the delicate competition between the Ru-$4d$ and Ga-$4p$ states is +responsible for the creation of these two sites. These two sites found here not +only present a unified picture for both Mn$_2$RuGa and GdFeCo, but also open +the door for the future applications. Specifically, we propose a +Mn$_2$Ru$_x$Ga-based magnetic tunnel junction where a single laser pulse can +control magnetoresistance.",2207.10443v1 +2022-08-01,Effect of magnetism and phonons on localized carriers in the ferrimagnetic kagome metals GdMn$_6$Sn$_6$ and TbMn$_6$Sn$_6$,"Kagome metals possess peculiar optical spectra consisting of contributions +from free charge carriers in a Drude-type response, localized carriers seen as +a strongly temperature-dependent localization peak, and, in some cases, phonons +displaying strong anomalies. The rare-earth kagome metal series, +$R$Mn$_6$Sn$_6$, provides a marvelous playground to study the electronic +properties of kagome metals in the presence of variable magnetic order. Here, +we report temperature-dependent reflectivity studies on two members of the +$R$Mn$_6$Sn$_6$ family, GdMn$_6$Sn$_6$ (in-plane ferrimagnet) and +TbMn$_6$Sn$_6$ (out-of-plane ferrimagnet), in a broad energy range (50 - 18000 +cm$^{-1}$, equivalent to 6.2 meV - 2.23 eV) down to 10 K. At high temperatures, +a phonon mode at approximately 160 cm$^{-1}$ is observed, which becomes +screened out in TbMn$_6$Sn$_6$ below $\sim$ 150 K as the localization peak +linearly passes through the mode. In GdMn$_6$Sn$_6$, the disappearance of the +phonon is accompanied by the onset of saturation of the peak position, +suggesting an unusual interplay between the two features.",2208.00756v2 +2022-08-15,"Two-Dimensional Semiconducting Metal Organic Frameworks with Auxetic Effect, Room Temperature Ferrimagnetism, Chiral Ferroelectricity, Bipolar Spin Polarization and Topological Nodal Lines/Points","Two-dimensional (2D) semiconductors integrated with two or more functions are +the cornerstone for constructing multifunctional nanodevices, but remain +largely limited. Here, by tuning the spin state of organic linkers and the +symmetry/topology of crystal lattice, we predict a class of unprecedented +multifunctional semiconductors in 2D Cr(II) five-membered heterocyclic metal +organic frameworks that simultaneously possess auxetic effect, room temperature +ferrimagnetism, chiral ferroe-lectricity, electrically reversible spin +polarization and topological nodal lines/points. Taking 2D Cr(TDZ)$_2$ +(TDZ=1.2.5-thiadiazole) as an exemplification, the auxetic effect is produced +by the anti-tetra-chiral lattice structure. The high temperature ferrimagnetism +originates from the strong d-p direct magnetic exchange interaction between Cr +cations and TDZ doublet radical anions. Meanwhile, the +clockwise-counterclockwise alignment of TDZ' dipoles results in unique 2D +chiral ferroelectricity with atomic-scale vortex-antivortex states. 2D +Cr(TDZ)$_2$ is an intrinsic bipolar magnetic semiconductor where half-metallic +conduction with switchable spin-polarization direction can be induced by +applying a gate voltage. Besides, the symmetry of the little group C$_4$ of +lattice structure endows 2D Cr(TDZ)$_2$ with topological nodal lines and a +quadratic nodal point in the Brillouin zone near the Fermi level.",2208.07024v1 +2022-09-07,Effects of site dilution on Compensation in Ising Spin-1/2 trilayered triangular Ferrimagnets with non-equivalent planes,"Using Monte Carlo simulations with the Metropolis algorithm, the magnetic and +thermodynamic behaviours of a spin-1/2, trilayered ferrimagnetic system on +triangular monolayers with quenched nonmagnetic impurities are studied. Two +different theoretical atoms, A and B, make up the ABA and AAB types of distinct +configurations. Like atoms (A-A and B-B) interact ferromagnetically, while +unlike atoms (A-B) interact antiferromagnetically. Only the A-layers are +randomly site-diluted with dilution percentages ranging from 5% to 45%. Such +diluted magnetic thin systems exhibit magnetic compensation which depends +sensitively on the concentration of impurities. The phase diagram in the +Hamiltonian parameter space related to the occurrence of magnetic compensation +phenomenon and the effect of site dilution is discussed in detail. Special +attention is given to the mathematical dependencies of compensation temperature +on the concentration of nonmagnetic impurities. Depending upon the +concentration of nonmagnetic impurities, the compensation and critical points +shift with the equilibrium magnetic behaviours changing between distinct +ferrimagnetic behaviours. For each combination of the coupling strengths, with +values of the impurity concentration above a threshold, compensation appears +where previously was absent. Suggested mathematical formulae show how threshold +impurity concentration relies on Hamiltonian parameters.",2209.03189v2 +2022-11-09,Magnetization reversal through an antiferromagnetic state,"Magnetization reversal in ferro- and ferrimagnets is a well-known archetype +of non-equilibrium processes, where the volume fractions of the oppositely +magnetized domains vary and perfectly compensate each other at the coercive +magnetic field. Here, we report on a fundamentally new pathway for +magnetization reversal that is mediated by an antiferromagnetic state. +Consequently, an atomic-scale compensation of the magnetization is realized at +the coercive field, instead of the mesoscopic or macroscopic domain +cancellation in canonical reversal processes. We demonstrate this unusual +magnetization reversal on the Zn-doped polar magnet Fe$_2$Mo$_3$O$_8$. Hidden +behind the conventional ferrimagnetic hysteresis loop, the surprising emergence +of the antiferromagnetic phase at the coercive fields is disclosed by a sharp +peak in the field-dependence of the electric polarization. In addition, at the +magnetization reversal our THz spectroscopy studies reveal the reappearance of +the magnon mode that is only present in the pristine antiferromagnetic state. +According to our microscopic calculations, this unusual process is governed by +the dominant intralayer coupling, strong easy-axis anisotropy and spin +fluctuations, which result in a complex interplay between the ferrimagnetic and +antiferromagnetic phases. Such antiferro-state-mediated reversal processes +offer novel concepts for magnetization control, and may also emerge for other +ferroic orders.",2211.05028v1 +2023-01-19,Current-driven dynamics and ratchet effect of skyrmion bubbles in a ferrimagnetic insulator,"Magnetic skyrmions are compact chiral spin textures that exhibit a rich +variety of topological phenomena and hold potential for developing high-density +memory devices and novel computing schemes driven by spin currents. Here, we +demonstrate room temperature interfacial stabilization and current-driven +control of skyrmion bubbles in the ferrimagnetic insulator Tm3Fe5O12 (TmIG) +coupled to Pt. We track the current-induced motion of individual skyrmion +bubbles. The ferrimagnetic order of the crystal together with the interplay of +spin-orbit torques and pinning determine the skyrmion dynamics in TmIG and +result in a strong skyrmion Hall effect characterized by a negative deflection +angle and hopping motion. Further, we show that the velocity and depinning +threshold of the skyrmion bubbles can be modified by exchange coupling TmIG to +an in-plane magnetized Y3Fe5O12 layer, which distorts the spin texture of the +skyrmions and leads to a directional-dependent rectification of their dynamics. +This effect, which is equivalent to a magnetic ratchet, is exploited to control +the skyrmion flow in a racetrack-like device.",2301.08183v1 +2023-03-08,Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa,"Spin semimetals are amongst the most recently discovered new class of +spintronic materials, which exhibit a band gap in one spin channel and +semimetallic feature in the other, thus facilitating tunable spin transport. +Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along +with giant coercivity and spin-valve characteristics using a combined +experimental and theoretical study. The alloy crystallizes in an inverse +Heusler structure (without any martensitic transition) with a para- to +ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant +coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient, +relatively low magnitude and weak temperture dependance of electrical +resistivity suggest the semimetallic character of the alloy. This is further +supported by our specific heat measurement. Magnetoresistance (MR) confirms an +irreversible nature (with its magnitude $\sim$1\%) along with a change of sign +across the magnetic transition indicating the potentiality of Mn$_2$IrGa in +magnetic switching applications. In addition, asymmetric nature of MR in the +positive and negative field cycles is indicative of spin-valve characteristics. +Our ab-initio calculations confirm the inverse Heusler structure with +ferrimagnetic ordering to be the lowest energy state, with a saturation +magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic +axis with considerable magneto-crystalline anisotropy energy. A large positive +Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall +conductivity ($\sim$-180 S/cm).",2303.04649v2 +2023-05-29,"Structural, Optical and Single-domain Magnetic Features of the Noncollinear Ferrimagnetic Nano-spinel Chromites ACr$_2$O$_4$ (A = Ni, Co, and Mn)","Spinel chromites ACr$_2$O$_4$ with inherent magnetic geometrical frustration +usually exhibit a noncollinear ferrimagnetic ground state when A are magnetic +ions, with possibly crystallite-size dependent intriguing magnetic features. +Here, we report single-domain magnetic properties of ACr$_2$O$_4$ (A = Ni, Co, +and Mn) nanocrystals, with an average crystallite size of 18, 15 and 10 nm, +exhibiting an optical energy gap of 2.87, 3.05 and 2.9 eV, respectively. The +temperature dependence of magnetization indicates the main bulk magnetic +transitions with a commonly coexisting spin-glass-like state and finite-size +effects on the noncolinear ferrimagnetic transitions. An anomaly observed at Ts += 15, 24 and 10 K is attributed to the bulk magnetic transition to a canted +antiferromagnetic state in NiCr$_2$O$_4$ and incommensurate spiral orders in +CoCr$_2$O$_4$ and MnCr$_2$O$_4$ NCs, respectively. A further bulk magnetic +transition to a commensurate spiral order is observed for CoCr$_2$O$_4$ NCs at +a lock-in temperature Tl = 5 K much lower than that reported using bulk +samples, while it is completely suppressed in the MnCr$_2$O$_4$ NCs. +Finite-size effects and single-domain magnetic behaviors indicated by anomalous +temperature-dependences of the coercive field and the hysteresis-loop +squareness, mainly driven by a magnetocrystalline anisotropy, are discussed in +comparison to results reported using bulk counterparts.",2305.17856v1 +2023-05-31,Ferrimagnetic Oscillator Magnetometer,"Quantum sensors offer unparalleled precision, accuracy, and sensitivity for a +variety of measurement applications. We report a compact magnetometer based on +a ferrimagnetic sensing element in an oscillator architecture that circumvents +challenges common to other quantum sensing approaches such as limited dynamic +range, limited bandwidth, and dependence on vacuum, cryogenic, or laser +components. The device exhibits a fixed, calibration-free response governed by +the electron gyromagnetic ratio. Exchange narrowing in the ferrimagnetic +material produces sub-MHz transition linewidths despite the high unpaired spin +density ($\sim 10^{22}$ cm$^{-3}$). The magnetometer achieves a minimum +sensitivity of 100 fT/$\sqrt{\text{Hz}}$ to AC magnetic fields of unknown phase +and a sensitivity below 200 fT/$\sqrt{\text{Hz}}$ over a bandwidth $\gtrsim \! +1$ MHz. By encoding magnetic field in frequency rather than amplitude, the +device provides a dynamic range in excess of 1 mT. The passive, thermal +initialization of the sensor's quantum state requires only a magnetic bias +field, greatly reducing power requirements compared to laser-initialized +quantum sensors. With additional development, this device promises to be a +leading candidate for high-performance magnetometry outside the laboratory, and +the oscillator architecture is expected to provide advantages across a wide +range of sensing platforms.",2305.19938v1 +2023-08-08,Ionically-Driven Synthesis and Exchange Bias in Mn$_{4}$N/MnN$_{x}$ Heterostructures,"Ferrimagnets have received renewed attention as a promising platform for +spintronic applications. Of particular interest is the Mn4N from the +${\epsilon}$-phase of the manganese nitride as an emergent rare-earth-free +spintronic material due to its perpendicular magnetic anisotropy, small +saturation magnetization, high thermal stability, and large domain wall +velocity. We have achieved high-quality (001)-ordered Mn$_{4}$N thin film by +sputtering Mn onto ${\eta}$-phase Mn$_{3}$N$_{2}$ seed layers on Si substrates. +As the deposited Mn thickness varies, nitrogen ion migration across the +Mn$_{3}$N$_{2}$/Mn layers leads to a continuous evolution of the layers to +Mn$_{3}$N$_{2}$/Mn$_{2}$N/Mn$_{4}$N, Mn$_{2}$N/Mn$_{4}$N, and eventually +Mn$_{4}$N alone. The ferrimagnetic Mn$_{4}$N indeed exhibits perpendicular +magnetic anisotropy, and forms via a nucleation-and-growth mechanism. The +nitrogen ion migration is also manifested in a significant exchange bias, up to +0.3 T at 5 K, due to the interactions between ferrimagnetic Mn$_{4}$N and +antiferromagnetic Mn$_{3}$N$_{2}$ and Mn$_{2}$N. These results demonstrate a +promising all-nitride magneto-ionic platform with remarkable tunability for +device applications.",2308.04274v2 +2023-09-25,"Magnetic States and Electronic Properties of Manganese-Based Intermetallic Compounds Mn$_2$YAl and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni; Z = Al, Ge, Sn, Si, Pt)","We present a brief review of experimental and theoretical papers on studies +of electron transport and magnetic properties in manganese-based compounds +Mn$_2$YZ and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni, etc.; Z = Al, Ge, Sn, Si, Pt, +etc.). It has been shown that in the electronic subsystem of Mn$_2$YZ +compounds, the states of a half-metallic ferromagnet and a spin gapless +semiconductor can arise with the realization of various magnetic states, such +as a ferromagnet, a compensated ferrimagnet, and a frustrated antiferromagnet. +Binary compounds Mn$_3$Z have the properties of a half-metallic ferromagnet and +a topological semimetal with a large anomalous Hall effect, spin Hall effect, +spin Nernst effect, and thermal Hall effect. Their magnetic states are also +very diverse: from a ferrimagnet and an antiferromagnet to a compensated +ferrimagnet and a frustrated antiferromagnet, as well as an antiferromagnet +with a kagome-type lattice. It has been demonstrated that the electronic and +magnetic properties of such materials are very sensitive to external influences +(temperature, magnetic field, external pressure), as well as the processing +method (cast, rapidly quenched, nanostructured, etc.). Knowledge of the +regularities in the behavior of the electronic and magnetic characteristics of +Mn$_2$YAl and Mn$_3$Z compounds can be used for applications in micro- and +nanoelectronics and spintronics.",2309.14140v1 +2023-12-25,Controllable magnon frequency comb in synthetic ferrimagnets,"Magnon frequency comb provides opportunities for exploring magnon nonlinear +effects and measuring the transmission magnon frequency in magnets, whose +controllability becomes vital for modulating the operating frequency and +improving the measurement accuracy. Nevertheless, such controllable frequency +comb remains to be explored. In this work, we investigate theoretically and +numerically the skyrmion-induced magnon frequency comb effect generated by +interaction between the magnon excitation mode and skyrmion breathing mode in +synthetic ferrimagnets. It is revealed that both the skyrmion breathing mode +and the magnon frequency gap closely depend on the net angular momentum +{\delta}s, emphasizing the pivotal role of {\delta}s as an effective control +parameter in governing the comb teeth. With the increase of {\delta}s, the +skyrmion size decreases, which results in the enlargement of the breathing +frequency and the distance between the comb teeth. Moreover, the dependences of +the magnon frequency gap on {\delta}s and the inter-layer coupling allow one to +modulate the comb lowest coherent frequency via structural control. +Consequently, the coherent modes generated by the comb may range from gigahertz +to terahertz frequencies, serving as a bridge between microwave and terahertz +waves. Thus, this work represents a substantial advance in understanding the +magnon frequency comb effect in ferrimagnets.",2312.15584v2 +2003-09-05,Induced Magnetic Ordering by Proton Irradiation in Graphite,"We provide evidence that proton irradiation of energy 2.25 MeV on +highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism. +Measurements performed with a superconducting quantum interferometer device +(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering +is stable at room temperature.",0309128v1 +2004-02-11,Unusual giant magnetostriction in the ferrimagnet Gd$_{2/3}$Ca$_{1/3}$MnO$_3$,This paper has been withdrawn by authors.,0402297v4 +2004-11-05,Universality Classes of Diagonal Quantum Spin Ladders,"We find the classification of diagonal spin ladders depending on a +characteristic integer $N_p$ in terms of ferrimagnetic, gapped and critical +phases. We use the finite algorithm DMRG, non-linear sigma model and +bosonization techniques to prove our results. We find stoichiometric contents +in cuprate $CuO_2$ planes that allow for the existence of weakly interacting +diagonal ladders.",0411132v1 +2006-03-31,Half-metallic diluted antiferromagnetic semiconductors,"The possibility of half-metallic antiferromagnetism, a special case of +ferrimagnetism with a compensated magnetization, in the diluted magnetic +semiconductors is highlighted on the basis of the first principles electronic +structure calculation. As typical examples, the electrical and magnetic +properties of II-VI compound semiconductors doped with 3d transition metal ion +pairs--(V, Co) and (Fe, Cr)--are discussed.",0603846v1 +2007-03-22,Nonmagnetic-Defect-Induced Magnetism in Graphene,"It is shown that a strong impurity potential induces short-range +antiferromagnetic (ferrimagnetic) order around itself in a Hubbard model on a +half-filled honeycomb lattice. This implies that short-range magnetic order is +induced in monolayer graphene by a nonmagnetic defect such as a vacancy with +full hydrogen termination or a chemisorption defect.",0703570v2 +2009-06-17,Magnetostructural Effect in the Multiferroic BiFeO3-BiMnO3 Checkerboard from First Principles,"Using first principles calculations, we present a magnetostructural effect in +the BiFeO3-BiMnO3 nanocheckerboard that is not found in either bulk parent +compound or in BiFeO3-BiMnO3 superlattices. We also demonstrate that the +atomic-scale checkerboard has a multiferroic ground state with the desired +properties of each constitutent material: polar and ferrimagnetic due to BiFeO3 +and BiMnO3 respectively.",0906.3201v1 +2012-08-22,Gap Generation in Topological Insulator Surface States by non-Ferromagnetic Magnets,"It is shown that, contrary to the naive expectation, single particle spectral +gaps can be opened on the surface states of three dimensional topological +insulators by using commensurate out- and in-plane antiferromagnetic or +ferrimagnetic insulating thin films.",1208.4615v1 +2016-02-28,"Effective field theory and the scattering process for magnons in the ferromagnet, antiferromagnet, and ferrimagnet","We discuss that a low-energy effective Lagrangian relying on SO(3) +$\rightarrow$ SO(2) is applicable for a ferrimagnet as well as a ferromagnet +and an antiferromagnet. The analysis of the particle states shows that there +exist not only massless modes with the dispersion relations $\omega \propto +|\bm{k}|,\, |\bm{k}|^2$, i.e., the so-called type-I and type-II Nambu-Goldstone +modes, respectively, but also gapped modes with $\omega \propto +m^2+|\bm{k}|^2$. We clarify how the coefficients of the terms with one time +derivative and those with two time derivatives in the effective Lagrangian +determine the order parameters specifying whether the system is in a +ferromagnetic, antiferromagnetic or ferrimagnetic state; we stress that the +gapped mode related to the spontaneous symmetry breaking appears only in the +ferrimagnetic system and not in the ferromagnetic and antiferromagnetic +systems. We also establish the power counting scheme and calculate the +scattering amplitudes and thereby the scattering lengths between the two +Nambu-Goldstone bosons. We show that the scattering length of the gapped mode +is finite and proportional to the gap. This characteristic property of the +gapped NG mode can be used to discriminate it from gapped excitations which +originate in other mechanisms. Finally, we study the effects of the explicit +symmetry breaking that are given by an external magnetic field and a single-ion +anisotropy, and show that the external magnetic fields do not have any effects +on the scattering amplitudes in all the spin systems as was known for the +ferromagnet system. In contrast, the anisotropy does affect the scattering +amplitudes, the phase shift, and the scattering length except for spin 1/2 +systems. This result supports the possibility of the Efimov effect in spin +systems discussed in previous studies.",1602.08692v2 +2019-02-01,Quantum thermodynamics of complex ferrimagnets,"High-quality magnets such as yttrium iron garnet (YIG) are electrically +insulating and very complex. By implementing a quantum thermostat into +atomistic spin dynamics we compute YIG's key thermodynamic properties, viz. the +magnon power spectrum and specific heat, for a large temperature range. The +results differ (sometimes spectacularly) from simple models and classical +statistics, but agree with available experimental data.",1902.00449v1 +2020-10-26,Effect of the Uniform Random External Magnetic Field with Spatio-temporal Variation on Compensation in Ising Spin-1/2 Trilayered Square Ferrimagnet,"Trilayered spin-1/2 Ising ferrimagnets are interesting thin systems for +compensation phenomenon. In this work, a Metropolis Monte Carlo study is +performed on the magnetic and thermodynamic response of such a system on square +Bravais lattice, driven by uniform random external magnetic field with +spatio-temporal variations. In two distinct configurations, the surface layers +are made up of A and the mid-layer is made up of B atoms in a ABA type stacking +while in AAB type stacking, the top-layer and the mid-layer is made up of +A-atoms while the bottom layer is made up of B-atoms. The magnetic coupling +between the like atoms (A-A and B-B) is ferromagnetic while between the unlike +atoms (A-B), it is antiferromagnetic. For the time-dependent external uniform +random field, the mean is always set to zero and the standard deviation is +varied until spin-field energy is comparable to the dominant cooperative energy +of the system. The findings show that the observed compensation and critical +points shift and steady-state magnetic behaviours shift between N-, L-, P- and +Q- etc. type of ferrimagnetic behaviours, depending upon the strength of +external uniform random field. The compensation phenomenon even vanishes after +crossing a finite threshold of standard deviation of the magnetic field for +particular choices of the other controlling parameters. Thus islands of +ferrimagnetic phase without compensation appear within the phase area with +compensation of field-free case, in the 2D Hamiltonian parameter space. For +both the configurations, the areas of such islands even grow with increasing +standard deviation of the external field, {\sigma}, obeying a scaling relation +of the form: $f ({\sigma}, A({\sigma})) = {\sigma}^{-b} A({\sigma})$ with +$b_{ABA} = 1.958 \pm 0.122$ and $b_{AAB} = 1.783 \pm 0.118$ .",2010.13643v4 +2022-08-17,Polarization-selective magneto-optical modulation,"We study magneto-optical coupling in a ferrimagnetic sphere resonator made of +Yttrium iron garnet. We find that the resonator can be operated in the telecom +band as a polarization-selective optical modulator. Intermodulation gain can be +employed in the nonlinear regime for amplification.",2208.08148v2 +2023-03-01,"Covalency, correlations, and inter-layer interactions governing the magnetic and electronic structure of Mn$_3$Si$_2$Te$_6$","Mn$_3$Si$_2$Te$_6$ is a rare example of a layered ferrimagnet. It has +recently been shown to host a colossal angular magnetoresistance as the spin +orientation is rotated from the in- to out-of-plane direction, proposed to be +underpinned by a topological nodal-line degeneracy in its electronic structure. +Nonetheless, the origins of its ferrimagnetic structure remain controversial, +while its experimental electronic structure, and the role of correlations in +shaping this, are little explored to date. Here, we combine x-ray and +photoemission-based spectroscopies with first-principles calculations, to probe +the elemental-selective electronic structure and magnetic order in +Mn$_3$Si$_2$Te$_6$. Through these, we identify a marked Mn-Te hybridisation, +which weakens the electronic correlations and enhances the magnetic anisotropy. +We demonstrate how this strengthens the magnetic frustration in +Mn$_3$Si$_2$Te$_6$, which is key to stabilising its ferrimagnetic order, and +find a crucial role of both exchange interactions extending beyond +nearest-neighbours and anti-symmetric exchange in dictating its ordering +temperature. Together, our results demonstrate a powerful methodology of using +experimental electronic structure probes to constrain the parameter space for +first-principles calculations of magnetic materials, and through this approach, +reveal a pivotal role played by covalency in stabilising the ferrimagnetic +order in Mn$_3$Si$_2$Te$_6$.",2303.00294v1 +1993-12-15,1/z-renormalization of the mean-field behavior of the dipole-coupled singlet-singlet system HoF_3,"The two main characteristics of the holmium ions in HoF_3 are that their +local electronic properties are dominated by two singlet states lying well +below the remaining 4f-levels, and that the classical dipole-coupling is an +order of magnitude larger than any other two-ion interactions between the +Ho-moments. This combination makes the system particularly suitable for testing +refinements of the mean-field theory. There are four Ho-ions per unit cell and +the hyperfine coupled electronic and nuclear moments on the Ho-ions order in a +ferrimagnetic structure at T_C=0.53 K. The corrections to the mean-field +behavior of holmium triflouride, both in the paramagnetic and ferrimagnetic +phase, have been calculated to first order in the high-density 1/z-expansion. +The effective medium theory, which includes the effects of the single-site +fluctuations, leads to a substantially improved description of the magnetic +properties of HoF_3, in comparison with that based on the mean-field +approximation.",9312060v1 +1995-12-13,First-principles studies of modulated Co/Cu superlattices with strongly and weakly exchange-biased Co-monolayers leading to a ferrimagnetic ground state,"First-principles calculations have been performed in order to determine +effective exchange integrals between strongly and weakly exchange-biased Co +monolayers in the modulated CoCu$_2$/CoCu$_n$ superlattices. For $3\le n\le 6$ +it has been found that the respective exchange integrals have opposite signs +and differ for $n\ne 4$ from each other by one order of magnitude and for $n=4$ +still by a factor of $\sim 1.7$. The obtained phase diagram, with all the +relevant magnetic phases, shows that for the $n$-values considered, the ground +state configuration is ferrimagnetic.",9512103v1 +1996-11-27,Critical Behaviour of Mixed Heisenberg Chains,"The critical behaviour of anisotropic Heisenberg models with two kinds of +antiferromagnetically exchange-coupled centers are studied numerically by using +finite-size calculations and conformal invariance. These models exhibit the +interesting property of ferrimagnetism instead of antiferromagnetism. Most of +our results are centered in the mixed Heisenberg chain where we have at even +(odd) sites a spin-S (S') SU(2) operator interacting with a XXZ like +interaction (anisotropy $\Delta$). Our results indicate universal properties +for all these chains. The whole phase, $1>\Delta>-1$, where the models change +from ferromagnetic $( \Delta=1 )$ to ferrimagnetic $(\Delta=-1)$ behaviour is +critical. Along this phase the critical fluctuations are ruled by a c=1 +conformal field theory of Gaussian type. The conformal dimensions and critical +exponents, along this phase, are calculated by studying these models with +several boundary conditions.",9611227v1 +1998-06-02,Kinetics of a mixed Ising ferrimagnetic system,"We present a study, within a mean-field approach, of the kinetics of a +classical mixed Ising ferrimagnetic model on a square lattice, in which the two +interpenetrating square sublattices have spins $\sigma = \pm1/2$ and $S = \pm +1,0$. The kinetics is described by a Glauber-type stochastic dynamics in the +presence of a time-dependent oscillating external field and a crystal field +interaction. We can identify two types of solutions: a symmetric one, where the +total magnetization, $M$, oscillates around zero, and an antisymmetric one +where $M$ oscillates around a finite value different from zero. There are +regions of the phase space where both solutions coexist. The dynamical +transition from one regime to the other can be of first or second order +depending on the region in the phase diagram. Depending on the value of the +crystal field we found up to two dynamical tricritical points where the +transition changes from continuous to discontinuous. Also, we perform a similar +study on the Blume-Capel ($S=\pm 1,0$) model and found strong differences +between its behavior and the one of the mixed model.",9806036v1 +1998-12-18,"Spinon signatures in the critical phase of the (1,1/2) ferrimagnet in a magnetic field","We propose an effective theory for the critical phase of a quantum +ferrimagnetic chain with alternating spins 1 and 1/2 in an external magnetic +field. With the help of the matrix product variational approach, the system is +mapped to a spin-1/2 XXZ chain in an (effective) magnetic field; as a +byproduct, we obtain an excellent description of the optical magnon branch in +the gapped phase. Recent finite-temperature DMRG results for the +low-temperature part of the specific heat are well described by the present +approach, and the ``pop-up'' peaks, developing near the critical field values +and in the middle of the critical phase, are identified with the contributions +from two different spinon bands of the effective spin-1/2 chain. The effect +should be as well observable in other spin-gap systems in an external field, +particularly in spin ladders.",9812326v1 +1999-04-08,Properties of the ferrimagnetic double-perovskite A_{2}FeReO_{6} (A=Ba and Ca),"Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied +for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with $a\approx +$8.0854(1) \AA whereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with +$a\approx 5.396(1) \AA, b\approx 5.522(1) \AA, c\approx 7.688(2) \AA$ and +$\beta =90.4^{\circ} (P21/n)$. The barium compound is metallic from 5 K to 385 +K, i.e. no metal-insulator transition has been seen up to 385 K, and the +calcium compound is semiconducting from 5 K to 385 K. Magnetization +measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K +for Ba_{2}FeReO_{6} and above 385 K for Ca_{2}FeReO_{6}. A specific heat +measurement on the barium compound gave an electron density of states at the +Fermi level, N(E_{F}) equal to 6.1$\times 10^{24} eV^{-1}mole^{-1}$. At 5 K, we +observed a negative magnetoresistance of 10 % in a magnetic field of 5 T, but +only for Ba_{2}FeReO_{6}. Electrical, thermal and magnetic properties are +discussed and compared to the analogous compounds Sr_{2}Fe(Mo,Re)O_{6}.",9904119v1 +1999-05-19,Ground State Property of an Alternating Spin Ladder Involving Two Kinds of Inter-Chain Interactions,"The ground state property of the alternating spin ladder is studied in the +case that the system involves an antiferromagnetic intra-chain interaction as +well as two kinds of inter-chain interactions; one is between spins of the same +magnitude and the other is between spins with different magnitudes. The +calculation has been carried out by the exact diagonalization method. As a +consequence of the competition among interactions, the system is revealed to +show an interesting variety of phases in the ground state property. Its phase +diagram is exhibited in the parameter space of the system. We find that, +however small the total amount of the inter-chain interactions is, the +ferrimagnetic ground state becomes unstable in a certain region. In this case, +which of the ferrimagnetic and the singlet ground state to appear is determined +only by the ratio between the inter-chain interactions regardless of their +total amount. The nature of two phases appearing in the singlet region of the +phase diagram and the type of the phase transition between them are also +discussed. The results are ensured by comparing with those of obtained in other +models which are contained in our model as special limiting cases.",9905269v1 +2000-04-14,Superconductivity and Antiferromagnetism: Hybridization Impurities in a Two-Band Spin-Gapped Electron System,"We present the exact solution of a one-dimensional model of a spin-gapped +correlated electron system with hybridization impurities exhibiting both +magnetic and mixed-valence properties. The host supports superconducting +fluctuations, with a spin gap. The localized electrons create a band of +antiferromagnetic spin excitations inside the gap for concentrations x of the +impurities below some critical value x_c. When x = x_c the spin gap closes and +a ferrimagnetic phase appears. This is the first example of an exactly solvable +model with coexisting superconducting and antiferromagnetic fluctuations which +in addition supports a quantum phase transition to a (compensated) +ferrimagnetic phase. We discuss the possible relevance of our results for +experimental systems, in particular the U-based heavy-fermion materials.",0004248v1 +2000-11-18,Magneto-electronic Properties of a Ferrimagnetic Semiconductor: The Hybrid Cupromanganite CaCu3Mn4O12,"The mixed manganite-cuprate CaCu3Mn4O12 is found, using density functional +methods, to be a narrow gap (90 meV calculated) ferrimagnetic semiconductor. Cu +(formally S=1/2) antialigns with Mn (formally S=3/2), and the net spin moment +is 9 \mu_B consistent with the formal spins. Holes have Cu d_{xy}-O p_{\sigma} +(i.e. antibonding dp\sigma) character with spins aligned antiparallel to the +net magnetization; electrons have the opposite spin and have mixed Cu d_{xy} - +Mn e_g character. Thermally excited electrons and holes will each be fully spin +polarized, but in opposite directions. The properties of this material are +strongly tied to the distorted quadruple perovskite structure, which is closely +related to the skutterudite structure. The observed resistivity, +magnetoresistance, and magnetization are discussed in terms of our results.",0011316v1 +2001-08-31,Inversion Phenomena of the Anisotropies of the Hamiltonian and the Wave-Function in the Distorted Diamond Type Spin Chain,"We investigate the ground-sate phase diagram of the XXZ version of the S=1/2 +distorted diamond chain by use of the degenerate perturbation theory near the +truncation point. In case of the XY-like interaction anisotropy, the phase +diagram consists of the Neel phase and the spin-fluid phase. For the Ising-like +interaction anisotropy case, it consists of three phases: the ferrimagnetic +phase, the Neel phase and the spin-fluid phase. The magnetization in the +ferrimagnetic phase is 1/3 of the saturation magnetization. The remarkable +nature of the phase diagram is the existence of the Neel phase, although the +interaction anisotropy is XY-like. And also, the spin-fluid phase appears in +spite of the Ising-like interaction anisotropy. We call these regions +""inversion regions"".",0108528v1 +2002-04-17,Quantum magnetization plateaux of an anisotropic ferrimagnetic spin chain,"The magnetization curve of the $(S,s)=(1,1/2)$ ferrimagnetic alternating spin +chain with the single-ion anisotropy $D$ is investigated with the numerical +exact diagonalization of finite clusters and size-scaling analyses. The system +has a plateau at 1/3 of the saturation moment, which corresponds to the +spontaneous magnetization for D=0. Varying $D$ in the 1/3-magnetized ground +state under the external field along the axis of $D$, a quantum phase +transition is revealed to occur at the critical value $D/J=1.114 \pm 0.001$ +where the plateau vanishes. Except for the critical point, the plateau is +always opening, but the mechanism is different between $DD_c$. The +change of mechanisms is an evidence to clarify that the plateau originates from +the quantization of magnetization.",0204375v2 +2003-06-26,Nuclear spin-lattice relaxation in ferrimagnetic clusters and chains: A contrast between zero and one dimensions,"Motivated by ferrimagnetic oligonuclear and chain compounds synthesized by +Caneschi et al., both of which consist of alternating manganese(II) ions and +nitronyl-nitroxide radicals, we calculate the nuclear spin-lattice relaxation +rate 1/T_1 employing a recently developed modified spin-wave theory. 1/T_1 as a +function of temperature drastically varies with the location of probe nuclei in +both clusters and chains, though the relaxation time scale is much larger in +zero dimension than in one dimension. 1/T_1 as a function of an applied field +in long chains forms a striking contrast to that in finite clusters, diverging +with decreasing field like inverse square root at low temperatures and +logarithmically at high temperatures.",0306685v1 +2005-04-26,"First-principles study of exchange interactions and Curie temperatures of half-metallic ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge)","We report the parameter-free, density functional theory calculations of +interatomic exchange interactions and Curie temperatures of half-metallic +ferrimagnetic full Heusler alloys Mn2VZ (Z=Al, Ge). To calculate the +interatomic exchange interactions we employ the frozen-magnon approach. The +Curie temperatures are calculated within the mean-field approximation to the +classical Heisenberg Hamiltonian by solving a matrix equation for a +multi-sublattice system. Our calculations show that, although a large magnetic +moment is carried by Mn atoms, competing ferromagnetic (inter sublattice) and +antiferromagnetic (intra sublattice) Mn-Mn interactions in Mn2VAl almost cancel +each other in the mean-field experienced by the Mn atoms. In Mn2VGe the leading +Mn-Mn exchange interaction is antiferromagnetic. In both compounds the +ferromagnetism of the Mn subsystem is favored by strong antiferromagnetic Mn-V +interactions. The obtained value of the Curie temperature of Mn2VAl is in good +agrement with experiment. For Mn2VGe there is no experimental information +available and our calculation is a prediction.",0504679v1 +2005-09-05,Magnetoelectric Coupling in epsilon-Fe2O3,"Nanoparticles of the ferrimagnetic epsilon-Fe2O3 oxide have been synthesized +by sol-gel method. Here, we report on the measurements of the dielectric +permittivity as a function of temperature, frequency and magnetic field. It is +found that, coinciding with the transition from collinear ferrimagnetic +ordering to an incommensurate magnetic state occurring at about 100 K, there is +an abrupt change (about 30 %) of permittivity suggesting the existence of a +magnetoelectric coupling in this material. Indeed, magnetic field dependent +measurements at 100 K have revealed an increase of the permittivity by about +0.3 % in 6 T. Prospective advantages of epsilon-Fe2O3 as multiferroic material +are discussed.",0509104v1 +2005-12-15,Phase Diagram of Lattice-Spin System RbCoBr$_3$,"We study the lattice-spin model of RbCoBr$_3$ which is proposed by Shirahata +and Nakamura, by mean field approximation. This model is an Ising spin system +on a distorted triangular lattice. There are two kinds of frustrated variables, +that is, the lattice and spin. We obtain a phase diagram of which phase +boundary is drawn continuously in a whole region. Intermediate phases that +include a partial disordered state appear. The model has the first-order phase +transitions in addition to the second-order phase transitions. We find a +three-sublattice ferrimagnetic state in the phase diagram. The three-sublattice +ferrimagnetic state does not appear when the lattice is not distorted.",0512332v1 +2005-12-24,Fermionic versus bosonic descriptions of one-dimensional spin-gapped antiferromagnets,"In terms of spinless fermions and spin waves, we describe magnetic properties +of a spin-1/2 ferromagnetic-antiferromagnetic bond-alternating chain which +behaves as a Haldane-gap antiferromagnet. On one hand, we employ the +Jordan-Wigner transformation and treat the fermionic Hamiltonian within the +Hartree-Fock approximation. On the other hand, we employ the Holstein-Primakoff +transformation and modify the conventional spin-wave theory so as to restore +the sublattice symmetry. We calculate the excitation gap, the specific heat, +the magnetic susceptibility, magnetization curves, and the nuclear spin-lattice +relaxation rate with varying bond alternation. These schemes are further +applied to a bond-alternating tetramerized chain which behaves as a +ferrimagnet. The fermionic language is particularly stressed as a useful tool +to investigate one-dimensional spin-gapped antiferromagnets, while the bosonic +one works better for ferrimagnets.",0512631v1 +2006-03-08,Anomalous impurity effect on magnetization in frustrated one-dimensional ferro- and ferrimagnets,"Significant decrease of spontaneous magnetization in frustrated +one-dimensional ferro- and ferrimagnets due to non-magnetic impurities is +predicted. Using the density-matrix renormalization group method and the exact +diagonalization method, we confirm that the total spin can vanish due to a +single impurity in finite chains. Introducing the picture of magnetic domain +inversion, we numerically investigate the impurity-density dependence of +magnetization. In particular, we show that even with an infinitesimal density +of impurities the magnetization in the ground state is reduced by about 40% +from that of the corresponding pure system. Conditions for the materials which +may show this anomalous impurity effect are formulated.",0603193v1 +2006-09-13,Current-induced magnetization switching in MgO barrier based magnetic tunnel junctions with CoFeB/Ru/CoFeB synthetic ferrimagnetic free layer,"We report the intrinsic critical current density (Jc0) in current-induced +magnetization switching and the thermal stability factor (E/kBT, where E, kB, +and T are the energy potential, the Boltzmann constant, and temperature, +respectively) in MgO based magnetic tunnel junctions with a +Co40Fe40B20(2nm)/Ru(0.7-2.4nm)/Co40Fe40B20(2nm) synthetic ferrimagnetic (SyF) +free layer. We show that Jc0 and E/kBT can be determined by analyzing the +average critical current density as a function of coercivity using the +Slonczewski's model taking into account thermal fluctuation. We find that high +antiferromagnetic coupling between the two CoFeB layers in a SyF free layer +results in reduced Jc0 without reducing high E/kBT.",0609306v2 +2006-11-24,Magnetic and transport properties of a one dimensional frustrated t-J model for vanadate nanotubes,"We propose a one-dimensional model consisting of a chain with a t-J +Hamiltonian coupled to a Heisenberg chain in a frustrated geometry to describe +the appearance of the ferromagnetic phase which has been experimentally +observed in vanadate nanotubes. This model contains a mechanism of frustration +suppressed by doping suggested by L. Krusin-Elbaum, et al. [Nature 431, 672 +(2004)]. We study, using numerical techniques in small clusters, the relation +between magnetic order and transport properties in the proposed model, and we +perform a detailed comparison of the physical properties of this model with +those of the ferromagnetic Kondo lattice model. For this comparison, a number +of results for the latter model, obtained using the same numerical techniques, +will be provided to complement those results already available in the +literature. We conclude that it does not appear to be a true ferromagnetic +order in the proposed model, but rather an incommensurate ferrimagnetic one, +and contrary to what happens in the ferromagnetic Kondo lattice model, +electronic transport is somewhat suppressed by this ferrimagnetic order.",0611603v2 +2006-11-30,"Role of the presence of transition-metal atoms at the antisites in CrAs, CrSe and VAs zinc-blende compounds","In a recent publication [Galanakis I et al 2006 \PR B \textbf{74} 140408(R)] +we have shown that in the case of CrAs and related transition-metal +chalcogenides and pnictides, crystallizing in the zinc-blende structure, the +excess of the transition-metal atoms leads to half-metallic ferrimagnetism. The +latter property is crucial for spintronic applications with respect to +ferromagnets due to the lower stray fields created by these materials. We +extend this study to cover the case where the transition-metal atoms sitting at +antisites are not identical to the ones in the perfect sites. In Cr-based +compounds, the creation of Mn antisites keeps the half-metallic ferrimagnetic +character produced also by the Cr antisites. In the case of VAs, Cr and Mn +antisites keep the half-metallic character of VAs (contrary to V antisites) due +to the larger exchange-splitting exhibited by these atoms.",0611777v1 +2006-06-04,"Structure, electronic properties and magnetic transition in manganese clusters","We systematically investigate the structural, electronic and magnetic +properties of Mn$_n$ clusters ($n =$ 2$-$20) within the {\it ab-initio} +pseudopotential plane wave method using generalized gradient approximation for +the exchange-correlation energy. A new kind of icosahedral structural growth +has been predicted in the intermediate size range. Calculated magnetic moments +show an excellent agreement with the Stern-Gerlach experiment. A transition +from ferromagnetic to ferrimagnetic Mn$-$Mn coupling takes place at $n=$ 5 and +the ferrimagnetic states continue to be the ground states for the entire size +range. Possible presence of multiple isomers in the experimental beam has been +argued. No signature of non-metal to metal transition is observed in this size +range and the coordination dependence of $d-$electron localization is +discussed.",0606032v1 +2007-04-24,Element-resolved x-ray ferrimagnetic and ferromagnetic resonance spectroscopy,"We report on the measurement of element-specific magnetic resonance spectra +at gigahertz frequencies using x-ray magnetic circular dichroism (XMCD). We +investigate the ferrimagnetic precession of Gd and Fe ions in Gd-substituted +Yttrium Iron Garnet, showing that the resonant field and linewidth of Gd +precisely coincide with Fe up to the nonlinear regime of parametric +excitations. The opposite sign of the Gd x-ray magnetic resonance signal with +respect to Fe is consistent with dynamic antiferromagnetic alignment of the two +ionic species. Further, we investigate a bilayer metal film, +Ni$_{80}$Fe$_{20}$(5 nm)/Ni(50 nm), where the coupled resonance modes of Ni and +Ni$_{80}$Fe$_{20}$ are separately resolved, revealing shifts in the resonance +fields of individual layers but no mutual driving effects. Energy-dependent +dynamic XMCD measurements are introduced, combining x-ray absorption and +magnetic resonance spectroscopies.",0704.3139v2 +2007-05-02,Sr2CrOsO6: Endpoint of a spin polarized metal-insulator transition by 5d band filling,"In the search for new spintronic materials with high spin-polarization at +room-temperature, we have synthesized an osmium based double perovskite with a +Curie-temperature of 725 K. Our combined experimental results confirm the +existence of a sizable induced magnetic moment at the Os site, supported by +band-structure calculations in agreement with a proposed kinetic energy driven +mechanism of ferrimagnetism in these compounds. The intriguing property of +Sr2CrOsO6 is that it is at the endpoint of a metal-insulator transition due to +5d band filling, and at the same time ferrimagnetism and high-spin polarization +is preserved.",0705.0336v1 +2007-06-19,Probing the Role of the Barrier Layer in Magnetic Tunnel Junction Transport,"Magnetic tunnel junctions with a ferrimagnetic barrier layer have been +studied to understand the role of the barrier layer in the tunneling process - +a factor that has been largely overlooked until recently. Epitaxial oxide +junctions of highly spin polarized La0.7Sr0.3MnO3 and Fe3O4 electrodes with +magnetic NiMn2O4 (NMO) insulating barrier layers provide a magnetic tunnel +junction system in which we can probe the effect of the barrier by comparing +junction behavior above and below the Curie temperature of the barrier layer. +When the barrier is paramagnetic, the spin polarized transport is dominated by +interface scattering and surface spin waves; however, when the barrier is +ferrimagnetic, spin flip scattering due to spin waves within the NMO barrier +dominates the transport.",0706.2726v2 +2007-09-21,Magnetism of NiMn2O4-Fe3O4 Spinel Interfaces,"We investigate the magnetic properties of the isostructural spinel-spinel +interface of NiMn2O4(NMO)-Fe3O4. Although the magnetic transition temperature +of the NMO film is preserved, both bulk and interface sensitive measurements +demonstrate that the interface exhibits strong interfacial magnetic coupling up +to room temperature. While NMO thin films have a ferrimagnetic transition +temperature of 60K, both NiFe2O4 and MnFe2O4 are ferrimagnetic at room +temperature. Our experimental results suggest that these magnetic properties +arise from a thin interdiffused region of (Fe,Mn,Ni)3O4 at the interface +leading to Mn and Ni magnetic properties similar to MnFe2O4 and NiFe2O4.",0709.3518v2 +2007-10-18,Numerical Study of a Three-Dimensional Mixed Ising Ferrimagnet in the Presence of an External Field,"We present a numerical study based on Monte Carlo algorithm of the magnetic +properties of a mixed Ising ferrimagnetic model on a cubic lattice where spins +$\sigma =\pm 1/2$ and spins $S=0,\pm 1$ are in alternating sites on the +lattice. We carried out exact ground state calculations and employ a Monte +Carlo simulation to obtain the finite-temperature phase diagram of the model. A +compensation point appears when the next-nearest-neighbor interaction between +the spins $\sigma =\pm 1/2$ exceeds a minimum value. We found a strong +dependence of the compensation temperature with the interactions in the +Hamiltonian, particulary the crystal field and the external field. An applied +field can change the range of values of the compensation temperature from zero +up to a maximum value that depends on the field.",0710.3592v1 +2007-12-14,Ordered Phases of the Anisotropic Kagome Lattice Antiferromagnet in a Field,"The antiferromagnetic Heisenberg model on an anisotropic kagome lattice may +be a good minimal model for real magnetic systems as well as a limit from which +the isotropic case can be better understood. We therefore study the +nearest-neighbor Heisenberg antiferromagnet on an anisotropic kagome lattice in +a magnetic field. Such a system should be well described by weakly interacting +spin chains, and we motivate a general form for the interaction by symmetry +considerations and by perturbatively projecting out the inter-chain spins. In +the spin 1/2 case, we find that the system exhibits a quantum phase transition +from a ferrimagnetic ordered state to an XY ordered state as the field is +increased. Finally, we discuss the appearance of magnetization plateaux in the +ferrimagnetic phase.",0712.2269v1 +2008-01-15,Fundamentals of half-metallic Full-Heusler alloys,"Intermetallic Heusler alloys are amongst the most attractive half-metallic +systems due to the high Curie temperatures and the structural similarity to the +binary semiconductors. In this review we present an overview of the basic +electronic and magnetic properties of the half-metallic full-Heusler alloys +like Co$_2$MnGe. Ab-initio results suggest that the electronic and magnetic +properties in these compounds are intrinsically related to the appearance of +the minority-spin gap. The total spin magnetic moment in the unit cell, $M_t$, +scales linearly with the number of the valence electrons, $Z_t$, such that +$M_t=Z_t-24$ for the full-Heusler alloys opening the way to engineer new +half-metallic alloys with the desired magnetic properties. Moreover we present +analytical results on the disorder in Co$_2$Cr(Mn)Al(Si) alloys, which is +susceptible to destroy the perfect half-metallicity of the bulk compounds and +thus degrade the performance of devices. Finally we discuss the appearance of +the half-metallic ferrimagnetism due to the creation of Cr(Mn) antisites in +these compounds and the Co-doping in Mn$_2$VAl(Si) alloys which leads to the +fully-compensated half-metallic ferrimagnetism.",0801.2252v1 +2008-06-10,Ferrimagnetism of MnV_2O_4 spinel,"The spinel MnV_2O_4 is a two-sublattice ferrimagnet, with site A occupied by +the Mn^{2+} ion and site B by the V^{3+} ion. The magnon of the system, the +transversal fluctuation of the total magnetization, is a complicated mixture of +the sublattice A and B transversal magnetic fluctuations. As a result, the +magnons' fluctuations suppress in a different way the manganese and vanadium +magnetic orders and one obtains two phases. At low temperature (0,T^*) the +magnetic orders of the Mn and V ions contribute to the magnetization of the +system, while at the high temperature (T^*,T_N), the vanadium magnetic order is +suppressed by magnon fluctuations, and only the manganese ions have non-zero +spontaneous magnetization. A modified spin-wave theory is developed to describe +the two phases and to calculate the magnetization as a function of temperature. +The anomalous $M(T)$ curve reproduces the experimentally obtained ZFC +magnetization.",0806.1641v1 +2008-08-10,Formation of guided spin-wave bullets in ferrimagnetic film stripes,"The formation of quasi-2D nonlinear spin-wave eigenmodes in longitudinally +magnetized stripes of a ferrimagnetic film, so-called guided spin-wave bullets, +was experimentally observed by using time- and space-resolved Brillouin light +scattering spectroscopy and confirmed by numerical simulation. They represent +stable spin-wave packets propagating along a waveguide structure, for which +both transversal instability and interaction with the side edges of the +waveguide are important. The experiments and the numerical simulation of the +evolution of the spin-wave excitations show that the shape of the formed +packets and their behavior are strongly influenced by the confinement +conditions. The discovery of these modes demonstrates the existence of +quasi-stable nonlinear solutions in the transition regime between +one-dimensional and two-dimensional wave packet propagation.",0808.1399v1 +2008-08-14,High-output CPP-GMR sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents,"It is shown that the maximum stable output of a CPP-GMR sensor is increased +significantly by using a synthetic ferrimagnet free layer, provided the +electron current flows from free layer to reference layer. This free layer +allows a larger magnetoresistance ratio for a given free layer magnetic moment, +and in addition results in a greater than three-fold increase in the critical +current above which spin-torque instability of the free layer occurs. In read +heads with net free layer moments equivalent to only 4.5nm of Ni80Fe20, this +effect is shown to result in sustainable sense current densities above 2e8 +A/cm2.",0808.2001v1 +2008-08-14,Co-resonant enhancement of spin-torque critical currents in spin-valves with synthetic-ferrimagnet free-layer,"It is experimentally shown that the critical current for onset of spin-torque +instability in current-perpendicular-to-plane spin-valves can be strongly +enhanced using ""synthetic ferrimagnet"" free-layers of form FM1/Ru/FM2 +(FM=ferrromagnet). However, this enhancement occurs for only one polarity of +bias current. A two-macrospin model is shown to reproduce the observations. The +model suggests that this phenomenon is related to a polarity-dependent, +spin-torque induced co-resonance between the two natural dynamic modes of the +FM1/FM2 couple. The resonance condition facilitates energy transfer out of the +spin-torque destabilized mode into the other stable mode whose effective +damping is actually enhanced by spin-torques, thereby delaying the onset of +instability of this coupled system to larger critical currents.",0808.2015v2 +2008-10-02,Structural phase stability and Magnetism in Co2FeO4 spinel oxide,"We report a correlation between structural phase stability and magnetic +properties of Co2FeO4 spinel oxide. We employed mechanical alloying and +subsequent annealing to obtain the desired samples. The particle size of the +samples changes from 25 nm to 45 nm. The structural phase separation of +samples, except sample annealed at 9000C, into Co rich and Fe rich spinel phase +has been examined from XRD spectrum, SEM picture, along with EDAX spectrum, and +magnetic measurements. The present study indicated the ferrimagnetic character +of Co2FeO4, irrespective of structural phase stability. The observation of +mixed ferrimagnetic phases, associated with two Curie temperatures at TC1 and +TC2 (>TC1), respectively, provides the additional support of the splitting of +single cubic spinel phase in Co2FeO4 spinel oxide.",0810.0449v1 +2008-10-22,Exchange bias effect in the phase separated Nd_{1-x}Sr_{x}CoO_3 at the spontaneous ferromagnetic/ferrimagnetic interface,"We report the new results of exchange bias effect in Nd_{1-x}Sr_{x}CoO_3 for +x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the +ferrimagnetic (FI) state in a spontaneously phase separated system. The +zero-field cooled magnetization exhibits the FI (T_{FI}) and ferromagnetic +(T_C) transitions at ~ 23 and \sim 70 K, respectively for x = 0.20. The +negative horizontal and positive vertical shifts of the magnetic hysteresis +loops are observed when the system is cooled through T_{FI} in presence of a +positive static magnetic field. Training effect is observed for x = 0.20, which +could be interpreted by a spin configurational relaxation model. The +unidirectional shifts of the hysteresis loops as a function of temperature +exhibit the absence of exchange bias above T_{FI} for x = 0.20. The analysis of +the cooling field dependence of exchange bias field and magnetization indicates +that the ferromagnetic (FM) clusters consist of single magnetic domain with +average size around \sim 20 and ~ 40 \AA ~ for x = 0.20 and 0.40, respectively. +The sizes of the FM clusters are close to the percolation threshold for x = +0.20, which grow and coalesce to form the bigger size for x = 0.40 resulting in +a weak exchange bias effect.",0810.4013v1 +2008-11-13,Selection rules for Single-Chain-Magnet behavior in non-collinear Ising systems,"The magnetic behavior of molecular Single-Chain Magnets is investigated in +the framework of a one-dimensional Ising model with single spin-flip Glauber +dynamics. Opportune modifications to the original theory are required in order +to account for reciprocal non-collinearity of local anisotropy axes and the +crystallographic (laboratory) frame. The extension of Glauber's theory to the +case of a collinear Ising ferrimagnetic chain is also discussed. Within this +formalism, both the dynamics of magnetization reversal in zero field and the +response of the system to a weak magnetic field, oscillating in time, are +studied. Depending on the geometry, selection rules are found for the +occurrence of slow relaxation of the magnetization at low temperatures, as well +as for resonant behavior of the a.c. susceptibility as a function of +temperature at low frequencies. The present theory applies successfully to some +real systems, namely Mn-, Dy-, and Co-based molecular magnetic chains, showing +that Single-Chain-Magnet behavior is not only a feature of collinear ferro- and +ferrimagnetic, but also of canted antiferromagnetic chains.",0811.2118v1 +2009-01-07,Real Space Visualization of Thermomagnetic Irreversibility within Supercooling and Superheating Spinodals in $Mn_{1.85}Co_{0.15}Sb$ using Scanning Hall Probe Microscopy,"Phase coexistence across disorder-broadened and magnetic-field-induced first +order antiferromagnetic to ferrimagnetic transition in polycrystalline +$Mn_{1.85}Co_{0.15}Sb$ has been studied mesoscopically by Scanning Hall Probe +Microscope at 120K and up to 5 Tesla magnetic fields. We have observed +hysteresis with varying magnetic field and the evolution of coexisting +antiferromagnetic and ferrimagnetic state on mesoscopic length scale. These +studies show that the magnetic state of the system at low field depends on the +path followed to reach 120 K. The low field magnetic states are mesoscopically +different for virgin and second field increasing cycle when 120 K is reached by +warming from 5K, but are the same within measurement accuracy when the +measuring temperature of 120K is reached from 300K by cooling.",0901.0758v1 +2009-03-13,Half-metallic ferrimagnetism in the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x} $V$_x$]Si alloys adopting the zinc-blende and wurtzite structures from first-principles,"Employing first-principles calculations we study the structural, electronic +and magnetic properties of the [Sc$_{1-x}$V$_x$]C and [Sc$_{1-x}$V$_x$]Si +alloys. In their equilibrium rocksalt structure all alloys are non-magnetic. +The zincblende and wurtzite structures are degenerated with respect to the +total energy. For all concentrations the alloys in these lattice structures are +half-metallic with the gap located in the spin-down band. The total spin moment +follows the Slater-Pauling behavior varying linearly between the -1 $\mu_B$ of +the perfect ScC and ScSi alloys and the +1 $\mu_B$ of the perfect VC and VSi +alloys. For the intermediate concentrations V and Sc atoms have antiparallel +spin magnetic moments and the compounds are half-metallic ferrimagnets. At the +critical concentration, both [Sc$_{0.5}$V$_{0.5}$]C and [Sc$_{0.5}$V$_{0.5}$]Si +alloys present zero total spin-magnetic moment but the C-based alloy shows a +semiconducting behavior contrary to the Si-based alloys which is a +half-metallic antiferromagnet.",0903.2331v1 +2009-04-24,Factorized ground state for a general class of ferrimagnets,"We have found the exact (factorized) ground state of a general class of +ferrimagnets in the presence of a magnetic field which covers the frustrated, +anisotropic and long range interactions for arbitrary dimensional space. In +particular cases, our model represents the bond-alternating, +ferromagnet-antiferromagnet and also homogeneous spin $s$ model. The factorized +ground state is a product of single particle kets on a bipartite lattice +composed of two different spins ($\rho, \sigma$). The spin waves analysis +around the exact ground state show two branch of excitations which is the +origin of two dynamics of the model. The signature of these dynamics is +addressed as a peak and a broaden bump in the specific heat.",0904.3843v3 +2009-06-18,Intrinsic exchange bias in Zn$_x$Mn$_{3-x}$O$_4$ ($x \leq 1$) solid solutions,"Bulk specimens of the hetaerolite solid solution Zn$_x$Mn$_{3-x}$O$_4$, with +$x$ = 0, 0.25, 0.5, 0.75, and 1 have been prepared as homogeneous, phase-pure +polycrystalline samples as ascertained by neutron diffraction measurements. +Samples with $x$ = 0.25, 0.5, and 0.75 exhibit shifted magnetic hysteresis +loops at low temperature, characteristic of exchange bias typically seen in +magnetic composites. We propose that the unusual magnetic behavior arises as a +result of a nanoscale mixture of ferrimagnetic and antiferromagnetic regions +that are distinct but lack long-range order. While some glassy behavior is seen +in AC magnetic measurements, its magnitude is not sufficient to account for the +observed dramatic exchange bias. Furthermore, isothermal and thermoremanent +magnetization measurements distinguish this material from a pure spin glass. +The title system offers insights into the alloying of a ferrimagnet Mn$_3$O$_4$ +with an antiferromagnet ZnMn$_2$O$_4$ wherein distinct magnetic clusters grow +and percolate to produce a smooth transition between competing orders.",0906.3534v2 +2009-06-26,Magnetic behavior of nanocrystalline ErCo2,"We have investigated the magnetic behavior of the nanocrystalline form of a +well-known Laves phase compound, ErCo2 - the bulk form of which has been known +to undergo an interesting first-order ferrimagnetic ordering near 32 K - +synthesized by high-energy ball-milling. It is found that, in these +nanocrystallites, Co exhibits ferromagnetic order at room temperature as +inferred from the magnetization data. However, the magnetic transition +temperature for Er sublattice remains essentially unaffected as though the +(Er)4f-Co(3d) coupling is weak on Er magnetism. The net magnetic moment as +measured at high fields, sat at 120 kOe, is significantly reduced with respect +to that for the bulk in the ferrimagnetically ordered state and possible +reasons are outlined. We have also compared the magnetocaloric behavior for the +bulk and the nano particles.",0906.4889v1 +2009-09-01,Directional Dichroism of X-Ray Absorption in a Polar Ferrimagnet GaFeO_3,"We study the directional dichroic absorption spectra in the x-ray region in a +polar ferrimagnet GaFeO_3. The directional dichroism on the absorption spectra +at the Fe pre-K-edge arises from the E1-E2 interference process through the +hybridization between the 4p and 3d states in the noncentrosymmetric +environment of Fe atoms. We perform a microscopic calculation of the spectra on +a model of FeO_6 with reasonable parameter values for Coulomb interaction and +hybridizations. We obtain the difference in the absorption coefficients when +the magnetic field is applied parallel and antiparallel to the c axis. The +spectra shus obtained have similar shapes to the experimental curves as a +function of photon energy in the Fe pre-K-edge region, although they have +opposite signs.",0909.0079v1 +2009-09-25,"Electrical, magnetic, magnetodielectric and magnetoabsorption studies in multiferroic GaFeO3","We report electrical, magnetic, magnetodielectric and magnetoabsorption +properties of a polycrystalline GaFeO3. The resistivity measurement shows that +the sample is highly insulating below 200 K and the resistivity above 200 K +obey the Arrhenius law with an activation energy of Ea = 0.67 eV. An anomaly +occurs in the temperature dependence of permittivity (e) near the ferrimagnetic +transition temperature (TC = 228 K) in a zero magnetic field and it is +suppressed under H = 60 mT which indicates a possible magnetoelectric coupling +in GaFeO3 with a fractional change of de/e = -1.8% at 60 mT around TC. The +coercivity (HC) of the sample increases dramatically with lowering temperature +below 200 K from 0.1 T at 200 K to 0.9 T at 5 K. Magnetoabsorption was studied +with a LC resonance technique and we found a close correlation between the +shift in the resonance frequency due to applied magnetic field and the coercive +field measured using dc magnetization measurements. Our results obtained with +multiple techniques suggest that GaFeO3 is an interesting ferrimagnet with +potential applications in future multiferroic devices.",0909.4609v1 +2009-10-02,Effect of strain on the stability and electronic properties of ferrimagnetic Fe$_{2-x}$Ti$_x$O$_3$ heterostructures from correlated band theory,"Based on density functional theory (DFT) calculations including an on-site +Hubbard $U$ term we investigate the effect of substrate-induced strain on the +properties of ferrimagnetic Fe$_2$O$_3$-FeTiO$_3$ solid solutions and +heterostructures. While the charge compensation mechanism through formation of +a mixed \fetw, \feth-contact layer is unaffected, strain can be used to tune +the electronic properties of the system, e.g. by changing the position of +impurity levels in the band gap. Straining hematite/ilmenite films at the +lateral parameters of Al$_{2}$O$_{3}$(0001), commonly used as a substrate, is +found to be energetically unfavorable as compared to films on +Fe$_{2}$O$_{3}$(0001) or FeTiO$_{3}$(0001)-substrates.",0910.0422v1 +2009-10-31,Compensation temperature of 3d mixed ferro-ferrimagnetic ternary alloy,"In this study, we have considered the three dimensional mixed +ferro-ferrimagnetic ternary alloy model of the type AB$_{p}$C$_{1-p}$ where the +A and X (X=B or C) ions are alternately connected and have different Ising +spins S$^{A}$=3/2, S$^{B}$=1 and S$^{C}$=5/2, respectively. We have +investigated the dependence of the critical and compensation temperatures of +the model on concentration and interaction parameters by using MC simulation +method. We have shown that the behavior of the critical temperature and the +existence of compensation points strongly depend on interaction and +concentration parameters. In particular, we have found that the critical +temperature of the model is independent on concentration of different types of +spins at a special interaction value and the model has one or two compensation +temperature points in a certain range of values of the concentration of the +different spins.",0911.0078v1 +2009-11-06,Frustrated spin ladder with alternating spin-1 and spin-1/2 rungs,"We study the impact of the diagonal frustrating couplings on the quantum +phase diagram of a two-leg ladder composed of alternating spin-1 and spin-1/2 +rungs. As the coupling strength is increased the system successively exhibits +two gapped paramagnetic phases (a rung-singlet and a Haldane-like +non-degenerate states) and two ferrimagnetic phases with different +ferromagnetic moments per rung. The first two states are similar to the phases +studied in the frustrated spin-1/2 ladder, whereas the magnetic phases appear +as a result of the mixed-spin structure of the model. A detailed +characterization of these phases is presented using density-matrix +renormalization-group calculations, exact diagonalizations of periodic +clusters, and an effective Hamiltonian approach inspired by the analysis of +numerical data. The present theoretical study was motivated by the recent +synthesis of the quasi-one-dimensional ferrimagnetic material +Fe$^{II}$Fe$^{III}$ (trans-1,4-cyclohexanedicarboxylate) exhibiting a similar +ladder structure.",0911.1216v2 +2010-02-01,Crystal and electronic structure of the room temperature organometallic ferrimagnet V(TCNE)$_2$. Analysis of numerical DoS and magnetic properties as related to orbital and spin-Hamiltonian models,"We present a detailed analysis of the results of our numerical study of the +crystal and electronic structure of the room temperature organometallic +ferrimagnet of general composition V(TCNE)$_{x}$ with $% x\approx 2$. The +results of the LSDA+$U$ study show that the experimentally determined structure +complies with the magnetic measurements and thus can serve as a prototype +structure for the entire family of the M(TCNE)$_{2}$ organometallic magnets. +The results of the numerical study and of the magnetic experiments are +interpreted using model Hamiltonians proposed here. This allowed us to obtain +estimates of the critical temperature in three- and two-dimensional regimes and +to give an explanation of the differences in behavior of probably isostructural +V(TCNE)$_{2}$ and Fe(TCNE)$_{2}$ species.",1002.0236v1 +2010-07-12,Second harmonic generation in a polar ferrimagnet GaFeO3,"We have studied second harmonic generation (SHG) in a polar ferrimagnet +GaFeO_3, employing a FeO_6 cluster model in which the Fe atom is slightly +shifted from the center of the octahedron. The electric-dipole transition could +take place between the 3d states through the effective hybridization of the 4p +states with the 3d states, due to the breaking of the space-inversion symmetry. +In the third-order perturbation with H_{int} = -(j.A)/c, we calculate the +probability per unit time, I_{\eta aa}, for the process that two photons are +absorbed with polarization parallel to the $a$ axis and one photon is emitted +with polarization parallel to the \eta (=a,b,c) axis. The calculated SHG +intensities consist of several peaks as a function of two-photon energy in +agreement with the experiments. It is found that the corresponding amplitude +S_{aaa} at each Fe site changes its sign while S_{baa} remains the same with +the reversal of the direction of the local magnetic moment. This implies that +I_{aaa} would disappear while I_{baa} would survive in the paramagnetic phase +in accordance with the experiment.",1007.1856v1 +2010-08-03,Electrical spin injection from an organic-based ferrimagnet in a hybrid organic/inorganic heterostructure,"We report the successful extraction of spin polarized current from the +organic-based room temperature ferrimagnetic semiconductor V[TCNE]x (x~2, TCNE: +tetracyanoethylene; TC ~ 400 K, EG ~ 0.5 eV, s ~ 10-2 S/cm) and its subsequent +injection into a GaAs/AlGaAs light-emitting diode (LED). The spin current +tracks the magnetization of V[TCNE]x~2, is weakly temperature dependent, and +exhibits heavy hole / light hole asymmetry. This result has implications for +room temperature spintronics and the use of inorganic materials to probe spin +physics in organic and molecular systems.",1008.0675v2 +2010-08-11,Ferrimagnetism of the magnetoelectric compound Cu$_2$OSeO$_3$ probed by $^{77}$Se NMR,"We present a thorough $^{77}$Se NMR study of a single crystal of the +magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the +local electronic moments extracted from the NMR data is fully consistent with a +magnetic phase transition from the high-T paramagnetic phase to a low-T +ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4 +aligned antiparallel to the applied field of 14.09 T. The transition to this +3up-1down magnetic state is not accompanied by any splitting of the NMR lines +or any abrupt modification in their broadening, hence there is no observable +reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3 +space group. These results are in agreement with high resolution x-ray +diffraction and magnetization data on powder samples reported previously by Bos +{\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean +field theory description of the problem based on a microscopic spin Hamiltonian +with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic +($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction.",1008.2010v1 +2011-01-31,Complex room temperature ferrimagnetism induced by zigzag oxygen-vacancy stripes in Sr3YCo4O10.72,"The high temperature ferromagnetism in Sr3YCo4O10+delta perovskite, whose +origin has been the subject of a considerable debate, has been studied by +neutron powder diffraction and synchrotron X-ray diffraction measurements. +Oxygen vacancy ordering creates a complex pattern of zigzag stripes in the +oxygen-deficient CoO4+delta layers, where the Co ions are found in three +distinct coordinations. The symmetry of this unprecedented structural +modulation, in conjunction with the existence of different Co spin states, +provide a straightforward explanation for the appearance of ferrimagnetism. A +model for the magnetic structure compatible with these structural features is +proposed, based on the refinement of powder neutron data. The macroscopic +moment as a function of temperature that can be calculated from the values of +the ordered spins extracted from refinements, is in excellent agreement with +bulk magnetization. Unlike previous models, a collinear G-type magnetic +structure with uncompensated moments due to distinct spin-states of Co imposed +by different coordination is found.",1101.5943v1 +2011-06-20,Magnetic Order of the Hexagonal Rare Earth Manganite Dy(0.5)Y(0.5)MnO3,"Hexagonal Dy(0.5)Y(0.5)MnO3, a multiferroic rare-earth manganite with +geometrically frustrated antiferromagnetism, has been investigated with +single-crystal neutron diffraction measurements. Below 3.4 K magnetic order is +observed on both the Mn (antiferromagnetic) and Dy (ferrimagnetic) sublattices +that is identical to that of undiluted hexagonal DyMnO3 at low temperature. The +Mn moments undergo a spin reorientation transition between 3.4 K and 10 K, with +antiferromagnetic order of the Mn sublattice persisting up to 70 K; the +antiferromagnetic order in this phase is distinct from that observed in +undiluted (h)DyMnO3, yielding a qualitatively new phase diagram not seen in +other hexagonal rare-earth manganites. A magnetic field applied parallel to the +crystallographic c axis will drive a transition from the antiferromagnetic +phase into the low-temperature ferrimagnetic phase with little hysteresis.",1106.3966v2 +2011-07-05,Theory of Half-metallic Ferrimagnetism in Double Perovskites,"We present a comprehensive theory of the temperature- and disorder-dependence +of half-metallic ferrimagnetism in the double perovskite Sr$_2$FeMoO$_6$ (SFMO) +with $T_c$ above room temperature. We show that the magnetization $M(T)$ and +conduction electron polarization $P(T)$ are both proportional to the +magnetization $M_S(T)$ of localized Fe spins. We derive and validate an +effective spin Hamiltonian, amenable to large-scale three-dimensional +simulations. We show how $M(T)$ and $T_c$ are affected by disorder, ubiquitous +in these materials. We suggest a way to enhance $T_c$ in SFMO without +sacrificing polarization.",1107.0983v2 +2011-07-29,Ferrimagnetism and spontaneous ordering of transition-metals in La2CrFeO6 double-perovskite films,"We report on atomic ordering of B-site transition-metals and magnetic +properties of epitaxial La2CrFeO6 double-perovskite films grown by pulsed-laser +deposition under various conditions. The highest ordered sample exhibited a +fraction of antisite-disorder of only 0.05 and a saturation magnetization of +~2\mu_{B} per formula unit at 5 K. The result is consistent with the +antiferromagnetic ordering of local spin moment +(3d^{3}_{\downarrow}3d^{5}_{\uparrow}; S = -3/2+5/2 = 1). Therefore, the +magnetic ground state of La2CrFeO6 double-perovskite that has been long debate +is unambiguously revealed to be ferrimagnetic. Our results present a wide +opportunity to explore novel magnetic properties of binary transition-metal +perovskites upon epitaxial stabilization of the ordered phase.",1107.5891v1 +2011-09-01,Unusual giant magnetostriction in the ferrimagnet Gd$_{2/3}$Ca$_{1/3}$MnO$_3$,"We report an unusual giant linear magnetostrictive effect in the ferrimagnet +Gd$_{2/3}$Ca$_{1/3}$MnO$_3$ ($T_{c} \approx$80 K). Remarkably, the +magnetostriction, negative at high temperature ($T \approx T_{c}$), becomes +positive below 15 K when the magnetization of the Gd sublattice overcomes the +magnetization of the Mn sublattice. A rather simple model where the magnetic +energy competes against the elastic energy gives a good account of the observed +results and confirms that Gd plays a crucial role in this unusual observation. +Unlike previous works in manganites where only striction associated with 3$d$ +Mn orbitals is considered, our results show that the lanthanide 4$f$ orbitals +related striction can be very important too and it cannot be disregarded.",1109.0259v2 +2011-10-20,Magnetism in nanometer-thick magnetite,"The oldest known magnetic material, magnetite, is of current interest for use +in spintronics as a thin film. An open question is how thin can magnetite films +be and still retain the robust ferrimagnetism required for many applications. +We have grown one-nanometer-thick magnetite crystals and characterized them in +situ by electron and photoelectron microscopies including selected-area x-ray +circular dichroism. Well-defined magnetic patterns are observed in individual +nano-crystals up to at least 520 K, establishing the retention of +ferrimagnetism in magnetite two-unit-cells thick.",1110.4568v1 +2012-03-13,Magnetic ground state and 2D behavior in pseudo-Kagome layered system Cu3Bi(SeO3)2O2Br,"Anisotropic magnetic properties of a layered kagome-like system +Cu3Bi(SeO3)2O2Br have been studied by bulk magnetization and magnetic +susceptibility measurements as well as powder and single-crystal neutron +diffraction. At T_N = 27.4 K the system develops an alternating +antiferromagnetic order of (ab) layers, which individually exhibit canted +ferrimagnetic moment arrangement, resulting from the competing ferro- and +antiferro-magnetic intralayer exchange interactions. A magnetic field B_C ~ 0.8 +T applied along the c axis (perpendicular to the layers) triggers a +metamagnetic transition, when every second layer flips, i.e., resulting in a +ferrimagnetic structure. Significantly higher fields are required to rotate the +ferromagnetic component towards the b axis (~7 T) or towards the a axis (~15 +T). The estimates of the exchange coupling constants and features indicative of +an XY character of this quasi-2D system are presented.",1203.2782v2 +2012-03-16,Universal low-temperature tricritical point in metallic ferromagnets and ferrimagnets,"An earlier theory of the quantum phase transition in metallic ferromagnets is +revisited and generalized in three ways. It is shown that the mechanism that +leads to a fluctuation-induced first-order transition in metallic ferromagnets +with a low Curie temperature is valid, (1) irrespective of whether the magnetic +moments are supplied by the conduction electrons or by electrons in another +band, (2) for ferromagnets in the XY and Ising universality classes as well as +for Heisenberg ferromagnets, and (3) for ferrimagnets as well as for +ferromagnets. This vastly expands the class of materials for which a +first-order transition at low temperatures is expected, and it explains why +strongly anisotropic ferromagnets, such as UGe2, display a first-order +transition as well as Heisenberg magnets.",1203.3826v1 +2012-03-20,Is the Yb2Ti2O7 pyrochlore a quantum spin ice?,"We use numerical linked cluster (NLC) expansions to compute the specific +heat, C(T), and entropy, S(T), of a quantum spin ice model of Yb2Ti2O7 using +anisotropic exchange interactions recently determined from inelastic neutron +scattering measurements and find good agreement with experimental calorimetric +data. In the perturbative weak quantum regime, this model has a ferrimagnetic +ordered ground state, with two peaks in C(T): a Schottky anomaly signalling the +paramagnetic to spin ice crossover followed at lower temperature by a sharp +peak accompanying a first order phase transition to the ferrimagnetic state. We +suggest that the two C(T) features observed in Yb2Ti2O7 are associated with the +same physics. Spin excitations in this regime consist of weakly confined +spinon-antispinon pairs. We suggest that conventional ground state with exotic +quantum dynamics will prove a prevalent characteristic of many real quantum +spin ice materials.",1203.4569v1 +2012-06-28,Frequency and power dependence of spin-current emission by spin pumping in a thin film YIG/Pt system,"This paper presents the frequency dependence of the spin current emission in +a hybrid ferrimagnetic insulator/normal metal system. The system is based on a +ferrimagnetic insulating thin film of Yttrium Iron Garnet (YIG, 200 nm) grown +by liquid-phase-epitaxy (LPE) coupled with a normal metal with a strong +spin-orbit coupling (Pt, 15 nm). The YIG layer presents an isotropic behaviour +of the magnetization in the plane, a small linewidth, and a roughness lower +than 0.4 nm. Here we discuss how the voltage signal from the spin current +detector depends on the frequency [0.6 - 7 GHz], the microwave power, Pin, [1 - +70 mW], and the in-plane static magnetic field. A strong enhancement of the +spin current emission is observed at low frequencies, showing the appearance of +non-linear phenomena.",1206.6671v2 +2012-06-28,Reentrant phase transitions and multicompensation points in the mixed-spin Ising ferrimagnet on a decorated Bethe lattice,"Mixed-spin Ising model on a decorated Bethe lattice is rigorously solved by +combining the decoration-iteration transformation with the method of exact +recursion relations. Exact results for critical lines, compensation +temperatures, total and sublattice magnetizations are obtained from a precise +mapping relationship with the corresponding spin-1/2 Ising model on a simple +(undecorated) Bethe lattice. The effect of next-nearest-neighbour interaction +and single-ion anisotropy on magnetic properties of the ferrimagnetic model is +investigated in particular. It is shown that the total magnetization may +exhibit multicompensation phenomenon and the critical temperature vs. the +single-ion anisotropy dependence basically changes with the coordination number +of the underlying Bethe lattice. The possibility of observing reentrant phase +transitions is related to a high enough coordination number of the underlying +Bethe lattice.",1206.6684v1 +2012-07-21,"Quantum phase transitions in alternating spin-(1/2, 5/2) Heisenberg chains","The ground state spin-wave excitations and thermodynamic properties of two +types of ferrimagnetic chains are investigated: the alternating spin-1/2 +spin-5/2 chain and a similar chain with a spin-1/2 pendant attached to the +spin-5/2 site. Results for magnetic susceptibility, magnetization and specific +heat are obtained through the finite-temperature Lanczos method with the aim in +describing available experimental data, as well as comparison with theoretical +results from the semiclassical approximation and the low-temperature +susceptibility expansion derived from Takahashi's modified spin-wave theory. In +particular, we study in detail the temperature vs. magnetic field phase diagram +of the spin-1/2 spin-5/2 chain, in which several low-temperature quantum phases +are identified: the Luttinger Liquid phase, the ferrimagnetic plateau and the +fully polarized one, and the respective quantum critical points and crossover +lines.",1207.5084v1 +2012-10-13,Promising ferrimagnetic double perovskite oxides towards high spin polarization at high temperature,"We predict through our first-principles calculations that four double +perovskite oxides of Bi2ABO6 (AB = FeMo, MnMo, MnOs, CrOs) are half-metallic +ferrimagnets. Our calculated results shows that the four optimized structures +have negative formation energy, from -0.42 to -0.26 eV per formula unit, which +implies that they could probably be realized. In the case of Bi2FeMoO6, the +half-metallic gap and Curie temperature are predicted to reach to 0.71 eV and +650 K, respectively, which indicates that high spin polarization could be kept +at high temperatures far beyond room temperature. It is believed that some of +them could be synthesized soon and would prove useful for spintronic +applications.",1210.3706v2 +2012-10-16,Mn$_2$FeSbO$_6$: a ferrimagnetic ilmenite and an antiferromagnetic perovskite,"Due of its polymorphism, Mn$_2$FeSbO$_6$ can be synthesized at high pressures +and temperatures as a ferrimagnetic ilmenite or an antiferromagnetic +perovskite. The structural phase transformation is discussed in detail, and +magnetic structures are proposed for both phases. The high-pressure +Mn$_2$FeSbO$_6$ polymorph is a rare example of $A_2 B'B""$O$_6$ perovskite with +solely Mn cations on the $A$-site. Fe and Sb cations are ordered on the +$B$-sites. Theoretical calculations for the perovskite phase suggest a complex +magnetic structure, holding an electronic polarization.",1210.4368v2 +2012-12-21,Phase diagram of a mixed spin-1 and spin-3/2 Ising ferrimagnet,"Critical and compensation properties of a mixed spin-1 and spin-3/2 Ising +ferrimagnet on a square lattice are investigated by standard and histogram +Monte Carlo simulations. The critical temperature is studied as a function of a +single-ion anisotropy strength. The second order of the phase transition is +established by finite-size scaling for the entire boundary. Some previously +obtained results, such as a tricritical point, predicted by the mean field +theory (MFT) and effective field theory (EFT), or a first-order transition line +separating two different ordered phases, obtained by the cluster variational +theory (CVT), are deemed artifacts of the respective approximations. So is a +reentrant phenomenon produced by CVT. Nevertheless, the multicompensation +behavior predicted by MFT and EFT was confirmed.",1212.5471v1 +2012-12-25,"Magnetic properties, Lyapunov exponent and superstability of the spin-1/2 Ising-Heisenberg model on diamond chain","The exactly solvable spin-1/2 Ising-Heisenberg model on diamond chain has +been considered. We have found the exact results for the magnetization by using +recursion relation method. The existence of the magnetization plateau has been +observed at one third of the saturation magnetization in the antiferromagnetic +case. Some ground-state properties of the model are examined. At low +temperatures, the system has two ferrimagnetic (FRI1 and FRI2) phases and one +paramagnetic (PRM) phase. Lyapunov exponents for the various values of the +exchange parameters and temperatures have been analyzed. It have also been +shown that the maximal Lyapunov exponent exhibits plateau. Lyapunov exponents +exhibit different behavior for two ferrimagnetic phases. We have found the +existence of the supercritical point for the multi-dimensional rational mapping +of the spin-1/2 Ising-Heisenberg model on diamond chain for the first time at +absence of the external magnetic field and $T \rightarrow 0$ in the +antiferromagnetic case.",1212.6008v1 +2013-01-11,Spin-filtering efficiency of ferrimagnetic spinels CoFe2O4 and NiFe2O4,"We assess the potential of the ferrimagnetic spinel ferrites CoFe2O4 and +NiFe2O4 to act as spin filtering barriers in magnetic tunnel junctions. Our +study is based on the electronic structure calculated by means of +first-principles density functional theory within different approximations for +the exchange correlation energy. We show that, in agreement with previous +calculations, the densities of states suggest a lower tunneling barrier for +minority spin electrons, and thus a negative spin-filter effect. However, a +more detailed analysis based on the complex band-structure reveals that both +signs for the spin-filtering efficiency are possible, depending on the band +alignment between the electrode and the barrier materials and depending on the +specific wave-function symmetry of the relevant bands within the electrode.",1301.2541v1 +2013-01-30,Thermally driven spin and charge currents in thin NiFe2O4/Pt films,"We present results on the longitudinal spin Seebeck effect (LSSE) shown by +semiconducting ferrimagnetic NiFe2O4/Pt films from room temperature down to 50K +base temperature. To the best of our knowledge, this is the first observation +of spin caloric effect in NiFe2O4 thin films. The temperature dependence of the +conductivity has been studied in parallel to obtain information about the +origin of the electric potentials detected at the Pt coverage of the +ferrimagnet in order to distinguish the LSSE from the anomalous Nernst effect. +Furthermore, the dependence of the LSSE on temperature gradients as well as the +influence of an external magnetic field direction is investigated.",1301.7313v1 +2013-02-11,Phase stability of chromium based compensated ferrimagnets with inverse Heusler structure,"Chromium based inverse Heusler compounds of the type Cr2YZ (Y=Co, Fe; Z=Al, +Ga, In, Si, Ge, Sn) have been proposed as fully compensated half-metallic +ferrimagnets. Such materials are of large interest for spintronics because they +combine small magnetic moment with high spin polarization over a wide +temperature range. We assess their thermodynamic stability by their formation +enthalpies obtained from density functional theory calculations. All compounds +under investigation are unstable. Cr2FeSi and Cr2CoAl are stable with respect +to the elemental constituents, but decompose into binary phases. Cr2FeGe, +Cr2CoGa, Cr2FeSn and Cr2CoIn are found to be unstable with respect to their +elemental constituents. We identify possible binary decompositions.",1302.2487v2 +2013-02-21,Large zero-field cooled exchange-bias in bulk Mn2PtGa,"We report a large exchange-bias (EB) effect after zero-field cooling the new +tetragonal Heusler compound Mn2PtGa from the paramagnetic state. The +first-principle calculation and the magnetic measurements reveal that Mn2PtGa +orders ferrimagnetically with some ferromagnetic (FM) inclusions. We show that +ferrimagnetic (FI) ordering is essential to isothermally induce the exchange +anisotropy needed for the zero-field cooled (ZFC) EB during the virgin +magnetization process. The complex magnetic behavior at low temperatures is +characterized by the coexistence of a field induced irreversible magnetic +behavior and a spin-glass-like phase. The field induced irreversibility +originates from an unusual first-order FI to antiferromagnetic transition, +whereas, the spin-glass like state forms due to the existence of anti-site +disorder intrinsic to the material.",1302.5229v1 +2013-04-16,Kinetic arrest related to a first-order ferrimagnetic to antiferromagnetic transition in the Heusler compound Mn2PtGa,"We report a magnetization study of the Heusler compound Mn2PtGa that shows +the existence of a magnetic-glass state. Mn2PtGa shows a first-order +ferromagnetic (FM)/ferrimagnetic (FI) to antiferromagnetic (AFM) transition in +contrast to the martensitic structural transition observed in several Heusler +alloys. The kinetic arrest of this first-order FM (FI) to AFM transition leads +to the observed magnetic-glass behavior. We show that the strength of the +applied magnetic field, which is the primary parameter to induce the +magnetic-glass state, is also responsible for the stability of the supercooled +FM (FI) phase in time.",1304.4459v1 +2013-04-29,The Mixed Spin 3 - Spin 3/2 Ferrimagnetic Ising Model on Cellular Automaton,"The mixed spin 3- spin 3/2 Ising model has been simulated using cooling +algorithm on cellular automaton (CA). The simulations have been made in the +interval -6<=D<=6 for J=1 for the square lattices with periodic boundary +conditions. The ground state phase diagram of the model has different type +ferrimagnetic orderings. Through D/J=2 line, compensation points occurs at +kT/J=0. The values of the critical exponents ( {\nu}, {\alpha}, {\beta} and +{\gamma}) are estimated within the framework of the finite-size scaling theory +and power law relations for selected D/J values (-2, 0, 1, 2 and 4). The +estimated critical exponent values are in a good agreement with their universal +values of the two dimensional Ising model.",1304.7740v3 +2013-06-17,Tailoring the ground state of the ferrimagnet La2Ni(Ni1/3Sb2/3)O6,"We report on the magnetic and structural properties of La2Ni(Ni1/3Sb2/3)O6 in +polycrystal, single crystal and thin film samples. We found that this material +is a ferrimagnet (Tc ~ 100 K) which possesses a very distinctive and uncommon +feature in its virgin curve of the hysteresis loops. We observe that bellow 20 +K it lies outside the hysteresis cycle, and this feature was found to be an +indication of a microscopically irreversible process possibly involving the +interplay of competing antiferromagnetic interactions that hinder the initial +movement of domain walls. This initial magnetic state is overcome by applying a +temperature dependent characteristic field. Above this field, an isothermal +magnetic demagnetization of the samples yield a ground state different from the +initial thermally demagnetized one.",1306.3894v1 +2013-10-31,Ground-State Phase Diagram of S=2 Heisenberg Chains with Alternating Single-Site Anisotropy,"The ground-state phase diagram of $S=2$ antiferromagnetic Heisenberg chains +with coexisting uniform and alternating single-site anisotropies is +investigated by the numerical exact diagonalization and density matrix +renormalization group methods. We find the Haldane, large-$D$, N\'eel, +period-doubled N\'eel, gapless spin fluid, quantized and partial ferrimagnetic +phases. The Haldane phase is limited to the close neighborhood of the isotropic +point. Within numerical accuracy, the transition from the gapless spin-fluid +phase to the period-doubled N\'eel phase is a direct transition. Nevertheless, +the presence of a narrow spin-gap phase between these two phases is suggested +on the basis of the low-energy effective theory. The ferrimagnetic ground state +is present in a wide parameter range. This suggests the realization of +magnetized single-chain magnets with a uniform spin magnitude by controlling +the environment of each magnetic ion without introducing ferromagnetic +interactions.",1310.8586v2 +2013-11-13,Exchange bias up to room temperature in the antiferromagnetic bulk hexagonal Mn3Ge,"This work reports an exchange bias (EB) effect up to room temperature in the +binary intermetallic bulk compound Mn3.04Ge0.96. The sample annealed at 700 K +crystallizes in a tetragonal structure with ferromagnetic ordering, whereas, +the sample annealed at 1073 K crystallizes in a hexagonal structure with +antiferromagnetic ordering. The hexagonal Mn3.04Ge0.96 sample exhibits an EB of +around 70 mT at 2 K that continues with a non-zero value up to room +temperature. The exchange anisotropy is proposed to be originating from the +exchange interaction between the triangular antiferromagnetic host and the +embedded ferrimagnetic like clusters. The ferrimagnetic clusters develop when +excess Mn atoms occupy empty Ge sites in the original triangular +antiferromagnet structure of Mn3Ge.",1311.3067v1 +2013-11-14,Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source,"Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic +model consisting of spin-1/2 and spin-3/2 on a square lattice under the +existence of a time dependent oscillating magnetic field have been investigated +by making use of Monte Carlo simulations with single-spin flip Metropolis +algorithm. A complete picture of dynamic phase boundary and magnetization +profiles have been illustrated and the conditions of a dynamic compensation +behavior have been discussed in detail. According to our simulation results, +the considered system does not point out a dynamic compensation behavior, when +it only includes the nearest-neighbor interaction, single-ion anisotropy and an +oscillating magnetic field source. As the next-nearest-neighbor interaction +between the spins-1/2 takes into account and exceeds a characteristic value +which sensitively depends upon values of single-ion anisotropy and only of +amplitude of external magnetic field, a dynamic compensation behavior occurs in +the system. Finally, it is reported that it has not been found any evidence of +dynamically first-order phase transition between dynamically ordered and +disordered phases, which conflicts with the recently published molecular field +investigation, for a wide range of selected system parameters.",1311.3537v2 +2013-12-12,Exact results for a generalized spin-1/2 Ising-Heisenberg diamond chain with the second-neighbor interaction between nodal spins,"The ground state and thermodynamics of a generalized spin-1/2 +Ising-Heisenberg diamond chain with the second-neighbor interaction between +nodal spins are calculated exactly using the mapping method based on the +decoration-iteration transformation. Rigorous results for the magnetization, +susceptibility, and heat capacity are investigated in dependence on temperature +and magnetic field for the frustrated diamond spin chain with the +antiferromagnetic Ising and Heisenberg interactions. It is demonstrated that +the second-neighbor interaction between nodal spins gives rise to a greater +diversity of low-temperature magnetization curves, which may include an +intermediate plateau at two-third of the saturation magnetization related to +the classical ferrimagnetic (up-up-up-down-up-up-...) ground state with +translationally broken symmetry besides an intermediate one-third magnetization +plateau reflecting the translationally invariant quantum ferrimagnetic +(monomer-dimer) spin arrangement.",1312.3439v1 +2014-04-28,High-Curie-temperature ferrimagnetism and ferroelectricity in Bi2FeMoO6,"BiFeO3 is the most famous multiferroic material, but its G-type +antiferromagnetism is highly desirable to be replaced by strong macroscopic +magnetism beyond room temperature. Here we obtain double perovskite Bi2FeMoO6 +with R3 (#146) space group by substituting Mo for 50% Fe in BiFeO3. Our +first-principles calculated results show that it is a semiconductor with gap +reaching to 0.725 eV, its net magnetic moment is 2\mu_B per formula unit, and +its ferroelectric polarization is 85\mu C/cm^2. This ferroelctricity is +comparable with that of BiFeO3, but here the magnetism is a strong +ferrimagnetism with Curie temperature of 650 K. Our first-principles phonon +spectra establishes that this R3 phase is stable. Electric polarization and +magnetic easy axis are shown to be in pseudo-cubic [111] axis. Our further +analysis shows that the multiferroic mechanism is similar to that in BiFeO3. +Therefore, this Bi2FeMoO6 can be used to achieve strong macroscopic magnetism +and ferroelectricity well above room temperature, being useful for designing +new multifunctional materials and devices.",1404.7058v2 +2014-08-08,Half Metal Transition Driven by Doping Effects in Osmium Double Perovskite,"Using the first-principles density functional approach, we investigate +Ca$_2$FeOsO$_6$, a material of double perovskite structure synthesized +recently. According to the calculations, Ca$_2$FeOsO$_6$ is a ferrimagnetic +Mott-insulator influenced by the cooperative effect of spin-orbit coupling +(SOC) and Coulomb interactions of Fe-3$d$ and Os-5$d$ electrons, as well as the +crystal field. When Fe is replaced with Ni, the system exhibits half metallic +(HM) states desirable for spintronic applications. In +[Ca$_2$Fe$_{1-x}$Ni$_x$OsO$_6$]$_2$, HM ferrimagnetism is observed with +$\mu_{\rm tot}=2\mu_{\rm B}$ per unit cell for doping rate $x=0.5$, whereas HM +antiferromagnetism (HMAFM) with nearly zero spin magnetization in the unit cell +for $x=1$, respectively. It is emphasized that half metallicity is retained +even with SOC effect due to the large exchange-splitting between spin-up and +spin-down bands close to the Fermi level.",1408.1771v1 +2014-10-16,"Understanding the Magnetic Puzzles of Double Perovskites A2FeOsO6 (A=Ca, Sr)","Double perovskites Sr2FeOsO6 and Ca2FeOsO6 show puzzling magnetic properties, +the former a low-temperature antiferromagnet while the later a high-temperature +insulating ferrimagnet. Here, in order to understand the underlying mechanism, +we have investigated the frustrated magnetism of A2FeOsO6 by employing density +functional theory and maximally-localized Wannier functions. We find that +lattice distortion enhances the antiferromagnetic nearest-neighboring Fe-O-Os +interaction but weakens the antiferromagnetic interactions through the +Os-O-O-Os and Fe-O-Os-O-Fe paths, which is responsible for the magnetic +transition from the low-temperature antiferromagnetism to the high-temperature +ferrimagnetism with the decrease of the radius of the A2+ ions. We also discuss +the 5d3-3d5 superexchange and propose such superexchange is intrinsically +antiferromagnetic instead of the expected ferromagnetic. Our work illustrate +that the magnetic frustration can be effectively relieved by lattice +distortion, which provides another dimension to tune the complex magnetism in +other 3d-5d (4d) double perovskites.",1410.4280v1 +2014-10-16,Vigorous thermal excitations in a double-tetrahedral chain of localized Ising spins and mobile electrons mimic a temperature-driven first-order phase transition,"A hybrid spin-electron system defined on one-dimensional double-tetrahedral +chain, in which the localized Ising spin regularly alternates with two mobile +electrons delocalized over a triangular plaquette, is exactly solved with the +help of generalized decoration-iteration transformation. It is shown that a +macroscopic degeneracy of ferromagnetic and ferrimagnetic ground states arising +from chiral degrees of freedom of the mobile electrons cannot be lifted by a +magnetic field in contrast to a macroscopic degeneracy of the frustrated ground +state, which appears owing to a kinetically-driven frustration of the localized +Ising spins. An anomalous behavior of all basic thermodynamic quantities can be +observed on account of massive thermal excitations, which mimic a +temperature-driven first-order phase transition from the non-degenerate +frustrated state to the highly degenerate ferrimagnetic state at non-zero +magnetic fields. A substantial difference in the respective degeneracies is +responsible for an immense low-temperature peak of the specific heat and very +abrupt (almost discontinuous) thermal variations of the entropy and sublattice +magnetizations.",1410.4313v2 +2014-10-31,Enhanced ferrimagnetism in auxetic NiFe2O4 in the crossover to the ultrathin film limit,"We investigate the sensitive interplay between magnetic, electronic and +structural properties in the ferrimagnetic oxide NiFe2O4. Emphasis is placed on +the impact of reduced dimensionality in the crossover from bulk-like to +ultrathin films. We observed an enhanced saturation magnetization $M_S$ for +ultrathin NiFe2O4 films on Nb-SrTiO3 (001) substrates that co-occurs with a +reduced out-of-plane lattice constant under compressive in-plane epitaxial +strain. We found a bulk-like cationic coordination of the inverse spinel +lattice independent of the NiFe2O4 film thickness -- thus ruling out a cationic +inversion that nominally could account for an enhanced $M_S$. Our study instead +uncovers a reduction of the unit cell volume, i.e. an auxetic behavior in +ultrathin NiFe2O4 films, which may result in an enhanced magnetic exchange +caused by an increased interatomic electronic localization.",1410.8782v1 +2014-12-01,All-optical magnetization switching in ferrimagnetic alloys: deterministic vs thermally activated dynamics,"Using photo-emission electron microscopy with X-ray magnetic circular +dichroism as a contrast mechanism, new insights into the all-optical +magnetization switching (AOS) phenomenon in GdFe based rare-earth transition +metal ferrimagnetic alloys are provided. From a sequence of static images taken +after single linearly polarized laser pulse excitation, the repeatability of +AOS can be measured with a correlation coefficient. It is found that low +coercivity enables thermally activated domain wall motion, limiting in turn the +repeatability of the switching. Time-resolved measurement of the magnetization +dynamics reveal that while AOS occurs below and above the magnetization +compensation temperature $T_\text{M}$, it is not observed in GdFe samples where +$T_\text{M}$ is absent. Finally, AOS is experimentally demonstrated against an +applied magnetic field of up to 180 mT.",1412.0396v1 +2015-01-01,A hybrid-exchange density-functional theory study of the electronic structure of $\mathrm{MnV}_2\mathrm{O}_4$: Exotic orbital ordering in the cubic structure,"The electronic structures of the cubic and tetragonal +$\mathrm{MnV}_2\mathrm{O}_4$ have been studied by using hybrid-exchange density +functional theory. The computed electronic structure of the tetragonal phase +shows an anti-ferro orbital ordering on V sites and a ferrimagnetic ground +state (the spins on V and Mn are anti-aligned). These results are in a good +agreement with the previous theoretical result obtained from the local-density +approximation+$U$ methods [S. Sarkar, et. al., Phys. Rev. Lett. 102, 216405 +(2009)]. Moreover, the electronic structure, especially the projected density +of states of the cubic phase has been predicted with a good agreement with the +recent soft x-ray spectroscopy experiment. Similar to the tetragonal phase, the +spins on V and Mn in the cubic structure favour a ferrimagnetic configuration. +Most interesting is that the computed charge densities of the spin-carrying +orbitals on V in the cubic phase show an exotic orbital ordering, i.e., a +ferro-orbital ordering along [110] but an anti-ferro-orbital ordering along +[$\overline{1}$10].",1501.00322v4 +2015-02-19,"Ferrimagnetism in 2D networks of porphyrin-X and -XO (X=Sc,...,Zn) with acetylene bridges","Magnetism in 2D networks of the acetylene-bridged transition metal porphyrins +M(P)-2(C-C)-2 (denoted P-TM), and oxo-TM-porphyrins OM(P)-2(C-C)-2 (denoted +P-TMO), is studied with the density functional theory (DFT) and the +self-interaction corrected pseudopotential scheme (pSIC). Addition of oxygen +lowers magnetism of P-TMO with respect to the corresponding P-TM for most of +the first-half $3d$-row TMs. In contrast, binding O with the second-half +$3d$-row TMs or Sc increases the magnetic moments. Ferrimagnetism is found for +the porphyrin networks with the TMs from V to Co and also for these cases with +oxygen. This is a long-range effect of the delocalized spin-polarization, +extended even to the acetylene bridges.",1502.05738v3 +2015-02-20,Classical dipoles on the kagome lattice,"Motivated by recent developments in magnetic materials, frustrated nanoarrays +and cold atomic systems, we investigate the behaviour of dipolar spins on the +frustrated two-dimensional kagome lattice. By combining the Luttinger-Tisza +approach, numerical energy minimization, spin-wave analysis and parallel +tempering Monte-Carlo, we study long-range ordering and finite-temperature +phase transitions for a Hamiltonian containing both dipolar and +nearest-neighbor interactions. For both weak and moderate dipolar interactions, +the system enters a three-sublattice long-range ordered state, with each +triangle having vanishing dipole and quadrupole moments; while for dominating +dipolar interactions we uncover ferrimagnetic three-sublattice order. These are +also the ground states for XY spins. We discuss excitations of, as well as +phase transitions into, these states. We find behaviour consistent with Ising +criticality for the 120-degree state, while the ferrimagnetic state appears to +be associated with drifting exponents. The celebrated flat band of zero-energy +excitations of the kagome nearest-neighbour Heisenberg model is lifted to +finite energies but acquires only minimal dispersion as dipolar interactions +are added.",1502.05960v1 +2015-03-26,Enhancing Magnetic Ordering in Cr-doped Bi2Se3 using High-TC Ferrimagnetic Insulator,"We report a study of enhancing the magnetic ordering in a model magnetically +doped topological insulator (TI), Bi2-xCrxSe3, via the proximity effect using a +high-TC ferrimagnetic insulator Y3Fe5O12. The FMI provides the TI with a source +of exchange interaction yet without removing the nontrivial surface state. By +performing the elemental specific X-ray magnetic circular dichroism (XMCD) +measurements, we have unequivocally observed an enhanced TC of 50 K in this +magnetically doped TI/FMI heterostructure. We have also found a larger (6.6 nm +at 30 K) but faster decreasing (by 80% from 30 K to 50 K) penetration depth +compared to that of diluted ferromagnetic semiconductors (DMSs), which could +indicate a novel mechanism for the interaction between FMIs and the nontrivial +TIs surface.",1503.07893v1 +2015-04-08,Magnetic and nonmagnetic phases in doped AB2 t-J Hubbard chains,"We discuss the rich phase diagram of doped AB2 $t-J$ chains by using data +from density matrix renormalization group and exact diagonalization techniques. +The $J$ vs $\delta$ (hole doping) phase diagram exhibits regions of itinerant +ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, +phase separation, and Luttinger liquid (LL) physics. Several features are +highlighted, such as the modulated ferrimagnetic structure, the occurrence of +Nagaoka spin polarons in the underdoped regime and small values of $J=4t^2/U$, +where $t$ is the first-neighbor hopping amplitude and $U$ is the on-site +repulsive Coulomb interaction, incommensurate structures with nonzero +magnetization, and strong-coupling LL physics in the high-doped regime. We also +verify that relevant findings are in agreement with the corresponding findings +in square and n-leg ladder lattices. In particular, we mention the instability +of Nagaoka ferromagnetism against $J$ and $\delta$.",1504.01951v1 +2015-05-04,Magnetic phase diagram of the Hubbard model in the Lieb lattice,"We study the mean-field phase diagram of the repulsive Hubbard model in the +Lieb lattice. Far from half-filling, the most stable phases are paramagnetism +for low on-site interaction $U/t$ and ferromagnetism for high $U/t$, as in the +case of the mean-field phase diagram of the square lattice Hubbard model +obtained by Dzierzawa [\onlinecite{Dzierzawa1992}]. At half-filling, the ground +state was found to be ferrimagnetic [a $(\pi,\pi)$ spiral phase], in agreement +with a theorem by Lieb [\onlinecite{Lieb1989}]. The total magnetization +approaches Lieb's prediction as $U/t$ becomes large. As we move away from +half-filling, this ferrimagnetic phase becomes a $(q_1,q_1)$ spiral phase with +$q_1 \approx \pi$ and then undergoes a series of first-order phase transitions, +$(q_1,q_1) \rightarrow (q_1,q_2) \rightarrow (q_1,0)$, with $q_2 \approx +\pi/2$, before becoming ferromagnetic at large $U/t$ or paramagnetic at low +$U/t$.",1505.00578v1 +2015-06-04,Low-moment ferrimagnetic phase of the Heusler compound Cr2CoAl,"Synthesizing half-metallic fully-compensated ferrimagnets that form in the +inverse Heusler phase could lead to superior spintronic devices. These +materials would have high spin polarization at room temperature with very +little fringing magnetic fields. Previous theoretical studies indicated that +Cr2CoAl should form in a stable inverse Heusler lattice due to its low +activation energy. Here, stoichiometric Cr2CoAl samples were arc-melted and +annealed at varying temperatures, followed by studies of their structural and +magnetic properties. High-resolution synchrotron X-ray diffraction revealed a +chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray +magnetic circular dichroism revealed that the Cr and Co magnetic moments are +antiferromagnetically oriented leading to the observed low magnetic moment in +Cr2CoAl.",1506.01738v1 +2015-07-24,Unveiling hidden ferrimagnetism and giant magnetoelectricity in polar magnet Fe2Mo3O8,"Magnetoelectric (ME) effect is recognized for its utility for low-power +electronic devices.Largest ME coefficients are often associated with phase +transitions in which ferroelectricity is induced by magnetic order. +Unfortunately, in these systems, large ME response is revealed only upon +elaborate poling procedures. These procedures may become unnecessary in +single-polar-domain crystals of polar magnets. Here we report giant ME effects +in a polar magnet Fe2Mo3O8 at temperatures as high as 60 K.Polarization jumps +of 0.3 {\mu}C/cm2, and repeated mutual control of ferroelectric and magnetic +moments with differential ME coefficients on the order of 10$^4$ ps/m are +achieved.Importantly, no electric or magnetic poling is needed, as necessary +for applications.The sign of the ME coefficients can be switched by changing +the applied ""bias"" magnetic field. The observed effects are associated with a +hidden ferrimagnetic order unveiled by application of a magnetic field.",1507.06847v1 +2015-08-06,Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect,"Due to its transverse nature, spin Hall effects (SHE) provide the possibility +to excite and detect spin currents and magnetization dynamics even in magnetic +insulators. Magnetic insulators are outstanding materials for the investigation +of nonlinear phenomena and for novel low power spintronics applications because +of their extremely low Gilbert damping. Here, we report on the direct imaging +of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the +ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and +detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly +imaged by spatially-resolved microfocused Brillouin light scattering (BLS) +spectroscopy. Previously, ST-FMR experiments assumed a uniform precession +across the sample, which is not valid in our measurements. A strong spin-wave +localization in the center of the sample is observed indicating the formation +of a nonlinear, self-localized spin-wave `bullet'.",1508.01427v1 +2015-09-02,Effect of Chemical Pressure on High Temperature Ferrimagnetic Double Perovskites Sr2CrOsO6 and Ca2CrOsO6,"The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized +and characterized with neutron powder diffraction, electrical transport +measurements, and high field magnetization experiments. Sr2CrOsO6 and Ca2CrOsO6 +crystallize with R-3 and P21/n space group symmetry, respectively. Both +materials are found to be ferrimagnetic insulators with saturation +magnetizations near 0.2 {\mu}B. Sr2CrOsO6 orders at 660 K, showing +non-monotonic magnetization temperature dependence, while Ca2CrOsO6 orders at +490 K and does not show non-monotonic behavior. Evidence for a theoretically +predicted canted magnetic structure in Sr2CrOsO6 is sought and not found.",1509.00901v1 +2015-09-14,Ground-state phases of rung-alternated spin-1/2 Heisenberg ladder,"The ground-state phase diagram of Heisenberg spin-1/2 system on a two-leg +ladder with rung alternation is studied by combining analytical approaches with +numerical simulations. For the case of ferromagnetic leg exchanges a unique +ferrimagnetic ground state emerges, whereas for the case of antiferromagnetic +leg exchanges several different ground states are stabilized depending on the +ratio between exchanges along legs and rungs. For the more general case of a +honeycomb-ladder model for the case of ferromagnetic leg exchanges besides +usual rung-singlet and saturated ferromagnetic states we obtain a ferrimagnetic +Luttinger liquid phase with both linear and quadratic low energy dispersions +and ground state magnetization continuously changing with system parameters. +For the case of antiferromagnetic exchanges along legs, different dimerized +states including states with additional topological order are suggested to be +realized.",1509.04062v1 +2015-10-19,Critical behavior of a triangular lattice Ising AF/FM bilayer,"We study a bilayer Ising spin system consisting of antiferromagnetic (AF) and +ferromagnetic (FM) triangular planes, coupled by ferromagnetic exchange +interaction, by standard Monte Carlo and parallel tempering methods. The AF/FM +bilayer is found to display the critical behavior completely different from +both the single FM and AF constituents as well as the FM/FM and AF/AF bilayers. +Namely, by finite-size scaling (FSS) analysis we identify at the same +temperature a standard Ising transition from the paramagnetic to FM state in +the FM plane that induces a ferrimagnetic state with a finite net magnetic +moment in the AF plane. At lower temperatures there is another phase +transition, that takes place only in the AF plane, to different ferrimagnetic +state with spins on two sublattices pointing parallel and on one sublattice +antiparallel to the spins on the FM plane. FSS indicates that the corresponding +critical exponents are close to the two-dimensional three-state ferromagnetic +Potts model values.",1510.05383v1 +2015-11-25,Designing a fully-compensated half-metallic ferrimagnet,"Recent experimental work on Mn2RuxGa demonstrates its potential as a +compensated ferrimagnetic half-metal (CFHM).Here we present a set of +high-throughput ab initio density functional theory calculations and detailed +experimental characterisation, that enable us to correctly describe the nominal +Mn2RuxGa thin films, in particular with regard to site-disorder and defects. We +then construct models that accurately capture all the key features of the +Mn-Ru-Ga system, including magnetic compensation and the spin gap at the Fermi +level. We find that electronic doping is neccessary, which is achieved with a +Mn/Ga ratio smaller than two. Our study shows how composition and +substrate-induced biaxial strain can be combined to design the first +room-temperature CFHM.",1511.07923v2 +2016-01-21,Spin pumping in strongly coupled magnon-photon systems,"We experimentally investigate magnon-polaritons, arising in ferrimagnetic +resonance experiments in a microwave cavity with a tuneable quality factor. To +his end, we simultaneously measure the electrically detected spin pumping +signal and microwave reflection (the ferrimagnetic resonance signal) of a +yttrium iron garnet (YIG) / platinum (Pt) bilayer in the microwave cavity. The +coupling strength of the fundamental magnetic resonance mode and the cavity is +determined from the microwave reflection data. All features of the magnetic +resonance spectra predicted by first principle calculations and an input-output +formalism agree with our experimental observations. By changing the decay rate +of the cavity at constant magnon-photon coupling rate, we experimentally tune +in and out of the strong coupling regime and successfully model the +corresponding change of the spin pumping signal. Furthermore, we observe the +coupling and spin pumping of several spin wave modes and provide a quantitative +analysis of their coupling rates to the cavity.",1601.05681v1 +2016-03-18,First-principles study of ferroelectricity induced by p-d hybridization in ferrimagnetic NiFe2O4,"We investigate the ferrimagnetism and ferroelectricity of bulk NiFe$_2$O$_4$ +with tetragonal $P4_122$ ~symmetry by means of density functional calculations +using generalized gradient approximation + Hubbard $U$ approach. Special +attention is paid to finding the most energetically favorable configuration on +magnetic ordering and further calculating the reliable spontaneous electric +polarization. With the fully optimized crystalline structure of the most stable +configuration, the spontaneous polarization is obtained to be 23 $\mu$C/cm$^2$ +along the z direction, which originates from the hybridization between the 3d +states of the Fe$^{3+}$ cation and the 2p states of oxygen induced by +Jahn-Teller effect.",1603.05974v2 +2016-03-21,Ferrimagnetic ordering and spin entropy of field-dependent intermediate spins in Na0.82CoO2,"The peculiar field-dependent magnetism of Na0.82CoO2 has been investigated +through an analysis of its DC and AC spin susceptibilities. To account for the +easily activated narrow b2g-a1g gap of the crystal field for Co in the cobalt +oxide layer, the spin-state transition of Co3+ (3d6) between the low spin (LS) +state b2g^2-a1g^0 of S=0 and the intermediate spin (IS) state b2g^1-a1g^1 of +S=1 is thus seen as thermally activated and exhibits a Boltzmann distribution. +The IS state of Co3+ within each sqrt(13a) hexagonal superlattice formed by the +S=1/2 state of the Co4+ ions appears randomly within each supercell and shows +significant temperature and field dependence. The magnetic field is found to +assist in pinning down the thermally activated state of Co3+ and swings the +Boltzmann distribution weight toward a higher fraction of the IS state. The +field dependence of the in-plane magnetic moment from the added number of S=1 +spins is used to explain the origin of A-type antiferromagnetic (AF) ordering, +particularly that the ferromagnetic (FM)-like behavior below TN at low field is +actually a ferrimagnetic IS spin ordering of Co3+.",1603.06451v1 +2016-04-05,Micromagnetic simulation of exchange coupled ferri-/ferromagnetic composite in bit patterned media,"Ferri-/ferromagnetic exchange coupled composites are promising candidates for +bit patterned media because of the ability to control the magnetic properties +of the ferrimagnet by its composition. A micromagnetic model for the bilayer +system is presented where we also incorporate the microstructural features of +both layers. Micromagnetic finite element simulations are performed to +investigate the magnetization reversal behaviour of such media. By adding the +exchange coupled ferrimagnet to the ferromagnet, the switching field could be +reduced by up to $40\,\%$ and also the switching field distribution is +narrowed. To reach these significant improvements, an interface exchange +coupling strength of $2\,\mathrm{mJ/m^2}$ is required.",1604.01180v1 +2016-04-17,Interface electronic structure at the topological insulator - ferrimagnetic insulator junction,"An interface electron state at the junction between a three-dimensional +topological insulator (TI) film of Bi2Se3 and a ferrimagnetic insulator film of +Y3Fe5O12 (YIG) was investigated by measurements of angle-resolved photoelectron +spectroscopy and X-ray absorption magnetic circular dichroism (XMCD). The +surface state of the Bi2Se3 film was directly observed and localized 3d spin +states of the Fe3+ state in the YIG film were confirmed. The proximity effect +is likely described in terms of the exchange interaction between the localized +Fe 3d electrons in the YIG film and delocalized electrons of the surface and +bulk states in the Bi2Se3 film. The Curie temperature (TC) may be increased by +reducing the amount of the interface Fe2+ ions with opposite spin direction +observable as a pre-edge in the XMCD spectra.",1604.04869v1 +2016-06-10,Effect of Gd/Nd doping on the magnetic properties of PrMnO3,"A study on temperature dependent magnetic properties of single phase +orthorhombic perovskites system associated with space group Pbnm compounds +Pr1-x(Gd/Nd)xMnO3 (x=0.3, 0.5, 0.7) was carried out. A magnetization reversal +is observed below the Neel temperature (TN), in DC magnetization measurements +(at 50 Oe) in the doped compounds. This may be due to the antiparallel coupling +between the two magnetic sublattices (|Pr+Gd/Nd | and Mn). With lowering of +temperature, the |Pr+ Gd/Nd|) ions begin to polarize under the negative +internal field due to canted moment of Mn moments. The hysteresis plot taken at +50K shows a ferrimagnetic characteristic and the presence of spin canting of +ions in the magnetic sublattices. Arrott plot indicates field induced second +order paramagnetic to ferrimagnetic (PM-FiM) phase transition in this system.",1606.03274v1 +2016-07-11,Low loss spin wave resonances in organic-based ferrimagnet vanadium tetracyanoethylene thin films,"We experimentally demonstrate high quality factor spin wave resonances in an +encapsulated thin film of the organic-based ferrimagnet vanadium +tetracyanoethylene (V[TCNE]$_\textit{x~2}$) coated on an a-plane sapphire +substrate by low temperature chemical vapor deposition. The thickness standing +wave modes are observed in a broad frequency range (1 GHz ~ 5 GHz) with high +quality factor exceeding 3,200 in ambient air at room temperature, rivaling +those of inorganic magnetic materials. The exchange constant of +V[TCNE]$_\textit{x~2}$, a crucial material parameter for future study and +device design of the V[TCNE]$_\textit{x~2}$, is extracted from the measurement +with a value of $(4.61\pm 0.35)\times 10^{-16} \mathrm{\: m^{2}}$. Our result +establishes the feasibility of using organic-based materials for building +hybrid magnonic devices and circuits.",1607.03041v2 +2016-07-25,Observation of an anisotropic Dirac cone reshaping and ferrimagnetic spin polarization in an organic conductor,"The Coulomb interaction among massless Dirac fermions in graphene is +unscreened around the isotropic Dirac points, causing a logarithmic velocity +renormalization and a cone reshaping. In less symmetric Dirac materials +possessing anisotropic cones with tilted axes, the Coulomb interaction can +provide still more exotic phenomena which have not been experimentally unveiled +yet. Here, using site-selective nuclear magnetic resonance, we find a +non-uniform cone reshaping accompanied by a bandwidth reduction and an emergent +ferrimagnetism in tilted Dirac cones that appear on the verge of charge +ordering in an organic compound. Our theoretical analyses based on the +renormalization-group approach and the Hubbard model show that these +observations are the direct consequences of the long-range and short-range +parts of the Coulomb interaction, respectively. The cone reshaping and the +bandwidth renormalization, as well as the novel magnetism revealed here, can be +ubiquitous and vital for many Dirac materials.",1607.07142v2 +2016-09-20,A coupled spin-electron diamond chain with different Landé g-factors of localized Ising spins and mobile electrons,"A coupled spin-electron diamond chain with localized Ising spins placed on +its nodal sites and mobile electrons delocalized over interstitial sites is +explored in a magnetic field taking into account the difference between Land\'e +g-factors of the localized spins and mobile electrons. The ground-state phase +diagram is constituted by two classical ferrimagnetic phases, the quantum +unsaturated paramagnetic phase and the saturated paramagnetic phase. Both +classical ferrimagnetic phases as well as the unsaturated paramagnetic phase +are reflected in a low-temperature magnetization curve as intermediate +magnetization plateaus. The unsaturated paramagnetic phase is quantum in its +character as evidenced by the fermionic concurrence calculated for a pair of +the mobile electrons hopping in between the interstitial sites. It is shown +that the magnetic field can under certain conditions induce a quantum +entanglement above the disentangled ground state.",1609.06072v2 +2016-10-11,Semiclassical analysis of a magnetization plateau in a 2D frustrated ferrimagnet,"We use a semiclassical large-$S$ expansion to study a plateau at $1/3$ +saturation in the magnetization curve of a frustrated ferrimagnet on a +spatially anisotropic kagom\'{e} lattice. The spins have both ferromagnetic and +antiferromagnetic nearest-neighbor Heisenberg couplings, and a frustrating +next-nearest-neighbor coupling in one lattice direction. The magnetization +plateau appears at the classical level for a certain range of couplings, and +quantum fluctuations significantly broaden it at both ends. Near the region of +the phase diagram where the classical plateau destabilizes, we find an exotic +""chiral liquid"" phase that preserves translational and $U(1)$ spin symmetry, in +which bound pairs of magnons with opposite spins are condensed. We show how +this state is obtained naturally from a relativistic field theory formulation. +We comment on the relevance of the model to the material +$\text{Cu}_3\text{V}_2\text{O}_7\text{(OH)}_2 \cdot 2\text{H}_2\text{O}$ +(volborthite).",1610.03135v3 +2018-02-01,Stability of Room Temperature Compensated Half-Metallicity in Cr-based Inverse-Heusler Compounds,"Using three correlated band approaches, namely the conventional band approach +plus on-site Coulomb repulsion $U$, the modified Becke-Johnson functional, and +hybrid functional, we have investigated inverse-Heusler ferrimagnets +Cr$_2$Co${\cal Z}$ (${\cal Z}$=Al, Ga, In). These approaches commonly indicate +that the Cr$_2$CoAl synthesized recently is a precise compensated half-metal +(CHM), whereas Cr$_2$CoGa and Cr$_2$CoIn are ferrimagnets with a small moment. +This is also confirmed by the fixed spin moment approach. Analysis of the Bader +charge decomposition and the radial charge densities indicates that this +contrast is due to chemical differences among the ${\cal Z}$ ions. +Additionally, in Cr$_2$CoAl, changing the volume by $\pm$ 5% or the ratio of +$c/a$ by $\pm$ 2% does not alter the CHM state, suggesting that this state is +robust even under application of moderate pressure or strain. Considering the +observed high Curie temperature of 750 K, our results suggest that Cr$_2$CoAl +is a promising candidate for robust high $T_C$ CHMs. Furthermore, the +electronic structure of the CHM Cr$_2$CoAl is discussed.",1802.00125v2 +2018-02-14,Moderate Magnetic Field Induced Large Exchange Bias Effect in Ferrimagnetic 314-Sr3YCo4O10.5 Material,"Herein, we report the appearance of a large exchange bias (EB) effect in a +moderate cooling field (cooling field, H$_{FC}$ = 1 kOe) for the +314-Sr3YCo4O10.5 material. The exchange bias has started to appear near room +temperature and reaches a maximum value of 5.5 kOe at 4 K. The existence of +ferrimagnetic clusters in the compensated host in this layered structure +originates the large exchange anisotropy. Remarkably, the observed value of +moderate magnetic field induced exchange bias field is extremely large in +comparison with material systems which are recognized to exhibit giant exchange +bias effect. In combination with the feasibility of room temperature +application, the appearance of large exchange bias in a moderate cooling field +exemplifying the present material system as a promising class of compounds for +designing coherent magnetic materials with huge exchange bias in low/moderate +magnetic field.",1802.05194v1 +2018-04-03,Phase diagram of the Hubbard-Kondo lattice model from variational cluster approximation,"The interplay between the Kondo effect and magnetic ordering driven by the +Ruderman-Kittel-Kasuya-Yosida interaction is studied within the two-dimensional +Hubbard-Kondo lattice model. In addition to the antiferromagnetic exchange +interaction, $J_\perp$, between the localized and the conduction electrons, +this model also contains the local repulsion, $U$, between the conduction +electrons. We use variational cluster approximation to investigate the +competition between the antiferromagnetic phase, the Kondo singlet phase, and a +ferrimagnetic phase on square lattice. At half-filling, the N\'eel +antiferromagnetic phase dominates from small to moderate $J_\perp$ and +$UJ_\perp$, and the Kondo singlet elsewhere. Sufficiently away from +half-filling, the antiferromagnetic phase first gives way to a ferrimagnetic +phase (in which the localized spins order ferromagnetically, and the conduction +electrons do likewise, but the two mutually align antiferromagnetically), and +then to the Kondo singlet phase.",1804.00917v1 +2018-11-21,Squeezed states of magnons and phonons in cavity magnomechanics,"We show how to create quantum squeezed states of magnons and phonons in a +cavity magnomechanical system. The magnons are embodied by a collective motion +of a large number of spins in a macroscopic ferrimagnet, and couple to cavity +microwave photons and phonons (vibrational modes of the ferrimagnet) via the +magnetic dipole interaction and magnetostrictive interaction, respectively. The +cavity is driven by a weak squeezed vacuum field generated by a flux-driven +Josephson parametric amplifier, which is essential to get squeezed states of +the magnons and phonons. We show that the magnons can be prepared in a squeezed +state via the cavity-magnon beamsplitter interaction, and by further driving +the magnon mode with a strong red-detuned microwave field, the phonons are +squeezed. We show optimal parameter regimes for obtaining large squeezing of +the magnons and phonons, which are robust against temperature and could be +realized with experimentally reachable parameters.",1811.09668v4 +2018-11-30,Half-metallicity of Mn2VAl ferrimagnet revealed by resonant inelastic soft x-ray scattering under magnetic field,"Detailed information on the electronic states of both V and Mn 3d electrons +in the ferrimagnet Mn2VAl is obtained by the bulk sensitive resonant inelastic +soft x-ray scattering (SX-RIXS) excited with the circularly polarized light +under an external magnetic field for the first time. The results under the V +L-edge excitation have revealed the negligible partial density of states (PDOS) +of the V 3d states around the Fermi energy as well as their rather localized +character. Under the Mn L-edge excitation, on the other hand, the spectra are +dominated by fluorescence with clear magnetic circular dichroism with +noticeable excitation photon energy dependence. Compared with the theoretical +prediction of the RIXS spectra based on the density-functional-theory band +structure calculation, an itinerant, spin-dependent character of the Mn 3d +states and decays of the Mn 2p core states are confirmed in consistence with +the half-metallicity of the Mn 3d states.",1811.12600v1 +2019-05-16,Transition between canted antiferromagnetic and spin-polarized ferromagnetic quantum Hall states in graphene on a ferrimagnetic insulator,"In the quantum Hall regime of graphene, antiferromagnetic and spin-polarized +ferromagnetic states at the zeroth Landau level compete, leading to a canted +antiferromagnetic state depending on the direction and magnitude of an applied +magnetic field. Here, we investigate this transition at 2.7 K in graphene Hall +bars that are proximity coupled to the ferrimagnetic insulator +Y$_{3}$Fe$_{5}$O$_{12}$. From nonlocal transport measurements, we demonstrate +an induced magnetic exchange field in graphene, which lowers the magnetic field +required to modulate the magnetic state in graphene. These results show that a +magnetic proximity effect in graphene is an important ingredient for the +development of two-dimensional materials in which it is desirable for ordered +states of matter to be tunable with relatively small applied magnetic fields (> +6 T).",1905.06866v2 +2020-07-01,Microscopic origin of magnetization reversal in exchange-coupled ferro-/ferrimagnetic bilayers,"In this study, the magnetic reversal process of exchange-coupled bilayer +systems, consisting of a ferrimagnetic TbFeCo alloy layer and a ferromagnetic +[Co/Ni/Pt]N multilayer, was investigated. In particular, minor loop studies, +probing solely the reversal characteristics of the softer ferromagnetic layer, +reveal two distinct reversal mechanisms, which depend strongly on the thickness +of the ferromagnetic layer. For thick layers, irreversible switching of the +macroscopic minor loop is observed. The underlying microscopic origin of this +reversal process was studied in detail by high-resolution magnetic force +microscopy, showing that the reversal is triggered by in-plane domain walls +propagating through the ferromagnetic layer. In contrast, thin ferromagnetic +layers show a hysteresis-free reversal, which is nucleation-dominated due to +grain-to-grain variations in magnetic anisotropy of the Co/Ni/Pt multilayer and +an inhomogeneous exchange coupling with the magnetically hard TbFeCo layer, as +confirmed by micromagnetic simulations.",2007.00333v1 +2020-07-07,Anisotropy induced spin re-orientation in chemically-modulated amorphous ferrimagnetic films,"The ability to tune the competition between the in-plane and out-of-plane +orientation of magnetization provides a means to construct thermal sensors with +a sharp spin re-orientation transition at specific temperatures. We have +observed such a tuneable, temperature driven spin re-orientation in +structurally amorphous, ferrimagnetic rare earth-transition metal (RE-TM) alloy +thin films using scanning transmission X-ray microscopy (STXM) and magnetic +measurements. The nature of the spin re-orientation transition in FeGd can be +fully explained by a non-equilibrium, nanoscale modulation of the chemical +composition of the films. This modulation leads to a magnetic domain pattern of +nanoscale speckles superimposed on a background of in-plane domains that form +Laudau configurations in micron-scale patterned elements. It is this speckle +magnetic structure that gives rise to a sharp two step-reversal mechanism that +is temperature dependent. The possibility to balance competing anisotropies +through the temperature opens opportunities to create and manipulate +topological spin textures.",2007.03657v1 +2020-07-09,Fe3Se4: A Possible Ferrimagnetic Half-Metal?,"Half-metallic ferromagnets show 100% spin-polarization at the Fermi level and +are ideal candidates for spintronic applications. Despite the extensive +research in the field, very few materials have been discovered so far. Here we +present results of electronic band structure calculations based on density +functional theory and extensive physical-property measurements for Fe3Se4 +revealing signatures of half-metallicity. The spin-polarized electronic band +structure calculations predict half-metallic ferrimagnetism for Fe3Se4. The +electrical resistivity follows exponentially suppressed electron-magnon +scattering mechanism in the low-temperature regime and show a magnetoresistance +effect that changes the sign from negative to positive with decreasing +temperature around 100 K. Other intriguing observations include the anomalous +behavior of Hall resistance below 100 K and an anomalous Hall coefficient that +roughly follows the \r{ho}2 behavior.",2007.04736v1 +2020-07-15,Spin-orbit coupling in single layer ferrimagnets: direct observation of spin-orbit torques and chiral spin textures,"We demonstrate that effects of spin-orbit coupling and inversion asymmetry +exist in a single GdFeCo ferrimagnetic layer, even without a heavy metal +interface. We use electric transport measurements to quantify the spin-orbit +torques. We measure the Dzyaloshinskii-Moriya interaction using Brillouin light +scattering measurement technique, and we observe the resulting chiral magnetic +textures using x-ray PEEM microscopy. We attribute these effects to a +composition variation along the thickness, that we observed by scanning +transmission electron microscopy. We show that these effects can be optimized +by varying the GdFeCo thickness or by combining them with interfacial effects.",2007.07569v2 +2020-07-28,Anomalous Hall Effect in Kagome Ferrimagnet GdMn$_6$Sn$_6$,"We present magnetotransport data on the ferrimagnet GdMn$_6$Sn$_6$. From the +temperature dependent data we are able to extract a large instrinsic +contribution to the anomalous Hall effect $\sigma_{xz}^{int} \sim$ 32 +$\Omega^{-1}cm^{-1}$ and $\sigma_{xy}^{int} \sim$ 223 $\Omega^{-1}cm^{-1}$, +which is comparable to values found in other systems also containing kagome +nets of transition metals. From our transport anisotropy, as well as our +density functional theory calculations, we argue that the system is +electronically best described as a three dimensional system. Thus, we show that +reduced dimensionality is not a strong requirement for obtaining large Berry +phase contributions to transport properties. In addition, the coexistence of +rare-earth and transition metal magnetism makes the hexagonal MgFe$_6$Ge$_6$ +structure type a promising system to tune the electronic and magnetic +properties in future studies.",2007.14436v1 +2013-08-05,Controlling the Polarity of the Transient Ferromagnetic-Like State in Ferrimagnets,"After the application of an ultrashort laser pulse, the antiferromagnetic +alignment in rare earth-transition metal alloys can temporarily become +ferromagnetic with the rare-earth polarity. + Proposed models merely describe this effect, without showing the route for +its manipulation. Here we use extensive atomistic spin model simulations and +micromagnetic theory for ferrimagnets at elevated temperatures to predict that +the polarity of this transient ferromagnetic-like state can be controlled by +initial temperature. We show that this arises because the magnetic response of +each lattice has a different temperature dependence, at low temperatures the +transition metal responds faster than the rare earth, while at high +temperatures this role is interchanged. Our findings contribute to the physical +understanding and control of this state and thus open new perspectives for its +use in ultrafast magnetic devices.",1308.0993v2 +2013-08-06,Loop Liquid in an Ising-Spin Kondo Lattice Model on a Kagome Lattice,"Phase diagram of an Ising-spin Kondo lattice model on a kagome lattice is +investigated by a Monte Carlo simulation. We find that the system exhibits a +peculiar ferrimagnetic state at a finite temperature, in which each triangle is +in a two-up one-down spin configuration but the spin correlation does not +develop any superstructure. We call this state the loop liquid, as it is +characterized by the emergent degree of freedom, self-avoiding up-spin loops. +We elucidate that the system shows phase transitions from the loop liquid to +ferrimagnetically ordered states and a crossover to a partially ferromagnetic +state by changing the electron density and temperature. These can be viewed as +crystallization and cohesion of the loops, respectively. We demonstrate that +the loop formation is observed in the optical conductivity as a characteristic +resonant peak.",1308.1441v1 +2016-11-08,Thermal and Magnetic Properties of Nanostructured Ferrimagnetic Composites with Graphene - Graphite Fillers,"We report the results of an experimental study of thermal and magnetic +properties of nanostructured ferrimagnetic iron oxide composites with graphene +and graphite fillers synthesized via the current activated pressure assisted +densification. The thermal conductivity was measured using the laser-flash and +transient plane source techniques. It was demonstrated that addition of 5 wt. % +of equal mixture of graphene and graphite flakes to the composite results in a +factor of x2.6 enhancement of the thermal conductivity without significant +degradation of the saturation magnetization. The microscopy and spectroscopic +characterization reveal that sp2 carbon fillers preserve their crystal +structure and morphology during the composite processing. The strong increase +in the thermal conductivity was attributed to the excellent phonon heat +conduction properties of graphene and graphite. The results are important for +energy and electronic applications of the nanostructured permanent magnets.",1611.02359v1 +2016-11-29,Diagonal magnetoelectric susceptibility and effect of Fe-doping in a polar ferrimagnet Mn2Mo3O8,"We investigate a large variation in a diagonal component of the linear +magnetoelectric (ME) susceptibility in a polar ferrimagnet Mn2Mo3O8 while +changing the magnetic-ion site from orbital-quenched Mn2+ to Fe2+ with strong +uniaxial anisotropy. In Mn2Mo3O8, the linear ME susceptibility is dominated by +the non-relativistic exchange striction mechanism, showing a positive value at +low temperature and a critical behavior toward negative divergence around the +transition temperature. This negative peak value becomes four times larger when +50% of Mn2+ ions are replaced with Fe2+ ion, highlighting the beneficial +perspective of the compositionally-tunable ME effect. As the doped Fe increases +in fraction, gradual negative shift of the ME coefficient is observed around +the lowest temperature, which manifests relativistic single-site origin of the +ME susceptibility. Further doping with x >= 75% in (Mn1-xFex)2Mo3O8, the ME +coefficient becomes negative in the entire temperature region. Such a +composition dependence can be explained in terms of the chemical preference for +the two types of magnetic sites of Mn/Fe ions. The present study demonstrates +the large tunability of ME effect by substituting the magnetic ion with the +primary structural/magnetic characters kept intact.",1611.09458v2 +2017-01-31,Tunable magnon-photon coupling in a compensating ferrimagnet - from weak to strong coupling,"We experimentally study the magnon-photon coupling in a system consitsing of +the compensating ferrimagnet gadolinium iron garnet (GdIG) and a +three-dimensional microwave cavity. The temperature is varied in order to tune +the GdIG magnetization and to observe the transition from the weak coupling +regime to the strong coupling regime. By measuring and modelling the complex +reflection parameter of the system the effective coupling rate g eff and the +magnetization M eff of the sample are extracted. Comparing g eff with the +magnon and the cavity decay rate we conclude that the strong coupling regime is +easily accessible using GdIG. We show that the effective coupling strength +follows the predicted square root dependence on the magnetization.",1701.08969v3 +2017-01-31,Ferrimagnetic and antiferromagnetic phase in bilayer graphene nanoflake controlled with external electric fields,"The paper presents a computational study of the ground-state magnetic phases +of a selected bilayer graphene nanoflake in external electric field and +magnetic field. The electric field has parallel and perpendicular component +while the magnetic field is oriented in plane. The system consists of two +rectangular layers having armchair edges and zigzag terminations with Bernal +stacking. The theoretical model is based on a tight binding Hamiltonian with +Hubbard term. The magnetic phase diagram involving the total spin is +constructed, showing the stability areas of phases with total spin values equal +to 0 and 1. A significant stability range of antiferromagnetic, layer-like +arrangements is found and extensively discussed. The possibility of switching +between nonmagnetic, antiferromagnetic and ferrimagnetic phases with both +components of external electric field is demonstrated, being a manifestation of +a magnetoelectric effect. The influence of magnetic field on the phase diagrams +is analysed.",1701.09128v2 +2012-01-03,Kondo Metal and Ferrimagnetic Insulator on the Triangular Kagomé Lattice,"We obtain the rich phase diagrams in the Hubbard model on the triangular +Kagom\'e lattice as a function of interaction, temperature and asymmetry, by +combining the cellular dynamical mean-field theory with the continuous time +quantum Monte Carlo method. The phase diagrams show the asymmetry separates the +critical points in Mott transition of two sublattices on the triangular +Kagom\'e lattice and produces two novel phases called plaquette insulator with +an obvious gap and a gapless Kondo metal. When the Coulomb interaction is +stronger than the critical value Uc, a short range paramagnetic insulating +phase, which is a candidate for the short rang resonating valence-bond spin +liquid, emerges before the ferrimagnetic order is formed independent of +asymmetry. Furthermore, we discuss how to measure these phases in future +experiments.",1201.0654v3 +2014-05-09,Magnetic excitations and anomalous spin wave broadening in multiferroic FeV2O4,"We report on the different roles of two orbital-active Fe$^{2+}$ at the A +site and V$^{3+}$ at the B site in the magnetic excitations and on the +anomalous spin wave broadening in FeV$_{2}$O$_{4}$. FeV$_{2}$O$_{4}$ exhibits +three structural transitions and successive paramagnetic (PM)-collinear +ferrimagnetic (CFI)-noncollinear ferrimagnetic (NCFI) transitions. The +high-temperature tetragonal/PM -orthorhombic/CFI transition is accompanied by +the appearance of an energy gap with a high magnitude in the magnetic +excitations due to strong spin-orbit coupling induced anisotropy at the +Fe$^{2+}$ site. While there is no measurable increase in the energy gap from +the orbital ordering of V$^{3+}$ at the orthorhombic/CFI-tetragonal/NCFI +transition, anomalous spin wave broadening is observed in the orthorhombic/CFI +state due to V$^{3+}$ spin fluctuations at the B site. The spin wave broadening +is also observed at the zone boundary without softening, which is discussed in +terms of magnon-phonon coupling.",1405.2272v2 +2014-06-12,Ferrimagnetism in the double perovskite Ca2FeOsO6: a density functional study,"Using density functional calculations, we find that the newly synthesized +Ca$_2$FeOsO$_6$ has the high-spin Fe$^{3+}$ ($3d^5$)-Os$^{5+}$ ($5d^3$) state. +The octahedral Os$^{5+}$ ion has a large intrinsic exchange splitting, and its +$t_{2g\uparrow}^3$ configuration makes the spin-orbit coupling ineffective. +Moreover, there is a strong antiferromagnetic (AF) coupling between the +neighboring Fe$^{3+}$ ($S$ = 5/2) and Os$^{5+}$ ($S$ = -3/2), but the AF +couplings within both the fcc Fe$^{3+}$ and Os$^{5+}$ sublattices are one order +of magnitude weaker. Therefore, a magnetic frustration is suppressed and a +stable ferrimagnetic (FiM) ground state appears. This FiM order is due to the +virtual hopping of the $t_{2g}$ electrons from Os$^{5+}$ ($t_{2g\downarrow}^3$) +to Fe$^{3+}$ ($t_{2g\uparrow}^3e_{g\uparrow}^2$). However, if the experimental +bended Fe$^{3+}$-O$^{2-}$-Os$^{5+}$ exchange path gets straight, the $e_g$ +hopping from Fe$^{3+}$ ($t_{2g\uparrow}^3e_{g\uparrow}^2$) to Os$^{5+}$ +($t_{2g\uparrow}^3$) would be facilitated and then a ferromagnetic (FM) +coupling would occur.",1406.3101v1 +2014-06-27,Spin-phonon coupling in BaFe12O19 M-type hexaferrite,"The spin-phonon coupling in magnetic materials is due to the modulation of +the exchange integral by lattice vibrations. BaFe12O19 M-type hexaferrite, +which is the most used magnetic material as permanent magnet, transforms into +ferromagnet at high temperatures, but no spin-phonon coupling was previously +observed at this transition. In this letter, we investigated the +temperature-dependent Raman spectra of polycrystalline BaFe12O19 M-type +hexaferrite from room temperature up to 780 K to probe spin-phonon coupling at +the ferrimagnetic transition. An anomaly was observed in the position of the +phonon attributed to the Fe(4)O6 octahedra, evidencing the presence of a +spin-phonon coupling in BaM in the ferrimagnetic transition at 720 K. The +results also confirmed the spin-phonon coupling is different for each phonon +even when they couple with the same spin configuration.",1406.7334v2 +2015-12-18,Exchange Bias and Bistable Magneto-Resistance States in Amorphous TbFeCo thin Films,"Amorphous TbFeCo thin films sputter deposited at room temperature on +thermally oxidized Si substrate are found to exhibit strong perpendicular +magnetic anisotropy (PMA). Atom probe tomography (APT), scanning transmission +electron microscopy (STEM), and energy dispersive spectroscopy (EDS) mapping +have revealed two nanoscale amorphous phases with different Tb atomic +percentages distributed within the amorphous film. Exchange bias accompanied by +bistable magneto-resistance states has been uncovered near room temperature by +magnetization and magneto-transport measurements. The exchange anisotropy +originates from the exchange interaction between the ferrimagnetic and +ferromagnetic components corresponding to the two amorphous phases. This study +provides a platform for exchange bias and magneto-resistance switching using +single-layer amorphous ferrimagnetic thin films that require no epitaxial +growth.",1512.06103v1 +2016-04-30,Micromagnetic Simulation of Amorphous Ferrimagnetic TbFeCo Films with Exchange Coupled Nanophases,"Amorphous ferrimagnetic TbFeCo thin films are found to exhibit exchange bias +effect near the compensation temperature by magnetic hysteresis loop +measurement. The observed exchange anisotropy is believed to originate from the +exchange interaction between the two nanoscale amorphous phases distributed +within the films. Here, we present a computational model of phase-separated +TbFeCo using micromagnetic simulation. Two types of cells with different Tb +concentration are distributed within the simulated space to obtain a +heterogeneous structure consisting of two nanoscale amorphous phases. Each cell +contains separated Tb and FeCo components, forming two antiferromagnetically +coupled sublattices. Using this model, we are able to show the existence of +exchange bias effect, and the shift in hysteresis loops is in agreement with +experiment. The micromagnetic model developed herein for a heterogeneous +magnetic material may also account for some recent measurements of exchange +bias effect in crystalline films.",1605.00099v1 +2016-05-24,Spin Hall Magnetoresistance in a Canted Ferrimagnet,"We study the spin Hall magnetoresistance effect in ferrimagnet/normal metal +bilayers, comparing the response in collinear and canted magnetic phases. In +the collinear magnetic phase, in which the sublattice magnetic moments are all +aligned along the same axis, we observe the conventional spin Hall +magnetoresistance. In contrast, in the canted phase, the magnetoresistance +changes sign. Using atomistic spin model calculations of the magnetic +configuration, we show that the electric transport for the different magnetic +phases can be rationalized considering the individual sublattice moment +orientations. This enables a magneto-transport based investigation of +non-collinear magnetic textures.",1605.07441v1 +2016-05-31,Spin-Orbit Torques in ferrimagnetic GdFeCo Alloys,"The spin-orbit torque switching of ferrimagnetic +Gd$_x$(Fe$_{90}$Co$_{10}$)$_{100-x}$ films was studied for both transition +metal (TM)-rich and rare earth (RE)-rich configurations. The spin-orbit torque +driven magnetization switching follows the same handedness in TM-rich and +RE-rich samples with respect to the total magnetization, but the handedness of +the switching is reversed with respect to the TM magnetization. This indicates +that the sign of the spin-orbit-torque-driven magnetic switching follows the +total magnetization, although transport based techniques such as anomalous Hall +effect are only sensitive to the transition metal magnetization. These results +provide important insight into the physics of spin angular momentum transfer in +materials with antiferromagnetically coupled sublattices.",1605.09498v1 +2017-06-20,"Room Temperature Magnetoresistance and Exchange Bias in ""314 - type"" Oxygen-Vacancy Ordered SrCo$_{0.85}$Fe$_{0.15}$O$_{2.62}$","Herein, we report the magneto-transport and exchange bias effect in a ""314 - +type"" oxygen - vacancy ordered material with composition +SrCo$_{0.85}$Fe$_{0.15}$O$_{2.62}$. This material exhibits a ferrimagnetic +transition above room temperature, at 315 K. The negative magnetoresistance +starts to appear from room temperature (-1.3 $\%$ at 295 K in 70 kOe) and +reaches a sizable value of 58 $\%$ at 4 K in 70 kOe. Large exchange bias effect +is observed below 315 K when the sample is cooled in the presence of a magnetic +field. The coexistence of nearly compensated and ferrimagnetic regions in the +layered structure originate magnetoresistance and exchange bias in this sample. +The appearance of a sizable magnetoresistance and giant exchange bias effect, +especially near room temperature indicates that ""314-type"" cobaltates are a +promising class of material systems for the exploration of materials with +potential applications as magnetic sensors or in the area of spintronics.",1706.06264v2 +2017-10-12,Temperature-dependent charge transport in the compensated ferrimagnet Mn$_{1.5}$V$_{0.5}$FeAl from first principles,"We present an ab-initio study of the temperature-dependent longitudinal and +anomalous Hall resistivities in the compensated collinear ferrimagnet +Mn$_{1.5}$V$_{0.5}$FeAl. Its transport properties are calculated using the +general fully relativistic Kubo--Bastin formalism and their temperature +dependency is accounted for magnetic and structural disorder. Both scattering +sources, together with the residual chemical disorder, were treated equally +provided by the CPA (Coherent Potential Approximation) SPR-KKR (Spin-Polarized +Relativistic Korringa-Kohn-Rostoker) method. All calculated properties showed +good agreement with a recent experimental results, providing useful specific +information on the chemical and magnetic arrangement as well as on the +influence of disorder. Finally, we demonstrated that the anomalous Hall effect +in such compensated systems occurs regardless of the vanishing net spin moment.",1710.04453v1 +2018-01-23,Correlation between Magnetic Properties and Depinning Field in Field-Driven Domain Wall Dynamics in GdFeCo Ferrimagnets,"The influence of temperature on the magnetic-field-driven domain wall (DW) +motion is investigated in GdFeCo ferrimagnets with perpendicular magnetic +anisotropy (PMA). We find that the depinning field strongly depends on +temperature. Moreover, it is also found that the saturation magnetization +exhibits a similar dependence on temperature to that of depinning field. From +the creep-scaling criticality, a simple relation between the depinning field +and the properties of PMA is clearly identified theoretically as well as +experimentally. Our findings open a way for a better understanding how the +magnetic properties influence on the depinning field in magnetic system and +would be valuably extended to depinning studies in other system.",1801.07436v1 +2018-10-02,Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully-compensated half-metallic Mn2RuxGa thin films,"Magnetotransport is investigated in thin films of the half-metallic +ferrimagnet Mn$_2$Ru$_x$Ga in pulsed magnetic fields of up to 58 T. A +non-vanishing Hall signal is observed over a broad temperature range, spanning +the compensation temperature 155 K, where the net magnetic moment is strictly +zero, the anomalous Hall conductivity is 6673 $\Omega^{-1}.m^{-1}$ and the +coercivity exceeds 9 T. Molecular field modelling is used to determine the +intra- and inter-sublattice exchange constants and from the spin-flop +transition we infer the anisotropy of the electrically active sublattice to be +216 kJ/m$^3$ and predict the magnetic resonances frequencies. Exchange and +anisotropy are comparable and hard-axis applied magnetic fields result in a +tilting of the magnetic moments from their collinear ground state. Our analysis +is applicable to collinear ferrimagnetic half-metal systems.",1810.01158v1 +2018-10-15,Realizing Magnetoelectric Coupling with Hydroxide as a Knob,"Materials with a coexistence of magnetic and ferroelectric order (i.e., +multiferroics) provide an efficient route for the control of magnetism by +electric fields. Unfortunately, a long-sought room temperature multiferroic +with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic) +orderings is still lacking. Here, we propose that hydrogen intercalation in +antiferromagnetic transition metal oxides is a promising way to realize +multiferroics with strong magnetoelectric coupling. Taking brownmillerite +SrCoO2.5 as an example, we show that hydrogen intercalated SrCoO2.5 displays +strong ferrimagnetism and large electric polarization in which the hydroxide +acts as a new knob to simultaneously control the magnetization and polarization +at room temperature. We expect that ion intercalation will become a general way +to design magnetoelectric and spintronic functional materials.",1810.06357v1 +2018-10-25,Revisiting Goodenough-Kanamori rules in a new series of double perovskites LaSr$_{1-x}$Ca$_x$NiReO$_6$,"The magnetic ground state in highly ordered double perovskites +LaSr$_{1-x}$Ca$_x$NiReO$_6$ ($x$ = 0.0, 0.5, 1.0) were studied in view of the +Goodenough-Kanamori rules of superexchange interactions. In LaSrNiReO$_6$, Ni +and Re sublattices are found to exhibit curious magnetic states, but do not +show any long range magnetic ordering. The magnetic transition at $\sim$ 255 K +is identified with the Re sublattic magnetic ordering. The sublattice +interactions are tuned by modifying the Ni-O-Re bond angles via changing the +lattice structure through Ca doping. Upon Ca doping, the Ni and Re sublattices +start to display a ferrimagnetically ordered state at low temperature. The +neutron powder diffraction reveals a canted alignment between the Ni and the Re +sublattices, while the individual sublattice is ferromagnetic. The transition +temperature of the ferrimagnetic phase increases monotonically with increasing +Ca concentration.",1810.10995v1 +2019-06-28,"Exploring the structural , electronic and magnetic properties of cation ordered 3d-5d double perovskite Bi$_2$FeReO$_6$ and Bi$_2$FeIrO$_6$ thin-films from first-principles","We report a first-principles study of Bi-based 3$d$-5$d$ ordered double +perovskite oxides (A$_2$BB$^\prime$O$_6$) with a 3$d$ atom (Fe) at the B-site +and 5$d$ atoms (Re,Ir) at the B$^\prime$-site while keeping highly polarizable +ions (Bi$^{3+}$) at the A-site. We find that, under coherent heteroepitaxy, +Bi$_2$FeReO$_6$} exhibits a strain-driven anti-ferromagnetic insulator to +ferrimagnetic semi-metal transition, while Bi$_2$FeIrO$_6$ shows correlation +driven ferromagnetic insulator to ferrimagnetic half-metal transition with +calculated magnetic moments of 5 $\mu_B$/f.u. and 3 $\mu_B$/f.u., respectively. +These properties along with the low band gaps in the insulating phases make the +compounds appealing for spintronics applications. Furthermore, in +Bi$_2$FeIrO$_6$, the conduction and valence states are localized on different +transition metal sublattices implying more efficient electron-hole separation +upon photoexcitation, a desirable feature for photovoltaic applications.",1907.00041v1 +2019-06-30,Large spatial Schrodinger cat using a levitated ferrimagnetic nanoparticle,"The superposition principle is one of the main tenets of quantum mechanics. +Despite its counter-intuitiveness, it has been experimentally verified using +electrons, photons, atoms, and molecules. However, a similar experimental +demonstration using a nano or a micro particle is non-existent. Here in this +Letter, exploiting macroscopic quantum coherence and quantum tunneling, we +propose an experiment using levitated magnetic nanoparticle to demonstrate such +an effect. It is shown that the spatial separation between the delocalized +wavepackets of a $20~$nm ferrimagnetic yttrium iron garnet (YIG) nanoparticle +can be as large as $5~$$\mu$m. We argue that this large spatial separation can +be used to test different modifications such as collapse models to the standard +quantum mechanics. Furthermore, we show that the spatial superposition of a +core-shell structure, a YIG core and a non-magnetic silica shell, can be used +to probe quantum gravity.",1907.00415v4 +2019-07-05,Theory for shift current of bosons: Photogalvanic spin current in ferrimagnetic and antiferromagnetic insulators,"We theoretically study the optical generation of dc spin current (i.e., a +spin-current solar cell) in ordered antiferromagnetic and ferrimagnetic +insulators, motivated by a recent study on the laser-driven spinon spin current +in noncentrosymmetric quantum spin chains [H. Ishizuka and M. Sato, Phys. Rev. +Lett. 122, 197702 (2019)]. Using a non-linear response theory for magnons, we +analyze the dc spin current generated by a linearly-polarized electromagnetic +wave (typically, terahertz or gigahertz waves). Considering noncentrosymmetric +two-sublattice magnets as an example, we find a finite dc spin current +conductivity at $T=0$, where no thermally-excited magnons exist; this is in +contrast to the case of the spinon spin current, in which the optical +transition of the Fermi degenerate spinons plays an essential role. We find +that the dc spin-current conductivity is insensitive to the Gilbert damping, +i.e., it may be viewed as a shift current carried by bosonic particles +(magnons). Our estimate shows that an electric-field intensity of +$E\sim10^4-10^6$ V/cm is sufficient for an observable spin current. Our theory +indicates that the linearly-polarized electromagnetic wave generally produces a +dc spin current in noncentrosymmetric magnetic insulators.",1907.02734v1 +2019-09-24,Ground-State Phases of Alternating-Bond S = 1 Diamond Chains,"The ground-state phases of alternating-bond spin-1 diamond chains are +investigated. Each ground state consists of an array of spin clusters separated +by singlet dimers owing to an infinite number of local conservation laws. If no +singlet dimers are present, the ground state is equivalent to that of a spin +chain with infinite length.For strong frustration, we find a series of quantum +phase transitions as in the case of alternating-bond mixed diamond chains with +spins 1 and 1/2. For intermediate frustration, we find the nonmagnetic Haldane +or dimer phases according to whether the bond alternation is weak or strong. +For weak frustration and weak bond alternation, we find the ferrimagnetic +states with spontaneous magnetizations $m=1/6$ and 1/3 per site. The +ferrimagnetic state with $m=1/6$ is accompanied by a spontaneous translational +symmetry breakdown. This phase vanishes for strong bond alternation.",1909.11026v2 +2019-10-16,Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria,"Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic +bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic +magnetite NC chain-like assemblies is reported. An easy green synthesis route +in a thermoreversible gelatin hydrogel matrix is used. The structure of these +magnetite chains prepared with and without gelatin is characterized by means of +transmission electron microscopy, including electron tomography (ET). These +structures indeed bear resemblance to the magnetite assemblies found in MTB, +known for their mechanical flexibility and outstanding magnetic properties and +known to crystallographically align their magnetite NCs along the strongest +<111> magnetization easy axis. Using electron holography (EH) and angular +dependent magnetic measurements, the magnetic interaction between the NCs and +the generation of a magnetically anisotropic material can be shown. The +electro- and magnetostatic modeling demonstrates that in order to precisely +determine the magnetization (by means of EH) inside chain-like NCs assemblies, +their exact shape, arrangement and stray-fields have to be considered (ideally +obtained using ET).",1910.07293v1 +2019-10-29,Laser induced ultrafast 3d and 4f spin dynamics in CoDy ferrimagnetic alloys as a function of temperature,"We report on an element- and time-resolved investigation of femtosecond laser +induced ultrafast dynamics of 3d and 4f spins in a ferrimagnetic Co80Dy20 alloy +as a function of temperature. We observe an increase of the Co3d characteristic +demagnetization time and a decrease of the Dy4f demagnetization time when the +temperature is approaching the Curie temperature. It suggests that the critical +slowing down regime, which affects the laser induced ultrafast dynamics in pure +3d transition metals and 4f rare-earth ferromagnetic layers, vanishes for the +Dy sublattice in the CoDy alloy, in line with the theoretical predictions of +the Landau-Lifshitz-Bloch model.",1910.13143v2 +2020-01-04,Observation of spin-motive force in ferrimagnetic GdFeCo alloy films,"Non-uniform magnetic structures produce emergent electromagnetic phenomena +such as the topological Hall effect and the spin-motive force (SMF). The +experimental reports on the SMF, however, are very few and the relationship +between the SMF and material parameters is still unclear. In this study, we +investigated the SMF in ferrimagnetic GdFeCo alloy films using the +spin-torque-induced ferromagnetic resonance method and clarified the +relationship. The amplitude of the detected SMF becomes larger than that of the +transition metal alloy FeCo by the Gd doping and reaches the maximum near a Gd +composition of the boundary between in-plane and perpendicularly magnetized +films. According to the analytical calculation, the enhancement is related to +the trajectory of the magnetization precession. Moreover, we find that the SMF +induced by the magnetic resonance is inversely proportional to the square of +the damping constant.",2001.01042v2 +2020-02-14,Low energy magnons in the chiral ferrimagnet $\text{Cu}_2\text{OSeO}_3$: a coarse-grained approach,"We report a comprehensive neutron scattering study of low energy magnetic +excitations in the breathing pyrochlore helimagnetic +$\text{Cu}_2\text{OSeO}_3$. Fully documenting the four lowest energy magnetic +modes that leave the ferrimagnetic configuration of the ""strong tetrahedra"" +intact ($|\hbar\omega|<13$ meV), we find gapless quadratic dispersion at the +$\Gamma$ point for energies above 0.2 meV, two doublets separated by 1.6(2) meV +at the $R$ point, and a bounded continuum at the $X$ point. Our constrained +rigid spin cluster model relates these features to Dzyaloshinskii-Moriya (DM) +interactions and the incommensurate helical ground state. Combining +conventional spin wave theory with a spin cluster form-factor accurately +reproduces the measured equal time structure factor through multiple Brillouin +zones. An effective spin Hamiltonian describing the complex anisotropic +inter-cluster interactions is obtained.",2002.06283v2 +2020-02-10,"Phase diagram of the mixed-spin (1,3/2) Ising ferrimagnetic system with two different anisotropies","In this work, we have performed Monte Carlo simulations to study phase +transitions in a mixed spin-1 and spin-3/2 Ising ferrimagnetic system on the +square and cubic lattices and with two different single-ion anisotropies. This +lattice is divided in two interpenetrating sublattices with spins $S^A = 1$ +(states $\pm1$ and 0) on the sublattice $A$ and $S^B = 3/2$ (states $\pm 3/2$, +$\pm 1/2$) on the sublattice $B$. We have used single-ion anisotropies $D_{A}$ +and $D_{B}$ acting on the sites of the sublattice $A$ and $B$, receptively. We +have determined the phase diagrams of the model in the temperature $T$ versus +the single-ion anisotropies strength $D_A$ and $D_B$ plane and shown that the +system exhibits both second- and first-order phase transitions. We also have +shown that this system displays compensation points for some values of the +anisotropies.",2002.08421v1 +2020-04-09,Hysteresis-free magnetization reversal of exchange-coupled bilayers with finite magnetic anisotropy,"Exchange-coupled structures consisting of ferromagnetic and ferrimagnetic +layers become technologically more and more important. We show experimentally +the occurrence of completely reversible, hysteresis-free minor loops of [Co(0.2 +nm)/Ni(0.4 nm)/Pt(0.6 nm)]$_N$ multilayers exchange-coupled to a 20 nm thick +ferrimagnetic Tb$_{28}$Co$_{14}$Fe$_{58}$ layer, acting as hard magnetic +pinning layer. Furthermore, we present detailed theoretical investigations by +means of micromagnetic simulations and most important a purely analytical +derivation for the condition of the occurrence of full reversibility in +magnetization reversal. Hysteresis-free loops always occur if a domain wall is +formed during the reversal of the ferromagnetic layer and generates an +intrinsic hard-axis bias field that overcomes the magnetic anisotropy field of +the ferromagnetic layer. The derived condition further reveals that the +magnetic anisotropy and the bulk exchange of both layers, as well as the +exchange coupling strength and the thickness of the ferromagnetic layer play an +important role for its reversibility.",2004.04419v1 +2020-04-11,Anomalous Hall Effect in Layered Ferrimagnet MnSb2Te4,"We report on low-temperature electron transport properties of MnSb2Te4, a +candidate of ferrimagnetic Weyl semimetal. Long -range magnetic order is +manifested as a nearly square-shaped hysteresis loop in the anomalous Hall +resistance, as well as sharp jumps in the magnetoresistance. At temperatures +below 4 K, a lnT-type upturn appears in the temperature dependence of +longitudinal resistance, which can be attributed to the electron-electron +interaction (EEI), since the weak localization can be excluded by the +temperature dependence of magnetoresistance. Although the anomalous Hall +resistance exhibits a similar lnT-type upturn in the same temperature range, +such correction is absent in the anomalous Hall conductivity. Our work +demonstrates that MnSb2Te4 microflakes provide an ideal system to test the +theory of EEI correction to the anomalous Hall effect.",2004.05397v1 +2021-01-20,Magnetic properties of alternating Hubbard ladders,"We investigate the Hubbard Hamiltonian on ladders where the number of sites +per rung alternates between two and three. These geometries are bipartite, with +a non-equal number of sites on the two sublattices. Thus they share a key +feature of the Hubbard model in a class of lattices which Lieb has shown +analytically to exhibit long-range ferrimagnetic order, while being amenable to +powerful numeric approaches developed for quasi-one-dimensional geometries. The +Density Matrix Renormalization Group (DMRG) method is used to obtain the ground +state properties, e.g. excitation gaps, charge and spin densities as well as +their correlation functions at half-filling. We show the existence of +long-range ferrimagnetic order in the one-dimensional ladder geometries. Our +work provides detailed quantitative results which complement the general +theorem of Lieb for generalized bipartite lattices. It also addresses the issue +of how the alternation between quasi-long range order and spin liquid behavior +for uniform ladders with odd and even numbers of legs might be affected by a +regular alternation pattern.",2101.08229v2 +2021-01-25,Raman Spectroscopy and Aging of the Low-Loss Ferrimagnet Vanadium Tetracyanoethylene,"Vanadium tetracyanoethylene (V[TCNE]$_{x}$, $x\approx 2$) is an organic-based +ferrimagnet with a high magnetic ordering temperature $\mathrm{T_C>600 ~K}$, +low magnetic damping, and growth compatibility with a wide variety of +substrates. However, similar to other organic-based materials, it is sensitive +to air. Although encapsulation of V[TCNE]$_{x}$ with glass and epoxy extends +the film lifetime from an hour to a few weeks, what is limiting its lifetime +remains poorly understood. Here we characterize encapsulated V[TCNE]$_{x}$ +films using confocal microscopy, Raman spectroscopy, ferromagnetic resonance +and SQUID magnetometry. We identify the relevant features in the Raman spectra +in agreement with \textit{ab initio} theory, reproducing $\mathrm{C=C,C\equiv +N}$ vibrational modes. We correlate changes in the effective dynamic +magnetization with changes in Raman intensity and in photoluminescence. Based +on changes in Raman spectra, we hypothesize possible structural changes and +aging mechanisms in V[TCNE]$_x$. These findings enable a local optical probe of +V[TCNE]$_{x}$ film quality, which is invaluable in experiments where assessing +film quality with local magnetic characterization is not possible.",2101.10240v1 +2012-05-23,Two-step transition in a magnetoelectric ferrimagnet Cu2OSeO3,"We report a detailed single crystal investigation of a magnetoelectric +ferrimagnet Cu2OSeO3 using dc magnetization and ac susceptibility along the +three principal directions [100], [110] and [111]. We have observed that in +small magnetic fields two magnetic transitions occur, one at Tc = 57 K and the +second one at TN = 58 K. At Tc the non-linear susceptibility reveals the +emergence of the ferromagnetic component and below Tc the magnetization +measurements show the splitting between field-cooled and zero-field-cooled +regimes. Above 1000 Oe the magnetization saturates and the system is in a +single domain state. The temperature dependence of the saturation below Tc can +be well described by m(T) = m(0)[1 - (T/Tc)^2]^{\beta}, with m(0) = 0.56 +(mu)B/Cu, corresponding to the 3-up-1-down configuration. The dielectric +constant measured on a thin single crystal shows a systematic deviation below +the transition, indicating an intrinsic magnetoelectric effect.",1205.5100v1 +2017-05-08,Exchange coupling of a perpendicular ferromagnet to a half-metallic compensated ferrimagnet via a thin hafnium interlayer,"A thin Hafnium film is shown to act both as an effective diffusion barrier +for manganese at a thickness of 0.7 nm, and as an effective exchange coupling +layer in a sandwich structure with perpendicular magnetic anisotropy. The +magnetic layers are Co$_{20}$Fe$_{60}$B$_{20}$ and the low moment ferrimagnet +Mn$_2$Ru$_x$Ga (MRG). The coupling changes sign at the compensation temperature +of MRG and the exchange energy reaches 0.11 mJm$^{-2}$ for the thinnest Hf +interlayers. Ruthenium, the usual metal of choice for coupling ferromagnetic +layers in thin film heterostructures, cannot be used with the zero-moment half +metal MRG because of Ru interdiffusion. Due to its large coercivity near +compensation, the MRG can act as an effective source of exchange pinning.",1705.02804v1 +2017-05-09,Low spin wave damping in the insulating chiral magnet Cu$_{2}$OSeO$_{3}$,"Chiral magnets with topologically nontrivial spin order such as Skyrmions +have generated enormous interest in both fundamental and applied sciences. We +report broadband microwave spectroscopy performed on the insulating chiral +ferrimagnet Cu$_{2}$OSeO$_{3}$. For the damping of magnetization dynamics we +find a remarkably small Gilbert damping parameter of about $1\times10^{-4}$ at +5 K. This value is only a factor of 4 larger than the one reported for the best +insulating ferrimagnet yttrium iron garnet. We detect a series of sharp +resonances and attribute them to confined spin waves in the mm-sized samples. +Considering the small damping, insulating chiral magnets turn out to be +promising candidates when exploring non-collinear spin structures for high +frequency applications.",1705.03416v1 +2017-05-29,Electronic Structure and Magnetic Properties of Half-metallic Ferrimagnet Mn$_{2}$VAl Probed by Soft X-ray Spectroscopies,"We have studied the electronic structure of ferrimagnetic Mn2VAl single +crystal by means of soft X-ray absorption spectroscopy (XAS), X-ray absorption +magnetic circular dichroism (XMCD) and resonant soft X-ray inelastic scattering +(RIXS). We have successfully observed the XMCD signals for all constitute +elements, supporting the spin polarized states at the Fermi level. The Mn +$L_{2,3}$ XAS and XMCD spectra are reproduced by the spectral simulation based +on density-functional theory (DFT), indicating itinerant character of the Mn 3d +states. On the other hand, V $3d$ electrons are rather localized since the +ionic model can qualitatively explain the V $L_{2,3}$ XAS and XMCD spectra as +well as the local dd excitation revealed by V $L_3$ RIXS.",1705.10027v2 +2017-11-03,Compressible Ferrimagnetism in the depleted Periodic Anderson Model,"Tight-binding Hamiltonians with single and multiple orbitals exhibit an +intriguing array of magnetic phase transitions. In most cases the spin ordered +phases are insulating, while the disordered phases may be either metallic or +insulating. In this paper we report a Determinant Quantum Monte Carlo study of +interacting electrons in a geometry which can be regarded as a two-dimensional +Periodic Anderson Model with depleted interacting ($f$) orbitals. For a single +depletion, we observe an enhancement of antiferromagnetic correlations and +formation of localized states. For half of the $f$-orbitals regularly depleted, +the system exhibits a ferrimagnetic ground state. We obtain a quantitative +determination of the nature of magnetic order, which we discuss in the context +of Tsunetsugu's theorem, and show that, although the dc conductivity indicates +insulating behavior at half-filling, the compressibility remains finite.",1711.00983v1 +2017-11-19,Ferroelectric Ferrimagnetic LiFe$_2$F$_6$: Charge Ordering Mediated Magnetoelectricity,"Trirutile-type LiFe$_2$F$_6$ is a charge-ordered material with +Fe$^{2+}$/Fe$^{3+}$ configuration. Here its physical properties, including +magnetism, electronic structure, phase transition, and charge ordering, are +studied theoretically. On one hand, the charge ordering leads to improper +ferroelectricity with a large polarization. On the other hand, its magnetic +ground state can be tuned from the antiferromagnetic to ferrimagnetic by +moderate compressive strain. Thus, LiFe$_2$F$_6$ can be a rare multiferroic +with both large magnetization and polarization. Most importantly, since the +charge ordering is the common ingredient for both ferroelectricity and +magnetization, the net magnetization may be fully switched by flipping the +polarization, rendering intrinsically strong magnetoelectric effect and +desirable function.",1711.06981v2 +2017-11-23,Magnetic and Electronic Properties of Spin-Orbit Coupled Dirac Electrons on a $(001)$ Thin Film of Double Perovskite Sr$_2$FeMoO$_6$,"We present an interacting model for the electronic and magnetic behavior of a +strained $(001)$ atomic layer of Sr$_2$FeMoO$_6,$ which shows room-temperature +ferrimagnetism and magnetoresistance with potential spintronics application in +the bulk. We find that the strong spin-orbit coupling in the molybdenum 4$d$ +shell gives rise to a robust ferrimagnetic state with an emergent +spin-polarized electronic structure consisting of flat bands and four massive +or massless Dirac dispersions. Based on the spin-wave theory, we demonstrate +that the magnetic order remains intact for a wide range of doping, leading to +the possibility of exploring flat band physics, such as Wigner crystallization +in electron-doped Sr$_{2-x}$La$_{x}$FeMoO$_6.$",1711.08674v3 +2018-06-04,Monte Carlo simulation of equilibrium and dynamic phase transition properties of an Ising bilayer,"Magnetic properties of an Ising bilayer system defined on a honeycomb lattice +with non-magnetic interlayers which interact via an indirect exchange coupling +have been investigated by Monte Carlo simulation technique. Equilibrium +properties of the system exhibit ferrimagnetism with $P$-, $N$- and $Q$- type +behaviors. Compensation phenomenon suddenly disappears with decreasing strength +of indirect ferrimagnetic interlayer exchange coupling. Qualitative properties +are in a good agreement with those obtained by effective field theory. In order +to investigate the stochastic dynamics of kinetic Ising bilayer, we have +introduced two different types of dynamic magnetic fields, namely a square +wave, and a sinusoidally oscillating magnetic field form. For both field types, +compensation point and critical temperature decrease with increasing amplitude +and field period. Dynamic ferromagnetic region in the presence of square wave +magnetic field is narrower than that obtained for sinusoidally oscillating +magnetic field when the amplitude and the field period are the same for each +type of dynamic magnetic fields.",1806.01002v2 +2018-06-28,Spin relaxation in multilayers with synthetic ferrimagnets,"We demonstrate a strong tunability of the spin-pumping contribution to +magnetic damping in a thin-film ferromagnetic free layer interfaced with a +synthetic ferrimagnet (SFM), acting as a spin-sink, via a thin Cu-spacer. The +effect strongly depends on the magnetic state of the SFM, a trilayer structure +composed of two Fe layers coupled via indirect exchange mediated by a Cr +spacer. With increasing Cr thickness, the SFM state undergoes a transition from +an antiparallel via a non-collinear to a parallel configuration. We can explain +the corresponding non-monotonous dependence of spin relaxation in the free +layer in terms of a modulation of the longitudinal spin transport as well as +relaxation of the transverse angular momentum in the SFM. The results should be +useful for designing high-speed spintronic devices where tunability of spin +relaxation is advantageous.",1806.10911v2 +2018-07-07,Topological multiferroic phases in the extended Kane-Mele-Hubbard Model in the Hofstadter regime,"We investigate the new quantum phases on the extended Kane-Mele-Hubbard model +of honeycomb lattice in the Hofstadter regime. In this regime, orbital motion +of the electrons can induce various topological phases with spontaneously +broken symmetries when the spin orbit coupling and electron correlations +coexist. Here, we consider the interaction effects in the Kane-Mele model and +discuss possible phases in the presence of magnetic field at integer fillings +of electrons. In particular, focusing on 2{\pi}/3 magnetic flux per plaquette, +the realization of numerous quantum phases are discussed within the mean field +framework; insulator with coplanar magnetic ordering, ferrimagnetic Chern +insulator with nematic charge order, ferrimagnetic-ferrielectric Chern +insulators etc. Many of these phase transitions are also accompanied with the +change in the topological invariants of the system. Based on our theoretical +study, we propose topological multiferroic phases with a scope of realization +in 2D van-der Waals materials and optical lattice system where the significant +interplay of magnetic field, spin orbit coupling and interactions can be +engineered.",1807.02686v1 +2018-08-25,Twisted magnetization states and inhomogeneous resonance modes in a Fe/Gd ferrimagnetic multilayer,"Static and dynamic magnetic properties of a ferrimagnetic +[Fe(35A)/Gd(50A)]x12 superlattice were investigated in a wide 4-300 K +temperature range using magneto-optical Kerr effect (MOKE) and ferromagnetic +resonance (FMR) techniques. The multilayer structure was sputtered on a +transparent glass substrate which made it possible to perform MOKE measurements +on both Fe and Gd terminated sides of the superlattice. These experiments +allowed us to detect a transition between field-aligned and canted magnetic +states on both sides of the film and to distinguish between the bulk and +surface twisted phases of the superlattice. As a result, the experimental H-T +magnetic phase diagram of the system was obtained. FMR studies at frequencies +7-36 GHz demonstrated a complex evolution of absorption spectra as temperature +decreased from room down to 4 K. Two spectral branches were detected in the +sample. Theoretical simulations show that the observed spectral branches +correspond to different types of inhomogeneous resonance modes in the +multilayer with non-uniform magnetization precession inside Gd layers.",1808.08466v1 +2018-12-13,Imaging Domains in a Zero-Moment Half Metal,"We have a choice of methods for examining domains at the surface of a +ferromagnet that depend on probing the stray field distribution, but these +methods do not work in antiferromagnets or compensated ferrimagnets, which +produce no stray field. The discovery of compensated ferrimagnetic half-metals +allows for the local magnetization state to be observed directly with polarized +light. The example considered here, Mn$_{2}$Ru$_{x}$Ga, has two inequivalent +but oppositely-aligned Mn sublattices with equal and opposite moments, but only +one of them contributes spin polarized conduction electrons at the Fermi +energy. The material looks like an antiferromagnet from the outside, but from +the point of view of electronic structure it resembles a spin-polarized +ferromagnetic metal. The anisotropy axis is perpendicular to the film plane, +which allows domains to be imaged directly by polar magneto-optic Kerr effect. +The domain structure in a film with a composition of Mn$_{2}$Ru$_{0.4}$Ga has +been imaged in a Kerr microscope and hysteresis loops traced. Domains have +dimensions of order 20 {\mu}m with meandering domain walls and a fractal +dimension D$_{f}$ = 1.85. Our results open new direct imaging possibilities for +magnetically-ordered materials with no net moment.",1812.05371v1 +2019-01-02,Giant negative magnetoresistance and kinetic arrest of first-order ferrimagnetic-antiferomagnetic transition in Ge doped Mn$_2$Sb,"Effect of Ge substitution on first order ferrimagnetic (FRI) - +antiferromagnetic (AFM) transition in Mn$_2$Sb has been studied. It shows that +transition temperature (T$_t$) can be tuned between 119~K - 271~K by +substituting 2.5-10\% Ge at Sb site in Mn$_2$Sb. The variation of density of +state at Fermi level N(E$_f$) with Ge substitution shows that dN(E)/dE is +positive at E$_f$ in the AFM state. With the application of magnetic field +T$_t$ shifts to low temperature, which results in a giant negative +magnetoresistance (MR) reaching a value of 70\% for 2.5\% substitution. Our +results show that FRI to AFM transformation during cooling stops around 35 K, +even though it remains incomplete. It along with non-monotonic variation of +lower critical field, open loop in isothermal MR and increasing difference in +zero field cooled warming (ZFCW) and field cooled warming (FCW) resistivity +with increasing magnetic field shows that FRI to AFM transition is kinetically +arrested in the case of 2.5\% Ge substitution.",1901.00442v1 +2019-01-21,Mn4N ferrimagnetic thin films for sustainable spintronics,"Spintronics, which is the basis of a low-power, beyond-CMOS technology for +computational and memory devices, remains up to now entirely based on critical +materials such as Co, heavy metals and rare-earths. Here, we show that Mn4N, a +rare-earth free ferrimagnet made of abundant elements, is an exciting candidate +for the development of sustainable spintronics devices. Mn4N thin films grown +epitaxially on SrTiO3 substrates possess remarkable properties, such as a +perpendicular magnetisation, a very high extraordinary Hall angle (2%) and +smooth domain walls, at the millimeter scale. Moreover, domain walls can be +moved at record speeds by spin polarised currents, in absence of spin-orbit +torques. This can be explained by the large efficiency of the adiabatic spin +transfer torque, due to the conjunction of a reduced magnetisation and a large +spin polarisation. Finally, we show that the application of gate voltages +through the SrTiO3 substrates allows modulating the Mn4N coercive field with a +large efficiency.",1901.06868v2 +2019-01-27,Correlation effects on ground-state properties of ternary Heusler alloys: first-principles study,"The strongly constrained and appropriately normed (SCAN) semi-local +functional for exchange-correlation is deployed to study the ground-state +properties of ternary Heusler alloys transforming martensitically. The +calculations are performed for ferromagnetic, ferrimagnetic, and +antiferromagnetic phases. Comparisons between SCAN and generalized gradient +approximation (GGA) are discussed. We find that SCAN yields smaller lattice +parameters and higher magnetic moments compared to the GGA corresponding values +for both austenite and martensite phases. Furthermore, in the case of +ferromagnetic and non-magnetic Heusler compounds, GGA and SCAN display similar +trends in the total energy as a function of lattice constant and tetragonal +ratio. However, for some ferrimagnetic Mn-rich Heusler compounds, different +magnetic ground states are found within GGA and SCAN.",1901.09460v1 +2019-02-04,Magnetic phase separation in a frustrated ferrimagnetic chain under a magnetic field,"We use density matrix renormalization group to study the first-order quantum +phase transition induced by a magnetic field $h$ in a frustrated ferrimagnetic +chain. The magnetization ($m$) curve as a function of $h$ presents a +macroscopic jump and the energy curve as a function of $m$ has two global +minima. We characterize the two competing phases and study the phase-separated +states in the coexistence region. Also, we observe that the transition is +accompanied by an increase in the number of itinerant singlet pairs between +sites in the unit cells of the chain. Finally, we identify the critical point +at the end of the first-order transition line and a crossover line.",1902.01292v1 +2019-03-19,H-T Phase Diagram of Rare-Earth -- Transition Metal Alloy in the Vicinity of the Compensation Point,"Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic +field and in the vicinity of the compensation temperature have so far been +explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for +ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic +rare-earth ion approximation and taking into account rare-earth (Gd) magnetic +anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice +is larger than that of the $d$-sublattice, the tricritical point can be at +higher temperature than the compensation point. The obtained phase diagram +explains the observed anomalous hysteresis loops as a result of high-field +magnetic phase transition, the order of which changes with temperature. It also +implies that in the vicinity of the magnetic compensation point the shape of +magnetic hysteresis loop is strongly temperature dependent.",1903.07941v1 +2019-04-03,"Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4","Using density-functional theory calculations and experimental investigations +on structural, magnetic and dielectric properties, we have elucidated a unique +tetragonal ground state for MnTi2O4, a Ti^{3+} (3d^1)-ion containing +spinel-oxide. With lowering of temperature around 164 K, cubic MnTi2O4 +undergoes a structural transition into a polar P4_1 tetragonal structure and at +further lower temperatures, around 45 K, the system undergoes a paramagnetic to +ferrimagnetic transition. Magnetic superexchange interactions involving Mn and +Ti spins and minimization of strain energy associated with co-operative +Jahn-Teller distortions plays a critical role in stabilization of the unique +tetramer-orbital ordered ground state which further gives rise to lattice +chirality through subtle Ti-Ti bond-length modulations.",1904.01792v1 +2019-04-03,Observation of Topological Hall Effect and Signature of Room Temperature Antiskyrmions in Mn-Ni-Ga D2d Heusler magnets,"Topologically stable nontrivial spin structures, such as skyrmions and +antiskyrmions, display a large topological Hall effect owing to their quantized +topological charge. Here, we present the finding of a large topological Hall +effect beyond room temperature in the tetragonal phase of a Mn-Ni-Ga based +ferrimagnetic Heusler shape memory alloy system. The origin of the field +induced topological phase, which is also evidenced by the appearance of dips in +the ac-susceptibility measurements, is attributed to the presence of magnetic +antiskyrmions driven by D2d symmetry of the inverse Heusler tetragonal phase. +Detailed micromagnetic simulations asserts that the antiskyrmionic phase is +stabilized as a result of interplay among inhomogeneous Dzyaloshinskii-Moriya +interaction, the Heisenberg exchange, and the magnetic anisotropy energy. The +robustness of the present result is demonstrated by stabilizing the +antiskyrmion hosting tetragonal phase up to a temperature as high as 550 K by +marginally varying the chemical composition, thereby driving us a step closer +to the realization of ferrimagnetic antiskyrmion based racetrack memory.",1904.01894v1 +2019-04-14,Evolution of magnetic ordering in FeCr$_2$Se$_{4-x}$Te$_x$; $x$ = 0 -- 4.0,"We have systematically studied the magnetic properties of chromium chalcogene +compounds FeCr$_2$Se$_{4-x}$Te$_x$. The FeCr2Se4 undergoes antiferromagnetic +ordering below 222 K. Substitution of tellurium lowers the antiferromagnetic +ordering temperature and leads to short range ferromagnetic cluster behavior +towards the tellurium end. Change over from antiferromagnetic to ferrimagnetic +like behavior is also reflected in the corresponding transformation from +semiconducting to metallic transport behavior. There is a large variation in +the Curie-Weiss temperature, effective magnetic moment and ordering temperature +(TN / TC) with Te substitution. The electronic band structure calculations +suggest antiferromagnetic and ferrimagnetic ground state for the FeCr2Se4 and +FeCr2Te4 respectively.",1904.06661v1 +2019-04-19,Sub-terahertz ferrimagnetic spin-transfer torque oscillator,"A theory of magnetization dynamics in ferrimagnetic materials with +antiparallel aligned spin sub-lattices under action of spin-transfer torques +(STT) is developed. We consider magnetization dynamics in GdFeCo layers in two +cases of magnetic anisotropy: easy plane and easy axis. We demonstrate that, +(i) for the easy plane anisotropy the precession of the N\'{e}el vector is +conical and the cone angle depends on the STT strength and the value of spin +non-compensation, while the frequency of precession can reach sub-THz +frequencies; (ii) for the easy axis anisotropy two regimes are possible: +deterministic switching of the net magnetization and a conical sub-THz +precession depending on the STT strength.",1904.09341v1 +2019-04-24,Anomalous thermodynamic response in the vicinity of pseudo-transition of a spin-1/2 Ising diamond chain,"The spin-1/2 Ising diamond chain in a magnetic field displays a remarkable +pseudo-transition whenever it is driven sufficiently close to a ground-state +phase boundary between a classical ferrimagnetic phase and a highly degenerate +frustrated phase. The pseudo-transition of the spin-1/2 Ising diamond chain +relates to intense thermal excitations from a nondegenerate ferrimagnetic +ground state to a highly degenerate manifold of excited states with a +frustrated character, which are responsible for an anomalous behavior of +thermodynamic quantities. Temperature dependences of entropy and specific heat +are indeed reminiscent of a temperature-driven phase transition of a +discontinuous (entropy) or continuous (specific heat) nature though there are +no true singularities of these thermodynamic quantities at a pseudo-critical +temperature.",1904.10704v3 +2019-08-20,Comparing all-optical switching in synthetic-ferrimagnetic multilayers and alloys,"We present an experimental and theoretical investigation of all-optical +switching by single femtosecond laser pulses. Our experimental results +demonstrate that, unlike rare earth-transition metal ferrimagnetic alloys, +Pt/Co/[Ni/Co]$_N$/Gd can be switched in the absence of a magnetization +compensation temperature, indicative for strikingly different switching +conditions. In order to understand the underlying mechanism, we model the +laser-induced magnetization dynamics in Co/Gd bilayers and GdCo alloys on an +equal footing, using an extension of the microscopic three-temperature model to +multiple magnetic sublattices and including exchange scattering. In agreement +with our experimental observations, the model shows that Co/Gd bilayers can be +switched for an arbitrary thickness of the Co layer, i.e, even far away from +compensating the total Co and Gd magnetic moment. We identify the switching +mechanism in Co/Gd bilayers as a front of reversed Co magnetization that +nucleates at the Co/Gd interface and propagates through the Co layer driven by +exchange scattering.",1908.07292v2 +2019-08-23,Precession-free domain wall dynamics in compensated ferrimagnets,"One fundamental obstacle to efficient ferromagnetic spintronics is magnetic +precession, which intrinsically limits the dynamics of magnetic textures, We +demonstrate that the domain wall precession fully vanishes with a record +mobility when the net angular momentum is compensated (TAC) in DWs driven by +spin-orbit torque in a ferrimagnetic GdFeCo/Pt track. We use transverse +in-plane fields to reveal the internal structure of DWs and provide a robust +and parameter-free measurement of TAC. Our results highlight the mechanism of +faster and more efficient dynamics in materials with multiple spin lattices and +reduced net angular momentum, promising for high-speed, low-power spintronics +applications.",1908.08867v2 +2019-08-26,Ferrimagnetism and anisotropic phase tunability by magnetic fields in Na$_2$Co$_2$TeO$_6$,"Na$_2$Co$_2$TeO$_6$ has recently been proposed to be a Kitaev-like honeycomb +magnet. To assess how close it is to realizing Kitaev quantum spin liquids, we +have measured magnetization and specific heat on high-quality single crystals +in magnetic fields applied along high-symmetry directions. Small training +fields reveal a weak but canonical ferrimagnetic behavior below 27 K, which +cannot be explained by the zigzag antiferromagnetic order alone and suggests +coexisting N\'{e}el-type order of moments canted away from the zigzag chains. +Moderate fields in the honeycomb plane suppress the thermal transition at 27 K, +and seem to partly reverse the moment-canting when applied perpendicular to the +zigzag chains. In contrast, out-of-plane fields leave the transition largely +unaffected, but promotes another transition below 10 K, possibly also related +to canting reversal. The magnetism in Na$_2$Co$_2$TeO$_6$ is highly anisotropic +and close to tipping points between competing phases.",1908.09427v1 +2019-11-05,Numerical methods for antiferromagnetics,"Compared with ferromagnetic counterparts, antiferromagnetic materials are +considered as the future of spintronic applications since these materials are +robust against the magnetic perturbation, produce no stray field, and display +ultrafast dynamics. There are (at least) two sets of magnetic moments in +antiferromagnets (with magnetization of the same magnitude but antiparallel +directions) and ferrimagnets (with magnetization of the different magnitude). +The coupled dynamics for the bipartite collinear antiferromagnets is modeled by +a coupled system of Landau-Lifshitz-Gilbert equations with an additional term +originated from the antiferromagnetic exchange, which leads to femtosecond +magnetization dynamics. In this paper, we develop three Gauss-Seidel projection +methods for micromagnetics simulation in antiferromagnets and ferrimagnets. +They are first-order accurate in time and second-order in space, and only solve +linear systems of equations with constant coefficients at each step. +Femtosecond dynamics, N\'{e}el wall structure, and phase transition in presence +of an external magnetic field for antiferromagnets are provided with the +femtosecond stepsize.",1911.01717v1 +2019-12-25,Hybrid nanophotonic-nanomagnonic SiC-YiG quantum sensor: I/ theoretical design and properties,"Here I present the theory of a new hybrid paramagnetic-ferrimagnetic SiC-YiG +quantum sensor. It is designed to allow sub-nanoscale single external spin +sensitivity optically detected pulsed electron electron double resonance +spectroscopy, using an X band pulsed EPR spectrometer and an optical fiber. The +sensor contains one single V2 negatively charged silicon vacancy color center +in 4H-SiC, whose photoluminescence is waveguided by a 4H-SiC nanophotonic +structure towards an optical fiber. This V2 spin probe is created by ion +implantation at a depth of few nanometers below the surface, determined by +optically detected paramagnetic resonance under the strong magnetic field +gradient of a YiG ferrimagnetic nanostripe located on the back-side of the +nanophotonic structure. This gradient also allow the study, slice by slice at +nanoscale, of the target paramagnetic sample. The fabrication process of this +quantum sensor, its magnetic and optical properties, its external spins sensing +properties in a structural biology context, and its integration to a standard +commercially available pulsed EPR spectrometer are all presented here.",1912.11634v1 +2020-03-03,Sub-picosecond exchange-relaxation in the compensated ferrimagnet Mn$_2$Ru$_x$Ga,"We study the demagnetization dynamics of the fully compensated half-metallic +ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled +sublattices are both composed of manganese, they exhibit different temperature +dependencies due to their differing local environments. The sublattice +magnetization dynamics triggered by femtosecond laser pulses are studied to +reveal the roles played by the spin and intersublattice exchange. We find a +two-step demagnetization process, similar to the well-established case of +Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization +rates. The behaviour is analysed using a four-temperature model, assigning +different temperatures to the two manganese spin baths. Even in this strongly +exchange-coupled system, the two spin reservoirs have considerably different +behaviour. The half-metallic nature and strong exchange coupling of +Mn$_2$Ru$_x$Ga lead to spin angular momentum conservation at much shorter time +scales than found for Gd(FeCo)$_3$ which suggests that low-power, +sub-picosecond switching of the net moment of Mn$_2$Ru$_x$Ga is possible.",2003.01420v1 +2020-03-05,Giant Thermal Enhancement of the Electric Polarization in Ferrimagnetic BiFe$_{1-x}$Co$_{x}$O$_{3}$ Solid Solutions Near Room Temperature,"Thermal excitations typically reduce the electric polarization in +ferroelectric materials. Here, we show by means of first-principles +calculations that multiferroic BiFe$_{1-x}$Co$_{x}$O$_{3}$ solid solutions with +$0.25 \le x \le 0.50$ (BFCO) represent a noteworthy exception to this +behaviour. In particular, we find that at room temperature and for moderate +pressures of $0.1$-$1.0$ GPa, depending on the composition, the electric +polarization of bulk BFCO increases by $\sim 200$%. The origin of such an +exceptional behavior is a phase transformation involving a low-$T$ rhombohedral +(${\cal R}$) phase and a high-$T$ super-tetragonal (${\cal T}$) phase. Both +${\cal R}$ and ${\cal T}$ phases are ferrimagnetic near room temperature with +an approximate net magnetization of $0.13$$\mu_{B}$ per formula unit. +Contrarily to what occurs in either bulk BiFeO$_{3}$ or BiCoO$_{3}$, the ${\cal +T}$ phase is stabilized over the ${\cal R}$ by increasing temperature due to +its higher vibrational entropy. This extraordinary $T$-induced ${\cal R} \to +{\cal T}$ phase transition is originated by polar phonon modes involving +concerted displacements of transition-metal and oxygen ions.",2003.02949v1 +2020-05-13,Waveguide cavity optomagnonics for broadband multimode microwave-to-optics conversion,"Cavity optomagnonics has emerged as a promising platform for studying +coherent photon-spin interactions as well as tunable microwave-to-optical +conversion. However, current implementation of cavity optomagnonics in +ferrimagnetic crystals remains orders of magnitude larger in volume than +state-of-the-art cavity optomechanical devices, resulting in very limited +magneto-optical interaction strength. Here, we demonstrate a cavity +optomagnonic device based on integrated waveguides and its application for +microwave-to-optical conversion. By designing a ferrimagnetic rib waveguide to +support multiple magnon modes with maximal mode overlap to the optical field, +we realize a high magneto-optical cooperativity which is three orders of +magnitude higher compared to previous records obtained on polished YIG spheres. +Furthermore, we achieve tunable conversion of microwave photons at around 8.45 +GHz to 1550 nm light with a broad conversion bandwidth as large as 16.1 MHz. +The unique features of the system point to novel applications at the crossroad +between quantum optics and magnonics.",2005.06429v1 +2020-06-14,Hypersonic heat-induced flows of magnons induced by femtosecond laser pulses,"In this work, we present evidence for the existence of a magnonic current on +the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on +ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to +undergo ultrafast switching within 1-2ps after excitation with femtosecond +laser pulses. Here, we show that the strong thermal gradients induced by +applying femtosecond laser pulses and the presence of chemical inhomogeneities +lead to local imbalances in the effective temperatures of the spins that +produces a rapid transfer of spin angular momentum, which we interpret as an +ultrafast spin Seebeck effect. We have quantified the typical magnon +propagation in such a system. The results show ballistic magnon propagation +with 30nm/ps velocities. The characteristic time scale of such magnon +propagation indicates that this magnon transport can play an important role in +switching, a crucial piece of understanding towards realising next generation +data processing devices that operate at much higher frequencies.",2006.07935v1 +2020-08-04,Two-step magnetic ordering into a canted state in ferrimagnetic monoclinic Mn$_3$As$_2$,"We report the magnetic structure of room-temperature-stable, monoclinic +Mn$_3$As$_2$ at 3 K and 250 K using neutron powder diffraction measurements. +From magnetometry data, the Curie temperature of Mn$_3$As$_2$ was confirmed to +be around 270 K. Calorimetry analysis showed the presence of another transition +at 225 K. At 270 K, Mn$_3$As$_2$ undergoes a $k = 0$ ferrimagnetic ordering in +the magnetic space group $C2/m$ (#12.58) with Mn moments pointing along $b$. +Below 225 K, there is a canting of Mn moments in the $ac$ plane which produces +a multi-$k$ non-collinear magnetic structure in space group $C2/c$ (#15.85). +The components of Mn moments along $b$ follow $k=0$ ordering and the components +along $a$ and $c$ have $k = [0 0 \frac{1}{2}]$ propagation vector. The change +in the magnetic ground state with temperature provides a deeper insight into +the factors that govern magnetic ordering in Mn-As compounds.",2008.01776v2 +2020-10-23,Magnetic and structural properties of Ni-substituted magnetoelectric Co$_4$Nb$_2$O$_9$,"The magnetic and structural properties of polycrystalline Co$_{4-x}$ Ni$_x$ +Nb$_2$ O$_9$ (x=1,2) have been investigated by neutron powder diffraction, +magnetization and heat capacity measurements, and density functional theory +(DFT) calculations. For x=1, the compound crystallizes in the trigonal +P$\bar{3}$c1 space group. Below T$_N$ = 31 K it develops a weakly non-collinear +antiferromagnetig structure with magnetic moments in the ab-plane. The compound +with x=2 has crystal structure of the orthorhombic Pbcn space group and shows a +hard ferrimagnetic behavior below T$_C$ =47 K. For this compound a weakly +non-collinear ferrimagnetic structure with two possible configurations in ab +plane was derived from ND study. By calculating magnetic anisotropy energy via +DFT, the ground-state magnetic configuration was determined for this compound. +The heat capacity study in magnetic fields up to 140 kOe provide further +information on the magnetic structure of the compounds.",2010.12285v1 +2020-10-29,Collective spin dynamics under dissipative spin Hall torque,"Current-induced spin torques in layered magnetic heterostructures have many +commonalities across broad classes of magnetic materials. These include not +only collinear ferromagnets, ferrimagnets, and antiferromagnets, but also more +complex noncollinear spin systems. We develop a general Lagrangian-Rayleigh +approach for studying the role of dissipative torques, which can pump energy +into long-wavelength magnetic dynamics, causing dynamic instabilities. While +the Rayleigh structure of such torques is similar for different magnetic +materials, their consequences depend sensitively on the nature of the order +and, in particular, on whether there is a net magnetic moment. The latter +endows the system with a unipolar switching capability, while magnetically +compensated materials tend to evolve towards limit cycles, at large torques, +with chirality dependent on the torque sign. Apart from the ferromagnetic and +antiferromagnetic cases, we discuss ferrimagnets, which display an intricate +competition between switching and limit cycles. As a simple case for +compensated noncollinear order, we consider isotropic spin glasses, as well as +a scenario of their coexistence with a collinear magnetic order.",2010.15994v1 +2020-10-19,Learning phase transitions in ferrimagnetic GdFeCo alloys,"We present results on the identification of phase transitions in +ferrimagnetic GdFeCo alloys using machine learning. The approach for finding +phase transitions in the system is based on the `learning by confusion' scheme, +which allows one to characterize phase transitions using a universal $W$-shape. +By applying the `learning by confusion' scheme, we obtain 2D $W$-a shaped +surface that characterizes a triple phase transition point of the GdFeCo alloy. +We demonstrate that our results are in the perfect agreement with the procedure +of the numerical minimization of the thermodynamical potential, yet our +machine-learning-based scheme has the potential to provide a speedup in the +task of the phase transition identification.",2010.16237v2 +2020-10-31,Facet-dependent magnon-polarons in epitaxial ferrimagnetic Fe3O4 thin films,"Magnon-polarons are coherently mixed quasiparticles that originate from the +strong magnetoelastic coupling of lattice vibrations and spin waves in +magnetic-ordered materials. Recently, magnon-polarons have attracted a lot of +attention since they provide a powerful tool to manipulate magnons, which is +essential for magnon-based spintronic devices. In this work, we report the +experimental observation of facet-dependent magnon-polarons in epitaxial +ferrimagnetic Fe3O4 thin films via spin Seebeck effect measurement. The +critical magnetic fields for the magnon-polarons in the (110)- and +(100)-oriented Fe3O4 films are 1.5 T and 1.8 T, respectively, which arises from +the different phonon velocities along the [110] and [100] directions. As the +temperature decreases, the magnon-polarons-enhanced spin Seebeck voltage +decreases in both (110)- and (100)-oriented Fe3O4 films, which could be +attributed to the enhanced magnon-polarons scattering at elevated temperatures. +This work demonstrates the crystal structure engineering in epitaxial magnetic +films as a promising route to manipulate the magnon-polarons for future magnon +spintronic applications.",2011.00195v1 +2020-11-19,Novel interpretation of recent experiments on the dynamics of domain walls along ferrimagnetic strips,"Domain wall motion along ferrimagnets is evaluated using micromagnetic +simulations and a collective-coordinates model, both considering two +sublattices with independent parameters. Analytical expressions are derived for +strips on top of either a heavy metal or a substrate with negligible +interfacial Dzyaloshinskii-Moriya Interaction. The work focuses its findings in +this latter case, with a field-driven domain wall motion depicting precessional +dynamics which become rigid at the angular momentum compensation temperature, +and a current-driven dynamics presenting more complex behavior, depending on +the polarization factors for each sublattice. Importantly, our analyses provide +also novel interpretation of recent evidence on current-driven domain wall +motion, where walls move either along or against the current depending on +temperature. Besides, our approach is able to substantiate the large +non-adiabatic effective parameters found for these systems.",2011.09736v1 +2021-02-11,Defect-driven ferrimagnetism and hidden magnetization in MnBi$_2$Te$_4$,"MnBi$_2$Te$_4$ (MBT) materials are promising antiferromagnetic topological +insulators where field driven ferromagnetism is predicted to cause a transition +between axion insulator and Weyl semimetallic states. However, the presence of +antiferromagnetic coupling between Mn/Bi antisite defects and the main Mn layer +can reduce the low-field magnetization, and it has been shown that such defects +are more prevalent in the structurally identical trivial magnetic insulator +MnSb$_2$Te$_4$ (MST). We use high-field magnetization measurements to show that +the magnetization of MBT and MST occur in stages and full saturation requires +fields of~$\sim$~60 Tesla. As a consequence, the low-field magnetization +plateau state in MBT, where many determinations of quantum anomalous Hall state +are studied, actually consists of ferrimagnetic septuple blocks containing both +a uniform and staggered magnetization component.",2102.05797v2 +2021-03-04,Strange electrical transport: Colossal magnetoresistance via avoiding fully polarized magnetization in ferrimagnetic insulator Mn3Si2Te6,"Colossal magnetoresistance is of great fundamental and technological +significance and exists mostly in the manganites and a few other materials. +Here we report colossal magnetoresistance that is starkly different from that +in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring +a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of +magnitude with an applied magnetic field above 9 Tesla, leading to an +insulator-metal transition at up to 130 K. However, the colossal +magnetoresistance occurs only when the magnetic field is applied along the +magnetic hard axis and is surprisingly absent when the magnetic field is +applied along the magnetic easy axis where magnetization is fully saturated. +The anisotropy field separating the easy and hard axes is 13 Tesla, unexpected +for the Mn ions with nominally negligible orbital momentum and spin-orbit +interactions. Double exchange and Jahn-Teller distortions that drive the +hole-doped manganites do not exist in Mn3Si2Te6. The phenomena fit no existing +models, suggesting a unique, intriguing type of electrical transport.",2103.02764v1 +2021-06-02,Ultrafast demagnetization in NiCo2O4 thin films probed by time-resolved microscopy,"Using a time-resolved magneto-optical Kerr effect (TR-MOKE) microscope, we +observed ultrafast demagnetization of inverse-spinel-type NiCo2O4 (NCO) +epitaxial thin films of the inverse spinel type ferrimagnet NCO with +perpendicular magnetic anisotropy. This microscope uses a pump-probe method, +where the sample is pumped at 1030 nm, and magnetic domain images are acquired +via MOKE microscopy at 515 nm (the second harmonic). We successfully observed +the dynamics of the magnetic domain of the NCO thin film via laser irradiation, +and obtained a demagnetization time constant of approximately 0.4 ps. This time +constant was significantly smaller than the large time constants reported for +other half-metallic oxides. These results, combined with the results of our +x-ray photoemission spectroscopy study, indicate that this NCO thin film is a +ferrimagnetic metal whose electronic structure deviates from the theoretically +predicted half-metallic one.",2106.01026v2 +2021-06-03,"Relationship between A-site Cation and Magnetic Structure in 3d-5d-4f Double Perovskite Iridates Ln2NiIrO6 (Ln=La, Pr, Nd)","We report a comprehensive investigation of Ln2NiIrO6 (Ln = La, Pr, Nd) using +thermodynamic and transport properties, neutron powder diffraction, resonant +inelastic x-ray scattering, and density functional theory (DFT) calculations to +investigate the role of A-site cations on the magnetic interactions in this +family of hybrid 3d-5d-4f compositions. Magnetic structure determination using +neutron diffraction reveals antiferromagnetism for La2NiIrO6, a collinear +ferrimagnetic Ni/Ir state that is driven to long range antiferromagnetism upon +the onset of Nd ordering in Nd2NiIrO6, and a non-collinear ferrimagnetic Ni/Ir +sublattice interpenetrated by a ferromagnetic Pr lattice for Pr2NiIrO6. For +Pr2NiIrO6 heat capacity results reveal the presence of two independent magnetic +sublattices and transport resistivity indicates insulating behavior and a +conduction pathway that is thermally mediated. First principles DFT calculation +elucidates the existence of the two independent magnetic sublattices within +Pr2NiIrO6 and offers insight into the behavior in La2NiIrO6 and Nd2NiIrO6. +Resonant inelastic x-ray scattering is consistent with spin-orbit coupling +splitting the t2g manifold of octahedral Ir4+ into a Jeff = 1/2 and Jeff = 3/2 +state for all members of the series considered.",2106.02025v1 +2021-06-15,Magnetic properties and phase diagrams of the ferrimagnetic triangular nanotube with core-shell structure: A Monte Carlo study,"Monte Carlo simulation has been employed to investigate the magnetic +properties and phase diagrams of ferrimagnetic mixed-spin (1/2, 1) triangular +Ising nanotube with core-shell structure. In particular, the effect of the +exchange couplings and the temperature on the magnetic and thermodynamic +properties, hysteresis loops as well as the compensation temperature have been +discussed in detail. Moreover, the effects of the single-ion anisotropy, as +well as external magnetic field, have been examined. The threshold values of +the exchange couplings and single-ion anisotropy have been found, determining +whether the system exhibits a compensation temperature. We have found that the +appearance of the compensation temperature is strongly linked with the system +parameters. Moreover, we have obtained the double and triple hysteresis loops +for certain physical parameters in the considered magnetic system.",2106.08397v1 +2021-06-17,Epitaxial growth and magnetic characterization of EuSe thin films with various crystalline orientations,"We report different growth modes and corresponding magnetic properties of +thin EuSe films grown by molecular beam epitaxy on BaF2, Pb1-xEuxSe, GaAs, and +Bi2Se3 substrates. We show that EuSe growth predominantly in (001) orientation +on GaAs(111) and Bi2Se3, but along (111) crystallographic direction on BaF2 +(111) and Pb1-xEuxSe (111). High-resolution transmission electron microscopy +measurements reveal an abrupt and highly crystalline interface for both (001) +and (111) EuSe films. In agreement with previous studies, ordered magnetic +phases include antiferromagnetic, ferrimagnetic, and ferromagnetic phases. In +contrast to previous studies, we found strong hysteresis for the +antiferromagnetic-ferrimagnetic transition. An ability to grow epitaxial films +of EuSe on Bi2Se3 and of Bi2Se3 on EuSe enables further investigation of +interfacial exchange interactions between various phases of an insulating +metamagnetic material and a topological insulator.",2106.09771v1 +2021-07-01,New type of half-metallic fully compensated ferrimagnet,"Half-metallic fully compensated ferrimagnets (HM-FCFMs), a special class of +half-metals exhibiting zero magnetization at absolute zero, are promising +candidates for next-generation spintronics applications. For over 25 years, +theoretical studies have been conducted to realize HM-FCFM materials for +practical applications. Herein, we experimentally demonstrate a NiAs-type +hexagonal-structured (CrFe)S compound that could serve as an HM-FCFM material. +It has a half-metallic nature, with 100% spin-polarized Fermi surfaces and zero +magnetization. Further, the magnetization shows a linear behavior as a function +of the magnetic field below the compensation temperature of around 200 K, with +high magnetic coercivity of 38 kOe at 300 K. These magnetic features are +expected to contribute to a quantum leap in the application of HM-FCFM layers +in spintronics devices.",2107.00258v1 +2021-07-12,Large anomalous Nernst effect in non-crystalline Gd-Fe ferrimagnetic alloy films for flexible thermoelectric applications,"The anomalous Nernst effect (ANE), a heat-charge conversion mechanism based +on a magnetic metal, has been extensively studied for application in thin +thermoelectric devices. The low magnetization and fabrication at room +temperature are important for flexible ANE thermoelectric devices on plastic +substrates. Therefore, we investigated the ANE in ferrimagnetic GdxFe100-x +films with low magnetization in this study by systematically varying the Gd +composition x. Although the Gd33Fe67 film with a Gd composition close to +magnetic compensation composition exhibited very low magnetization, an ANE +coefficient |S_ANE| of 2.13 uV/K was obtained, which is close to the highest +value reported thus far. Finally, we demonstrated the ANE in a Gd33Fe67 film +deposited on a flexible sheet. A sufficient ANE voltage was obtained while +maintaining the flexibility of the sample, indicating the potential application +of this material in thermoelectric devices exploiting the ANE of Gd-Fe films.",2107.05215v2 +2021-07-14,Ultrafast Optomagnonics in Ferrimagnetic Multi-Sublattice Garnets,"This review discusses the ultrafast magnetization dynamics within the +gigahertz to terahertz frequency range in ferrimagnetic rare-earth iron garnets +with different substitutions. In these garnets, the roles of spin-orbit and +exchange interactions have been detected using femtosecond laser pulses via the +inverse Faraday effect. The all-optical control of spin-wave and Kaplan-Kittel +exchange resonance modes in different frequency ranges is shown. Generation and +localization of the electric field distribution inside the garnet through the +metal-bound surface plasmon-polariton strongly enhance the amplitude of the +exchange resonance modes. The exchange resonance mode in yttrium iron garnets +was observed using circularly polarized Raman spectroscopy. The results of this +study may be utilized in the development of a wide class of optomagnonic +devices in the gigahertz to terahertz frequency range.",2107.06597v1 +2021-08-09,Phase diagram of CeSb$_2$ from magnetostriction and magnetization measurements: Evidence for ferrimagnetic and antiferromagnetic states,"Cerium diantimonide (CeSb$_2$) is one of a family of rare earth based +magnetic materials that exhibit metamagnetism, enabling control of the magnetic +ground state through an applied magnetic field. At low temperatures, CeSb$_2$ +hosts a rich phase diagram with multiple magnetically ordered phases for many +of which the order parameter is only poorly understood. In this paper, we +report a study of its metamagnetic properties by Scanning Tunneling Microscopy +(STM) and magnetization measurements. We use STM measurements to characterize +the sample magnetostriction with sub-picometer resolution from magnetic field +and temperature sweeps. This allows us to directly assess the bulk phase +diagram as a function of field and temperature and relate spectroscopic +features from tunneling spectroscopy to bulk phases. Our magnetostriction and +magnetisation measurements indicate that the low temperature ground state at +zero field is ferrimagnetic. Quasiparticle interference mapping shows evidence +for a reconstruction of the electronic structure close to the Fermi energy upon +entering the magnetically ordered phase.",2108.04245v1 +2021-09-04,"Anomalous Hall effect in ferrimagnetic metal RMn6Sn6 (R = Tb, Dy, Ho) with clean Mn kagome lattice","Kagome lattice, made of corner-sharing triangles, provides an excellent +platform for hosting exotic topological quantum states. Here we systematically +studied the magnetic and transport properties of RMn6Sn6 (R = Tb, Dy, Ho) with +clean Mn kagome lattice. All the compounds have a collinear ferrimagnetic +structure with different easy axis at low temperature. The low-temperature +magnetoresistance (MR) is positive and has no tendency to saturate below 7 T, +while the MR gradually declines and becomes negative with the increasing +temperature. A large intrinsic anomalous Hall conductivity about 250 +{\Omega}-1cm-1, 40 {\Omega}-1cm-1, 95 {\Omega}-1cm-1 is observed for TbMn6Sn6, +DyMn6Sn6, HoMn6Sn6, respectively. Our results imply that RMn6Sn6 system is an +excellent platform to discover other intimately related topological or quantum +phenomena and also tune the electronic and magnetic properties in future +studies.",2109.01866v1 +2021-09-09,Adjustable 3D magnetic configuration in ferrimagnetic multilayers with competing interactions visualized by soft X-ray vector tomography,"Soft X-ray magnetic vector tomography has been used to visualize with +unprecedented detail and solely from experimental data the 3D magnetic +configuration of a ferrimagnetic Gd12Co88/Nd17Co83/Gd24Co76 multilayer with +competing anisotropy, exchange and magnetostatic interactions at different +depths. The trilayer displays magnetic stripe domains, arranged in a chevron +pattern, which are imprinted from the central Nd17Co83 into the bottom Gd12Co88 +layer with a distorted closure domain structure across the thickness. Near the +top Gd24Co76 layer, local exchange springs with out-of-plane magnetization +reversal, modulated ripple patterns and magnetic vortices and antivortices +across the thickness are observed. The detailed analysis of the magnetic +tomogram shows that the effective strength of the exchange spring at the +NdCo/GdCo interface can be finely tuned by GdxCo1-x composition and anisotropy +(determined by sample fabrication) and in-plane stripe orientation +(adjustable), demonstrating the capability of 3D magnetic visualization +techniques in magnetic engineering research.",2109.04064v1 +2021-09-21,Influence of a spatial anisotropy on presence of the intermediate one-half magnetization plateau of a spin-1/2 Ising-Heisenberg branched chain,"A spin-1/2 Ising-Heisenberg branched chain constituted by regularly +alternating Ising spins and Heisenberg dimers involving an additional side +branching is exactly solved in a magnetic field by the transfer-matrix method. +The spin-1/2 Ising-Heisenberg branched chain involves two different Ising and +one Heisenberg coupling constants. The overall ground-state phase diagram is +formed by three different ground states emergent depending on a mutual +interplay between the magnetic field and three considered coupling constants: +the modulated quantum antiferromagnetic phase, the quantum ferrimagnetic phase, +and the classical ferromagnetic phase. It is shown that the interaction +anisotropy connected to two different Ising coupling constants substantially +influences a breakdown of the intermediate one-half magnetization plateau, +which represents a macroscopic manifestation of the quantum ferrimagnetic +phase.",2109.10026v1 +2021-10-07,Multitude of Topological Phase Transitions in Bipartite Dice and Lieb Lattices with Interacting Electrons and Rashba Coupling,"We report the results of a Hartree-Fock study applied to interacting +electrons moving in two different bipartite lattices: the dice and the Lieb +lattices, at half-filling. Both lattices develop ferrimagnetic order in the +phase diagram $U$-$\lambda$, where $U$ is the Hubbard onsite repulsion and +$\lambda$ the Rashba spin-orbit coupling strength. Our main result is the +observation of an unexpected multitude of topological phases for both lattices. +All these phases are ferrimagnetic, but they differ among themselves in their +set of six Chern numbers (six numbers because the unit cells have three atoms). +The Chern numbers $|C|$ observed in our study range from 0 to 3, showing that +large Chern numbers can be obtained by the effect of electronic correlations, +adding to the recently discussed methodologies to increase $|C|$ based on +extending the hopping range in tight-binding models, using sudden quenches, or +photonic crystals, all without including electronic interactions.",2110.03813v2 +2021-10-12,Manipulating Ferrimagnets by Fields and Currents,"Ferrimagnets (FIMs) can function as high-frequency antiferromagnets while +being easy to detect as ferromagnets, offering unique opportunities for +ultrafast device applications. While the physical behavior of FIMs near the +compensation point has been widely studied, there lacks a generic understanding +of FIMs where the ratio of sublattice spins can vary freely between the +ferromagnetic and antiferromagnetic limits. Here we investigate the physical +properties of a model two-sublattice FIM manipulated by static magnetic fields +and current-induced torques. By continuously varying the ratio of sublattice +spins, we clarify how the dynamical chiral modes in an FIM are intrinsically +connected to their ferro- and antiferromagnetic counterparts, which reveals +unique features not visible near the compensation point. In particular, we find +that current-induced torques can trigger spontaneous oscillation of the +terahertz exchange mode. Compared with its realization in antiferromagnets, a +spin-torque oscillator using FIMs not only has a reduced threshold current +density but also can be self-stabilized, obviating the need for dynamic +feedback.",2110.06204v3 +2021-10-22,Ultra-low energy threshold engineering for all-optical switching of magnetization in dielectric-coated Co/Gd based synthetic-ferrimagnet,"A femtosecond laser pulse is able to switch the magnetic state of a 3d-4f +ferrimagnetic material on a pico-second time scale. Devices based on this +all-optical switching (AOS) mechanism are competitive candidates for ultrafast +memory applications. However, a large portion of the light energy is lost by +reflection from the metal thin film as well as transmission to the substrate. +In this paper, we explore the use of dielectric coatings to increase the light +absorption by the magnetic metal layer based on the principle of constructive +interference. We experimentally show that the switching energy oscillates with +the dielectric layer thickness following the light interference profile as +obtained from theoretical calculations. Furthermore, the switching threshold +fluence can be reduced by at least $80\%$ to 0.6 mJ/cm$^2$ using two dielectric +SiO$_2$ layers sandwiching the metal stack, which scales to 15 fJ of incident +energy for a cell size of $50^2$ nm$^2$.",2110.12063v1 +2021-12-13,Origins of transverse voltages generated by applied thermal gradients and applied electric fields in ferrimagnetic-insulator/heavy-metal bilayers,"We compare thermal-gradient-driven transverse voltages in +ferrimagnetic-insulator/heavy-metal bilayers (Tm3Fe5O12/W and Tm3Fe5O12/Pt) to +corresponding electrically-driven transverse resistances at and above room +temperature. We find for Tm3Fe5O12/W that the thermal and electrical effects +can be explained by a common spin-current detection mechanism, the physics +underlying spin Hall magnetoresistance (SMR). However, for Tm3Fe5O12/Pt the +ratio of the electrically-driven transverse voltages (planar Hall +signal/anomalous Hall signal) is much larger than the ratio of corresponding +thermal-gradient signals, a result which is very different from expectations +for a SMR-based mechanism alone. We ascribe this difference to a +proximity-induced magnetic layer at the Tm3Fe5O12/Pt interface.",2112.06591v2 +2021-12-24,Three-dimensional ferrimagnetic ground state of triangular-lattice system Ca3Co2O6,"High temperature one-dimensional (1D) ferromagnetic (FM) chains in Ca3Co2O6 +spin system are subjected to a magnetic field and temperature induced first +order phase transition (FOPT) to 3D ferrimagnetic (FIM) ground state with +decrease in temperature (T). Weak-FM interaction of third nearest-neighbor(nn) +interchain removes the frustration effect arising from antiferromagnetic (AFM) +interactions of first-nn and second-nn interchains in the underlying +triangular-lattice resulting a 3D FIM ordering of 1D FM chains at low T. +However, hindered kinetics of FOPT partially masks this tranformation giving +rise to coexistence of non-interacting 1D FM chains with 3D-FIM state at low-T. +The existence of all these couplings is further confirmed here by random +substitution of S = 5/2 magnetic-impurity into the spin chain of original +system. It reveals weakening of FM interactions of both intrachain and third-nn +surrounding chains respectively without significant modulation in the AFM +coupling of first-nn and second-nn interchains. Thus, influence of AFM +interactions is enhanced as compared to effective FM coupling with increase of +S = 5/2 impurity content resulting instability of 3D long-range FIM state at +low-T.",2112.13080v1 +2022-01-06,Large Magnetic-Field-Induced Strain at the Spin-Reorientation Transition in the A-Site Ordered Spinel Oxide LiFeCr4O8,"Sintered samples of a spinel oxide LiFeCr4O8, where Cr3+ and Fe3+ ions have +localized moments, were found to show a large magnetic-field-induced volume +increase approaching 500 ppm by applying a magnetic field of 9 T. This large +volume increase appeared only at around 30 K. At 30 K, a spin-reorientation +transition from ferrimagnetic to conical order occurs, giving rise to this +large volume increase. The coexistence of ferrimagnetic and conical phases at +this transition was found to be important, suggesting that such a large +magnetic-field-induced volume change can be realized at various magnetic +transitions in localized magnets with strong spin-lattice coupling.",2201.01897v1 +2022-01-15,Physical Nature of Magnon Spin Seebeck Effect in Ferrimagnetic Insulators,"The spin Seebeck effect (SSE) in ferrimagnetic insulators (FMI) provides a +simple method of using heat to manipulate magnons, which could be used as +carriers of information and energy conversion. However, a theory that can +quantitively interpret experimental results is still lacking. In this paper, we +develop a transport theory of magnons in FMI at low temperatures by combining +the macroscopic Boltzmann equation with microscopic quantum scattering theory. +It is found that the scattering of magnons is dominated by phonons rather than +magnons, and the relaxation time of magnon is inversely proportional to the +cube of temperature. At extremely low temperature region, the magnon enters the +ballistic transport process. In addition, we also derive the linear spatial +distribution of the transverse SSE signal with sample position. All the +theoretical results are in excellent agreement with the experimental data.",2201.05806v1 +2022-02-01,Ferrimagnetically ordered states in the Hubbard model on the hexagonal golden-mean tiling,"We study magnetic properties of the half-filled Hubbard model on the +two-dimensional hexagonal golden-mean tiling. We find that the vertex model of +the tiling is bipartite, with a sublattice imbalance of $\sqrt{5}/(6\tau^3)$ +(where $\tau$ is the golden mean), and that the non-interacting tight-binding +model gives macroscopically degenerate states at $E=0$. We clarify that each +sublattice has specific types of confined states, which in turn leads to an +interesting spatial pattern in the local magnetizations in the weak coupling +regime. Furthermore, this allows us to analytically obtain the lower bound on +the fraction of the confined states as $(\tau+9)/(6\tau^6)\sim 0.0986$, which +is conjectured to be the exact fraction. These results imply that a +ferrimagnetically ordered state is realized even in the weak coupling limit. +The introduction of the Coulomb interaction lifts the macroscopic degeneracy at +the Fermi level, and induces finite staggered magnetization as well as uniform +magnetization. Likewise, the spatial distribution of the magnetizations +continuously changes with increasing interaction strength. The crossover +behavior in the magnetically ordered states is also addressed in terms of the +perpendicular space analysis.",2202.00205v1 +2022-02-09,Exchange-biased topological transverse thermoelectric effects in a Kagome ferrimagnet,"Kagome metal TbMn6Sn6 was recently discovered to be a ferrimagnetic +topological Dirac material by scanning tunneling microscopy/spectroscopy +measurements. Here, we report the observation of large anomalous Nernst effect +and anomalous thermal Hall effect in this compound. The anomalous transverse +transport is consistent with the Berry curvature contribution from the massive +Dirac gaps in the 3D momentum space as demonstrated by our first-principles +calculations. Furthermore, the transverse thermoelectric transport exhibits +asymmetry with respect to the applied magnetic field, i.e., an exchange-bias +behavior. Together, these features place TbMn6Sn6 as a promising system for the +outstanding thermoelectric performance based on anomalous Nernst effect.",2202.04484v1 +2022-03-08,Coupling between improper ferroelectricity and ferrimagnetism in hexagonal ferrites,"Antisymmetric Dzyaloshinskii-Moriya (DM) interactions generating from the +spin-orbit coupling induce various fascinating properties, like magnetoelectric +(ME) effect, weak ferromagnetism and non-trivial topological spin textures like +skyrmions, in real materials. Compared to their symmetric isotropic exchange +counterpart, these interactions are generally of a weaker order of strength, +creating modest twisting in the spin structure which results in weak +ferromagntism or weak linear ME effect. Our proposed two-sublattice model, in +contrast, predicts a hitherto unobserved, charge ordered non-collinear +ferrimagnetic behavior with a considerably high magnetization $\textbf{M}$ +coexisting with a ferroelectric (FE) order with an electric polarization +$\textbf{P}$ and a strong cross coupling between them which is primarily driven +by the inter-sublattice DM interactions. The key to realize these effects is +the coupling between these microscopic interactions and the FE primary order +parameter. We predict microscopic mechanisms to achieve electric field +$\textbf{E}$ induced spin-reorientation transitions and 180$^{\circ}$ switching +of the direction of $\textbf{M}$. This model was realized in the hexagonal +phase of LuFeO$_3$ doped with electrons. This system shows $P \sim$ 15 +$\mu$C/cm$^2$, $M \sim$ 1.3 $\mu_B$/Fe and magnetic transition near room +temperature ($\sim$ 290 K). Our theoretical results are expected to stimulate +further quest for energy-efficient routes to control magnetism for spintronics +applications.",2203.03841v1 +2022-04-10,Unveiling a Pump-Induced Magnon Mode via its Strong Interaction with Walker Modes,"We observe a power-dependent anticrossing of Walker spin-wave modes under +microwave pumping when a ferrimagnet is placed in a microwave waveguide that +does not support any discrete photon mode. We interpret this unexpected +anticrossing as the generation of a pump-induced magnon mode that couples +strongly to the Walker modes of the ferrimagnet. This anticrossing inherits an +excellent tunability from the pump, which allows us to control the anticrossing +via the pump power, frequency, and waveform. Further, we realize a remarkable +functionality of this anticrossing, namely, a microwave frequency comb, in +terms of the nonlinear interaction that mixes the pump and probe frequencies. +Such a frequency comb originates from the magnetic dynamics and thereby does +not suffer from the charge noise. The unveiled hybrid magnonics driven away +from its equilibrium enriches the utilization of anticrossing for coherent +information processing.",2204.04590v2 +2022-05-24,Steady entangled-state generation via cross-Kerr effect in a ferrimagnetic crystal,"For solid-state spin systems, the collective spin motion in a single crystal +embodies multiple magnetostatic modes. Recently, it was found that the +cross-Kerr interaction between the higher-order magnetostatic mode and the +Kittel mode introduces a new operable degree of freedom. In this work, we +propose a scheme to entangle two magnon modes via the cross-Kerr nonlinearity +when the bias field is inhomogeneous and the system is driven. Quantum +entanglement persists at the steady state, as demonstrated by numerical results +using experimentally feasible parameters. Furthermore, we also demonstrate that +entangled states can survive better in the system where self-Kerr and +cross-Kerr nonlinearities coexist. Our work provides insights and guidance for +designing experiments to observe entanglement between different degrees of +freedom within a single ferrimagnetic crystal. Additionally, it may stimulate +potential applications in quantum information processing using spintronic +devices.",2205.11865v1 +2022-06-17,Theory of ultrafast magnetization of non-magnetic semiconductors with localized conduction bands,"The magnetization of a non-magnetic semiconductor by femtosecond light pulses +is crucial to achieve an all-optical control of the spin dynamics in materials +and to develop faster memory devices. However, the conditions for its detection +are largely unknown. In this work we identify the criteria for the observation +of ultrafast magnetization and critically discuss the difficulties hindering +its experimental detection. We show that ultrafast magnetization of a non +magnetic semiconductor can be observed in compounds with very localized +conduction band states and more delocalized valence bands, such as in the case +of a p-d charge transfer gap. By using constrained and time dependent density +functional theory simulations, we demonstrate that a transient ferrimagnetic +state can be induced in diamagnetic semiconductor V2O5 via ultrafast pulses at +realistic fluences. The ferrimagnetic state has opposite magnetic moments on +vanadium (conduction) and oxygen (valence) states. Our methodology outruns the +case of V2O5 as it identifies the key requirements for a computational +screening of ultrafast magnetism in non-magnetic semiconductors.",2206.08624v1 +2022-08-02,Finite-frequency spin conductance of a ferro-/ferrimagnetic-insulator|normal-metal interface,"The interface between a ferro-/ferrimagnetic insulator and a normal metal can +support spin currents polarized collinear with and perpendicular to the +magnetization direction. The flow of angular momentum perpendicular to the +magnetization direction (""transverse"" spin current) takes place via spin torque +and spin pumping. The flow of angular momentum collinear with the magnetization +(""longitudinal"" spin current) requires the excitation of magnons. In this +article we extend the existing theory of longitudinal spin transport [Bender +and Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in the zero-frequency +weak-coupling limit in two directions: We calculate the longitudinal spin +conductance non-perturbatively (but in the low-frequency limit) and at finite +frequency (but in the limit of low interface transparency). For the +paradigmatic spintronic material system YIG|Pt, we find that non-perturbative +effects lead to a longitudinal spin conductance that is ca. 40% smaller than +the perturbative limit, whereas finite-frequency corrections are relevant at +low temperatures < 100 K only, when only few magnon modes are thermally +occupied.",2208.01420v1 +2022-08-08,Size-dependent mobility of skyrmions beyond pinning in ferrimagnetic GdCo thin films,"Magnetic skyrmions are swirling magnetic textures that can be efficiently +driven with spin-orbit torques with a deflected trajectory. However, pinning +slows skyrmions down and alters their trajectory, which prevents a quantitative +comparison to analytical models. Here, we study skyrmions driven by spin-orbit +torques at room temperature in ferrimagnetic GdCo thin films, an amorphous +material with low pinning. Above a sharp current depinning threshold, we +observe a clearly linear velocity increase with current that extrapolates to +zero and a constant deflection angle, reaching high velocities up to 200 m/s. +The mobility increases and the depinning threshold current decreases with the +skyrmion diameter, which we vary using an external magnetic field. An +analytical model based on the Thiele equation quantitatively reproduces these +findings with a single fitting parameter. This validates the linear flow regime +description and shows, in particular, the important role of skyrmion size in +its dynamics.",2208.04384v2 +2022-10-11,Self organized criticality of magnetic avalanches in disordered ferrimagnetic material,"We observe multiple step-like jumps in a Dy-Fe-Ga-based ferrimagnetic alloy +in its magnetic hysteresis curve at 2 K. The observed jumps have a stochastic +character with respect to their magnitude and the critical field of occurrence, +and the jumps do not show any temporal effect. The jump size distribution +follows a power law variation indicating the scale invariance nature of the +jumps. We have invoked a simple two-dimensional random bond Ising-type spin +system to model the dynamics. Our computational work can qualitatively +reproduce the jumps and their scale invariant character. It also elucidates +that the flipping of antiferromagnetically coupled Dy and Fe clusters is +responsible for the observed discrete avalanche-like features in the hysteresis +loop. These characteristics indicate that the present phenomenon can be well +described within the realm of self-organized criticality",2210.05183v1 +2023-01-24,Ru$_{2-x}$Mn$_{1+x}$Al thin films,"The cubic Heusler alloy Ru$_{2-x}$Mn$_{1+x}$Al is grown in thin film form on +MgO and MgAl$_2$O$_4$ substrates. It is a highly spin-polarised ferrimagnetic +metal, with weak magnetocrystalline anisotropy. Although structurally and +chemically similar to $\text{Mn}_2\text{Ru}_x\text{Ga}$, it does not exhibit +ferrimagnetic compensation, or large magneto galvanic effects. The differences +are attributed to a combination of atomic order and the hybridisation with the +group 13 element Al or Ga. The spin polarisation is around 50 to 60 %. There is +a gap in the density of states just above the Fermi level in fully ordered +compounds.",2301.10148v2 +2023-02-17,Entangling ferrimagnetic magnons with an atomic ensemble via opto-magnomechanics,"We show how to prepare macroscopic entanglement between an atomic ensemble +and a large number of magnons in a ferrimagnetic YIG crystal. Specifically, we +adopt an opto-magnomechanical configuration where the magnetostriction-induced +magnomechanical displacement couples to an optical cavity via radiation +pressure, and the latter further couples to an ensemble of two-level atoms that +are placed inside the cavity. We show that by properly driving the cavity and +magnon modes, optomechanical entanglement is created which is further +distributed to the atomic and magnonic systems, yielding stationary +entanglement between atoms and magnons. The atom-magnon entanglement is a +result of the combined effect of opto- and magnomechanical cooling and +optomechanical parametric down-conversion interactions. A competition mechanism +between two mechanical cooling channels is revealed. We further show that +genuine tripartite entanglement of three massive subsystems, i.e., atoms, +magnons and phonons, can also be achieved in the same system. Our results +indicate that the hybrid opto-magnomechanical system may become a promising +system for preparing macroscopic quantum states involving magnons, photons, +phonons and atoms.",2302.08684v2 +2023-02-27,Anomalous Nernst effect in a ferrimagnetic nodal-line semiconductor Mn$_3$Si$_2$Te$_6$,"In the ferrimagnetic nodal-line semiconductor Mn$_3$Si$_2$Te$_6$, colossal +magnetoresistance (CMR) arises below $T_\mathrm{c}=78$ K due to the interplay +of magnetism and topological nodal-line fermiology. The Berry curvature +associated with the topological nodal-line is expected to produce an anomalous +Nernst effect. Here, we present sizable anomalous Nernst signal in +Mn$_3$Si$_2$Te$_6$ below $T_\mathrm{c}$. In the low-magnetic-field region where +CMR is most apparent, the scaling ratio between the Nernst signal and +magnetization is significantly enhanced compared to that in conventional +magnetic materials. The enhanced Nernst effect and CMR likely share the same +mechanisms, which are closely linked to the nodal-line topology.",2302.13735v1 +2023-03-05,Electrical detection of antiferromagnetic dynamics in Gd-Co thin films by using a 154-GHz gyrotron irradiation,"THz magnetization dynamics is a key property of antiferromagnets as well as +ferrimagnets that could harness the THz forefront and spintronics. While most +of the present THz measurement techniques are for bulk materials whose +sensitivities rely on the volume of the material, measurement techniques +suitable for thin films are quite limited. In this study, we explored and +demonstrated electrical detection of the antiferromagnetic dynamics in +ferrimagnetic Gd-Co thin films by using a 154 GHz gyrotron, a high-power +electromagnetic wave source. Captured resonant modes allow us to characterize +the peculiar magnetization dynamics of the Gd-Co around the net angular +momentum compensation. As the gyrotron frequency is scalable up to THz, our +demonstration can be an important milestone toward the THz measurements for +antiferro- and ferri- magnetic thin films.",2303.02639v1 +2023-03-28,Exploring terahertz-scale exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents,"Using spin currents generated by fs laser pulses, we demonstrate excitation +of GHz ferromagnetic resonance and THz ferrimagnetic exchange resonances in +Co/Gd/Co/Gd multilayers by time-resolved magneto-optic Kerr effect +measurements. Varying the Gd layer thickness allows for a tuning of the +resonance spectrum by manipulating the total angular momentum and strength of +effective exchange fields between the antiferromagnetically coupled layers. +Close to the compensation point of angular momentum, a minimum in the frequency +of the exchange-dominated mode and a maximum in the frequency of the +ferromagnetic resonance mode is observed. Finally, to gain better understanding +of the excitation mechanism, we analyze the anomalous variation in the measured +exchange mode amplitude as a function of its frequency. A peak in this +amplitude in the vicinity of the compensation point of angular momentum is +explained using a macrospin model, taking nonlinear effects at finite +precession amplitudes into account.",2303.15985v2 +2023-04-05,Intrinsic Origin and Enhancement of Topological Responses in Ferrimagnetic Antiperovskite Mn4N,"Using first-principles calculations we investigate the intrinsic origins of +the anomalous Hall effect (AHE) and the anomalous Nernst effect (ANE) in +antiperovskite ferrimagnet Mn4N. We predict that the AHE is significantly +enhanced under both compressive and tensile strain, however, the ANE generally +decreases under epitaxial strain, except for 1% compressive strain. We connect +this behavior to the evolution of the Berry curvature with strain, suggesting +similar strategies for achieving large AHE and ANE changes with modest amounts +of strain. Finally, we find that the non-monotonic characteristics of the AHE +and ANE stem from the formation and movement of new Weyl points at the +periphery of the Brillouin Zone under compressive and tensile strains.",2304.02750v1 +2023-04-13,Finite Temperature Dynamics of Spin Solitons with Applications in Thermocouples and Refrigerators,"The exploitation of spin Berry phases to generate emergent fields for +producing miniaturized and high-quality inductors has enjoyed considerable +popularity among proponents of quantum technologies [Nature 586, 202 (2020)}]. +Inspired by this breakthrough, we extend its mechanism to spin thermoelectrics +by probing responses of ferrimagnetic domain walls (DWs) to thermal gradients. +Similarly, voltages here stem from DW-spin collective motion, in contrast to +normal electron transport phenomena. We further develop finite-temperature +dynamics to investigate thermoelectric figures of merit and attribute +corresponding quantum superiority to ultrafast spin evolution of ferrimagnetism +with tunable non-Abelian phases. We propose a more likely cause of DW motion +towards hot or cold regions (contrary to conclusions of previous reports) and +verify existence of efficient magnon-momentum transfers. These findings deepen +our understanding of heat-driven DW kinetics and suggest profitable new +directions in an emerging realm of spincaloritronics.",2304.06608v1 +2023-04-18,Efficient characteristics of exchange coupling and spin-flop transition in Py/Gd bilayer using anisotropic magnetoresistance,"The interlayer antiferromagnetic coupling rare-earth/transition-metal bilayer +ferrimagnet systems have attracted much attention because they present +variously unusual temperature-and field-dependent nontrivial magnetic states +and dynamics. These properties and the implementation of their applications in +spintronics highly depend on the significant temperature dependence of the +magnetic exchange stiffness constant A. Here, we quantitatively determine the +temperature dependence of magnetic exchange stiffness A_{Py-Gd} and A_{Gd} in +the artificially layered ferrimagnet consisting of a Py/Gd bilayer, using a +measurement of anisotropic magnetoresistance (AMR) of the bilayer thin film at +different temperatures and magnetic fields. The obtained temperature dependence +of A_{Py-Gd} and A_{Gd} exhibit a scaling power law with the magnetization of +Gd. The critical field of spin-flop transition and its temperature dependence +can also be directly obtained by this method. Additionally, the experimental +results are well reproduced by micromagnetic simulations with the obtained +parameters A_{Py-Gd} and A_{Gd}, which further confirms the reliability of this +easily accessible technique.",2304.08858v1 +2023-05-02,Magnetic inhomogeneities in the quadruple perovskite manganite [Y$_{2-x}$Mn$_x$]MnMnMn$_4$O$_{12}$,"A combination of competing exchange interactions and substitutional disorder +gives rise to magnetic inhomogeneities in the +[Y$_{2-x}$Mn$_x$]MnMnMn$_4$O$_{12}$ $x = 0.23$ and $x = 0.16$ quadruple +perovskite manganites. Our neutron powder scattering measurements show that +both the $x = 0.23$ and $x = 0.16$ samples separate into two distinct magnetic +phases; below T$_{1}$ = 120 $\pm$ 10 K the system undergoes a transition from a +paramagnetic phase to a phase characterised by short range antiferromagnetic +clusters contained in a paramagnetic matrix, and below T$_{2}$ $\sim$ 65 K, the +system is composed of well correlated long range collinear ferrimagnetic order, +punctuated by short range antiferromagnetic clusters. A sharp increase in the +antiferromagnetic phase fraction is observed below $\sim$ 33 K, concomitant +with a decrease in the ferrimagnetic phase fraction. Our results demonstrate +that the theoretically proposed AFM phase is stabilised in the +[Y$_{2-x}$Mn$_x$]MnMnMn$_4$O$_{12}$ manganites in the presence of dominant B-B +exchange interactions, as predicted.",2305.01804v1 +2023-05-25,Random-anisotropy mixed-spin Ising on a triangular lattice,"We have studied the mixed spin-1/2 and 1 Ising ferrimagnetic system with a +random anisotropy on a triangular lattice with three interpenetrating +sublattices $A$, $B$, and $C$. The spins on the sublattices are represented by +$\sigma_{A}$ (states $\pm1/2$), $\sigma_{B}$ (states $\pm1/2$), and $S_{C}$ +(states $\pm1$, $0$). We have performed Monte Carlo simulations to obtain the +phase diagram temperature $k_{\text{B}}T/\left|J\right|$ versus the strength of +the random anisotropy $D/\left|J\right|$. The phase boundary between two +ferrimagnetic $FR_{1}$ and $FR_{2}$ phases at lower temperatures are always +first-order for $p<0.25$ and second-order phase transition between the +$FR_{1}$, $FR_{2}$ and the paramagnetic $P$ phases. On the other hand, for +values of $p\gtrapprox0.5$, the phase diagram presents only second-order phase +transition lines.",2305.15866v1 +2023-06-02,Ultrafast single-pulse all-optical switching in synthetic ferrimagnetic Tb/Co/Gd multilayers,"In this work, we investigate single-shot all-optical switching (AOS) in +Tb/Co/Gd/Co/Tb multilayers in an attempt to establish AOS in synthetic +ferrimagnets with high perpendicular magnetic anisotropy. In particular, we +study the effect of varying Tb thicknesses to disentangle the role of the two +rare earth elements. Even though the role of magnetic compensation has been +considered to be crucial, we find that the threshold fluence for switching is +largely independent of the Tb content. Moreover, we identify the timescale for +the magnetization to cross zero to be within the first ps after laser +excitation using time-resolved MOKE. We conclude that the switching is governed +mostly by interactions between Co and Gd.",2306.01419v3 +2023-08-16,Even-Odd-Layer-Dependent Symmetry Breaking in Synthetic Antiferromagnets,"In this work we examine synthetic antiferromagnetic structures consisting of +two, three, and four antiferromagnetic coupled layers, i.e., bilayers, +trilayers, and tetralayers. We vary the thickness of the ferromagnetic layers +across all structures and, using a macrospin formalism, find that the nearest +neighbor exchange interaction between layers is consistent across all +structures for a given thickness. Our model and experimental results +demonstrate significant differences in how the magnetostatic equilibrium states +of even and odd-layered structures evolve as a function of the external field. +Even layered structures continuously evolve from a collinear antiferromagnetic +state to a spin canted non-collinear magnetic configuration that is +mirror-symmetric about the external field. In contrast, odd-layered structures +begin with a ferrimagnetic ground state; at a critical field, the ferrimagnetic +ground state evolves into a non-collinear state with broken symmetry. +Specifically, the magnetic moments found in the odd-layered samples possess +stable static equilibrium states that are no longer mirror-symmetric about the +external field after a critical field is reached. Our results reveal the rich +behavior of synthetic antiferromagnets.",2308.08684v1 +2023-08-28,Coherent Spin-Phonon Coupling in the Layered Ferrimagnet Mn3Si2Te6,"We utilize ultrafast photoexcitation to drive coherent lattice oscillations +in the layered ferrimagnetic crystal Mn3Si2Te6, which significantly stiffen +below the magnetic ordering temperature. We suggest that this is due to an +exchange-mediated contraction of the lattice, stemming from strong +magneto-structural coupling in this material. Additionally, simulations of the +transient incoherent dynamics reveal the importance of spin relaxation channels +mediated by optical and acoustic phonon scattering. Our findings highlight the +importance of spin-lattice coupling in van der Waals magnets and a promising +route for their dynamic optical control through their intertwined electronic, +lattice, and spin degrees of freedom.",2308.14931v1 +2023-09-25,Low-temperature giant coercivity in Co$_{6.2}$Ga$_{3.8-x}$Ge$_{x}$ ($x$=2.4 to 3.2),"The observation of giant coercivity exceeding 20 kOe at low temperatures in +several transition-metal-based compounds has attracted significant attention +from a fundamental perspective. This research is also relevant to developing +rare-earth-free permanent magnets, wherein cobalt is one of the primary +elements used. To facilitate easy fabrication, rare-earth-free and Co-based +inorganic bulk magnets that exhibit giant coercivity are highly demanded but +rarely reported. Herein, we report the observation of low-temperature giant +coercivity in polycrystalline metallic Co$_{6.2}$Ga$_{3.8-x}$Ge$_{x}$ ($x$=2.4 +to 3.2) with the hexagonal Fe$_{13}$Ge$_{8}$-type structure composed of Kagome +and triangular lattices. As the Ge content $x$ decreases from 3.2, the magnetic +ground state changes from ferrimagnetism to ferromagnetism at $x$=2.6. In the +ferrimagnetic state, we observed a signature of spin frustration arising from +the Kagome and/or triangular lattices of Co atoms. The ferromagnetic ordering +temperatures for the $x$=2.6 and 2.4 samples are 46 K and 60 K, respectively. +The coercive fields rapidly increase upon cooling and reach values of 26 kOe +and 44 kOe in the $x$=2.6 and 2.4 samples, respectively, at 2 K.",2309.14565v1 +2023-10-20,Surface-symmetry-driven Dzyaloshinskii--Moriya interaction and canted ferrimagnetism in collinear magnetoelectric antiferromagnet Cr$_2$O$_3$,"Antiferromagnets are normally thought of as materials with compensated +magnetic sublattices. This adds to their technological advantages but +complicates readout of the antiferromagnetic state. We demonstrate +theoretically the existence of a Dzyaloshinskii-Moriya interaction (DMI) which +is determined by the magnetic symmetry classes of Cr$_2$O$_3$ surfaces with an +in-plane magnetic easy axis. The DMI explains a previously predicted +out-of-plane magnetization at the nominally compensated surfaces of chromia, +leading to a surface-localized canted ferrimagnetism. This is in agreement with +magnetotransport measurements and with density functional theory predictions +which further allow us to quantify the strength of DMI. The temperature +dependence of the transversal resistance for these planes shows distinct +behavior in comparison with that of the Cr$_2$O$_3$ $c$ plane, which we +attribute to the influence of DMI. Our work provides a framework to analyze +surface-driven phenomena in antiferromagnets, and motivates the use of +nominally compensated chromia surfaces for antiferomagnetic spintronics and +magnonics.",2310.13438v1 +2023-12-15,Hyperbolic Bloch points in ferrimagnetic exchange spring,"Bloch points in magnetic materials are attractive entities in view of +magnetic information transport. Here, Bloch point configuration has been +investigated and experimentally determined in a magnetic trilayer +($Gd_{12}Co_{88}/Nd_{17}Co_{83}/Gd_{24}Co_{76}$) with carefully adjusted +composition within the ferrimagnetic $Gd_{x}Co_{1-x}$ alloys in order to +engineer saturation magnetization, exchange length, and interlayer couplings +(ferromagnetic vs antiferromagnetic). X-ray vector magnetic tomography has +allowed us to determine experimentally Bloch point polarity (related to +topological charge) and Bloch point helicity ${\gamma}$ (determined by +magnetostatic energy). At the bottom layer (close to the ferromagnetic +interface), Bloch points adopt a standard circulating configuration with +helicity ${\gamma}$ close to ${\pi}/2$. Within the top layer (with much lower +saturation magnetization), Bloch points nucleate within a Neel-like exchange +spring domain wall created by the antiferromagnetic coupling and adopt an +uncommon hyperbolic configuration, characterized by much larger helicity +angles. Our results indicate a path for Bloch point engineering in future +applications adjusting material parameters and domain wall characteristics.",2312.09836v1 +2023-12-16,Spin-torque nano-oscillator based on two in-plane magnetized synthetic ferrimagnets,"We report the dynamic characterization of the spin-torque-driven in-plane +precession modes of a spin-torque nano-oscillator based on two different +synthetic ferrimagnets: a pinned one characterized by a strong RKKY interaction +which is exchange coupled to an antiferromagnetic layer; and a second one, +non-pinned characterized by weak RKKY coupling. The microwave properties +associated with the steady-state precession of both SyFs are characterized by +high spectral purity and power spectral density. However, frequency dispersion +diagrams of the damped and spin transfer torque modes reveal drastically +different dynamical behavior and microwave emission properties in both SyFs. In +particular, the weak coupling between the magnetic layers of the non-pinned SyF +raises discontinuous dispersion diagrams suggesting a strong influence of mode +crossing. An interpretation of the different dynamical features observed in the +damped and spin torque modes of both SyF systems was obtained by solving +simultaneously, in a macrospin approach, a linearized version of the +Landau-Lifshitz-Gilbert equation including the spin transfer torque term.",2312.10451v2 +2024-01-19,Diversity of Ultrafast Spin Dynamics Near the Tricritical Point in a Ferrimagnetic Gd/FeCo Multilayer,"It is found that subtle changes in the external magnetic field and +temperature result in dramatic changes in the ultrafast response of spins to a +femtosecond laser excitation in a ferrimagnetic Gd/FeCo multilayer. A total of +six distinct types of spin dynamics were observed and explained by considering +the spin-flop transition to the noncollinear phase and the concept of a +tricritical point in the $H$-$T$ phase diagram. A particularly interesting type +of dynamics is the exchange-driven reversal. These exchange-driven dynamics +provide new insights into the tricritical point, which is shown to separate two +thermodynamically distinct noncollinear phases with the transition-metal +magnetization pointing on adjacent sides of the anisotropy plane.",2401.10671v1 +2024-02-09,Level attraction in a quasi-closed cavity,"We provide a comprehensive analytical description of the effective coupling +associated with an antiresonance within a hybrid system comprised of a +quasi-closed photonic cavity and a ferrimagnetic material. Whilst so-called +level attraction between a resonant system inside an open cavity is well +understood, the physical underpinnings of this phenomena within quasi-closed +cavities have remained elusive. Leveraging the input-output theory, we +successfully differentiate between the repulsive and attractive aspects of this +coupling. Our proposed model demonstrates that by understanding the phase-jump +at the resonances and the studied antiresonance, we can predict the nature of +the effective coupling of the antiresonance for a given position of the +ferrimagnet in the cavity.",2402.06258v2 +2024-04-08,Multiple Floquet Chern insulator phases in the spin-charge coupled triangular-lattice ferrimagnet: Crucial roles of higher-order terms in the high-frequency expansion,"We study the effects of photoirradiation with circularly polarized light on +the Dirac half-metal state induced by the ferrimagnetic order in a triangular +Kondo-lattice model. Our analysis based on the Floquet theory reveals that two +types of Floquet Chern insulator phases appear as photoinduced nonequilibrium +steady states and that these two phases can be experimentally detected and +distinguished by measurements of the Hall conductivity. It is elucidated that +these rich nonequilibrium topological phases come from higher-order terms in +the high-frequency expansion called Brillouin-Wigner expansion, which is in +striking contrast to usually discussed Floquet Chern insulator phases +originating from the lowest-order terms of the expansion. So far, the lattice +electron models on simple non-multipartite lattices such as triangular lattices +and square lattices have not been regarded as targets of the Floquet +engineering because the lowest-order terms of the high-frequency expansion for +Floquet effective Hamiltonians cancel each other to vanish in these systems. +Our findings of the Floquet Chern insulator phases in a triangular +Kondo-lattice model are expected to expand the range of potential models and +even materials targeted by the Floquet engineering.",2404.05385v1 +2014-04-21,"Re-t2g-splitting-driven semiconductor gaps in ferrimagnetic double perovskite Ca2MReO6 (M=Cr,Fe) from first principles","Motivated by the observation of nonmetallic nature in double perovskite +Ca2CrReO6 and Ca2FeReO6 with high magnetic Curie temperatures of 360 and 522 K, +we systematically investigate the structural, electronic, and magnetic +properties of Ca2MReO6 (M=Cr,Fe) using the full-potential linear augmented +plane wave (FP-LAPW) method within the density functional theory. Our full +optimization confirms the stable ground-state structure with $P2_1/n$ symmetry. +The modified Becke-Johnson (mBJ) exchange potential is used for investigating +electronic structures. Our mBJ calculation shows that they are both +ferrimagnetic semiconductors with semiconductor gaps of 0.38 eV and 0.05 eV, +respectively, in contrast with wrong metallic phases from the generalized +gradient approximation (GGA). The origin of semiconductor gap is due to the +further distortion of ReO$_6$ octahedra caused by John-Teller effect, which +drives the three partially-occupied Re $t_{2g}$ bands split into two +fully-filled bands and one empty band in the minority-spin channel. With the +spin-orbit coupling (SOC) taken into account, the Ca2MReO6 (M=Cr,Fe) shows high +magneto-crystalline anisotropy (MCA) with the magnetic easy axis along +pseudocubic [010] direction, and the total magnetic moments increase by +0.209$\mu_B$ and 0.258$\mu_B$ per formula unit, respectively, due to the strong +SOC effect on Re ion. Although reducing to 0.31 and 0.03 eV, the semiconductor +gaps remain open in spite of the SOC broadening of the Re $t_{2g}$-related +bands. Therefore, our DFT investigation with mBJ has established the correct +ferrimagnetic semiconductor ground state for the double perovskites Ca2MReO6 +(M=Cr,Fe). This mechanism, different from that in double perovskite Sr2CrOsO6, +can help understand physical properties of other similar compounds.",1404.5091v2 +2020-02-04,Magnetic behavior of a ferro-ferrimagnetic ternary alloy AB$_ρ$C$_{1-ρ}$ with a selective site disorder: the case study of a mixed-spin Ising model on a honeycomb lattice,"Phase transitions, compensation phenomenon and magnetization of a +ferro-ferrimagnetic ternary alloy AB$_{\rho}$C$_{1-\rho}$ composed of three +different kinds of magnetic ions A, B and C with the spin magnitude 1/2, 1 and +3/2 are examined within the framework of a mixed-spin Ising model on a +honeycomb lattice with a selective annealed site disorder on one of its two +sublattices. It is supposed that the first sublattice of a bipartite honeycomb +lattice is formed by the spin-1/2 magnetic ions, while the sites of the second +sublattice are randomly occupied either by the spin-1 magnetic ions with a +probability $\rho$ or the spin-3/2 magnetic ions with a probability $1-\rho$, +both being subject to a uniaxial single-ion anisotropy. The model under +investigation can be exactly mapped into an effective spin-1/2 Ising model on a +triangular lattice through the generalized star-triangle transformation. For a +specific concentration of the spin-1 (spin-3/2) magnetic ions, it is shown that +the ferro-ferrimagnetic version of the studied model may display a compensation +temperature at which the total magnetization vanishes below a critical +temperature. The critical temperature strikingly may also become independent of +the concentration of the randomly mixed spin-1 and spin-3/2 magnetic ions for a +specific value of a uniaxial single-ion anisotropy. The spontaneous magnetic +order may be notably restored at finite temperatures through the +order-by-disorder mechanism above a disordered ground state, which results in +an anomalous temperature dependence of the total magnetization with double +reentrant phase transitions.",2002.01572v1 +2020-12-10,Magnetic order and magneto-transport in half-metallic ferrimagnetic Mn$_y$Ru$_x$Ga thin films,"The ruthenium content of half-metallic Mn$_2$Ru$_x$Ga thin films, with a +biaxially-strained inverse Heusler structure, controls the ferrimagnetism that +determines their magnetic and electronic properties. An extensive study of +Mn$_y$Ru$_x$Ga films on MgO (100) substrates with $1.8 \leq y \leq 2.6$ and $x += 0.5$, 0.7 or 0.9, including crystallographic, magnetic order, +magneto-transport and spin polarisation is undertaken to map specific +composition-dependent properties in this versatile ternary system. A comparison +of experimental densities obtained from X-ray reflectivity with calculated +densities indicates full site occupancy for all compositions, which implies +chemical disorder. All moments lie on the Slater-Pauling plot with slope 1 and +all except $x = 0.5$, $y = 2.2$ exhibit magnetic compensation at \tcmp~below +500~K. The coercivity near \tcmp~exceeds 10~T. Increasing the Mn or Ru content +raises \tcmp, but increasing Ru also decreases the spin polarisation determined +by point contact Andreev reflection. Molecular field theory is used to model +the temperature dependence of the net ferrimagnetic moment and three principal +exchange coefficients are deduced. Marked differences in the shape of anomalous +Hall and net magnetisation hysteresis loops are explained by substantial +canting of the small net moment by up to \SI{40}{\degree} relative to the +$c$-axis in zero field, which is a result of slight non-collinearity of the +Mn$^{4c}$ sublattice moments due to competing intra-sublattice exchange +interactions arising from antisite disorder and excess Mn in the unit cell. +Consequences are reduced spin polarisation and an enhanced intrinsic +contribution to the anomalous Hall effect. The systematic investigation of the +physical properties as a function of $x$ and $y$ will guide the selection of +compositions to meet the requirements for magnonic and spintronic MRG-based +devices.",2012.05736v5 +2021-01-14,Intriguing magnetism of the topological kagome magnet TbMn_6Sn_6,"Magnetic topological phases of quantum matter are an emerging frontier in +physics and material science. Along these lines, several kagome magnets have +appeared as the most promising platforms. Here, we explore magnetic +correlations in the transition-metal-based kagome magnet TbMn$_{6}$Sn$_{6}$ +using muon spin rotation, combined with local field analysis and neutron +diffraction. Our results show that the system exhibits an out-of-plane +ferrimagnetic structure $P6/mm'm'$ (comprised by Tb and Mn moments) with slow +magnetic fluctuations below $T_{\rm C2}$~=~320~K. These fluctuations exhibit a +slowing down below $T_{\rm C1}^{*}$~${\simeq}$~120~K, and we see the formation +of static patches with ideal out-of-plane order below $T_{\rm +C1}$~${\simeq}$~20~K which grow in a volume with decreasing temperature. The +appearance of the static patches has a similar onset to the interesting +phenomenon such as spin-polarized Dirac dispersion with a large Chern gap and +topological edge states. We further show that the temperature evolution of the +anomalous Hall conductivity (AHC) is strongly influenced by the low temperature +magnetic crossover. Our presented experimental results show that the onset of +the topological electronic properties tied to the Dirac band is promoted only +by true static out-of-plane ferrimagnetic order in TbMn$_{6}$Sn$_{6}$ and is +washed out by the slow magnetic fluctuations above $T_{\rm +C1}$~${\simeq}$~20~K. Remarkably, hydrostatic pressure of 2.1 GPa stabilises +static out-of-plane topological ferrimagnetic ground state in the whole volume +of the sample. Therefore the exciting perspective arises of a magnetic system +in which the topological response can be controlled, and thus explored, over a +wide range of parameters.",2101.05763v2 +2020-03-20,"Neutron Diffraction Evidence for Local Spin Canting, Weak Jahn-Teller Distortion, and Magnetic Compensation in Ti$_{1-x}$Mn$_{x}$Co$_2$O$_4$ Spinel","A systematic study using neutron diffraction and magnetic susceptibility are +reported on Mn substituted ferrimagnetic inverse spinel +Ti$_{1-x}$Mn$_{x}$Co$_2$O$_4$ in the temperature interval 1.6 K $\leq$ $T$ +$\leq$ 300 K. Our neutron diffraction study reveals cooperative distortions of +the $T$O$_6$ octahedral for all the Jahn-Teller active ions $T$ = Mn$^{3+}$, +Ti$^{3+}$ and Co$^{3+}$, which are confirmed by the X-ray photoelectron +spectroscopy. Two specific compositions ($x$ = 0.2 and 0.4) have been chosen +because of their unique features: noncollinear Yafet-Kittel type ordering, and +weak tetragonal distortion with ${c/a}$ $<$ 1, in which the apical bond length +$d_c$($T_B$-O) is longer than the equatorial $d_{ab}$($T_B$-O) due to the +splitting of the $e_g$ level of Mn$^{3+}$ ions into $d_{x^2-y^2}$ and +$d_{z^2}$. For $x$ = 0.4, the distortion in the $T_B$O$_6$ octahedra is +stronger as compared to $x$ = 0.2 because of the higher content of trivalent +Mn. Ferrimagnetic ordering in $x$ = 0.4 and $x$ = 0.2 sets in at 110.3 and 78.2 +K, respectively due to the unequal magnetic moments of cations, where +Ti$^{3+}$, Mn$^{3+}$, and Co$^{3+}$ occupying the octahedral, whereas, +Co$^{2+}$ sits in the tetrahedral site. In addition, weak antiferromagnetic +component could be observed lying perpendicular to the ferrimagnetic component. +The analysis of static and dynamic magnetic susceptibilities combined with the +heat-capacity data reveals a magnetic compensation phenomenon at $T_{COMP}$ = +25.4 K in $x$ = 0.2 and a reentrant spin-glass behaviour in $x$ = 0.4 with a +freezing temperature $\sim$110.1 K. The compensation phenomenon is +characterized by sign reversal of magnetization and bipolar exchange bias +effect below $T_{COMP}$ with its magnitude depending on the direction of +external magnetic field and the cooling protocol.",2003.09308v1 +2021-07-16,Intra-unitcell cluster-cluster magnetic compensation and large exchange bias in cubic alloys,"Composite quantum materials are the ideal examples of multifunctional systems +which simultaneously host more than one novel quantum phenomenon in physics. +Here, we present a combined theoretical and experimental study to demonstrate +the presence of an extremely large exchange bias in the range 0.8 T - 2.7 T and +a fully compensated magnetic state (FCF) in a special type of Pt and Ni doped +Mn$_3$In cubic alloy. Here, oppositely aligned uncompensated moments in two +different atomic clusters sum up to zero which are responsible for the FCF +state. Our Density functional theory (DFT) calculations show the existence of +several possible ferrimagnetic configurations with the FCF as the energetically +most stable one. The microscopic origin of the large exchange bias can be +interpreted in terms of the exchange interaction between the FCF background and +the uncompensated ferrimagnetic clusters stabilized due to its negligible +energy difference with respect to the FCF phase. We utilize pulsed magnetic +field up to 60 T and 30 T static field magnetization measurements to confirm +the intrinsic nature of exchange bias in our system. Finally, our Hall effect +measurements demonstrate the importance of uncompensated noncoplanar +interfacial moments for the realization of large EB. The present finding of +gigantic exchange bias in a unique compensated ferrimagnetic system opens up a +direction for the design of novel quantum phenomena for the technological +applications.",2107.07742v1 +2022-05-05,Origins of multi-sublattice magnetism and superexchange interactions in double-double perovskite CaMnCrSbO6,"We have deployed density functional theory, Wannier function analysis and +mean-field calculations to investigate the double-double perovskite compound +CaMnCrSbO_{6}. The crystallographically non-equivalent Mn atoms in the unit +cell have tetrahedral and planar oxygen coordinations (labelled as Mn(1) and +Mn(2)), while the Cr atom is in the centre of distorted oxygen octahedron. +While the bulk magnetization and neutron diffraction suggest a simpler +ferrimagnetic order (T_C=49 K) between Mn2+ and Cr3+ spins, the exchange +interactions are more complex than that expected from a two sublattice magnetic +system. The electronic structure calculations yield a ferrimagnetic insulating +ground state even in absence of Hubbard U which persists for a wide range of U. +The Mn(1)-O-Mn(2) (out of plane and in-plane), Mn(1)-O-Cr and Mn(2)-O-Cr +superexchange interactions are found to be anti-ferromagnetic, while the +Cr-O-O-Cr super-superexchange is found to be ferromagnetic. The Mn(2)-O-Cr +superexchange is weaker than the Mn(1)-O-Cr superexchange, thus effectively +resulting in ferrimagnetism. From a simple 3-site Hubbard model, we derived +expressions for the antiferromagnetic superexchange strength J_AFM and the +weaker ferromagnetic J_FM. The relative strengths of JAFM for the various +superexchange interactions are in agreement with those obtained from DFT. The +expression for Cr-O-O-Cr super-superexchange strength (J_SS), which is derived +considering a 4-site Hubbard model, predicts a ferromagnetic exchange in +agreement with DFT. Finally, our mean field calculations reveal that assuming a +set of four magnetic sub-lattice for Mn2+ spins and a single magnetic +sublattice for Cr3+ spins yields a much improved T_C, while a simple two +magnetic sublattice model yields a much higher T_C.",2205.02452v2 +2022-05-06,Tuning the dynamics of chiral domain walls of ferrimagnetic films with the magneto-ionic effect,"The manipulation of magnetism with a gate voltage is expected to lead the way +towards the realization of energy-efficient spintronics devices and +high-performance magnetic memories. Exploiting magneto-ionic effects under +micro-patterned electrodes in solid-state devices adds the possibility to +modify magnetic properties locally, in a non-volatile and reversible way. +Tuning magnetic anisotropy, magnetization and Dzyaloshinskii-Moriya interaction +allows modifying at will the dynamics of non trivial magnetic textures such as +skyrmions and chiral domain walls in magnetic race tracks. In this work, we +illustrate efficient magneto-ionic effects in a ferrimagnetic Pt/Co/Tb stack +using a ZrO2 thin layer as a solid state ionic conductor. When a thin layer of +terbium is deposited on top of cobalt, it acquires a magnetic moment that +aligns antiparallel to that of cobalt, reducing the effective magnetization. +Below the micro-patterned electrodes, the voltage-driven migration of oxygen +ions in a ZrO2 towards the ferrimagnetic stack partially oxidizes the Tb layer, +leading to the local variation not only of the spontaneous magnetization, but +also of the effective magnetic anisotropy and of the Dzyaloshinskii-Moriya +interaction. This leads to a huge increase of the domain wall velocity, which +varies from 10 m/s in the pristine state to 250 m/s after gating. This +non-volatile and reversible tuning of the domain wall dynamics may lead to +applications to reprogrammable magnetic memories or other spintronic devices.",2205.03158v1 +2024-03-18,Tuning of the ultrafast demagnetization by ultrashort spin polarized currents in multi-sublattice ferrimagnets,"Femtosecond laser pulses can be used to induce ultrafast changes of the +magnetization in magnetic materials. Several microscopic mechanisms have been +proposed to explain the observations, including the transport of ultrashort +spin-polarized hot-electrons (SPHE). Such ultrafast spin currents find growing +interest because of the recent challenges in ultrafast spintronics however they +are only poorly characterized. One of the key challenges is to characterize the +spin-polarized ultrafast currents and the microscopic mechanisms behind SPHE +induced manipulation of the magnetization, especially in the case of +technologically relevant ferrimagnetic alloys. Here, we have used a combined +approach using time- and element-resolved X-ray magnetic circular dichroism and +theoretical calculations based on atomistic spin-dynamics simulations to +address the ultrafast transfer of the angular momentum from spin-polarized +currents into ferrimagnetic Fe74Gd26 films and the concomitant reduction of +sub-lattice magnetization. Our study shows that using a Co/Pt multilayer as a +polarizer in a spin-valve structure, the SPHE drives the demagnetization of the +two sub-lattices of the Fe74Gd26 film. This behaviour is explained based on two +physical mechanisms, i.e., spin transfer torque and thermal fluctuations +induced by the SPHE. We provide a quantitative description of the heat transfer +of the ultrashort SPHE pulse to the Fe74Gd26 films, as well as the degree of +spin-polarization of the SPHE current density responsible for the observed +magnetization dynamics. Our work finally characterizes the spin-polarization of +the SPHEs revealing unexpected opposite spin polarization to the Co +magnetization, explaining our experimental results.",2403.11739v2 +1995-09-26,Global Bethe lattice consideration of the spin-1 Ising model,"The spin-1 Ising model with bilinear and biquadratic exchange interactions +and single-ion crystal field is solved on the Bethe lattice using exact +recursion equations. The general procedure of critical properties investigation +is discussed and full set of phase diagrams are constructed for both positive +and negative biquadratic couplings. In latter case we observe all remarkable +features of the model, uncluding doubly-reentrant behavior and ferrimagnetic +phase. A comparison with the results of other approximation schemes is done.",9509158v2 +1996-10-14,Low Temperature Properties of Quantum Antiferromagnetic Chains with Alternating Spins S=1 and 1/2,"We study the low-temperature properties of S=1 and 1/2 alternating spin +chains with antiferromagnetic nearest-neighbor exchange couplings using +analytical techniques as well as a quantum Monte Carlo method. The spin-wave +approach predicts two different low-lying excitations, which are gapped and +gapless, respectively. The structure of low-lying levels is also discussed by +perturbation theory in the strength of the Ising anisotropy. These analytical +findings are compared with the results of quantum Monte Carlo calculations and +it turns out that spin-wave theory well describes the present system. We +conclude that the quantum ferrimagnetic chain exhibits both ferromagnetic and +antiferromagnetic aspects.",9610109v1 +1997-03-14,The ground state of the Kondo model with large spin,"In this paper, we prove that the ground state of the Kondo model with large +spin is nondegenerate, apart from a SU(2) spin degeneracy in the case of half +filling. The ground state spin is found for the system, and the energy level +orderings are discussed. Finally, the existence of ferrimagnetism in some cases +is proved.",9703145v1 +1999-05-15,Critical Behavior of Anisotropic Heisenberg Mixed-Spin Chains in a Field,"We numerically investigate the critical behavior of the spin-(1,1/2) +Heisenberg ferrimagnet with anisotropic exchange coupling in a magnetic field. +A quantized magnetization plateau as a function of the field, appearing at a +third of the saturated magnetization, is stable over whole the +antiferromagnetic coupling region. The plateau vanishes in the ferromagnetic +coupling region via the Kosterlitz-Thouless transition. Comparing the quantum +and classical magnetization curves, we elucidate what are essential quantum +effects.",9905224v1 +1999-05-21,Breakdown of a Magnetization Plateau due to Anisotropy in Heisenberg Mixed-Spin Chains,"We discuss the critical behavior of the spin-(1,1/2) Heisenberg ferrimagnetic +chain in a magnetic field, whose magnetization curve exhibits a plateau at a +third of the full magnetization. A bond alternation stabilizes the massive +state, whereas an exchange anisotropy causes the breakdown of the plateau and +the onset of a gapless spin-fluid state, where the transition, lying in the XY +but ferromagnetic region, is of Kosterlitz-Thouless type. In order to elucidate +significant quantum effects, we investigate the model of classical version as +well.",9905311v1 +2000-03-15,"Magnetic Double Structure for S=1, 1/2 Mixed-Spin Systems","We investigate the zero-temperature and the finite-temperature properties of +the two-dimensional antiferromagnetic quantum spin system composed of the s=1/2 +and s=1 spins. The spin excitation spectrum as well as the thermodynamic +quantities are computed by means of the Schwinger-boson mean-field theory. We +discuss how the magnetic double structure with the gapful and the gapless +excitations is generated, and apply the results systematically to the Haldane +gap system in a staggered magnetic field and also to the weakly coupled +ferrimagnetic mixed-spin chains. It is confirmed that the results obtained are +consistent with the experiments for the quasi-one-dimensional Haldane compounds +$R_2 \rm BaNiO_5$.",0003252v1 +2000-04-18,Modified spin-wave description of the nuclear spin relaxation in ferrimagnetic Heisenberg chains,"We make a modified spin-wave description of the nuclear spin relaxation in +Heisenberg alternating-spin chains with antiferromagnetic exchange coupling. In +contrast with the conventional one-dimensional antiferromagnetic spin-wave +theory, which is plagued with the divergence of the sublattice magnetization +even in the ground state, the present spin-wave description is highly +successful over a wide temperature range. The temperature dependence of the +relaxation rate $T_1^{-1}$ significantly varies with the crystalline structure, +exhibiting both ferromagnetic and antiferromagnetic aspects. $T_1^{-1}$ further +shows a unique dependence on the applied field, which turns out an indirect +observation of the quadratic dispersion relations.",0004297v1 +2001-05-25,Half-metallic antiferromagnets in thiospinels,"We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs) +in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm +Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure +studies in the local-spin-density approximation (LSDA). We have also explored +electronic and magnetic properties of parent spinel compounds of the above +systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM +ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a +ferrimagnetic insulator. We have discussed the feasibility of material +synthesis of HM-AFM thiospinel systems.",0105492v1 +2001-06-05,Modulated replica symmetry breaking schemes for antiferromagnetic spin glasses,"We define modulated replica symmetry breaking (RSB)-schemes which combine +tree- and wave-like structures. A modulated scheme and unmodulated RSB are +applied at 1-step level to a semiconductor model with antiferromagnetic +Korenblit-Shender interaction. By comparison of the free energies we find +evidence that a T=0 phase transition in the ferrimagnetic phase leads to a +transition between the different RSB-schemes. An embedding factor of Parisi +block matrices with sublattice-asymmetrical size is employed as a new +variational parameter in the modulated scheme.",0106066v3 +2001-06-25,Magnetization Process of the S=1 and 1/2 Uniform and Distorted Kagome Heisenberg Antiferromagnets,"The magnetization process of the S=1 and 1/2 kagome Heisenberg +antiferromagnet is studied by means of the numerical exact diagonalization +method. It is found that the magnetization curve at zero temperature has a +plateau at 1/3 of the full magnetization. In the presence of $\sqrt{3} \times +\sqrt{3}$ lattice distortion, this plateau is enhanced and eventually the +ferrimagnetic state is realized. There also appear the minor plateaux above the +main plateau. The physical origin of these phenomena is discussed.",0106498v2 +2001-11-21,Extraordinary magnetization behavior of single crystalline TbFe_4.4Al_7.6,"We report the observation of a field-induced transformation from the +easy-plane antiferromagnetic structure to the easy-axis ferrimagnetic structure +in a single crystal of TbFe_4.4Al_7.6 (tetragonal ThMn_12 structure) at 5 K. +Such a field-induced, irreversible transition has been identified for the first +time. This transition is accompanied by a giant orthorhombic distortion: +epsilon_aa = - epsilon_bb ~ 3.5x10^-4 that is associated with a magnetic +hardness (mu_0H_C ~ 3 T) that is unprecedented in this category of materials.",0111408v1 +2002-06-10,Realization of La2MnVO6: Search for half-metallic antiferromagnetism?,"Single-phase polycrystalline La2MnVO6 samples were synthesized by arc melting +and characterized by X-ray diffraction, magnetization and resistivity +measurements. We find that the compound has cubic (space group), partly ordered +double perovskite structure. The sample exhibits ferrimagnetic behavior and +variable-range hopping conductivity. We conclude based on the magnetic +properties that both Mn and V ions are trivalent; moreover, the Mn3+ ions are +in a high-spin state, which is the reason that the compound is not a +half-metallic antiferromagnet.",0206146v1 +2002-07-22,Thermodynamic properties of the exactly solvable transverse Ising model on decorated planar lattices,"The generalized mapping transformation technique is used to obtain the exact +solution for the transverse Ising model on decorated planar lattices. Within +this scheme, the basic thermodynamic quantities are calculated for different +planar lattices with arbitrary spins of decorating atoms. The particular +attention has been paid to the investigation of the transverse-field effects on +magnetic properties of the system under investigation. The most interesting +numerical results for the phase diagrams, compensation temperatures and several +thermodynamic quantities are discussed in detail for the ferrimagnetic version +of the model.",0207522v1 +2002-12-24,XY ring-exchange model on the triangular lattice,"We study ring-exchange models for bosons or XY-spins on the triangular +lattice. A four-spin exchange leads to a manifold of ground states with gapless +excitations and critical power-law correlations. With a nearest-neighbour +exchange, fluctuations select a four-fold ferrimagnetically ordered ground +state with a small spin/superfluid stiffness which breaks the global U(1) and +translational symmetry. We explore consequences for phase transitions at finite +temperature and in an in-plane magnetic field.",0212589v2 +2003-05-06,Ferrimagnetism and compensation points in a decorated 3D Ising models,"We give a precise numerical solution for decorated Ising models on the simple +cubic lattice which show ferromagnetism, compensation points, and reentrant +behaviour. The models, consisting of $S={1\over 2}$ spins on a simple cubic +lattice, and decorating S=1 or $S=3/2$ spins on the bonds, can be mapped +exactly onto the normal spin-1/2 Ising model, whose properties are well known.",0305095v1 +2003-12-03,Effective collective barrier for magnetic relaxation in frozen ferrofluids,"Magnetic relaxation and frequency response were measured in frozen +ferrimagnetic colloids of different concentrations. A crossover from reversible +to irreversible behavior is observed for concentrated colloids. In irreversible +state, magnetic relaxation is time-logarithmic over seven orders of magnitude +of experimental time windows. A master curve construction within mean field +phenomenological model is applied to extract effective collective barrier as a +function of the irreversible magnetization. The barrier logarithmically +diverges, providing evidence for self-organized critical behavior during +magnetic relaxation in frozen ferrofluids.",0312087v1 +2004-04-20,Cooperative ordering of gapped and gapless spin networks in Cu$_2$Fe$_2$Ge$_4$O$_{13}$,"The unusual magnetic properties of a novel low-dimensional quantum +ferrimagnet Cu$_2$Fe$_2$Ge$_4$O$_{13}$ are studied using bulk methods, neutron +diffraction and inelastic neutron scattering. It is shown that this material +can be described in terms of two low-dimensional quantum spin subsystems, one +gapped and the other gapless, characterized by two distinct energy scales. +Long-range magnetic ordering observed at low temperatures is a cooperative +phenomenon caused by weak coupling of these two spin networks.",0404468v1 +2004-04-29,Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds,"Using exact numerical diagonalization and the conformal field theory +approach, we study the effect of magnetic frustrations due to diagonal exchange +bonds in a system of two coupled mixed-spin $(1,{1/2})$ Heisenberg chains. It +is established that relatively moderate frustrations are able to destroy the +ferrimagnetic state and to stabilize the critical spin-liquid phase typical for +half-integer-spin antiferromagnetic Heisenberg chains. Both phases are +separated by a narrow but finite region occupied by a critical +partially-polarized ferromagnetic phase.",0404703v1 +2005-04-01,Exact ground states of quantum spin-2 models on the hexagonal lattice,"We construct exact non-trivial ground states of spin-2 quantum +antiferromagnets on the hexagonal lattice. Using the optimum ground state +approach we determine the ground state in different subspaces of a general +spin-2 Hamiltonian consistent with some realistic symmetries. These states, +which are not of simple product form, depend on two free parameters and can be +shown to be only weakly degenerate. We find ground states with different types +of magnetic order, i.e. a weak antiferromagnet with finite sublattice +magnetization and a weak ferromagnet with ferrimagnetic order. For the latter +it is argued that a quantum phase transition occurs within the solvable +subspace.",0504023v1 +2005-04-26,The electronic structure of the antiferromagnetic semiconductor MnSb_2S_4,"The electronic band structures of orthorhombic (oP28) and monoclinic (mC28) +MnSb_2S_4 were investigated with ab initio calculations in the local spin +density approximation (LSDA) to the density functional theory (DFT). An +analysis of the electronic properties and of the chemical bonding is provided +using the augmented spherical wave (ASW) method considering nonmagnetic, +ferromagnetic, ferrimagnetic and antiferromagnetic model orderings. In +agreement with experimental results both modifications of MnSb_2S_4 are +predicted to be antiferromagnetic. While the experimental band gap is missed +for the monoclinic polymorph, the calculated band gap for orthorhombic +MnSb_2S_4 is close to the experimental one.",0504669v1 +2005-09-28,Magnetic properties of antiferromagnetically coupled CoFeB/Ru/CoFeB,"This work reports on the thermal stability of two amorphous CoFeB layers +coupled antiferromagnetically via a thin Ru interlayer. The saturation field of +the artificial ferrimagnet which is determined by the coupling, J, is almost +independent on the annealing temperature up to more than 300 degree C. An +annealing at more than 325 degree C significantly increases the coercivity, Hc, +indicating the onset of crystallization.",0509753v1 +2005-12-24,Low-temperature thermodynamics of one-dimensional alternating-spin Heisenberg ferromagnets,"Motivated by a novel bimetallic chain compound in which alternating magnetic +centers are ferromagnetically coupled, we investigate thermodynamic properties +of one-dimensional spin-$(S,s)$ Heisenberg ferromagnets both numerically and +analytically. On the one hand, quantum Monte Carlo calculations illuminate the +overall thermal behavior. The specific heat may exhibit a double-peaked +structure at intermediate temperatures for $S\agt 3s$ in general. On the other +hand, a modified spin-wave theory precisely describes the low-temperature +properties. Expanding the specific heat and the magnetic susceptibility, we +reveal an analogy and a contrast between mixed-spin ferromagnets and +ferrimagnets.",0512630v1 +2006-02-03,X-ray magnetic circular dichroism study of Re 5d magnetism in Sr2CrReO6,"We have measured Re 5d spin and orbital magnetic moments in the ferrimagnetic +double perovskite Sr2CrReO6 by X-ray magnetic circular dichroism at the L_{2,3} +edges. In fair agreement with recent band-structure calculations [Vaitheeswaran +et. al., Ref 1], at the Re site a large 5d spin magnetic moment of -0.68 mu_B +and a considerable orbital moment of +0.25 mu_B have been detected. We found +that the Curie temperature of the double perovskites A2BB'O6 scales with the +spin magnetic moment of the 'non-magnetic' B' ion.",0602071v1 +2006-02-24,Magnetocaloric effect in hexacyanochromate Prussian blue analogs,"We report on the magnetocaloric properties of two molecule-based +hexacyanochromate Prussian blue analogs, nominally CsNi[Cr(CN)_6](H_2O) and +Cr_3[Cr(CN)_6]_2x12(H_2O). The former orders ferromagnetically below Tc=90 K, +whereas the latter is a ferrimagnet below Tc=230 K. For both, we find +significantly large magnetic entropy changes DSm associated to the magnetic +phase transitions. Notably, our studies represent the first attempt to look at +molecule-based materials in terms of the magnetocaloric effect for temperatures +well above the liquid helium range.",0602589v1 +2006-04-20,Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model,"We study the magnetic phase diagram of two coupled mixed-spin $(1,{1/2})$ +Heisenberg chains as a function of the frustration parameter related to +diagonal exchange couplings. The analysis is performed by using spin-wave +series and exact numerical diagonalization techniques. The obtained phase +diagram--containing the Luttinger liquid phase, the plateau phase with a +magnetization per rung $M=1/2$, and the fully polarized phase--is closely +related to the generic $(J/U,\mu/U)$ phase diagram of the one-dimensional boson +Hubbard model.",0604495v1 +2006-07-13,The SU(3) bosons and the spin nematic state on the spin-1 bilinear-biquadratic triangular lattice,"A bond-operator mean-field theory in the SU(3) bosons representation is +developed to describe the antiferro-nematic phase of the spin-1 +bilinear-biquadratic model. The calculated static structure factors reveal +delicately that the antiferro-nematic state may exhibit both the ferro- and +antiferro-quadruple long-range orders, which is reminiscent of the ferrimagnets +or the canted antiferromagnets. This result may influence the spin wave theory +concerned with this phase. Possible relevance of this unconventional state to +the quasi-two-dimensional triangular material NiGa2S4 is addressed.",0607330v1 +2007-03-29,Thermo-reversible permanent magnets in the quasi-binary GdCo5-xCux system,"Ferrimagnetic GdCo5-xCux alloys exhibiting the effect of Gd- and +3d-sublattice magnetization compensation at defined temperatures were studied +with respect to their use as thermo-reversible permanent magnets (PM). Coercive +fields 0Hc in the range 0.3 to 1.6 T were measured for annealed single +crystals with x = 1 - 2.2 having compensation points in the vicinity of room +temperature. Two applications of such a thermo-reversible PM, namely a +thermally controlled actuator and a contactless temperature sensor, are +demonstrated.",0703775v1 +1994-11-29,Which Higgs-Yukawa systems can possess non-trivial fixed points,"We argue that non-trivial fixed points bordering on the paramagnetic and +ferromagnetic phases are most likely to exist in the Higgs-Yukawa systems that +have a connected domain with the paramagnetic phase and no ferrimagnetic phase. +We find three examples of such systems; among them is the U(1) system with +naive fermions.",9411069v1 +1992-06-01,q--Magnetism at roots of unity,"We study the thermodynamic properties of a family of integrable 1D spin chain +hamiltonians associated with quantum groups at roots of unity. These +hamiltonians depend for each primitive root of unit on a parameter $s$ which +plays the role of a continuous spin. The model exhibits ferrimagnetism even +though the interaction involved is between nearest neighbors. The latter +phenomenon is interpreted as a genuine quantum group effect with no +``classical"" analog. The discussion of conformal properties is given.",9206001v1 +2004-08-11,A Ferromagnetic Lieb-Mattis Theorem,"We prove ferromagnetic ordering of energy levels for XXX Heisenberg chains of +any spin and XXZ spin chains with all spins equal to 1/2. Ferromagnetic +ordering means that the minimum energies in the invariant subspaces of fixed +total spin are monotone decreasing as a function of the total spin. This result +provides a ferromagnetic analogue of the well-known theorem by Lieb and Mattis +about ordering of energy levels in antiferromagnetic and ferrimagnetic systems +on bipartite graphs.",0408020v3 +2007-04-19,Classical Heisenberg Hamiltonian Solution of Oriented Spinel Ferrimagnetic Thin Films,"The classical Heisenberg Hamiltonian was solved for oriented spinel thin and +thick cubic ferrites. The dipole matrix of complicated cubic cell could be +simplified into the form of dipole Matrix of simple cubic cells. This study was +confined only to the highly oriented thin films of ferrite. The variation of +total energy of Nickel ferrite thin films with angle and number of layers was +investigated. Also the change of energy with stress induced anisotropy for +Nickel ferrite films with N=5 and 1000 has been studied. Films with the +magnetic moments ratio 1.86 can be easily oriented in 90 direction when N is +greater than 400.",0704.2456v1 +2007-07-06,Field induced magnetic transition and metastability in Co substituted $Mn_{2}Sb$,"A detailed investigation of first order ferrimagnetic (FRI) to +antiferromagnetic (AFM) transition in Co (15%) doped $Mn_2Sb$ is carried out. +These measurements demonstrate anomalous thermomagnetic irreversibility and +glass-like frozen FRI phase at low temperatures. The irreversibility arising +between the supercooling and superheating spinodals is distinguised in an +ingenious way from the irreversibility arising due to kinetic arrest. Field +annealing measurements shows reentrant FRI-AFM-FRI transition with increasing +temperature. These measurements also show that kinetic arrest band and +supercooling band are anitcorrelated i.e regions which are kinetically arrested +at higher temperature have lower supercooling temperature and vice versa.",0707.0950v1 +2007-11-26,Ab initio prediction on ferrotoroidic olivine Li4MnFeCoNiP4O16,"First-principles calculation predict that olivine Li4MnFeCoNiP4O16 has +ferrotoroidic characteristic and ferrimagnetic configuration with magnetic +moment of 1.56 \muB per formula unit. The ferrotoroidicity of this material +makes it a potential candidate for magnetoelectric materials . Based on the +orbital-resolved density of states for the transtion-metal ions in +Li4MnFeCoNiP4O16, the spin configuration for Mn2+,Fe3+,Co2+, and Ni2+ is +t2g3eg2, t2g3eg2,t2g1t2g3eg1eg2, and t2g2t2g3eg1eg2, respectively. Density +functional theory plus U (DFT+U) shows a indirect band gap of 1.25 eV in this +predicted material, which is not simply related to the electronic conductivity +in terms of being used as cathode material in rechargeable Li-ion batteries.",0711.3904v1 +2008-03-12,Spin-lattice model of Magneto-electric Transitions in RbCoBr$_3$,"Extensive Monte Carlo simulations are performed to analyze a recent neutron +diffraction experiment on a distorted triangular lattice compound RbCoBr$_3$. +We consider a spin-lattice model, where both spin and lattice are Ising +variables. This model explains well successive magnetic and dielectric +transitions observed in the experiment. The exchange interaction parameters and +the spin-lattice coupling are estimated. It is found that the spin-lattice +coupling is important to explain the slow growth of a ferrimagnetic order. The +present simulations were made possible by developing a new Monte Carlo +algorithm, which accelerates slow Monte Carlo dynamics of quasi-one-dimensional +frustrated systems.",0803.1710v2 +2009-08-21,Nonzero macroscopic magnetization in half-metallic antiferromagnets at finite temperatures,"Combining density-functional theory calculations with many-body +Green's-function technique, we reveal that the macroscopic magnetization in +half-metallic antiferromagnets does not vanish at finite temperature as for the +T=0 limit. This anomalous behavior stems from the inequivalent magnetic +sublattices which lead to different intrasublattice exchange interactions. As a +consequence, the spin fluctuations suppress the magnetic order of the +sublattices in a different way leading to a ferrimagnetic state at finite +temperatures. Computational results are presented for the half-metallic +antiferromagnetic CrMnZ (Z=P,As,Sb) semi-Heusler compounds.",0908.3044v1 +2009-10-30,Interplay of Quantum Criticality and Geometric Frustration in Columbite,"Motivated by CoNb2O6 (belonging to the columbite family of minerals), we +theoretically study the physics of quantum ferromagnetic Ising chains coupled +anti-ferromagnetically on a triangular lattice in the plane perpendicular to +the chain direction. We combine exact solutions of the chain physics with +perturbative approximations for the transverse couplings. When the triangular +lattice has an isosceles distortion (which occurs in the real material), the +T=0 phase diagram is rich with five different states of matter: ferrimagnetic, +N\'eel, anti-ferromagnetic, paramagnetic and incommensurate phases, separated +by quantum phase transitions. Implications of our results to experiments on +CoNb2O6 are discussed.",0911.0038v1 +2009-11-20,Superparamagnetic nanoparticle ensembles,"Magnetic single-domain nanoparticles constitute an important model system in +magnetism. In particular ensembles of superparamagnetic nanoparticles can +exhibit a rich variety of different behaviors depending on the inter-particle +interactions. Starting from isolated single-domain ferro- or ferrimagnetic +nanoparticles the magnetization behavior of both non-interacting and +interacting particle-ensembles is reviewed. A particular focus is drawn onto +the relaxation time of the system. In case of interacting nanoparticles the +usual Neel-Brown relaxation law becomes modified. With increasing interactions +modified superparamagnetism, spin glass behavior and superferromagnetism is +encountered.",0911.4031v2 +2010-04-26,Ferromagnetism of cold fermions loaded into a decorated square lattice,"We investigate two-component ultracold fermions loaded into a decorated +square lattice, which are described by the Hubbard model with repulsive +interactions and nearest neighbor hoppings. By combining the real-space +dynamical mean-field theory with the numerical renormalization group method, we +discuss how a ferromagnetically ordered ground state in the weak coupling +regime, which originates from the existence of a dispersionless band, is +adiabatically connected to a Heisenberg ferrimagnetic state in the strong +coupling limit. The effects of level splitting and hopping imbalance are also +addressed.",1004.4650v1 +2010-06-23,Multiferroic BiFeO3-BiMnO3 Nanocheckerboard From First Principles,"We present a first principles study of an unusual heterostructure, an +atomic-scale checkerboard of BiFeO3-BiMnO3, and compare its properties to the +two bulk constituent materials, BiFeO3 and BiMnO3. The ""nanocheckerboard"" is +found to have a multiferroic ground state with the desired properties of each +constituent: polar and ferrimagnetic due to BiFeO3 and BiMnO3, respectively. +The effect of B-site cation ordering on magnetic ordering in the BiFeO3-BiMnO3 +system is studied. The checkerboard geometry is seen to give rise to a a novel +magnetostructural effect that is neither present in the bulk constituent +materials, nor in the layered BiFeO3-BiMnO3 superlattice.",1006.4648v1 +2010-08-06,Ferromagnetic phases in spin-Fermion systems,"Spin-Fermion systems which obtain their magnetic properties from a system of +localized magnetic moments being coupled to conducting electrons are +considered. The dynamical degrees of freedom are spin-$s$ operators of +localized spins and spin-1/2 Fermi operators of itinerant electrons. +Renormalized spin-wave theory, which accounts for the magnon-magnon +interaction, and its extension are developed to describe the two ferrimagnetic +phases in the system: low temperature phase $0 1/2$. In this paper we present for the first time an analytical way +of calculating thermal entanglement in a dimension $2\otimes3$ Heisenberg chain +through the distance between states. We use the Hilbert-Schmidt norm to obtain +entanglement. The result obtained can be used to calculate entanglement in +chains with spin-$1/2$ coupling with spin-$1$, such as ferrimagnetic compounds +as well as compounds with dimer-trimer coupling.",2103.02019v1 +2021-08-16,Losses of Interface Waves in Plasmonic and Gyrotropic Structures,"The loss mechanisms of slow interface waves in the layered resonant media are +examined and illustrated by the examples of (i) surface plasmon polaritons in +an isotropic plasma layer, (ii) magnetoplasmons in magnetised plasma and (iii) +spin waves in ferrimagnetic layers. It is shown that losses of all these +interface waves grow at the same rate of Im(gamma) ~ Re(gamma^3), where gamma +is the wavenumber. These abnormal losses are caused by vortices of the power +flow of the interface waves near their resonance cut-off. The basic properties +of the slow interface waves discussed in the paper are inherent to the waves of +hyperbolic type in the layered resonant media.",2108.07180v1 +2021-10-07,Mössbauer measurements of GaFeO$_3$ single crystal multiferroic,"M\""ossbauer measurements on single crystal absorbers at room and at low +temperatures were performed. The results are fully consistent with previously +published reports by other groups. Spectra of single crystals were +simultaneously analyzed including magnetic dipole and electric quadrupole +interactions. The analysis shows that there is a small component of magnetic +moments perpendicular to the magnetic easy axis. M\""ossbauer data seem not +agree with commonly accepted ferrimagnetic structure of GaFeO$_3$.",2110.03285v1 +2023-03-20,"Anapole, chiral and orbital states in Mn3Si2Te6","The ferrimagnet Mn3Si2Te6 attracts attention because of a recently discovered +colossal magnetoresistance (CMR) with unique magnetic field properties. An +improved magnetic structure for the material has emerged from a neutron +diffraction study linked to understanding the CMR. A deeper theoretical +investigation of the magnetic structure has now revealed anapole, chiral and +orbital states of manganese ions not previously mentioned. Moreover, it is +shown that existence of these states in the low temperature form of Mn3Si2Te6, +with a magnetic field applied, can be tested by neutron and resonant x-ray +diffraction.",2303.10979v2 +2023-07-02,Unveiling Stable One-dimensional Magnetic Solitons in Magnetic Bilayers,"We propose a novel model which efficiently describes the magnetization +dynamics in a magnetic bilayer system. By applying a particular gauge +transformation to the Landau-Lifshitz-Gilbert (LLG) equation, we successfully +convert the model into an exactly integrable framework. Thus the obtained +analytical solutions allows us to predict a 1D magnetic soliton pair existed by +tunning the thickness of the spacing layer between the two ferrimagnetic +layers. The decoupling-unlocking-locking transition of soliton motion is +determined at various interaction intensitiy. Our results have implications for +the manipulation of magnetic solitons and the design of magnetic soliton-based +logic devices.",2307.00471v1 +2003-09-04,Coupled Cluster Method Calculations Of Quantum Magnets With Spins Of General Spin Quantum Number,"We present a new high-order coupled cluster method (CCM) formalism for the +ground states of lattice quantum spin systems for general spin quantum number, +$s$. This new ``general-$s$'' formalism is found to be highly suitable for a +computational implementation, and the technical details of this implementation +are given. To illustrate our new formalism we perform high-order CCM +calculations for the one-dimensional spin-half and spin-one antiferromagnetic +{\it XXZ} models and for the one-dimensional spin-half/spin-one ferrimagnetic +{\it XXZ} model. The results for the ground-state properties of the isotropic +points of these systems are seen to be in excellent quantitative agreement with +exact results for the special case of the spin-half antiferromagnet and results +of density matrix renormalisation group (DMRG) calculations for the other +systems. Extrapolated CCM results for the sublattice magnetisation of the +spin-half antiferromagnet closely follow the exact Bethe Ansatz solution, which +contains an infinite-order phase transition at $\Delta=1$. By contrast, +extrapolated CCM results for the sublattice magnetisation of the spin-one +antiferromagnet using this same scheme are seen to go to zero at $\Delta +\approx 1.2$, which is in excellent agreement with the value for the onset of +the Haldane phase for this model. Results for sublattice magnetisations of the +ferrimagnet for both the spin-half and spin-one spins are non-zero and finite +across a wide range of $\Delta$, up to and including the Heisenberg point at +$\Delta=1$.",0309099v1 +2006-11-27,Subtle competition between ferromagnetic and antiferromagnetic order in a Mn(II) - free radical ferrimagnetic chain,"The macroscopic magnetic characterization of the Mn(II) - nitronyl nitroxide +free radical chain (Mn(hfac)2(R)-3MLNN) evidenced its transition from a +1-dimensional behavior of ferrimagnetic chains to a 3-dimensional ferromagnetic +long range order below 3 K. Neutron diffraction experiments, performed on a +single crystal around the transition temperature, led to a different conclusion +: the magnetic Bragg reflections detected below 3 K correspond to a canted +antiferromagnet where the magnetic moments are mainly oriented along the chain +axis. Surprisingly in the context of other compounds in this family of magnets, +the interchain coupling is antiferromagnetic. This state is shown to be very +fragile since a ferromagnetic interchain arrangement is recovered in a weak +magnetic field. This peculiar behavior might be explained by the competition +between dipolar interaction, shown to be responsible for the antiferromagnetic +long range order below 3 K, and exchange interaction, the balance between these +interactions being driven by the strong intrachain spin correlations. More +generally, this study underlines the need, in this kind of molecular compounds, +to go beyond macroscopic magnetization measurements.",0611684v2 +2007-01-04,Exact solution of the mixed-spin Ising model on a decorated square lattice with two different kinds of decorating spins on horizontal and vertical bonds,"The mixed spin-(1/2, S_B, S_C) Ising model on a decorated square lattice with +two different kinds of decorating spins S_B and S_C placed on its horizontal +and vertical bonds, respectively, is exactly solved by establishing a precise +mapping relationship with the corresponding spin-1/2 Ising model on an +anisotropic square (rectangular) lattice. The effect of uniaxial single-ion +anisotropy acting on both types of decorating spins S_B and S_C is examined in +particular. If decorating spins S_B and S_C are integer and half-odd-integer, +respectively, or if the reverse is the case, the model under investigation +displays a very peculiar critical behavior beared on the spontaneously ordered +'quasi-1D' spin system, which appears as a result of the single-ion anisotropy +strengthening. We have found convincing evidence that this remarkable +spontaneous ordering virtually arises even though all integer-valued decorating +spins tend towards their 'non-magnetic' spin state S=0 and the system becomes +disordered only upon further increase of the single-ion anisotropy. The +single-ion anisotropy parameter is also at an origin of various temperature +dependences of the total magnetization when imposing the pure ferrimagnetic or +the mixed ferro-ferrimagnetic character of the spin arrangement.",0701071v2 +2007-04-11,Heisenberg antiferromagnet with anisotropic exchange on the Kagome lattice: Description of the magnetic properties of volborthite,"We study the properties of the Heisenberg antiferromagnet with spatially +anisotropic nearest-neighbour exchange couplings on the kagome net, i.e. with +coupling J in one lattice direction and couplings J' along the other two +directions. For J/J' > 1, this model is believed to describe the magnetic +properties of the mineral volborthite. In the classical limit, it exhibits two +kinds of ground states: a ferrimagnetic state for J/J' < 1/2 and a large +manifold of canted spin states for J/J' > 1/2. To include quantum effects +self-consistently, we investigate the Sp(N) symmetric generalisation of the +original SU(2) symmetric model in the large-N limit. In addition to the +dependence on the anisotropy, the Sp(N) symmetric model depends on a parameter +kappa that measures the importance of quantum effects. Our numerical +calculations reveal that in the kappa-J/J' plane, the system shows a rich phase +diagram containing a ferrimagnetic phase, an incommensurate phase, and a +decoupled chain phase, the latter two with short- and long-range order. We +corroborate these results by showing that the boundaries between the various +phases and several other features of the Sp(N) phase diagram can be determined +by analytical calculations. Finally, the application of a block-spin +perturbation expansion to the trimerised version of the original spin-1/2 model +leads us to suggest that in the limit of strong anisotropy, J/J' >> 1, the +ground state of the original model is a collinearly ordered antiferromagnet, +which is separated from the incommensurate state by a quantum phase transition.",0704.1441v3 +2008-01-09,Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB based synthetic ferrimagnetic free layers,"We investigated the effect of using a synthetic ferrimagnetic (SyF) free +layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced +magnetization switching (CIMS), particularly for application to spin-transfer +torque random access memory (SPRAM). The employed SyF free layer had a +Co40Fe40B20/ Ru/ Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20 structures, and the +MTJs(100x(150-300) nm^2) were annealed at 300oC. The use of SyF free layer +resulted in low intrinsic critical current density (Jc0) without degrading the +thermal-stability factor (E/kBT, where E, kB, and T are the energy potential, +the Boltzmann constant, and temperature,respectively). When the two CoFeB +layers of a strongly antiferromagnetically coupled SyF free layer had the same +thickness, Jc0 was reduced to 2-4x10^6 A/cm^2. This low Jc0 may be due to the +decreased effective volume under the large spin accumulation at the CoFeB/Ru. +The E/kBT was over 60, resulting in a retention time of over ten years and +suppression of the write current dispersion for SPRAM. The use of the SyF free +layer also resulted in a bistable (parallel/antiparallel) magnetization +configuration at zero field, enabling the realization of CIMS without the need +to apply external fields to compensate for the offset field.",0801.1355v1 +2008-01-17,Towards the theory of ferrimagnetism,"Two-sublattice ferrimagnet, with spin-$s_1$ operators $\bf{S_{1i}}$ at the +sublattice $A$ site and spin-$s_2$ operators $\bf{S_{2i}}$ at the sublattice +$B$ site, is considered. The magnon of the system, the transversal fluctuation +of the total magnetization, is a complicate mixture of the transversal +fluctuations of the sublattice $A$ and $B$ spins. As a result, the magnons' +fluctuations suppress in a different way the magnetic orders of the $A$ and $B$ +sublattices and one obtains two phases. At low temperature $(0,T^*)$ the +magnetic orders of the $A$ and $B$ spins contribute to the magnetization of the +system, while at the high temperature $(T^*,T_N)$, the magnetic order of the +spins with a weaker intra-sublattice exchange is suppressed by magnon +fluctuations, and only the spins with stronger intra-sublattice exchange has +non-zero spontaneous magnetization. The $T^*$ transition is a transition +between two spin-ordered phases in contrast to the transition from spin-ordered +state to disordered state ($T_N$-transition). There is no additional symmetry +breaking, and the Goldstone boson has a ferromagnetic dispersion in both +phases. A modified spin-wave theory is developed to describe the two phases. +All known Neel's anomalous $M(T)$ curves are reproduced, in particular that +with ""compensation point"". The theoretical curves are compared with +experimental ones for sulpho-spinel $MnCr2S_{4-x}Se_{x}$ and rare earth iron +garnets.",0801.2651v1 +2008-02-13,Magnetoresistance behavior of a ferromagnetic shape memory alloy: Ni_1.75Mn_1.25Ga,"A negative-positive-negative switching behavior of magnetoresistance (MR) +with temperature is observed in a ferromagnetic shape memory alloy +Ni_1.75Mn_1.25Ga. In the austenitic phase between 300 and 120 K, MR is negative +due to s-d scattering. Curiously, below 120K MR is positive, while at still +lower temperatures in the martensitic phase, MR is negative again. The positive +MR cannot be explained by Lorentz contribution and is related to a magnetic +transition. Evidence for this is obtained from ab initio density functional +theory, a decrease in magnetization and resistivity upturn at 120 K. Theory +shows that a ferrimagnetic state with anti-ferromagnetic alignment between the +local magnetic moments of the Mn atoms is the energetically favoured ground +state. In the martensitic phase, there are two competing factors that govern +the MR behavior: a dominant negative trend up to the saturation field due to +the decrease of electron scattering at twin and domain boundaries; and a weaker +positive trend due to the ferrimagnetic nature of the magnetic state. MR +exhibits a hysteresis between heating and cooling that is related to the first +order nature of the martensitic phase transition.",0802.1801v2 +2008-08-27,Magnetic phase evolution in the spinel compounds Zn$_{1-x}$Co$_x$Cr$_2$O$_4$,"We present the magnetic properties of complete solid solutions of +ZnCr$_2$O$_4$ and CoCr$_2$O$_4$: two well-studied oxide spinels with very +different magnetic ground states. ZnCr$_2$O$_4$, with non-magnetic $d^{10}$ +cations occupying the A site and magnetic $d^3$ cations on the B site, is a +highly frustrated antiferromagnet. CoCr$_2$O$_4$, with magnetic $d^7$ cations +(three unpaired electrons) on the A site as well, exhibits both N\'eel +ferrimagnetism as well as commensurate and incommensurate non-collinear +magnetic order. More recently, CoCr$_2$O$_4$ has been studied extensively for +its polar behavior which arises from conical magnetic ordering. Gradually +introducing magnetism on the A site of ZnCr$_2$O$_4$ results in a transition +from frustrated antiferromagnetism to glassy magnetism at low concentrations of +Co, and eventually to ferrimagnetic and conical ground states at higher +concentrations. Real-space Monte-Carlo simulations of the magnetic +susceptibility suggest that the first magnetic ordering transition and features +of the susceptibility across $x$ are captured by near-neighbor self- and +cross-couplings between the magnetic A and B atoms. We present as a part of +this study, a method for displaying the temperature dependence of magnetic +susceptibility in a manner which helps distinguish between compounds possessing +purely antiferromagnetic interactions from compounds where other kinds of +ordering are present.",0808.3789v3 +2010-04-28,"Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers","Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were +synthesized. Their temperature- and applied magnetic field-dependent +structural, transport, thermal, and magnetic properties were characterized by +means of x-ray and neutron diffraction, electrical resistivity rho, heat +capacity, magnetization and magnetic susceptibility measurements. These +compounds have a body-centered-tetragonal crystal structure (space group +I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the +CuO2 layers in high superconducting transition temperature Tc cuprate +superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the +FeAs layers in high-Tc pnictides. These two types of layers alternate along the +crystallographic c-axis and are separated by Sr atoms. The site occupancies of +Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron +powder diffraction data. The temperature dependences of rho suggest metallic +character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and +Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie +temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state +structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to +an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each +layer are ferromagnetically aligned, but are antiferromagnetically aligned +between layers.",1004.5038v1 +2010-07-01,Exactly solvable mixed-spin Ising-Heisenberg diamond chain with the biquadratic interactions and single-ion anisotropy,"An exactly solvable variant of mixed spin-(1/2,1) Ising-Heisenberg diamond +chain is considered. Vertical spin-1 dimers are taken as quantum ones with +Heisenberg bilinear and biquadratic interactions and with single-ion +anisotropy, while all interactions between spin-1 and spin-1/2 residing on the +intermediate sites are taken in the Ising form. The detailed analysis of the +$T=0$ ground state phase diagram is presented. The phase diagrams have shown to +be rather rich, demonstrating large variety of ground states: saturated one, +three ferrimagnetic with magnetization equal to 3/5 and another four +ferrimagnetic ground states with magnetization equal to 1/5. There are also two +frustrated macroscopically degenerated ground states which could exist at zero +magnetic filed. + Solving the model exactly within classical transfer-matrix formalism we +obtain an exact expressions for all thermodynamic function of the system. The +thermodynamic properties of the model have been described exactly by exact +calculation of partition function within the direct classical transfer-matrix +formalism, the entries of transfer matrix, in their turn, contain the +information about quantum states of vertical spin-1 XXZ dimer (eigenvalues of +local hamiltonian for vertical link).",1007.0098v2 +2011-01-12,Gigantic terahertz magnetochromism via electromagnons in hexaferrite magnet Ba$_2$Mg$_2$Fe$_{12}$O$_{22}$,"Effects of temperature (6--225 K) and magnetic field (0--7 T) on the +low-energy (1.2--5 meV) electrodynamics of the electromagnon, the magnetic +resonance driven by the light electric field, have been investigated for a +hexaferrite magnet Ba$_2$Mg$_2$Fe$_{12}$O$_{22}$ by using terahertz time-domain +spectroscopy. We find the gigantic terahertz magnetochromism via +electromagnons; the magnetochromic change, as defined by the difference of the +absorption intensity with and without magnetic field, exceeds 500% even at 0.6 +T. The results arise from the fact that the spectral intensity of the +electromagnon critically depends on the magnetic structure. With changing the +conical spin structures in terms of the conical angle $\theta$ from the proper +screw ($\theta=0^\circ$) to the ferrimagnetic ($\theta=90^\circ$) through the +conical spin-ordered phases ($0^\circ<\theta<90^\circ$) by external magnetic +fields, we identify the maximal magnetochromism around $\theta\approx45^\circ$. +On the contrary, there is no remarkable signature of the electromagnon in the +proper screw and spin-collinear (ferrimagnetic) phases, clearly indicating the +important role of the conical spin order to produce the +magnetically-controllable electromagnons. The possible origin of this +electromagnon is argued in terms of the exchange-striction mechanism.",1101.2303v1 +2011-02-24,"Unusual field-induced transitions in exactly solved mixed spin-(1/2,1) Ising chain with axial and rhombic zero-field splitting parameters","The mixed spin-(1/2,1) Ising chain with axial and rhombic zero-field +splitting parameters in a presence of the longitudinal magnetic field is +exactly solved within the framework of decoration-iteration transformation and +transfer-matrix method. Our particular emphasis is laid on an investigation of +the influence of the rhombic term, which is responsible for an onset of quantum +entanglement between two magnetic states S_k^z = 1 and -1 of the spin-1 atoms. +It is shown that the rhombic term gradually destroys a classical ferrimagnetic +order in the ground state and simultaneously causes diversity in magnetization +curves including intermediate plateau regions, regions with a continuous change +in the magnetization as well as several unusual field-induced transitions +accompanied with magnetization jumps. Another interesting findings concern with +an appearance of the round minimum in the temperature dependence of +susceptibility times temperature data, the double-peak zero-field specific heat +curves and the enhanced magnetocaloric effect. The temperature dependence of +the specific heat with three separate maxima may also be detected when driving +the system through the axial and rhombic zero-field splitting parameters close +enough to a phase boundary between the ferrimagnetic and disordered states and +applying sufficiently small longitudinal magnetic field.",1102.4928v1 +2011-05-06,"Investigation of element-specific and bulk magnetism, electronic and crystal structures of La{0.70}Ca{0.30}Mn{1-x}Cr{x}O{3}","The magnetic interactions in La{0.70}Ca{0.30}Mn{1-x}Cr{x}O{3} (x = 0.15, 0.50 +and 0.70) are investigated by x-ray absorption spectroscopy (XAS), x-ray +magnetic circular dichroism (XMCD), high-resolution x-ray powder diffraction, +and bulk magnetization measurements. XAS in the Mn and Cr L{2,3} edges support +stable single valent Cr{3+} ions and a varying Mn valence state with x, while +the O K edge XAS spectrum reveals local maxima in the O 2p density of states +close to the Fermi level due to mixing with Mn and Cr 3d states. A robust +antiferromagnetic state is found for x=0.70 below TN = 258 K. For x=0.15, +combined XMCD and bulk magnetization measurements indicate a fully polarized +ferrimagnetic state for the Mn and Cr spins below Tc=224 K. For x=0.50, a +reduced ferrimagnetic component dominated by Mn spins is present below Tc=154 +K. No evidence of lattice anomalies due to cooperative charge and orbital +orderings is found by x-ray diffraction for all samples. The magnetic +properties of this system are rationalized in terms of a competition of +ferromagnetic Mn-Mn double exchange and antiferromagnetic Cr-Cr and Cr-Mn +superexchange interactions.",1105.1392v2 +2011-07-05,Magnetocaloric effect and critical behavior near the paramagnetic to ferrimagnetic phase transition temperature in TbCo2-xFex,"Magnetocaloric effect (MCE) in TbCo2-xFex has been studied by dc +magnetization measurements.On substituting Fe in TbCo2, not only the magnetic +transition temperature is tuned to room temperature, but also the operating +temperature range for MCE is increased from 50 K for TbCo2 to 95 K for +TbCo1.9Fe0.1. The maximum magnetic entropy change (-{\Delta}SM) for +TbCo1.9Fe0.1 is found to be 3.7 J kg-1 K-1 for a 5 T field change, making it a +promising candidate for magnetic refrigeration near room temperature. The +temperature dependent neutron diffraction study shows a structural phase +transition (from cubic to rhombohedral phase with lowering of temperature) +which is associated with the magnetic phase transition and these transitions +broaden on Fe substitution. To investigate the nature of the paramagnetic to +ferrimagnetic phase transition, we performed a critical exponent study. From +the derived values of critical exponents, we conclude that TbCo2 belongs to the +3D Heisenberg class with short-range interaction, while on Fe substitution it +tends towards mean-field with long-range interaction. The derived values of +critical exponents represent the phenomenological universal curve for the field +dependence of {\Delta}SM, indicating that TbCo2 and TbCo1.9Fe0.1 belong to two +different universality classes.",1107.0866v1 +2012-06-04,Effects of Zeroline and Ferrimagnetic Fluctuation on Nuclear Magnetic Resonance for Dirac Electrons in Molecular Conductor alpha-(BEDT-TTF)2I3,"We re-examine the wave function of two-dimensional massless Dirac electron in +alpha-(BEDT-TTF)2I3 consisting of four molecules A, A', B and C in a unit cell, +using a tight-binding model. We find zerolines in the Brillouin zone, on which +the component of the wave function becomes zero for B or C sites. The +zerolines, which are bounded by two Dirac points at k0 and pass through the M- +or Y-points, result in a fact that the density of states of the B site exhibits +no the Van Hove singularity near the energy of the Dirac points. By taking +account of the on-site Coulomb interaction within the random phase +approximation, we examine the spin fluctuation in order to investigate +properties of the nuclear magnetic resonance for temperatures T > 50K. In the +region for 100 < T < 300K, it is shown that the Knight sift for B-site +monotonously decreases with decreasing temperature, owing to lack of the Van +Hove singularity, while it shows a maximum for the other sites (A, A' and C +sites). In the region for 50 < T < 100K, it is shown that the Knight sift is +convex downward and the Korringa ratio increases with decreasing temperature +for B-site. Such a behavior originates from the ferrimagnetic spin fluctuation +related to the zerolines. These results are consistent with those of the +nuclear magnetic resonance experiments.",1206.0527v1 +2012-07-09,Dynamic phase transition properties and hysteretic behavior of a ferrimagnetic core-shell nanoparticle in the presence of a time dependent magnetic field,"We have presented dynamic phase transition features and stationary-state +behavior of a ferrimagnetic small nanoparticle system with a core-shell +structure. By means of detailed Monte Carlo simulations, a complete picture of +the phase diagrams and magnetization profiles have been presented and the +conditions for the occurrence of a compensation point $T_{comp}$ in the system +have been investigated. According to N\'{e}el nomenclature, the magnetization +curves of the particle have been found to obey P-type, N-type and Q-type +classification schemes under certain conditions. Much effort has been devoted +to investigation of hysteretic response of the particle and we observed the +existence of triple hysteresis loop behavior which originates from the +existence of a weak ferromagnetic core coupling $J_{c}/J_{sh}$, as well as a +strong antiferromagnetic interface exchange interaction $J_{int}/J_{sh}$. Most +of the calculations have been performed for a particle in the presence of +oscillating fields of very high frequencies and high amplitudes in comparison +with exchange interactions which resembles a magnetic system under the +influence of ultrafast switching fields. Particular attention has also been +paid on the influence of the particle size on the thermal and magnetic +properties, as well as magnetic features such as coercivity, remanence and +compensation temperature of the particle. We have found that in the presence of +ultrafast switching fields, the particle may exhibit a dynamic phase transition +from paramagnetic to a dynamically ordered phase with increasing ferromagnetic +shell thickness.",1207.2023v2 +2012-08-20,Spin-1/2 Heisenberg antiferromagnet on an anisotropic kagome lattice,"We use the coupled cluster method to study the zero-temperature properties of +an extended two-dimensional Heisenberg antiferromagnet formed from spin-1/2 +moments on an infinite spatially anisotropic kagome lattice of corner-sharing +isosceles triangles, with nearest-neighbor bonds only. The bonds have exchange +constants $J_{1}>0$ along two of the three lattice directions and $J_{2} \equiv +\kappa J_{1} > 0$ along the third. In the classical limit the ground-state (GS) +phase for $\kappa < 1/2$ has collinear ferrimagnetic (N\'{e}el$'$) order where +the $J_2$-coupled chain spins are ferromagnetically ordered in one direction +with the remaining spins aligned in the opposite direction, while for $\kappa > +1/2$ there exists an infinite GS family of canted ferrimagnetic spin states, +which are energetically degenerate. For the spin-1/2 case we find that quantum +analogs of both these classical states continue to exist as stable GS phases in +some regions of the anisotropy parameter $\kappa$, namely for +$0<\kappa<\kappa_{c_1}$ for the N\'{e}el$'$ state and for (at least part of) +the region $\kappa>\kappa_{c_2}$ for the canted phase. However, they are now +separated by a paramagnetic phase without either sort of magnetic order in the +region $\kappa_{c_1} < \kappa < \kappa_{c_2}$, which includes the isotropic +kagome point $\kappa = 1$ where the stable GS phase is now believed to be a +topological ($\mathbb{Z}_2$) spin liquid. Our best numerical estimates are +$\kappa_{c_1} = 0.515 \pm 0.015$ and $\kappa_{c_2} = 1.82 \pm 0.03$.",1208.3989v2 +2012-12-02,Moderate interaction between 3d- and 4f-electrons and ferrimagnetism in Co-doped GdFeAsO,"We synthesized a series of GdFe$_{1-x}$Co$_x$AsO polycrystalline samples ($0 +\leq x \leq 1$) by using a solid state reaction method and present a systematic +study on the physical properties by means of electrical resistivity $\rho(T)$, +magnetic susceptibility $\chi(T)$ and specific heat $C(T)$. The parent compound +GdFeAsO undergoes a spin-density-wave (SDW) transition associated with Fe +3d-electrons around 130 K, followed by an antiferromagnetic (AFM) transition of +Gd at $T^\textup{Gd}_\textup{N} \approx$ 4 K. The SDW transition is quickly +suppressed by Fe/Co substitution and superconductivity appears in a narrow +doping range of $0.05 < x < 0.25$, showing a maximum $T_\textup{sc}$ $\approx$ +20 K around $x = 0.1$. On the other hand, the 4f-electrons of Gd are +antiferromagnetically ordered over the entire doping concentration ($0 \leq x +\leq 1$), while the Co 3d-electrons exhibit a ferromagnetic (FM) transition +above $x \approx 0.8$, with the Curie temperature ($T^\textup{Co}_\textup{C}$) +reaching 75 K in GdCoAsO. These two magnetic species (Gd and Co) are coupled +antiferromagnetically to give rise to ferrimagnetic behavior in magnetic +susceptibility on the Co-rich side. For $0.7 \leq x < 1.0$, the system +undergoes a possible magnetic reorientation below $T^\textup{Gd}_\textup{N}$.",1212.0222v1 +2012-12-12,Ferrimagnetism and spin canting of ZnFe2O4 nanoparticles embedded in ZnO matrix,"The structural and magnetic properties of ZnFe2O4 nanoparticles embedded in a +non-magnetic ZnO matrix are presented. X-ray diffractograms and Transmission +Electron Microscopy (TEM) images showed that the resulting samples are composed +of crystalline ferrite nanoparticles with average crystallite size = +23.4(0.9) nm, uniformly dispersed within the ZnO matrix. Magnetization data +indicated a superparamagnetic-like behavior from room temperature down to T_{M} +~ 20 K, where a transition to a frozen state is observed. The M(H) curves +displayed nearly zero coercive field down to TM, where a sharp increase in the +H_C value is observed. The measured saturation magnetization M_S values at 200 +and 2 K were M_S = 0.028(3) and 0.134(7) muB/f.u. ZnFe2O4 respectively, showing +the existence of small amounts of non compensated atomic moments. M\""ossbauer +measurements at low temperatures confirmed the transition to a magnetically +ordered state for T < 25 K, where two magnetically split sextets develop. +Whereas these two sextets show strong overlap due to the similar hyperfine +fields, in-field M\""ossbauer spectra clearly showed two different Fe3+ sites, +demonstrating that the sample is ferrimagnetically ordered. The two spinel +sites are found to behave differently under an external field of 12 T: whereas +the moments located at A sites show a perfect alignment with the external +field, spins at B sites are canted by an angle alpha_B = 49(2){\deg}. We +discuss the significance of this particle structure for the observed magnetic +behavior.",1212.2798v1 +2013-02-26,Resonant state selection in synthetic ferrimagnets,"Resonant activation of a synthetic antiferromagnet (SAF) is known to result +in a dynamic running state, where the SAF's symmetric spin-flop pair +continuously rotates between the two antiparallel ground states of the system, +with the two magnetic moments in-phase in the so-called acoustical +spin-resonance mode. The symmetry of an ideal SAF does not allow, however, to +deterministically select a particular ground state using a resonant excitation. +In this work, we study asymmetric SAF's, or synthetic ferrimagnets (SFi), in +which the two magnetic particles are different in thickness or are biased +asymmetrically with an external field. We show how the magnetic phase space of +the system can be reversibly tuned, post-fabrication, between the antiferro- +and ferri-magnetic behavior by exploiting these two asymmetry parameters and +applying a uniform external field. We observe a splitting of the optical +spin-resonance for the two ground states of the SFi system, with a frequency +spacing that can be controlled by a quasistatic uniform external field. We +demonstrate how the tunable magnetic asymmetry in SFi allows to +deterministically select a particular ground state using the splitting of the +optical spin-resonance. These results offer a new way of controlling the +magnetic state of a spin-flop bilayer, currently used in such large scale +applications as magnetic memory.",1302.6483v2 +2015-02-27,Effects of chemical pressure on the magnetic ground states of the osmate double perovskites SrCaCoOsO6 and Ca2CoOsO6,"The magnetic ground state in the double perovskite system Sr2-xCaxCoOsO6 +changes from an antiferromagnet (x = 0), to a spin glass (x = 1), to a +ferrimagnet (x = 2) as the Ca content increases. This crossover is driven by +chemical pressure effects that control the relative strength of magnetic +exchange interactions. The synthesis, crystal structure, and magnetism of +SrCaCoOsO6 and Ca2CoOsO6 are investigated and compared with Sr2CoOsO6. Both +compounds adopt a monoclinic crystal structure with rock salt ordering of Co2+ +and Os6+ and a-a-b+ octahedral tilting, but the average Co-O-Os bond angle +evolves from 158.0(3) degrees in SrCaCoOsO6 to 150.54(9) degrees in Ca2CoOsO6 +as the smaller Ca2+ ion replaces Sr2+. While this change may seem minor it has +a profound effect on the magnetism, changing the magnetic ground state from +antiferromagnetic in Sr2CoOsO6 (TN1 = 108 K, TN2 = 70 K), to a spin glass in +SrCaCoOsO6 (Tf1 = 32 K, Tf2 = 13 K), to ferrimagnetic in Ca2CoOsO6 (TC = 145 +K). In the first two compounds the observation of two transitions is consistent +with weak coupling between the Co and Os sublattices.",1503.00029v3 +2015-05-14,"First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors","Employing first principles electronic structure calculations in conjunction +with the frozen-magnon method we calculate exchange interactions, spin-wave +dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin +gapless semiconductor (SGS) compounds Mn$_2$CoAl, Ti$_2$MnAl, Cr$_2$ZnSi, +Ti$_2$CoSi and Ti$_2$VAs. We find that their magnetic behavior is similar to +the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice +exchange interactions play an essential role in the formation of the magnetic +ground state and in determining the Curie temperature, $T_\mathrm{c}$. All +compounds, except Ti$_2$CoSi possess a ferrimagnetic ground state. Due to the +finite energy gap in one spin channel, the exchange interactions decay sharply +with the distance, and hence magnetism of these SGSs can be described +considering only nearest and next-nearest neighbor exchange interactions. The +calculated spin-wave dispersion curves are typical for ferrimagnets and +ferromagnets. The spin-wave stiffness constants turn out to be larger than +those of the elementary 3$d$-ferromagnets. Calculated exchange parameters are +used as input to determine the temperature dependence of the magnetization and +$T_\mathrm{c}$ of the SGSs. We find that the $T_\mathrm{c}$ of all compounds is +much above the room temperature. The calculated magnetization curve for +Mn$_2$CoAl as well as the Curie temperature are in very good agreement with +available experimental data. The present study is expected to pave the way for +a deeper understanding of the magnetic properties of the inverse-Heusler-based +SGSs and enhance the interest in these materials for application in spintronic +and magnetoelectronic devices.",1505.03632v1 +2016-02-26,Magnetic evolution of Spinel Mn1-xZnxCr2O4 single crystals,"Mn1-xZnxCr2O4 (0 5.63$, where $n$ is the number of unit cells; and a +reentrant nonmagnetic phase at $4.74 < J_1 < 5.44$. The system also shows the +presence of spin current at specific $J_1$ values due to simultaneous breaking +of both reflection and spin parity symmetries.",2012.07486v3 +2021-01-11,Current-driven domain wall dynamics in ferrimagnetic Ni-doped Mn4N films : very large domain wall velocities and reversal of motion direction across the magnetic compensation point,"Spin-transfer torque (STT) and spin-orbit torque (SOT) are spintronic +phenomena allowing magnetization manipulation using electrical currents. Beyond +their fundamental interest, they allow developing new classes of magnetic +memories and logic devices, in particular based on domain wall (DW) motion. In +this work, we report the study of STT driven DW motion in ferrimagnetic +manganese nickel nitride (Mn4-xNixN) films, in which a fine adjustment of the +Ni content allows setting the magnetic compensation at room temperature. The +reduced magnetization, combined with the large spin polarization of conduction +electrons, strongly enhances the STT so that domain wall velocities approaching +3000 m/s can be obtained for Ni compositions close to the compensation point. +In addition, a reversal of the domain wall motion direction is observed when +the magnetic compensation composition is crossed. This striking feature, +related to the change of direction of the spin polarization with respect to +that of the net magnetization, is clarified by ab initio band structure +calculations.",2101.04220v2 +2021-01-21,Field-free spin-orbit torque-induced switching of perpendicular magnetization in a ferrimagnetic layer with vertical composition gradient,"Current-induced spin-orbit torques (SOTs) are of interest for fast and +energy-efficient manipulation of magnetic order in spintronic devices. To be +deterministic, however, switching of perpendicularly magnetized materials by +SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do +so involve the application of an in-plane bias magnetic field, or incorporation +of in-plane structural asymmetry in the device, both of which can be difficult +to implement in practical applications. Here, we reported bias-field-free SOT +switching in a single perpendicular CoTb layer with an engineered vertical +composition gradient. The vertical structural inversion asymmetry induces +strong intrinsic SOTs and a gradient-driven Dzyaloshinskii-Moriya interaction +(g-DMI), which breaks the in-plane symmetry during the switching process. +Micromagnetic simulations are in agreement with experimental results, and +elucidate the role of g-DMI in the deterministic switching. This +bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI +provides a strategy for efficient and compact SOT device design.",2101.08518v1 +2017-05-03,Linearly polarized GHz magnetization dynamics of spin helix modes in the ferrimagnetic insulator Cu$_{2}$OSeO$_{3}$,"Linear dichroism -- the polarization dependent absorption of electromagnetic +waves -- is routinely exploited in applications as diverse as structure +determination of DNA or polarization filters in optical technologies. Here +filamentary absorbers with a large length-to-width ratio are a prerequisite. +For magnetization dynamics in the few GHz frequency regime strictly linear +dichroism was not observed for more than eight decades. Here, we show that the +bulk chiral magnet Cu$_{2}$OSeO$_{3}$ exhibits linearly polarized magnetization +dynamics at an unexpectedly small frequency of about 2 GHz. Unlike optical +filters that are assembled from filamentary absorbers, the magnet provides +linear polarization as a bulk material for an extremely wide range of +length-to-width ratios. In addition, the polarization plane of a given mode can +be switched by 90$^\circ$ via a tiny variation in width. Our findings shed a +new light on magnetization dynamics in that ferrimagnetic ordering combined +with anisotropic exchange interaction offers strictly linear polarization and +cross-polarized modes for a broad spectrum of sample shapes. The discovery +allows for novel design rules and optimization of microwave-to-magnon +transduction in emerging microwave technologies.",1705.01582v1 +2017-09-03,Femtosecond formation dynamics of the spin Seebeck effect revealed by terahertz spectroscopy,"Understanding the transfer of spin angular momentum is essential in modern +magnetism research. A model case is the generation of magnons in magnetic +insulators by heating an adjacent metal film. Here, we reveal the initial steps +of this spin Seebeck effect with <27fs time resolution using terahertz +spectroscopy on bilayers of ferrimagnetic yttrium-iron garnet and platinum. +Upon exciting the metal with an infrared laser pulse, a spin Seebeck current +$j_\textrm{s}$ arises on the same ~100fs time scale on which the metal +electrons thermalize. This observation highlights that efficient spin transfer +critically relies on carrier multiplication and is driven by conduction +electrons scattering off the metal-insulator interface. Analytical modeling +shows that the electrons' dynamics are almost instantaneously imprinted onto +$j_\textrm{s}$ because their spins have a correlation time of only ~4fs and +deflect the ferrimagnetic moments without inertia. Applications in material +characterization, interface probing, spin-noise spectroscopy and terahertz spin +pumping emerge.",1709.00768v5 +2019-01-16,"Magnetic properties of double perovskite $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho): hetero-tri-spin $3d$-$5d$-$4f$ systems","The field of double perovskites is now advancing to three magnetic elements +on the A, B and B$'$ sites. A series of iridium-based double perovskite +compounds, $Ln_2$CoIrO$_6$ ($Ln$ = Eu, Tb, Ho) with three magnetic elements +were synthesized as polycrystalline samples. The compounds crystalize in +monoclinic structures with the space group $P2_1/n$. Magnetic properties of +these hetero-tri-spin $3d$-$5d$-$4f$ systems were studied by magnetic +susceptibility and field dependent magnetization in both DC and pulsed magnetic +fields. All these compounds show ferrimagnetic transitions at temperatures +$T_C$ above 100 K, which are attributable to antiferromagnetic coupling between +Co$^{2+}$ and Ir$^{4+}$ spins. For Eu$_2$CoIrO$_6$, the magnetic properties are +similar to those of La$_2$CoIrO$_6$. The Eu$^{3+}$ spins show Van Vleck +paramagnetism that don't significantly interact with transition-metal cations. +By contrast, Tb$_2$CoIrO$_6$ and Ho$_2$CoIrO$_6$ reveal a second transition to +antiferromagnetic order below a lower temperature $T_N$. The +temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might +be explained by a spin-reorientation transition. Moreover, a +magnetic-field-induced spin-flop transition with a small hysteresis was +observed below $T_N$ in these two compounds. The magnetic moment of all three +compounds do not saturate up to 60 T at low temperatures. Moderate +magnetocaloric effect was also observed in all three compounds. Our results +should motivate further investigation of the spin configuration on single +crystals of these iridium-based double perovskites.",1901.05412v1 +2019-01-28,Spin Hall magnetoresistance in heterostructures consisting of noncrystalline paramagnetic YIG and Pt,"The spin Hall magnetoresistance (SMR) effect arises from spin-transfer +processes across the interface between a spin Hall active metal and an +insulating magnet. While the SMR response of ferrimagnetic and +antiferromagnetic insulators has been studied extensively, the SMR of a +paramagnetic spin ensemble is not well established. Thus, we investigate herein +the magnetoresistive response of as-deposited yttrium iron garnet/platinum thin +film bilayers as a function of the orientation and the amplitude of an +externally applied magnetic field. Structural and magnetic characterization +show no evidence for crystalline order or spontaneous magnetization in the +yttrium iron garnet layer. Nevertheless, we observe a clear magnetoresistance +response with a dependence on the magnetic field orientation characteristic for +the SMR. We propose two models for the origin of the SMR response in +paramagnetic insulator/Pt heterostructures. The first model describes the SMR +of an ensemble of non-interacting paramagnetic moments, while the second model +describes the magnetoresistance arising by considering the total net moment. +Interestingly, our experimental data are consistently described by the net +moment picture, in contrast to the situation in compensated ferrimagnets or +antiferromagnets.",1901.09986v1 +2019-02-27,"Charge and Orbital Orderings, and Frustration in Quasi-one-dimensional Ferrimagnetic Insulator $β$-V$_2$O(PO$_4$)","Using ab initio calculations based on the correlated band theory, we have +investigated the quasi-one-dimensional chain system $\beta$-V$_2$O(PO$_4$), +showing both charge and spin orderings. Even in the uncorrelated region, the +pure transition from the tetragonal to the monoclinic structure leads to a +sizable charge difference between the two types of V ions, regardless of +magnetic orders. In the ferrimagnetic phase, inclusion of the on-site Coulomb +repulsion $U$ leads to a full orbital-polarization of V1 ($t_{2g}^{3\uparrow}$, +$S=\frac{3}{2}$) and V2 ($a_{1g}^{1\downarrow}e_g^{\prime{1\downarrow}}$, +$S=1$) above $U^c_{eff}\approx3.5$ eV, leading to local spin moments of 2.30 +and --1.54 $\mu_B$, respectively, with small orbital moments of several +hundredth $\mu_B$. So, the net moment is nearly 1 $\mu_B$ per formula unit, +which is about 2--3 times larger than the experimental value. Our results show +significant variations, strongly depending on the strength of $U_{eff}$, in +energy differences between various magnetic states as well as a small magnetic +anisotropy. These results suggest that the substantial difference between the +calculated and experimental moments is attributed to quantum fluctuation of the +pyrochlore-like weakly linked V$_4$ tetrahedral structure. Our findings are +expected to provide a good platform to investigate the interplay among the +charge-, spin-, and lattice-degrees of freedom, and geometrical frustration.",1902.10359v1 +2019-03-08,Spin-transfer torques for domain walls in antiferromagnetically coupled ferrimagnets,"Antiferromagnetic materials are outstanding candidates for next generation +spintronic applications, because their ultrafast spin dynamics makes it +possible to realize several orders of magnitude higher-speed devices than +conventional ferromagnetic materials1. Though spin-transfer torque (STT) is a +key for electrical control of spins as successfully demonstrated in +ferromagnetic spintronics, experimental understanding of STT in +antiferromagnets has been still lacking despite a number of pertinent +theoretical studies2-5. Here, we report experimental results on the effects of +STT on domain-wall (DW) motion in antiferromagnetically-coupled ferrimagnets. +We find that non-adiabatic STT acts like a staggered magnetic field and thus +can drive DWs effectively. Moreover, the non-adiabaticity parameter {\beta} of +STT is found to be significantly larger than the Gilbert damping parameter +{\alpha}, challenging our conventional understanding of the non-adiabatic STT +based on ferromagnets as well as leading to fast current-induced +antiferromagnetic DW motion. Our study will lead to further vigorous +exploration of STT for antiferromagnetic spin textures for fundamental physics +on spin-charge interaction as wells for efficient electrical control of +antiferromagnetic devices.",1903.03251v1 +2019-11-25,Flat Bands and Ferrimagnetic Order in Electronically Correlated Dice-Lattice Ribbons,"We study ribbons of the dice two-dimensional lattice (that we call ``dice +ladders'') known to have nontrivial topological properties, such as Chern +numbers 2 [Wang and Y. Ran, Phys. Rev. B {\bf 84}, 241103 (2011)]. Our main +results are two folded: (1) Analyzing the tight-binding model in the presence +of Rashba spin-orbit coupling and an external magnetic field, we observed that +dice ladders qualitatively display properties similar to their two-dimensional +counterpart all the way to the limit of only two legs in the short direction. +This includes flat bands near the Fermi level, edge currents and edge charge +localization near zero energy when open boundary conditions are used, two +chiral edge modes, and a nonzero Hall conductance. (2) We studied the effect of +Hubbard correlation $U$ in the two-leg dice ladder using Lanczos and density +matrix renormalization group techniques. We show that increasing $U$ the flat +bands split without the need of introducing external fields. Moreover, robust +ferrimagnetic order develops. Overall, our work establishes dice ladders as a +promising playground to study the combined effect of topology and correlation +effects, one of the frontiers in Quantum Materials.",1911.11267v2 +2020-05-08,Enhanced all-optical switching and domain wall velocity in annealed synthetic-ferrimagnetic multilayers,"All optical switching (AOS) of the magnetization in synthetic ferrimagnetic +Pt/Co/Gd stacks has received considerable interest due to its high potential +towards integration with spintronic devices, such as magnetic tunnel junctions +(MTJs), to enable ultrafast memory applications. Post-annealing is an essential +process in the MTJ fabrication to obtain optimized tunnel magnetoresistance +(TMR) ratio. However, with integrating AOS with an MTJ in prospect, the +annealing effects on single-pulse AOS and domain wall (DW) dynamics in the +Pt/Co/Gd stacks haven't been systematically investigated yet. In this study, we +experimentally explore the annealing effect on AOS and field-induced DW motion +in Pt/Co/Gd stacks. The results show that the threshold fluence (F_0) for AOS +is reduced significantly as a function of annealing temperature (T_a) ranging +from 100C to 300C. Specifically, a 28% reduction of F_0 can be observed upon +annealing at 300C, which is a critical T_a for MTJ fabrication. Lastly, we also +demonstrate a significant increase of the DW velocity in the creep regime upon +annealing, which is attributed to annealing-induced Co/Gd interface +intermixing. Our findings show that annealed Pt/Co/Gd system facilitates +ultrafast and energy-efficient AOS, as well as enhanced DW velocity, which is +highly suitable towards opto-spintronic memory applications.",2005.03971v1 +2020-05-29,Direction-sensitive magnetophotonic surface crystal,"Nanometer-thin rare-earth-transition metal (RE-TM) alloys with precisely +controlled compositions and out-of-plane magnetic anisotropy are currently in +the focus for ultrafast magnetophotonic applications. However, achieving +lateral nanoscale dimensions, crucial for potential device downscaling, while +maintaining designable optomagnetic functionality and out-of-plane magnetic +anisotropy is extremely challenging. Here we integrate nanosized +Tb$_{18}$Co$_{82}$ ferrimagnetic alloys, having strong out-of-plane magnetic +anisotropy, within a gold plasmonic nanoantenna array to design +micrometer-scale a magnetophotonic crystal that exhibit abrupt and narrow +magneto-optical spectral features that are both magnetic field and light +incidence direction controlled. The narrow Fano-type resonance arises through +the interference of the individual nanoantenna's surface plasmons and a +Rayleigh anomaly of the whole nanoantenna array, in both optical and +magneto-optical spectra, which we demonstrate and explain using Maxwell-theory +simulations. This robust magnetophotonic crystal opens the way for conceptually +new high-resolution light incidence direction sensors, as well as for building +blocks for plasmon-assisted all-optical magnetization switching in +ferrimagnetic RE-TM alloys.",2005.14478v3 +2020-06-18,Current-induced in-plane magnetization switching in biaxial ferrimagnetic insulator,"Ferrimagnetic insulators (FiMI) have been intensively used in microwave and +magneto-optical devices as well as spin caloritronics, where their +magnetization direction plays a fundamental role on the device performance. The +magnetization is generally switched by applying external magnetic fields. Here +we investigate current-induced spin-orbit torque (SOT) switching of the +magnetization in Y3Fe5O12 (YIG)/Pt bilayers with in-plane magnetic anisotropy, +where the switching is detected by spin Hall magnetoresistance. Reversible +switching is found at room temperature for a threshold current density of 10^7 +A cm^-2. The YIG sublattices with antiparallel and unequal magnetic moments are +aligned parallel or antiparallel to the direction of current pulses, which is +consistent to the Neel order switching in antiferromagnetic system. It is +proposed that such a switching behavior may be triggered by the +antidamping-torque acting on the two antiparallel sublattices of FiMI. Our +finding not only broadens the magnetization switching by electrical means and +promotes the understanding of magnetization switching, but also paves the way +for all-electrically modulated microwave devices and spin caloritronics with +low power consumption.",2006.10313v1 +2020-08-18,Compensation and its systematics in spin-1/2 Ising trilayered triangular ferrimagnet,"Trilayered, Ising, spin-1/2, ferrimagnets are an interesting subject for +simulational studies for they show compensation effect. A Monte Carlo study on +such a system with sublayers on triangular lattice is performed in the current +work. Three layers, making up the bulk, is formed completely by either A or B +type of atoms. The interactions between like atoms (A-A; B-B) are ferromagnetic +and between unlike ones (A-B) are anti-ferromagnetic. Thus the system has three +coupling constants and manifests into two distinct trilayer compositions: AAB +and ABA. Metropolis single spin flip algorithm is employed for the simulation +and the location of the critical points (sublattice magnetisations vanish, +leading to zero bulk magnetisation) and the compensation points (bulk +magnetisation vanishes but nonzero sublattice magnetisations exist) are +estimated. Close range simulations with variable lattice sizes for compensation +point and Binder's cumulant crossing technique for critical points are employed +for analysis and conditions for the existence of compensation points are +determined. Comprehensive phase diagrams are obtained in the Hamiltonian +parameter space and morphological studies at critical and compensation +temperatures for both the configurations are also reported. The alternative +description in terms of Inverse absolute of reduced residual magnetisation and +Temperature interval between Critical and Compensation temperatures is also +proposed and compared with traditional simulational results. Such simulational +studies and the proposed systematics of compensation effect are useful in +designing materials for specific technological applications.",2008.07808v5 +2020-08-28,"Unconventional strengthening of a bipartite entanglement of a mixed spin-(1/2,1) Heisenberg dimer achieved through Zeeman splitting","The bipartite quantum and thermal entanglement is quantified within pure and +mixed states of a mixed spin-(1/2,1) Heisenberg dimer with the help of +negativity. It is shown that the negativity, which may serve as a measure of +the bipartite entanglement at zero as well as nonzero temperatures, strongly +depends on intrinsic parameters as for instance exchange and uniaxial +single-ion anisotropy in addition to extrinsic parameters such as temperature +and magnetic field. It turns out that a rising magnetic field unexpectedly +reinforces the bipartite entanglement due to the Zeeman splitting of energy +levels, which lifts a two-fold degeneracy of the quantum ferrimagnetic ground +state. The maximal bipartite entanglement is thus reached within a quantum +ferrimagnetic phase at sufficiently low but nonzero magnetic fields on +assumption that the gyromagnetic g-factors of the spin-1/2 and spin-1 magnetic +ions are equal and the uniaxial single-ion anisotropy is a half of the exchange +constant. It is suggested that the heterodinuclear complex +[Ni(dpt)(H$_2$O)Cu(pba)]$\cdot$2H$_2$O (pba=1,3-propylenebis(oxamato) and +dpt=bis-(3-aminopropyl)amine), which affords an experimental realization of the +mixed spin-(1/2,1) Heisenberg dimer, remains strongly entangled up to +relatively high temperatures (about 140~K) and magnetic fields (about 140~T) +being comparable with the relevant exchange constant.",2008.12555v1 +2020-09-06,Ferrimagnetism Induced by Off-Site Coulomb Interaction in an Itinerant Electron System,"Motivated by weak ferromagnetism (FM) in a $\tau$-type molecular conductor +($\tau$-MC), we examine its mechanism using a two-band extended Hubbard model. +Applying the random phase approximation, we elucidate the uniform spin and +charge fluctuations between unit cells in the presence of on-site and off-site +interactions. Applying the mean-field approximation, we find the ordered state +mixing with antiferromagnetism (AFM), weak FM, and charge ordering (CO) +components in each unit cell: we classify this state as ferrimagnetism (FIM). +We reveal the phase diagrams in the interaction and interaction-temperature +spaces. The former shows that the off-site interaction induces FIM from pure +AFM and the latter shows that lowering the temperature stabilizes FIM. To +clarify the stabilization mechanism of the phases, we focus on the microscopic +nature of the ordered states, including the band structure, Fermi surface, and +density of states. We find that the FIM state is obtained from mixing features +of AFM, CO, and FM; therefore, the emergence of FIM requires both the on-site +and off-site interactions. Then, we discuss the effect of lowering the +temperature and predict that the AFM gap assists the emergence of FIM based on +AFM. This FIM state is possibly related to the observation of the weak FM in +$\tau$-MC.",2009.02675v1 +2020-10-08,Ferrimagnetic 120$^\circ$ magnetic structure in Cu2OSO4,"We report magnetic properties of a 3d$^9$ (Cu$^{2+}$) magnetic insulator +Cu2OSO4 measured on both powder and single crystal. The magnetic atoms of this +compound form layers, whose geometry can be described either as a system of +chains coupled through dimers or as a Kagom\'e lattice where every 3rd spin is +replaced by a dimer. Specific heat and DC-susceptibility show a magnetic +transition at 20 K, which is also confirmed by neutron scattering. Magnetic +entropy extracted from the specific heat data is consistent with a $S=1/2$ +degree of freedom per Cu$^{2+}$, and so is the effective moment extracted from +DC-susceptibility. The ground state has been identified by means of neutron +diffraction on both powder and single crystal and corresponds to a $\sim120$ +degree spin structure in which ferromagnetic intra-dimer alignment results in a +net ferrimagnetic moment. No evidence is found for a change in lattice symmetry +down to 2 K. Our results suggest that \sample \ represents a new type of model +lattice with frustrated interactions where interplay between magnetic order, +thermal and quantum fluctuations can be explored.",2010.03838v1 +2020-10-13,"Loss of classicality in alternating spin-$\frac{1}{2}$/spin-$1$ chain, in the presence of next-neighbor couplings and Dzyaloshinskii-Moriya interactions","We have considered and alternating Heisenberg spin chain with +nearest-neighbor ($J_1$), next-nearest neighbor ($J_2$) antiferromagnetic +couplings along with z-component of the Dzyaloshinskii-Moriya(DM) ($D_z$) +interactions. The Hamiltonian has been studied using (a) Linear Spin-Wave +Theory(LSWT) and (b) Density Matrix Renormalization Group (DMRG). The system +had been reported earlier as a classical ferrimagnet only when nearest neighbor +exchange interactions are present. Both the antiferromagnetic next-nearest +neighbor interactions and DM interactions introduce strong quantum fluctuations +and due to which all the signatures of ferrimagnetism vanishes. We find that +the nonzero $J_2$ introduces strong quantum fluctuations in each of the spin +sites due to which the z-components of both spin-1 and spin-1/2 sites average +out to be zero. The ground state becomes a singlet. The presence of $J_1$ along +with $D_z$ introduces a short range order but develops long range order along +the XY plane. $J_1$ along with $J_2$ induces competing phases with structure +factor showing sharp and wide peaks, at two different angles reflecting the +spin spiral structure locally as well as in the underlying lattice. +Interestingly, we find that the $D_z$ term removes the local spin spiral +structure in z-direction, while developing a spiral order in the XY plane.",2010.06258v2 +2020-10-29,Domain wall dynamics in antiferromagnetically-coupled double-lattice systems,"In ferromagnetic materials, the rich dynamics of magnetic domain walls (DWs) +under magnetic field or current have been successfully described using the +well-known q-{\phi} analytical model. We demonstrate here that this simple +unidimensional model holds for multiple-sublattice materials such as +ferrimagnetic alloys or synthetic antiferromagnets (SAF) by using effective +parameters, and is in excellent agreement with double-lattice micromagnetic +simulations. We obtain analytical laws for the DW velocity and internal +precession angle as a function of net magnetisation for different driving +forces (magnetic field, spin transfer and spin-orbit torques) and different +propagation regimes in ferrimagnetic alloys and SAFs. The model predicts that +several distinctive dynamical features occur near or at the magnetic and the +angular compensation points when the net magnetization or the net angular +momentum of the system vanishes, and we discuss the experimental observations +that have been reported for some of them. Using a higher degree-of-freedom +analytical model that accounts for inter-sublattice distortions, we give +analytical expressions for these distortions that agree with the micromagnetic +simulations. This model shows that the DW velocity and precession rate are +independent of the strength of the inter-sublattice exchange coupling, and +justifies the use of the simpler effective parameters model.",2010.15443v1 +2020-11-03,Fully-Compensated Ferrimagnetic Spin Filter Materials within the Cr$\textit{M}\textit{N}$Al Equiatomic Quaternary Heusler Alloys,"XX'YZ equiatomic quaternary Heusler alloys (EQHA's) containing Cr, Al, and +select Group IVB elements ($\textit{M}$ = Ti, Zr, Hf) and Group VB elements +($\textit{N}$ = V, Nb, Ta) were studied using state-of-the-art density +functional theory to determine their effectiveness in spintronic applications. +Each alloy is classified based on their spin-dependent electronic structure as +a half-metal, a spin gapless semiconductor, or a spin filter material. We +predict several new fully-compensated ferrimagnetic spin filter materials with +small electronic gaps and large exchange splitting allowing for robust spin +polarization with small resistance. CrVZrAl, CrVHfAl, CrTiNbAl, and CrTiTaAl +are identified as particularly robust spin filter candidates with an exchange +splitting of $\sim 0.20$ eV. In particular, CrTiNbAl and CrTiTaAl have +exceptionally small band gaps of $\sim 0.10$ eV. Moreover, in these compounds, +a spin asymmetric electronic band gap is maintained in 2 of 3 possible atomic +arrangements they can take, making the electronic properties less susceptible +to random site disorder. In addition, hydrostatic stress is applied to a subset +of the studied compounds in order to determine the stability and tunability of +the various electronic phases. Specifically, we find the CrAlV$\textit{M}$ +subfamily of compounds to be exceptionally sensitive to hydrostatic stress, +yielding transitions between all spin-dependent electronic phases.",2011.01389v1 +2020-11-18,Domain Wall Motion in Magnetic Nanostrips,"Domain walls are the transition regions between two magnetic domains. These +objects have been very relevant during the last decade, not only due to their +intrinsic interest in the development of novel spintronics devices but also +because of their fundamental interest. The study of domain wall has been linked +to the research on novel spin-orbit coupling phenomena such as the +Dzyaloshinskii-Moriya interaction and the spin Hall effect amount others. +Domain walls can be nucleated in ferromagnetic nanostrips and can be driven by +conventional magnetic fields and spin currents due to the injection of +electrical pulses, which make them very promising for technological +applications of recording and logic devices. In this review, based on full +micromagnetic simulations supported by extended one-dimensional models, we +describe the static and dynamic properties of domain walls in thin +ferromagnetic and ferrimagnetic wires with perpendicular magnetic anisotropy. +The present chapter aims to provide a fundamental theoretical description of +the fundaments of domain walls, and the numerical tools and models which allow +describing the DW dynamics in previous and future experimental setups.",2011.09423v2 +2021-02-17,Axion search with quantum nondemolition detection of magnons,"The axion provides a solution for the strong CP problem and is one of the +leading candidates for dark matter. This paper proposes an axion detection +scheme based on quantum nondemolition detection of magnon, i.e., quanta of +collective spin excitations in solid, which is expected to be excited by the +axion-electron interaction predicted by the Dine-Fischer-Srednicki-Zhitnitsky +(DFSZ) model. The prototype detector is composed of a ferrimagnetic sphere as +an electronic spin target and a superconducting qubit. Both of these are +embedded inside a microwave cavity, which leads to a coherent effective +interaction between the uniform magnetostatic mode in the ferrimagnetic crystal +and the qubit. An upper limit for the coupling constant between an axion and an +electron is obtained as $g_{aee}<2.6\times10^{-6}$ at the 95% confidence level +for the axion mass of $33.117$$\mu$eV $= 0.6 electrons/cell. We propose that the found phenomenon is due to +competition between Stoner exchange dominated inter-chain ferromagnetic order +and super-exchange dominated inter-chain AFM order at different doping level. +Our studies provide a viable way to exploit correlation between electronic +structures and magnetic properties of 2D magnetic materials for realization of +magnetoelectric effect.",2112.02544v2 +2021-12-11,Optical excitation of electromagnons in hexaferrite,"Understanding ultrafast magnetization dynamics on the microscopic level is of +strong current interest due to the potential for applications in information +storage. In recent years, the spin-lattice coupling has been recognized to be +essential for ultrafast magnetization dynamics. Magnetoelectric multiferroics +of type II possess intrinsic correlations among magnetic sublattices and +electric polarization (P) through spin-lattice coupling, enabling fundamentally +coupled dynamics between spins and lattice. Here we report on ultrafast +magnetization dynamics in a room-temperature multiferroic hexaferrite +possessing ferrimagnetic and antiferromagnetic sublattices, revealed by +time-resolved resonant x-ray diffraction. A femtosecond above-bandgap +excitation triggers a coherent magnon in which the two magnetic sublattices +entangle and give rise to a transient modulation of P. A novel microscopic +mechanism for triggering the coherent magnon in this ferrimagnetic insulator +based on the spin-lattice coupling is proposed. Our finding opens up a novel +but general pathway for ultrafast control of magnetism.",2112.05961v1 +2021-12-25,Spin-wave-driven skyrmion dynamics in ferrimagnets: Effect of net angular momentum,"Searching for low-power-consuming and high-efficient methods for well +controllable driving of skyrmion motion is one of the most concerned issues for +future spintronic applications, raising high concern with an appreciated choice +of magnetic media and driving scenario. In this work, we propose a novel +scenario of spin wave driven skyrmion motion in a ferrimagnetic (FiM) lattice +with the net angular momentum {\delta}s. We investigate theoretically the +effect of both {\delta}s and the circular polarization of spin wave on the +skyrmion dynamics. It is revealed that the momentum onto the skyrmion imposed +by the excited spin wave can be partitioned into a ferromagnetic term plus an +antiferromagnetic term. The ratio of these two terms and consequently the Hall +angle of skyrmion motion can be formulated as the functions of {\delta}s, +demonstrating the key role of {\delta}s as an effective control-parameter for +the skyrmion motion. Moreover, the spin wave frequency dependent skyrmion +motion is discussed, predicting the frequency enhanced skyrmion Hall motion. +This work thus represents an essential contribution to understand the skyrmion +dynamics in a FiM lattice.",2112.13232v2 +2022-01-03,Handedness-filter and Doppler shift of spin waves in ferrimagnetic domain walls,"Excitation and propagation of spin waves inside magnetic domain walls has +received attention because of their potentials in spintronic and communication +applications. Besides wave amplitude and frequency, spin-wave has its third +character: handedness, whose manipulation is certainly of interest. We propose +in this Letter that the handedness of low energy spin-wave excitations can be +controlled by tuning the net angular momentum {\delta}s in a ferrimagnetic +(FiM) domain wall, attributing to the inequivalent magnetic sublattices. The +results indicate that the spin-wave dispersion depends on both {\delta}s and +wave handedness. For a positive (negative) {\delta}s, a gapless dispersion is +observed for the left-handed (righ-handed) spin waves, while a frequency gap +appears for the right-handed (left-handed) spin waves. Thus a FiM wall could +serve as a multifold filter of low energy spin-wave in which only spin waves +with particular handedness can propagate. Furthermore, the energy consumption +loss for spin-wave excitation in the wall is much lower than that inside the +domain, while the group velocity is much faster too, demonstrating the +advantages of domain walls serving as spin waveguides. Moreover, the +current-induced spin-wave Doppler shift in the FiM wall is also revealed, and +can be controlled by {\delta}s. This work unveils for the first time the +interesting spin-wave dynamics in FiM domain walls, benefiting future spin-wave +applications.",2201.00623v2 +2022-01-07,First-principles study on phase stability and physical properties of B-site ordered Nd$_{2}$FeCrO$_{6}$ double perovskite,"Here, the first-principles predictions on the structural stability, magnetic +behavior and electronic structure of B-site ordered double perovskite +Nd$_{2}$FeCrO$_{6}$ have been reported. Initially, the ground state of the +parent single perovskites NdCrO$_{3}$ and NdFeO$_{3}$ have been studied to +determine the relevant Hubbard U parameter to investigate the properties of +Nd2CrFeO6. The thermodynamic, mechanical, and dynamic stability analyses +suggest the possibility of the synthesis of Nd$_{2}$FeCrO$_{6}$ double +perovskite at ambient pressure. The compound shows ferrimagnetic (FiM) nature +with 2 $\mu$B net magnetic moments and the magnetic ordering temperature has +been estimated to be $\sim$265 K. Electronic structure indicates higher +probability of direct photon transition over the indirect transition with a +bandgap of $\sim$1.85 eV. Additional effect of Nd (4f) spin and spin-orbit +coupling (SOC) on the band edges have been found to be negligible for this +4f-3d-3d spin system. This first-principles investigation predicts that due to +the ferrimagnetic nature and significantly lower bandgap compared to its +antiferromagnetic parent single perovskites, B-site ordered Nd$_{2}$FeCrO$_{6}$ +double perovskite could be a promising material for spintronic and +visible-light-driven energy applications.",2201.02341v1 +2022-03-31,Anomalous Hall Effect and Perpendicular Magnetic Anisotropy in Ultrathin Ferrimagnetic NiCo$_2$O$_4$ Films,"The inverse spinel ferrimagnetic NiCo$_2$O$_4$ possesses high magnetic Curie +temperature $T_C$, high spin polarization, and strain-tunable magnetic +anisotropy. Understanding the thickness scaling limit of these intriguing +magnetic properties in NiCo$_2$O$_4$ thin films is critical for their +implementation in nanoscale spintronic applications. In this work, we report +the unconventional magnetotransport properties of epitaxial (001) NiCo$_2$O$_4$ +films on MgAl$_2$O$_4$ substrates in the ultrathin limit. Anomalous Hall effect +measurements reveal strong perpendicular magnetic anisotropy for films down to +1.5 unit cell (1.2 nm), while $T_C$ for 3 unit cell and thicker films remains +above 300 K. The sign change in the anomalous Hall conductivity ($\sigma_{xy}$) +and its scaling relation with the longitudinal conductivity ($\sigma_{xx}$) can +be attributed to the competing effects between impurity scattering and band +intrinsic Berry curvature, with the latter vanishing upon the thickness driven +metal-insulator transition. Our study reveals the critical role of film +thickness in tuning the relative strength of charge correlation, Berry phase +effect, spin orbit interaction, and impurity scattering, providing important +material information for designing scalable epitaxial magnetic tunnel junctions +and sensing devices using NiCo$_2$O$_4$.",2204.00133v2 +2022-04-26,A puzzling insensitivity of magnon spin diffusion to the presence of 180$^\circ$ domain walls in a ferrimagnetic insulator,"We present room-temperature measurements of magnon spin diffusion in +epitaxial ferrimagnetic insulator MgAl$_{0.5}$Fe$_{1.5}$O$_{4}$ (MAFO) thin +films near zero applied magnetic field where the sample forms a multi-domain +state. Due to a weak uniaxial magnetic anisotropy, the domains are separated +primarily by 180$^\circ$ domain walls. We find, surprisingly, that the presence +of the domain walls has very little effect on the spin diffusion -- nonlocal +spin transport signals in the multi-domain state retain at least 95% of the +maximum signal strength measured for the spatially-uniform magnetic state, over +distances at least five times the typical domain size. This result is in +conflict with simple models of interactions between magnons and static domain +walls, which predict that the spin polarization carried by the magnons reverses +upon passage through a 180$^\circ$ domain wall.",2204.12377v1 +2022-06-21,Laser induced ultrafast Gd 4f spin dynamics in Co100-xGdx alloys by means of time-resolved XMCD,"We have studied the laser induced ultrafast quenching of Gd 4f magnetic order +in ferrimagnetic Co100-xGdx alloys to highlight the role of the inter-atomic +exchange coupling. We have taken advantage of the ultrashort soft X-ray pulses +deliver by the femtoslicing beamline at the BESSY II synchrotron radiation +source at the Helmholtz-Zentrum Berlin to perform element- and time-resolved +X-ray Magnetic Circular Dichroism spectroscopy.Our results show that the laser +induced quenching of Gd 4f magnetic order occurs on very different time-scales +for the Co72Gd28, the Co77Gd23 and the Co79Gd21 alloys. Most of the magnetic +moment losses occur within the first picosecond (ps) while the electron +distribution is strongly out of equilibrium. After the equilibration of the +electrons and lattice temperatures (t > 1 ps), the magnetic losses occur on +slower rates that depend on the alloy composition: increasing the Co +composition speeds up the demagnetization of Gd 4f sublattice. The strength of +the inter-atomic exchange coupling which depends on composition, determines the +efficiency of the angular momentum flow from the Gd 4f spin towards the +lattice. Our results are in qualitative agreements with the predictions of the +microscopic three temperatures model for ferrimagnetic alloys.",2206.10422v1 +2022-06-22,Probing Laser-Induced Spin-Current Generation in Synthetic Ferrimagnets Using Spin Waves,"Several rare-earth transition-metal ferrimagnetic systems exhibit all-optical +magnetization switching upon excitation with a femtosecond laser pulse. +Although this phenomenon is very promising for future opto-magnetic data +storage applications, the role of non-local spin transport in these systems is +scarcely understood. Using Co/Gd and Co/Tb bilayers we isolate the contribution +of the rare-earth materials to the generated spin currents by using the +precessional dynamics they excite in an adjacent ferromagnetic layer as a +probe. By measuring THz standing spin-waves as well as GHz homogeneous +precessional modes, we probe both the high- and low-frequency components of +these spin currents. The low-frequency homogeneous mode indicates a significant +contribution of Gd to the spin current, but not from Tb, consistent with the +difficulty in achieving all-optical switching in Tb-containing systems. +Measurements on the THz frequency spin waves reveal the inability of the +rare-earth generated spin currents to excite dynamics at the sub-ps timescale. +We present modelling efforts using the $s$-$d$ model, which effectively +reproduce our results and allow us to explain the behavior in terms of the +temporal profile of the spin current.",2206.10934v1 +2022-06-27,Thermal spin current generation in the multifunctional ferrimagnet Ga$_{0.6}$Fe$_{1.4}$O$_{3}$,"In recent years, multifunctional materials have attracted increasing interest +for magnetic memories and energy harvesting applications. Magnetic insulating +materials are of special interest for this purpose, since they allow the design +of more efficient devices due to the lower Joule heat losses. In this context, +Ga$_{0.6}$Fe$_{1.4}$O$_3$ (GFO) is a good candidate for spintronics +applications, since it can exhibit multiferroicity and presents a spin Hall +magnetoresistance similar to the one observed in a yttrium iron garnet (YIG)/Pt +bilayer. Here, we explore GFO utilizing thermo-spin measurements in an on-chip +approach. By carefully considering the geometry of our thermo-spin devices we +are able to quantify the spin Seebeck effect and the spin current generation in +a GFO/Pt bilayer, obtaining a value comparable to that of YIG/Pt. This further +confirms the promises of an efficient spin current generation with the +possibility of an electric-field manipulation of the magnetic properties of the +system in an insulating ferrimagnetic material.",2206.13426v2 +2022-07-15,Enhancing All-Optical Switching of Magnetization by He Ion Irradiation,"All-optical switching (AOS) of magnetization by a single femtosecond laser +pulse in Co/Gd based synthetic ferrimagnets is the fastest magnetization +switching process. On the other hand, He ion irradiation has become a promising +tool for interface engineering of spintronic material platforms, giving rise to +significant modification of magnetic properties. In this paper, we explore the +use of He ion irradiation to enhance single pulse AOS of Co/Gd bilayer-based +synthetic ferrimagnets. The intermixing of the constituent magnetic layers by +He ion irradiation was both numerically simulated and experimentally verified. +We theoretically modelled the effects of intermixing on AOS using the layered +microscopic 3-temperature model and found that AOS is enhanced significantly by +breaking the pristine Co/Gd interface through intermixing. Following this +notion, we studied the threshold fluence of AOS as a function of He ion +irradiation fluence. We found that the AOS threshold fluence can be reduced by +almost 30%. Our study reveals the control of AOS by He ion irradiation, which +opens up an industrially compatible approach for local AOS engineering.",2207.07766v1 +2022-07-17,Quantum spin spiral ground state of the ferrimagnetic sawtooth chain,"The ferrimagnetic phase of the sawtooth chain with mixed ferromagnetic +nearest-neighbour interactions $J$ and antiferromagnetic next-nearest-neighbour +interactions $J'$ (within the isotropic Heisenberg model) was previously +characterized as a phase with commensurate order. In this paper, we demonstrate +that the system in fact exhibits an incommensurate quantum spin spiral. Even +though the ground state is translationally invariant in terms of the local spin +expectations $\avg{\vec{S}_i}$, the spiral can be detected via the connected +spin-spin correlations +$\avg{\vec{S}_i\cdot\vec{S}_j}-\avg{\vec{S}_i}\cdot\avg{\vec{S}_j}$ between the +apical spins. It has a long wavelength that grows with $J'$ and that soon +exceeds finite-system sizes typically employed in numerical simulations. A +faithful treatment thus requires the use of state-of-the-art simulations for +large, periodic systems. + In this work, we are able to accurately treat up to $L=400$ sites (200 unit +cells) with periodic boundary conditions using the density-matrix +renormaliztion group (DMRG). Exploiting the SU(2) symmetry allows us to +directly compute the lowest-energy state for a given total spin. Our results +are corroborated by variational uniform matrix product state (VUMPS) +calculations, which work directly in the thermodynamic limit at the cost of a +lower accuracy.",2207.08273v2 +2022-07-25,Insight into ground-state spin arrangement and bipartite entanglement of the polymeric coordination compound [Dy$_2$Cu$_2$]$_n$ through the symmetric spin-1/2 Ising-Heisenberg orthogonal-dimer chain,"The ground-state spin arrangement and the bipartite entanglement within +Cu$^{2+}$-Cu$^{2+}$ dimers across the magnetization process of the 4f-3d +heterometallic coordination polymer +[{Dy(hfac)$_2$(CH$_3$OH)}$_2${Cu(dmg)(Hdmg)}$_2$]$_n$ (H$_2$dmg = +dimethylglyoxime, Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) are +theoretically examined using the symmetric isotropic spin-$1/2$ +Ising-Heisenberg orthogonal-dimer chain. The numerical results point to five +possible ground states of the compound with three different degrees of the +quantum entanglement within Cu$^{2+}$-Cu$^{2+}$. Besides the standard +ferrimagnetic and saturated phases without quantum entanglement of Cu$^{2+}$ +ions, which are manifested in low-temperature magnetization curve as wide +plateaus at the non-saturated magnetization $16.26\mu_{\rm B}$ and at the +saturation value $20.82\mu_{\rm B}$, respectively, one also finds an intriguing +singlet-like phase with just partial entanglement within Cu$^{2+}$-Cu$^{2+}$ +and two singlet phases with fully entangled Cu$^{2+}$-Cu$^{2+}$ dimers. The +former quantum phase can be identified in the low-temperature magnetization +process as very narrow intermediate plateau at the magnetization $9.27\mu_{\rm +B}$ per unit cell, while the latter ones as zero magnetization plateau and +intermediate plateau at the magnetization $18.54\mu_{\rm B}$. Non-monotonous +temperature variations of the concurrence, through which the entanglement +within cooper dimers is quantified, point to the possible temporary thermal +activation of the entangled states of Cu$^{2+}$-Cu$^{2+}$ also above +non-entangled ferrimagnetic and saturated phases.",2207.11943v1 +2022-08-04,Interfacial Mixing Effect in a Promising Skyrmionic Material: Ferrimagnetic Mn$_4$N,"Interfacial mixing of elements is a well-known phenomenon found in thin film +deposition. For thin-film magnetic heterostructures, interfacial compositional +inhomogeneities can have drastic effects on the resulting functionalities. As +such, care must be taken to characterize the compositional and magnetic +properties of thin films intended for device use. Recently, ferrimagnetic +Mn$_4$N thin films have drawn considerable interest due to exhibiting +perpendicular magnetic anisotropy, high domain-wall mobility, and good thermal +stability. In this study, we employed X-ray photoelectron spectroscopy (XPS) +and polarized neutron reflectometry (PNR) measurements to investigate the +interfaces of an epitaxially-grown MgO/Mn$_4$N/Pt trilayer deposited at 450 +$^{\circ}$C. XPS revealed the thickness of elemental mixing regions of near 5 +nm at both interfaces. Using PNR, we found that these interfaces exhibit +essentially zero net magnetization at room temperature. Despite the +high-temperature deposition at 450 $^{\circ}$C, the thickness of mixing regions +is comparable to those observed in magnetic films deposited at room +temperature. Micromagnetic simulations show that this interfacial mixing should +not deter the robust formation of small skyrmions, consistent with a recent +experiment. The results obtained are encouraging in terms of the potential of +integrating thermally stable Mn$_4$N into future spintronic devices.",2208.02681v1 +2022-08-19,Tuning the Magnetic Properties of the CrMnFeCoNi Cantor Alloy,"Magnetic properties of more than twenty Cantor alloy samples of varying +composition were investigated over a temperature range of 5 K to 300 K and in +fields of up to 70 kOe using magnetometry and muon spin relaxation. Two +transitions are identified: a spin-glass-like transition that appears between +55 K and 190 K depending on composition, and a ferrimagnetic transition that +occurs at approximately 43 K in multiple samples with widely varying +compositions. The magnetic signatures at 43 K are remarkably insensitive to +chemical composition. A modified Curie-Weiss model was used to fit the +susceptibility data and to extract the net effective magnetic moment for each +sample. The resulting values for the net effective moment were either +diminished with increasing Cr or Mn concentrations or enhanced with decreasing +Fe, Co, or Ni concentrations. Beyond a sufficiently large effective moment, the +magnetic ground state transitions from ferrimagnetism to ferromagnetism. The +effective magnetic moments, together with the corresponding compositions, are +used in a global linear regression analysis to extract element-specific +effective magnetic moments, which are compared to the values obtained by +ab-initio based density functional theory (DFT) calculations. These moments +provide the information necessary to controllably tune the magnetic properties +of Cantor alloy variants.",2208.09537v1 +2022-09-18,Control of chiral orbital currents in a colossal magnetoresistance material,"Colossal magnetoresistance (CMR) is an extraordinary enhancement of the +electric conductivity in the presence of a magnetic field. It is conventionally +associated with a field-induced spin polarization, which drastically reduces +spin scattering and thus electric resistance. However, ferrimagnetic Mn3Si2Te6 +is an intriguing exception to this rule: it exhibits a 7-order-of-magnitude +reduction in ab-plane resistivity with a 13-Tesla anisotropy field which occur +only when a magnetic polarization is avoided [1]. Here we report an exotic +quantum state that is driven by ab-plane chiral orbital currents (COC) flowing +along edges of MnTe6 octahedra. The c-axis orbital moments of ab-plane COC +couple to the ferrimagnetic Mn spins to drastically increase the ab-plane +conductivity (CMR) when an external magnetic field is aligned along the +magnetic hard c-axis. Both the COC state and its CMR are extraordinarily +susceptible to small DC currents exceeding a critical threshold, and a hallmark +of this COC state is an exotic time-dependent, bistable switching mimicking a +first-order melting transition. The control of the COC-enabled CMR and bistable +switching offers a fundamentally new paradigm for quantum technologies.",2209.08672v1 +2022-09-27,Magnetic Structure and Spin Fluctuations in Colossal Magnetoresistance Ferrimagnet Mn3Si2Te6,"The ferrimagnetic insulator Mn3Si2Te6, which features a Curie temperature Tc +at 78 K and a delicate yet consequential magnetic frustration, exhibits +colossal magnetoresistance (CMR) when the magnetic field is applied along the +magnetic hard axis, surprisingly inconsistent with existing precedents [Y. Ni, +H. Zhao, Y. Zhang et al. Phys. Rev. B 103, L161105 (2021)]. This discovery +motivates a thorough single-crystal neutron diffraction study in order to gain +insights into the magnetic structure and its hidden correlation with the new +type of CMR. Here we report a noncollinear magnetic structure below the Tc +where the moments lie predominantly within the basal plane but tilt toward the +c axis by ~10o at ambient conditions. A substantial magnetic diffuse scattering +decays slowly and persists well above the Tc. The evolution of the spin +correlation lengths agrees well with the electrical resistivity, underscoring +the role of spin fluctuation contributing to the magnetoresistivity near the +transition. Application of magnetic field along the c axis, renders a swift +occurrence of CMR but only a slow tilting of the magnetic moments toward the c +axis. The unparalleled changes indicate a non-consequential role of magnetic +polarization.",2209.13664v2 +2022-09-30,Design of an integrated hybrid plasmonic-photonic device for all-optical switching and reading of spintronic memory,"We introduce a novel integrated hybrid plasmonic-photonic device for +all-optical switching and reading of nanoscale ferrimagnet bits. The racetrack +memory made of synthetic ferrimagnetic material with a perpendicular magnetic +anisotropy is coupled on to a photonic waveguide onto the indium phosphide +membrane on silicon platform. The device which is composed of a double V-shaped +gold plasmonic nanoantenna coupled with a photonic crystal cavity can enable +switching and reading of the magnetization state in nanoscale magnetic bits by +enhancing the absorbed energy density and polar magneto-optical Kerr effect +(PMOKE) locally beyond the diffraction limit. Using a three-dimensional +finite-difference time-domain method, we numerically show that our device can +switch and read the magnetization state in targeted bits down to ~100 nm in the +presence of oppositely magnetized background regions in the racetrack with +widths of 30 to 120 nm, clearly outperforming a bare photonic waveguide. Our +hybrid device tackles the challenges of nonlinear absorption in the waveguide, +weak PMOKE, and size mismatch between spintronics and integrated photonics. +Thus, it provides missing link between the integrated photonics and nanoscale +spintronics, expediting the development of ultrafast and energy efficient +advanced on-chip applications.",2209.15556v1 +2022-10-27,Phases of the spin-1/2 Heisenberg antiferromagnet on the diamond-decorated square lattice in a magnetic field,"The spin-1/2 Heisenberg antiferromagnet on the frustrated diamond-decorated +square lattice is known to feature various zero-field ground-state phases, +consisting of extended monomer-dimer and dimer-tetramer ground states as well +as a ferrimagnetic regime. Using a combination of analytical arguments, density +matrix renormalization group (DMRG), exact diagonalization, as well as +sign-problem-free quantum Monte Carlo (QMC) calculations, we investigate the +properties of this system and the related Lieb lattice in the presence of a +finite magnetic field, addressing both the ground-state phase diagram as well +as several thermodynamic properties. In addition to the zero-field ground +states, we find at high magnetic field a spin-canted phase with a continuously +rising magnetization for increasing magnetic field strength, as well as the +fully polarized paramagnetic phase. At intermediate field strength, we identify +a first-order quantum phase transition line between the ferrimagnetic and the +monomer-dimer regime. This first-order line extends to finite temperatures, +terminating in a line of critical points that belong to the universality class +of the two-dimensional Ising model.",2210.15330v2 +2022-12-02,FeRhCrSi: A new spin semimetal with room temperature spin-valve behavior,"Spin semimetals are a recently discovered new class of spintronic materials, +which exhibit a band gap in one spin channel while a semimetallic feature in +the other and thus allows for tunable spin transport. Here, we present +experimental verification of spin semimetallic behavior in FeRhCrSi, a +quaternary Heusler alloy with saturation moment 2 $\mu_B$ and Curie temperature +$>$ 400 K. It crystallises in the L2$_1$ structure with 50$\%$ antisite +disorder between Fe and Rh. Below 300 K, it shows a weakly temperature +dependent electrical resistivity with negative temperature coefficient, +indicating the normal semimetal or spin semimetal behavior. Anomalous +magnetoresistance data reveals dominant contribution from asymmetric part, a +clear signature of spin-valve nature, which is retained even at room +temperature. \textcolor{black}{The asymmetric part of magneto-resistance shows +an unusual increase with increasing temperature.} Hall measurements confirm the +anomalous nature of conductivity originating from the intrinsic Berry +curvature, with holes being the majority carriers. Ab-initio simulation +confirms a unique long-range ferrimagnetic ordering to be the ground state, +explaining the origin behind the unexpected low saturation moment. The +ferrimagnetic disordered structure confirms the spin semimetallic feature of +FeRhCrSi, as observed experimentally.",2212.00924v2 +2022-12-08,Strong photon-magnon coupling using a lithographically defined organic ferrimagnet,"We demonstrate a hybrid quantum system composed of superconducting resonator +photons and magnons hosted by the organic-based ferrimagnet vanadium +tetracyanoethylene (V[TCNE]$_x$). Our work is motivated by the challenge of +scalably integrating an arbitrarily-shaped, low-damping magnetic system with +planar superconducting circuits, thus enabling a host of quantum magnonic +circuit designs that were previously inaccessible. For example, by leveraging +the inherent properties of magnons, one can enable nonreciprocal +magnon-mediated quantum devices that use magnon propagation rather than +electrical current. We take advantage of the properties of V[TCNE]$_x$, which +has ultra-low intrinsic damping, can be grown at low processing temperatures on +arbitrary substrates, and can be patterned via electron beam lithography. We +demonstrate the scalable, lithographically integrated fabrication of hybrid +quantum magnonic devices consisting of a thin-film superconducting resonator +coupled to a low-damping, thin-film V[TCNE]$_x$ microstructure. Our devices +operate in the strong coupling regime, with a cooperativity as high as 1181(44) +at T$\sim$0.4 K, suitable for scalable quantum circuit integration. This work +paves the way for the exploration of high-cooperativity hybrid magnonic quantum +devices in which magnonic circuits can be designed and fabricated as easily as +electrical wires.",2212.04423v1 +2023-02-05,Origin of magnetically dead layers in spinel ferrites $M\text{Fe}_2\text{O}_4$ grown on $\text{Al}_2\text{O}_3$: Effects of post-deposition annealing studied by XMCD,"We study the electronic and magnetic states of as-grown and annealed +$M\text{Fe}_2\text{O}_4$(111)/$\text{Al}_2\text{O}_3$(111) ($M=\text{Co, Ni}$) +thin films with various thicknesses grown on Si(111) substrates with the +$\gamma$-$\text{Al}_2\text{O}_3$(111) buffer layers by using x-ray absorption +spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), to investigate +magnetically dead layers in these films. Although the magnetically dead layers +in the as-grown samples are formed near the interface with the +$\text{Al}_2\text{O}_3$ buffer layer, we reveal that ferrimagnetic order is +partially recovered by post-deposition annealing at 973 K for 48 hours in air. +By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in +the dead layers, there are a significant number of vacancies at the $T_d$ sites +of the spinel structure, which may be the microscopic origin of the degraded +ferrimagnetic order in the $M\text{Fe}_2\text{O}_4$(111) thin films.",2302.02322v1 +2023-04-18,Anomalous impact of thermal fluctuations on spintransfer torque induced ferrimagnetic switching,"The dynamics of a spin torque driven ferrimagnetic (FiM) system is +investigated using the two-sublattice macrospin model. We demonstrate an +ultrafast switching in the picosecond range. However, we find that the +excessive current leads to the magnetic oscillation. Therefore, faster +switching cannot be achieved by unlimitedly increasing the current. By +systematically studying the impact of thermal fluctuations, we find the +dynamics of FiMs can also be distinguished into the precessional region, the +thermally activated region, and the cross-over region. However, in the +precessional region, there is a significant deviation between FiM and +ferromagnet (FM), i.e., the FM is insensitive to thermal fluctuations since its +switching is only determined by the amount of net charge. In contrast, we find +that the thermal effect is pronounced even a very short current pulse is +applied to the FiM. We attribute this anomalous effect to the complex relation +between the anisotropy and overdrive current. By controlling the magnetic +anisotropy, we demonstrate that the FiM can also be configured to be +insensitive to thermal fluctuations. This controllable thermal property makes +the FiM promising in many emerging applications such as the implementation of +tunable activation functions in the neuromorphic computing.",2304.08765v1 +2023-04-24,Magnetism and metal-insulator transitions in the anisotropic kagome lattice,"The interest in the physical properties of kagome lattices has risen +considerably. In addition to the synthesis of new materials, the possibility of +realizing ultracold atoms on an optical kagome lattice (KL) raises interesting +issues. For instance, by considering the Hubbard model on an anisotropic KL, +with a hopping $t^\prime$ along one of the directions, one is able to +interpolate between the Lieb lattice ($t^\prime=0$) and the isotropic KL +($t^\prime=t$). The ground state of the former is a ferrimagnetic insulator for +any on-site repulsion, $U$, while the latter displays a transition between a +paramagnetic metal and a Mott insulator. One may thus consider $t^\prime$ as a +parameter controlling the degree of magnetic frustration in the system. By +means of extensive quantum Monte Carlo simulations, we have examined magnetic +and transport properties as $t^\prime$ varies between these limits in order to +set up a phase diagram in the $(U/t, t^\prime/t)$ parameter space. As an +auxiliary response, analysis of the average sign of the fermionic determinant +provides consistent predictions for critical points in the phase diagram. We +observe a metal-insulator transition occurring at some critical point +$U_c^\text{M}(t^\prime)$, which increases monotonically with $ t^\prime $, from +the unfrustrated lattice limit. In addition, we have found that the boundary +between the ferrimagnetic insulator and the Mott insulator rises sharply with +$t^\prime$.",2304.12476v1 +2023-05-30,Aging and passivation of magnetic properties in Co/Gd bilayers,"Synthetic ferrimagnets based on Co and Gd bear promise for directly bridging +the gap between volatile information in the photonic domain and non-volatile +information in the magnetic domain, without the need for any intermediary +electronic conversion. Specifically, these systems exhibit strong spin-orbit +torque effects, fast domain wall motion and single-pulse all-optical switching +of the magnetization. An important open challenge to bring these materials to +the brink of applications is to achieve long-term stability of their magnetic +properties. In this work, we address the time-evolution of the magnetic moment +and compensation temperature of magnetron sputter grown Pt/Co/Gd trilayers with +various capping layers. Over the course of three months, the net magnetic +moment and compensation temperature change significantly, which we attribute to +quenching of the Gd magnetization. We identify that intermixing of the capping +layer and Gd is primarily responsible for this effect, which can be alleviated +by choosing nitrides for capping as long as reduction of nitride to oxide is +properly addressed. In short, this work provides an overview of the relevant +aging effects that should be taken into account when designing synthetic +ferrimagnets based on Co and Gd for spintronic applications.",2305.18984v1 +2023-05-30,Driving skyrmions in flow regime in synthetic ferrimagnets,"Despite significant advances in the last decade regarding the room +temperature stabilization of skyrmions or their current induced dynamics, the +impact of local material inhomogeneities still remains an important issue that +impedes to reach the regime of steady state motion of these spin textures. +Here, we study the spin-torque driven motion of skyrmions in synthetic +ferrimagnetic multilayers with the aim of achieving high mobility and reduced +skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses +with antiferromagnetic coupling between the Co and Tb magnetization. The +increase of Tb thickness in the multilayers allows to reduce the total magnetic +moment and increases the spin-orbit torques allowing to reach velocities up to +400 m.s-1 for skyrmions with diameters of about 160 nm. We demonstrate that due +to reduced skyrmion Hall effect, combined with the edge repulsion of the +magnetic track making the skyrmions moving along the track without any +transverse deflection. Further, by comparing the field-induced domain wall +motion and current-induced skyrmion motion, we demonstrate that the skyrmions +at the largest current densities present all the characteristics of a dynamical +flow regime.",2305.19208v2 +2023-06-30,3D oxygen vacancy order and defect-property relations in multiferroic (LuFeO$_3$)$_9$/(LuFe$_2$O$_4$)$_1$ superlattices,"Oxide heterostructures exhibit a vast variety of unique physical properties. +Examples are unconventional superconductivity in layered nickelates and +topological polar order in (PbTiO$_3$)$_n$/(SrTiO$_3$)$_n$ superlattices. +Although it is clear that variations in oxygen content are crucial for the +electronic correlation phenomena in oxides, it remains a major challenge to +quantify their impact. Here, we measure the chemical composition in +multiferroic (LuFeO$_3$)$_9$/(LuFe$_2$O$_4$)$_1$ superlattices, revealing a +one-to-one correlation between the distribution of oxygen vacancies and the +electric and magnetic properties. Using atom probe tomography, we observe +oxygen vacancies arranging in a layered three-dimensional structure with a +local density on the order of 10$^{14}$ cm$^{-2}$, congruent with the +formula-unit-thick ferrimagnetic LuFe$_2$O$_4$ layers. The vacancy order is +promoted by the locally reduced formation energy and plays a key role in +stabilizing the ferroelectric domains and ferrimagnetism in the LuFeO$_3$ and +LuFe$_2$O$_4$ layers, respectively. The results demonstrate the importance of +oxygen vacancies for the room-temperature multiferroicity in this system and +establish an approach for quantifying the oxygen defects with atomic-scale +precision in 3D, giving new opportunities for deterministic defect-enabled +property control in oxide heterostructures.",2307.00139v1 +2023-07-12,Quasi-static magnetization dynamics in a compensated ferrimagnetic half-metal -- Mn$_2$Ru$_x$Ga,"Exploring anisotropy and diverse magnetization dynamics in specimens with +vanishing magnetic moments presents a significant challenge using traditional +magnetometry, as the low resolution of existing techniques hinders the ability +to obtain accurate results. In this study, we delve deeper into the examination +of magnetic anisotropy and quasi-static magnetization dynamics in \mrg\,(MRG) +thin films, as an example of a compensated ferrimagnetic half-metal, by +employing anomalous Hall effect measurements within a tetragonal crystal +lattice system. Our research proposes an innovative approach to accurately +determine the complete set of anisotropy constants of these MRG thin films. To +achieve this, we perform anomalous Hall voltage curve fitting, using torque +models under the macrospin approximation, which allow us to obtain out-of-plane +anisotropy constants $K_1=4.0\times10^4$ J m$^{-3}$ ($K_1/M=0.655$\,T) and +$K_2=2.54\times10^4$ J m$^{-3}$ ($K_2/M=0.416$\,T), along with a weaker +in-plane anisotropy constant $K_3=3.48\times10^3$ J m$^{-3}$ +($K_3/M=0.057$\,T). By additionally employing first-order reversal curves +(FORC) and classical Preisach hysteresis (hysterons) models, we are able to +validate the efficacy of the macrospin model in capturing the magnetic behavior +of MRG thin films. Furthermore, our investigation substantiates that the +complex quasi-static magnetization dynamics of MRG thin films can be +effectively modelled using a combination of hysteronic and torque models. This +approach facilitates the exploration of both linear and non-linear quasi-static +magnetization dynamics, in the presence of external magnetic field and/or +current-induced effective fields, generated by the spin-orbit torque and spin +transfer torque mechanisms.",2307.06403v1 +2023-07-31,Ballistic spin-transport properties of magnetic tunnel junctions with MnCr-based ferrimagnetic quaternary Heusler alloys,"We investigate the suitability of nearly half-metallic ferrimagnetic +quaternary Heusler alloys, CoCrMnZ (Z=Al, Ga, Si, Ge) to assess the feasibility +as electrode materials of MgO-based magnetic tunnel junctions (MTJ). Low +magnetic moments of these alloys originated from the anti-ferromagnetic +coupling between Mn and Cr spins ensure a negligible stray field in spintronics +devices as well as a lower switching current required to flip their spin +direction. We confirmed mechanical stability of these materials from the +evaluated values of elastic constants, and the absence of any imaginary +frequency in their phonon dispersion curves. The influence of swapping +disorders on the electronic structures and their relative stability are also +discussed. A high spin polarization of the conduction electrons are observed in +case of CoCrMnZ/MgO hetrojunctions, independent of terminations at the +interface. Based on our ballistic transport calculations, a large coherent +tunnelling of the majority-spin $s$-like $\Delta_1$ states can be expected +through MgO-barrier. The calculated tunnelling magnetoresistance (TMR) ratios +are in the order of 1000\%. A very high Curie temperatures specifically for +CoCrMnAl and CoCrMnGa, which are comparable to $bcc$ Co, could also yield a +weaker temperature dependece of TMR ratios for CoCrMnAl/MgO/CoCrMnAl (001) and +CoCrMnGa/MgO/CoCrMnGa (001) MTJ.",2307.16442v1 +2023-10-17,Low-energy electronic interactions in ferrimagnetic Sr2CrReO6 thin films,"We reveal in this study the fundamental low-energy landscape in the +ferrimagnetic Sr2CrReO6 double perovskite and describe the underlying +mechanisms responsible for the three low-energy excitations below 1.4 eV. Based +on resonant inelastic x-ray scattering and magnetic dynamics calculations, and +experiments collected from both Sr2CrReO6 powders and epitaxially strained thin +films, we reveal a strong competition between spin-orbit coupling, Hund's +coupling, and the strain-induced tetragonal crystal field. We also demonstrate +that a spin-flip process is at the origin of the lowest excitation at 200 meV, +and we bring insights into the predicted presence of orbital ordering in this +material. We study the nature of the magnons through a combination of ab initio +and spin-wave theory calculations, and show that two nondegenerate magnon bands +exist and are dominated either by rhenium or chromium spins. The rhenium band +is found to be flat at about 200 meV ($\pm$25 meV) through X-L-W-U +high-symmetry points and is dispersive toward $\Gamma$",2310.11585v1 +2023-11-09,Optically Induced Ferromagnetic Order in a Ferrimagnet,"The parallel or antiparallel arrangement of electron spins plays a pivotal +role in determining the properties of a physical system. To meet the demands +for innovative technological solutions, extensive efforts have been dedicated +to exploring effective methods for controlling and manipulating this +arrangement [1]. Among various techniques, ultrashort laser pulses have emerged +as an exceptionally efficient tool to influence magnetic order. Ultrafast +suppression of the magnetic order [2,3], all-optical magnetization switching +[4, 5, 6, 7], and light-induced magnetic phase transitions [8] are just a few +notable examples. However, the transient nature of light-induced changes in the +magnetic state has been a significant limitation, hindering their practical +implementation. In this study, we demonstrate that infrared ultrashort laser +pulses can induce a ferromagnetic arrangement of magnetic moments in an +amorphous TbCo alloy, a material that exhibits ferrimagnetism under equilibrium +conditions. Strikingly, the observed changes in the magnetic properties persist +for significantly longer durations than any previously reported findings. Our +results reveal that ultrashort optical pulses can generate materials with +identical chemical composition and structural state but entirely distinct +magnetic arrangements, leading to unique magnetic properties. This breakthrough +discovery marks a new era in light-driven control of matter, offering the +exciting potential to create materials with properties that were once +considered unattainable.",2311.05507v2 +2023-11-26,Electric Field Switching of Magnon Spin Current in a Compensated Ferrimagnet,"Manipulation of directional magnon propagation, known as magnon spin current, +is essential for developing magnonic memory and logic devices featuring +nonvolatile functionalities and ultralow power consumption. Magnon spin current +can usually be modulated by magnetic field or current-induced spin torques. +However, these approaches may lead to energy dissipation caused by Joule +heating. Electric-field switching of magnon spin current without charge current +is highly desired but very challenging to realize. By integrating magnonic and +piezoelectric materials, we demonstrate manipulation of the magnon spin current +generated by the spin Seebeck effect in the ferrimagnetic insulator Gd3Fe5O12 +(GdIG) film on a piezoelectric substrate. We observe reversible electric-field +switching of magnon polarization without applied charge current. Through +strain-mediated magnetoelectric coupling, the electric field induces the +magnetic compensation transition between two magnetic states of the GdIG, +resulting in its magnetization reversal and the simultaneous switching of +magnon spin current. Our work establishes a prototype material platform that +pave the way for developing magnon logic devices characterized by all electric +field reading and writing and reveals the underlying physics principles of +their functions.",2311.15183v1 +2023-11-30,Criteria to observe single-shot all-optical switching in Gd-based ferrimagnetic alloys,"Single-shot all-optical helicity-independent switching (AO-HIS) induced by a +femto-second laser pulse has been mainly reported in Gadolinium based rare +earth-transition metal (RE-TM) alloys such as GdFeCo or GdCo, but the mechanism +leading to magnetization switching is a hotly debated topic. Here, we elaborate +on a large number of GdyRE1-x-yCox (RE = Dy, Tb, Ho) alloys to tune various +magnetic parameters in order to define what the criteria are for observing +AO-HIS in such systems. The state diagrams show that two laser fluences +thresholds must be considered:the fluence which induces the single laser pulse +switching (FSwitch) and the fluence at which the material breaks into a +multi-domain state (FMulti). Those two fluences are shown to behave very +differently as a function of the material properties and the laser pulse +duration. Taking into account the parameters defining the conditions for which +multi-domain states are created and considering only the angular momentum +transfer from the Gd sublattice to the rest of the system explains in large our +experimental results. The importance of the compensation in the ferrimagnetic +alloys is also discussed. We believe the defined criteria will be an important +tool for designing new ultra-fast spintronic devices based on all optical +switching.",2311.18359v1 +2023-12-07,Features of magnetization and spin reorientation in weak ferrimagnets of the YFe$_{1-x}$Cr$_x$O$_3$ type,"A brief critical review is given of the 50-year history of experimental and +theoretical studies of the magnetic properties of a new promising class of weak +ferrimagnets such as RFe$_{1-x}$Cr$_x$O$_3$ with a non-magnetic R-ion (R = La , +Y, Lu), i.e. systems with competing signs of the Dzyaloshinsky vectors Fe-Fe, +Cr-Cr and Fe-Cr. The spin Hamiltonian of the system is considered taking into +account isotropic exchange, antisymmetric Dzyaloshinsky-Moriya exchange, and +second- and fourth-order single-ion anisotropy. Within the framework of the +molecular field approximation, calculations were made of the Neel temperatures, +the average magnetic moments of $3d$ ions, total and partial magnetizations, +and effective anisotropy constants. The existence in the model system +YFe$_{1-x}$Cr$_x$O$_3$ of two regions of negative magnetization $0.25 \leq +x\leq 0.5$ and $x\approx 0.8$ with the corresponding magnetization reversal +points reaching room temperature at $x\approx 0.45$. The phenomenon of spin +reorientation observed for single-crystal samples in a wide range of +concentrations is explained by a sharp decrease in the contribution of +antisymmetric exchange to magnetic anisotropy with increasing deviation from +the parent compositions and competition between the contributions of single-ion +anisotropy of Fe and Cr ions. It has been suggested that the spatial +orientation of the Neel ${\bf G}$ vector and the $G_{xyz}$ configuration are +the reason for the small value of saturation magnetization observed +experimentally for compositions inside or near the region of negative +magnetization.",2312.04381v2 +2024-01-03,Spin-Transfer-Torque Induced Spatially Nonuniform Switching in Ferrimagnets,"Ferrimagnet (FiM), (FeCo)1-xGdx, attracts research attention due to its +ultrafast magnetic dynamics and finite net magnetization. Incorporating FiM +into the magnetic tunnel junction will be beneficial to further improve the +writing speed of magnetic random access memory (MRAM). It is commonly assumed +that the FeCo and Gd atoms are switched together due to the strong exchange +coupling, which remains valid even if one performs the two-sublattice macrospin +simulation. Interestingly, using the atomistic model developed by our group, it +is clearly seen that different atoms are not switched together. In addition, +our study reveals that the nature of switching is spatially nonuniform even in +the small sample with the dimension of 20 nm-20 nm. Furthermore, the +characteristics of nonuniformity are completely different for samples with +different Gd composition (x). When x is close to the magnetization compensation +point, successful switching cannot be obtained, but is accompanied by the +stable oscillation. The atom type that dominates the oscillation is different +from that predicted by the two-sublattice macrospin model. In addition, the +size of singular region is a non-monotonic function of current density. All +these results can only be understood by considering the spatial nonuniform +magnetization dynamics.",2401.01741v1 +2024-01-09,Coexistence of large anomalous Nernst effect and large coercive force in amorphous ferrimagnetic TbCo alloy films,"The Anomalous Nernst Effect (ANE) has garnered significant interest for +practical applications, particularly in energy harvesting and heat flux +sensing. For these applications, it is crucial for the module to operate +without an external magnetic field, necessitating a combination of a large ANE +and a substantial coercive force. However, most materials exhibiting a large +ANE typically have a relatively small coercive force. In our research, we have +explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the +coercive force peaks at the magnetization compensation point (MCP). We observed +that transverse Seebeck coefficients are amplified with Tb doping, reaching +more than 1.0 uV/K over a wide composition range near the MCP, which is three +times greater than that of pure Co. Our findings indicate that this enhancement +is primarily due to direct conversion, a product of the transverse +thermoelectric component and electrical resistivity. TbCo films present several +significant advantages for practical use: a large ANE, the capability to +exhibit both positive and negative ANE, the flexibility to be deposited on any +substrate due to their amorphous nature, a low thermal conductivity, and a +large coercive force. These attributes make TbCo films a promising material for +advancing ANE-based technologies.",2401.04445v1 +2024-01-09,Microwave magnetic excitations in U-type hexaferrite Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics,"Microwave (MW) spectra of ferrimagnetic U-hexaferrite +Sr$_4$CoZnFe$_{36}$O$_{60}$ ceramics were studied using several experimental +techniques from 100 MHz to 50 GHz at temperatures between 10 and 390 K. They +revealed 9 excitations, which exhibit remarkable temperature dependences near +the magnetic phase transitions at 145 K and 305 K. Some of them also change +under the application of a weak bias magnetic field at room temperature. Three +lowest-frequency modes seen between 200 MHz and 3 GHz were assigned to the +dynamics of the magnetic domains. The mode attributed to the natural +ferromagnetic resonance exhibits a dramatic critical slowing-down from 25 GHz +at 390 K to 5 GHz near the 305 K phase transition, and again a hardening to ~11 +GHz on further cooling. The higher-frequency excitations are most likely spin +wave (magnon) modes arising from the complex ferrimagnetic structure of +Sr$_4$CoZnFe$_{36}$O$_{60}$. The high sensitivity of the MW spectra to the weak +magnetic bias field $H$ < 700 Oe at room temperature is shown to be caused by +the transformation of the polydomain magnetic structure in randomly oriented +ceramic grains to a monodomain one. The MW response measured above 2 GHz using +coplanar and microstrip lines with different electromagnetic field distribution +and sample coupling revealed the same excitations with similar temperature and +bias field dependences. It confirms the reliability of the results and proves +the effectiveness of the used MW techniques.",2401.04678v1 +2024-02-06,Magnon mediated spin pumping by coupled ferrimagnetic garnets heterostructure,"Spin pumping has significant implications for spintronics, providing a +mechanism to manipulate and transport spins for information processing. +Understanding and harnessing spin currents through spin pumping is critical for +the development of efficient spintronic devices. The use of a magnetic +insulator with low damping, enhances the signal-to-noise ratio in crucial +experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping. +A magnetic insulator coupled with a heavy metal or quantum material offers a +more straight forward model system, especially when investigating spin-charge +interconversion processes to greater accuracy. This simplicity arises from the +absence of unwanted effects caused by conduction electrons unlike in +ferromagnetic metals. Here, we investigate the spin pumping in coupled +ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with +heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that +magnon transmission occurs at both of the FiMs FMR positions. The enhancement +of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed +to the strong interfacial exchange coupling between FiMs. The modulation of Vsp +is achieved by tuning the bilayer structure. Further, the spin mixing +conductance for these coupled systems is found to be 10^18 m^-2. Our findings +describe a novel coupled FiM system for the investigation of magnon coupling +providing new prospects for magnonic devices.",2402.03734v1 +2024-03-19,Interlayer Dzyaloshinskii-Moriya interaction in synthetic ferrimagnets,"The antisymmetric interlayer exchange interaction, i.e., interlayer +Dzyaloshinskii-Moriya interaction (IL-DMI) has attracted significant interest +since this long-range chiral spin interaction provides a new dimension for +controlling spin textures and dynamics. However, the role of IL-DMI in the +field induced and spin-orbit torque (SOT) induced switching of synthetic +ferrimagnets (SFi) has not been uncovered. Here, we exploit interlayer chiral +exchange bias fields in SFi to address both the sign and magnitude of the +IL-DMI. Depending on the degree of imbalance between the two magnetic moments +of the SFi, the amount of asymmetry, addressed via loop shifts of the +hysteresis loops under an in-plane field reveals a unidirectional and chiral +nature of the IL-DMI. The devices are then tested with SOT switching +experiments and the process is examined via both transient state and steady +state detection. In addition to field-free SOT switching, we find that the +combination of IL-DMI and SOT give rise to multi-resistance states, which +provides a possible direction for the future design of neuromorphic computing +devices based on SOT. This work is a step towards characterizing and +understanding the IL-DMI for spintronic applications.",2403.12642v1 +2024-04-06,Insights on induced magnetic moments and spin textures in synthetic ferrimagnetic Pt/Co/Gd heterolayers,"To develop new devices based on synthetic ferrimagnetic (S-FiM) +heterostructures, understanding the material's physical properties is pivotal. +Here, the induced magnetic moment (IMM), magnetic exchange-coupling, and spin +textures were investigated at room-temperature in Pt/Co/Gd multilayers using a +multiscale approach. The magnitude and direction of the IMM were interpreted +experimentally and theoretically in the framework of both X-ray magnetic +circular dichroism (XMCD) and density functional theory (DFT). The results +demonstrate that the IMM transferred by Co across the Gd paramagnetic (PM) +thickness leads to a flipped spin state (FSS) within the Gd layers, in which +their magnetic moments couple antiparallel/parallel with the ferromagnetic (FM) +Co near/far from the Co/Gd interface, respectively. For the Pt, in both Pt/Co +and Gd/Pt interfaces the IMM follows the same direction as the Co magnetic +moment, with negligible IMM in the Gd/Pt interface. Additionally, zero-field +spin spirals were imaged using scanning transmission X-ray microscopy (STXM), +while micromagnetic simulations employed to unfold the interactions stabilizing +the FiM configurations, where the existence of a sizable Dzyaloshinskii-Moriya +interaction is demonstrated to be crucial for the formation of those spin +textures. Our outcomes may add fundamental physical and technological aspects +for using FiM films in antiferromagnetic spintronic devices.",2404.04655v1 +2008-08-27,Epitaxial Zn(x)Fe(3-x)O(4) Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties,"The ferrimagnetic spinel oxide Zn(x)Fe(3-x)O(4) combines high Curie +temperature and spin polarization with tunable electrical and magnetic +properties, making it a promising functional material for spintronic devices. +We have grown epitaxial thin films with 0<=x<=0.9 on MgO(001) substrates with +excellent structural properties both in pure Ar atmosphere and an Ar/O2 mixture +by laser molecular beam epitaxy. We find that the electrical conductivity and +the saturation magnetization can be tuned over a wide range during growth. Our +extensive characterization of the films provides a clear picture of the +underlying physics of this spinel ferrimagnet with antiparallel Fe moments on +the A and B sublattice: (i) Zn substitution removes both Fe3+ moments from the +A sublattice and itinerant charge carriers from the B sublattice, (ii) growth +in finite oxygen partial pressure generates Fe vacancies on the B sublattice +also removing itinerant charge carriers, and (iii) application of both Zn +substitution and excess oxygen results in a compensation effect as Zn +substitution partially removes the Fe vacancies. A decrease (increase) of +charge carrier density results in a weakening (strengthening) of double +exchange and thereby a decrease (increase) of conductivity and the saturation +magnetization. This scenario is confirmed by the observation that the +saturation magnetization scales with the longitudinal conductivity. The +combination of tailored films with semiconductor materials such as ZnO in +multi-functional heterostructures seems to be particularly appealing.",0808.3642v3 +2010-04-14,Magnetic order on a frustrated spin-1/2 Heisenberg antiferromagnet on the Union Jack lattice,"We use the coupled cluster method (CCM) to study the zero-temperature phase +diagram of a 2D frustrated spin-half antiferromagnet, the so-called Union Jack +model. It is defined on a square lattice such that all nearest-neighbor bonds +are present with a strength $J_{1} > 0$, but only half the +next-nearest-neighbor bonds are present with a strength $J_{2} \equiv \kappa +J_{1} > 0$. The bonds are arranged such that on the $2 \times 2$ unit cell they +form the pattern of the Union Jack flag. We find strong evidence for a first +phase transition between a N\'{e}el phase and a canted ferrimagnetic phase at a +critical coupling $\kappa_{c_{1}} = 0.66 \pm 0.02$. At the transition the +energy and its first derivative seem continuous, thus providing a typical +scenario of a second-order transition, although a weakly first-order transition +cannot be excluded. By contrast, the average on-site magnetization $M$ +approaches a nonzero value $M_{c_{1}}=0.195 \pm 0.005$ on both sides of the +transition, which is more typical of a first-order transition. The slope +$dM/d\kappa$ also appears to be continuous, or very nearly so, at the critical +point $\kappa_{c_{1}}$. We find strong evidence that the canted phase becomes +unstable at large values of $\kappa$, and hence we have also used the CCM with +a model collinear semi-stripe-ordered ferrimagnetic state in which alternating +rows (and columns) are ferromagnetically and antiferromagnetically ordered. We +find tentative evidence, based on the relative energies of the two states, for +a second (first-order) phase transition between the canted and +semi-stripe-ordered states at a large value of the coupling parameter around +$\kappa_{c_{2}} \approx 125 \pm 5$. This prediction, however, is based on an +extrapolation of the CCM results for the canted state into regimes where the +CCM equations at any level of approximation beyond the lowest have no +solutions.",1004.2339v2 +2010-10-25,A frustrated quantum spin-${\boldmath s}$ model on the Union Jack lattice with spins ${\boldmath s>1/2}$,"The zero-temperature phase diagrams of a two-dimensional frustrated quantum +antiferromagnetic system, namely the Union Jack model, are studied using the +coupled cluster method (CCM) for the two cases when the lattice spins have spin +quantum number $s=1$ and $s=3/2$. The system is defined on a square lattice and +the spins interact via isotropic Heisenberg interactions such that all +nearest-neighbour (NN) exchange bonds are present with identical strength +$J_{1}>0$, and only half of the next-nearest-neighbour (NNN) exchange bonds are +present with identical strength $J_{2} \equiv \kappa J_{1} > 0$. The bonds are +arranged such that on the $2 \times 2$ unit cell they form the pattern of the +Union Jack flag. Clearly, the NN bonds by themselves (viz., with $J_{2}=0$) +produce an antiferromagnetic N\'{e}el-ordered phase, but as the relative +strength $\kappa$ of the frustrating NNN bonds is increased a phase transition +occurs in the classical case ($s \rightarrow \infty$) at $\kappa^{\rm +cl}_{c}=0.5$ to a canted ferrimagnetic phase. In the quantum cases considered +here we also find strong evidence for a corresponding phase transition between +a N\'{e}el-ordered phase and a quantum canted ferrimagnetic phase at a critical +coupling $\kappa_{c_{1}}=0.580 \pm 0.015$ for $s=1$ and $\kappa_{c_{1}}=0.545 +\pm 0.015$ for $s=3/2$. In both cases the ground-state energy $E$ and its first +derivative $dE/d\kappa$ seem continuous, thus providing a typical scenario of a +second-order phase transition at $\kappa=\kappa_{c_{1}}$, although the order +parameter for the transition (viz., the average ground-state on-site +magnetization) does not go to zero there on either side of the transition.",1010.5161v1 +2011-08-01,"Ferrimagnetism, Antiferromagnetism and Magnetic Frustration in La$_{2-x}$Sr$_{x}$CuRuO$_{6}$ (0 <= x <= 1)","We studied structural and magnetic properties of a series of insulating +double perovskite compounds, La$_{2-x}$Sr$_{x}$CuRuO$_{6}$ (0 $\le$ x $\le$ 1), +representing doping via \textit{A}-site substitution. The end members +La$_{2}$CuRuO$_{6}$ and LaSrCuRuO$_{6}$ form in monoclinic structure while the +intermediate Sr doped compounds stabilise in triclinic structure. The Cu and Ru +ions sit on alternate B-sites of the perovskite lattice with $\sim$15% +anti-site defects in the undoped sample while the Sr doped samples show a +tendency to higher ordering at B-sites. The undoped (x = 0) compound shows a +ferrimagnetic-like behaviour at low temperatures. In surprising contrast to the +usual expectation of an enhancement of ferromagnetic interaction on doping, an +antiferromagnetic-like ground state is realized for all doped samples (x $>$ +0). Heat capacity measurements indicate the absence of any long range magnetic +order in any of these compounds. The magnetic relaxation and memory effects +observed in all compounds suggest glassy dynamical properties associated with +magnetic disorder and frustration. We show that the observed magnetic +properties are dominated by the competition between the nearest neighbour Ru -- +O -- Cu 180$^\circ$ superexchange interaction and the next nearest neighbour Ru +-- O -- O -- Ru 90$^\circ$ superexchange interaction as well as by the +formation of anti-site defects with interchanged Cu and Ru positions. Our +calculated exchange interaction parameters from first principles calculations +for $x$ = 0 and $x$ = 1 support this interpretation.",1108.0334v3 +2020-07-22,"Origin of the metamagnetic transitions in Y1-xErxFe2(H,D)4.2 compounds","The structural and magnetic properties of Y1-xErxFe2 intermetallic compounds +and their hydrides and deuterides Y1-xErxFe2H(D)4.2 have been investigated +using X-ray diffraction and magnetic measurements under static and pulsed +magnetic field up to 60 T. The intermetallics crystallize in the C15 cubic +structure , whereas corresponding hydrides and deuterides crystallize in a +monoclinic structure. All compounds display a linear decrease of the unit cell +volume versus Er concentration; the hydrides have a 0.8% larger cell volume +compared to the deuterides with same Er content. They are ferrimagnetic at low +field and temperature with a compensation point at x = 0.33 for the +intermetallics and x = 0.57 for the hydrides and deuterides. A sharp first +order ferromagnetic-antiferromagnetic (FM-AFM) transition is observed upon +heating at TFM-AFM for both hydrides and deuterides. These compounds show two +different types of field induced transitions, which have different physical +origin. At low temperature (T < 50 K), a forced ferri-ferromagnetic +metamagnetic transition with Btrans1 = 8 T, related to the change of the Er +moments orientation from antiparallel to parallel Fe moment, is observed. +Btrans1 is not sensitive to Er concentration, temperature and isotope effect. A +second metamagnetic transition resulting from antiferromagnetic to +ferrimagnetic state is also observed. The transition field Btrans2 increases +linearly versus temperature and relates to the itinerant electron metamagnetic +behavior of the Fe sublattice. An onset temperature TM0 is obtained by +extrapolating TFM-AFM (B) at zero field. TM0 decreases linearly versus the Er +content and is 45(5) K higher for the hydrides compared to the corresponding +deuteride. The evolution of TM0 versus cell volume shows that it cannot be +attributed exclusively to a pure volume effect and that electronic effects +should also be considered.",2007.11672v1 +2017-04-05,"Structure, site-specific magnetism and magneto-transport properties of epitaxial D0$_{22}$ Mn$_2$Fe$_x$Ga thin films","Ferrimagnetic Mn$_2$Fe$_x$Ga $(0.26 \leq x \leq 1.12)$ thin films have been +characterised by X-ray diffraction, SQUID magnetometry, X-ray absorption +spectroscopy, X-ray magnetic circular dichroism and M\""{o}ssbauer spectroscopy +with the aim of determining the structure and site-specific magnetism of this +tetragonal, D0$_{22}$-structure Heusler compound. High-quality epitaxial films +with low RMS surface roughness ($\sim 0.6$ nm) are grown by magnetron +co-sputtering. The tetragonal distortion induces strong perpendicular magnetic +anisotropy along the $c$-axis with a typical coercive field $\mu_0 H\sim 0.8$ T +and an anisotropy field ranging from $6$ to $8$ T. Upon increasing the Fe +content $x$, substantial uniaxial anisotropy, $K_\mathrm{u} \geq 1.0$ MJ/m$^3$ +can be maintained over the full $x$ range, while the magnetisation of the +compound is reduced from $400$ to $280$ kA/m. The total magnetisation is almost +entirely given by the sum of the spin moments originating from the +ferrimagnetic Mn and Fe sublattices, with the latter being coupled +ferromagnetically to one of the former. The orbital magnetic moments are +practically quenched, and have negligible contributions to the magnetisation. +The films with $x=0.73$ exhibit a high anomalous Hall angle of $2.5$ % and a +high Fermi-level spin polarisation, above $51$ %, as measured by point contact +Andreev reflection. The Fe-substituted Mn$_2$Ga films are highly tunable with a +unique combination of high anisotropy, low magnetisation, appreciable spin +polarisation and low surface roughness, making them very strong candidates for +thermally-stable spin-transfer-torque switching nanomagnets with lateral +dimensions down to $10$ nm.",1704.01326v1 +2012-04-17,Magnetoelectric effects in single crystals of the cubic ferrimagnetic helimagnet Cu2OSeO3,"We present magnetodielectric measurements in single crystals of the cubic +spin-1/2 compound Cu$_2$OSeO$_3$. A magnetic field-induced electric +polarization ($\vec{P}$) and a finite magnetocapacitance (MC) is observed at +the onset of the magnetically ordered state ($T_c = 59$ K). Both $\vec{P}$ and +MC are explored in considerable detail as a function of temperature (T), +applied field $\vec{H}_a$, and relative field orientations with respect to the +crystallographic axes. The magnetodielectric data show a number of anomalies +which signal magnetic phase transitions, and allow to map out the phase diagram +of the system in the $H_a$-T plane. Below the 3up-1down collinear ferrimagnetic +phase, we find two additional magnetic phases. We demonstrate that these are +related to the field-driven evolution of a long-period helical phase, which is +stabilized by the chiral Dzyalozinskii-Moriya term $D \vec{M} +\cdot(\bs{\nabla}\times\vec{M})$ that is present in this non-centrosymmetric +compound. We also present a phenomenological Landau-Ginzburg theory for the +ME$_H$ effect, which is in excellent agreement with experimental data, and +shows three novel features: (i) the polarization $\vec{P}$ has a uniform as +well as a long-wavelength spatial component that is given by the pitch of the +magnetic helices, (ii) the uniform component of $\vec{P}$ points along the +vector $(H^yH^z, H^zH^x, H^xH^y)$, and (iii) its strength is proportional to +$\eta_\parallel^2-\eta_\perp^2/2$, where $\eta_\parallel$ is the longitudinal +and $\eta_\perp$ is the transverse (and spiraling) component of the magnetic +ordering. Hence, the field dependence of P provides a clear signature of the +evolution of a conical helix under a magnetic field. A similar phenomenological +theory is discussed for the MC.",1204.3783v1 +2018-01-10,Prediction of a magnetic Weyl semimetal without spin-orbit coupling and strong anomalous Hall effect in the Heusler compensated ferrimagnet Ti2MnAl,"We predict a magnetic Weyl semimetal in the inverse Heusler Ti2MnAl, a +compensated ferrimagnet with a vanishing net magnetic moment and a Curie +temperature of over 650 K. Despite the vanishing net magnetic moment, we +calculate a large intrinsic anomalous Hall effect (AHE) of about 300 S/cm. It +derives from the Berry curvature distribution of the Weyl points, which are +only 14 meV away from the Fermi level and isolated from trivial bands. +Different from antiferromagnets Mn3X (X= Ge, Sn, Ga, Ir, Rh, and Pt), where the +AHE originates from the non-collinear magnetic structure, the AHE in Ti2MnAl +stems directly from the Weyl points and is topologically protected. The large +anomalous Hall conductivity (AHC) together with a low charge carrier +concentration should give rise to a large anomalous Hall angle. In contrast to +the Co-based ferromagnetic Heusler compounds, the Weyl nodes in Ti2MnAl do not +derive from nodal lines due to the lack of mirror symmetries in the inverse +Heusler structure. Since the magnetic structure breaks spin-rotation symmetry, +the Weyl nodes are stable without SOC. Moreover, because of the large +separation between Weyl points of opposite topological charge, the Fermi arcs +extent up to 75% of the reciprocal lattice vectors in length. This makes +Ti2MnAl an excellent candidate for the comprehensive study of magnetic Weyl +semimetals. It is the first example of a material with Weyl points, large +anomalous Hall effect and angle despite a vanishing net magnetic moment.",1801.03273v3 +2019-10-31,Time-resolving magnetic scattering on rare-earth ferrimagnets with a bright soft-X-ray high-harmonic source,"We demonstrate the first time-resolved X-ray resonant magnetic scattering +(tr-XRMS) experiment at the N edge of Tb at 155 eV performed using a tabletop +high-brightness high-harmonic generation (HHG) source. In contrast to static +X-ray imaging applications, such optical-pump X-ray-probe studies pose a +different set of challenges for the ultrafast driver laser because a high +photon flux of X-rays resonant with the N edge must be attained at a low +repetition rate to avoid thermal damage of the sample. This laboratory-scale +X-ray magnetic diffractometer is enabled by directly driving HHG in helium with +terawatt-level 1 um laser fields, which are obtained through pulse compression +after a high-energy kHz-repetition-rate Yb:CaF2 amplifier. The high peak power +of the driving fields allows us to reach the fully phase-matching conditions in +helium, which yields the highest photon flux (>2x10^9 photons/s/1% bandwidth) +in the 100-220 eV spectral range, to the best of our knowledge. Our +proof-of-concept tr-XRMS measurements clearly resolve the spatio-temporal +evolution of magnetic domains in Co/Tb ferrimagnetic alloys with femtosecond +and nanometer resolution. In addition to the ultrafast demagnetization, we +observe magnetic domain expansion with a domain wall velocity similar to that +induced by spin transfer torque. The demonstrated method opens up new +opportunities for time-space-resolved magnetic scattering with elemental +specificity on various magnetic, orbital and electronic orderings in condensed +matter systems.",1910.14263v1 +2020-01-03,"Effect of N, C and B interstitials on the structural and magnetic properties of alloys with Cu$_3$Au-structure","High-throughput density functional calculations are used to investigate the +effect of interstitial B, C and N atoms on 21 alloys reported to crystallize in +the cubic Cu$_3$Au structure. It is shown that the interstitials can have a +significant impact on the magneto-crystalline anisotropy energy (MAE), the +thermodynamic stability and the magnetic ground state structure, making these +alloys interesting for hard magnetic, magnetocaloric and other applications. +For 29 alloy/interstitial combinations the formation of stable alloys with +interstitial concentrations above 5\% is expected. In Ni$_3$Mn interstitial N +induces a tetragonal distortion with substantial uniaxial MAE for realistic N +concentrations. Mn$_3X$N$_x$ ($X$=Rh, Ir, Pt and Sb) are identified as alloys +with strong magneto-crystalline anisotropy. For Mn$_3$Ir we find a strong +enhancement of the MAE upon N alloying in the most stable collinear +ferrimagnetic state as well as in the non-collinear magnetic ground state. +Mn$_3$Ir and Mn$_3$IrN show also interesting topological transport properties. +The effect of N concentration and strain on the magnetic properties are +discussed. Further, the huge impact of N on the MAE of Mn$_3$Ir and a possible +impact of interstitial N on amorphous Mn$_3$Ir, a material that is +indispensable in today's data storage devices, are discussed at hand of the +electronic structure. For Mn$_3$Sb, non-collinear, ferrimagnetic and +ferromagnetic states are very close in energy, making this material potentially +interesting for magnetocaloric applications. For the investigated Mn alloys and +competing phases, the determination of the magnetic ground state is essential +for a reliable prediction of the phase stability.",2001.00959v1 +2019-11-13,"Electronic structure investigation of GdNi using X-ray absorption, magnetic circular dichroism and hard x-ray photoemission spectroscopy","GdNi is a ferrimagnetic material with a Curie temperature Tc = 69 K which +exhibits a large magnetocaloric effect, making it useful for magnetic +refrigerator applications. We investigate the electronic structure of GdNi by +carrying out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular +dichroism (XMCD) at T = 25 K in the ferrimagnetic phase. We analyze the Gd +M$_{4,5}$-edge ($3d$ - $4f$) and Ni L$_{2,3}$-edge ($2p$ - $3d$) spectra using +atomic multiplet and cluster model calculations, respectively. The atomic +multiplet calculation for Gd M$_{4,5}$-edge XAS indicates that Gd is trivalent +in GdNi, consistent with localized $4f$ states. On the other hand, a model +cluster calculation for Ni L$_{2,3}$-edge XAS shows that Ni is effectively +divalent in GdNi and strongly hybridized with nearest neighbour Gd states, +resulting in a $d$-electron count of 8.57. The Gd M$_{4,5}$-edge XMCD spectrum +is consistent with a ground state configuration of S = 7/2 and L=0. The Ni +L$_{2,3}$-edge XMCD results indicate that the antiferromagnetically aligned Ni +moments exhibit a small but finite magnetic moment ( $m_{tot}$ $\sim$ 0.12 +$\mu_B$ ) with the ratio $m_{o}/m_{s}$ $\sim$ 0.11. Valence band hard x-ray +photoemission spectroscopy shows Ni $3d$ features at the Fermi level, +confirming a partially filled $3d$ band, while the Gd $4f$ states are at high +binding energies away from the Fermi level. The results indicate that the Ni +$3d$ band is not fully occupied and contradicts the charge-transfer model for +rare-earth based alloys. The obtained electronic parameters indicate that GdNi +is a strongly correlated charge transfer metal with the Ni on-site Coulomb +energy being much larger than the effective charge-transfer energy between the +Ni $3d$ and Gd $4f$ states.",1911.05306v2 +2019-11-22,"Role of Element-Specific Damping on the Ultrafast, Helicity-Independent All-Optical Switching Dynamics in Amorphous (Gd,Tb)Co Thin Films","Ultrafast control of the magnetization in ps timescales by fs laser pulses +offers an attractive avenue for applications such as fast magnetic devices for +logic and memory. However, ultrafast helicity-independent all-optical switching +(HI-AOS) of the magnetization has thus far only been observed in Gd-based, +ferrimagnetic amorphous (\textit{a}-) rare earth-transition metal +(\textit{a}-RE-TM) systems, and a comprehensive understanding of the reversal +mechanism remains elusive. Here, we report HI-AOS in ferrimagnetic +\textit{a}-Gd$_{22-x}$Tb$_x$Co$_{78}$ thin films, from x = 0 to x = 18, and +elucidate the role of Gd in HI-AOS in \textit{a}-RE-TM alloys and multilayers. +Increasing Tb content results in increasing perpendicular magnetic anisotropy +and coercivity, without modifying magnetization density, and slower +remagnetization rates and higher critical fluences for switching but still +shows picosecond HI-AOS. Simulations of the atomistic spin dynamics based on +the two-temperature model reproduce these results qualitatively and predict +that the lower damping on the RE sublattice arising from the small spin-orbit +coupling of Gd (with $L = 0$) is instrumental for the faster dynamics and lower +critical fluences of the Gd-rich alloys. Annealing +\textit{a}-Gd$_{10}$Tb$_{12}$Co$_{78}$ leads to slower dynamics which we argue +is due to an increase in damping. These simulations strongly indicate that +acounting for element-specific damping is crucial in understanding HI-AOS +phenomena. The results suggest that engineering the element specific damping of +materials can open up new classes of materials that exhibit low-energy, +ultrafast HI-AOS.",1911.09803v3 +2020-08-31,"Structural, magnetic and electronic properties of CaBaCo4-xMxO7 (M= Fe, Zn)","The effect of substituting iron and zinc for cobalt in CaBaCo$_4$O$_7$ has +been investigated using neutron diffraction and x-ray absorption spectroscopy. +The orthorhombic distortion present in the parent compound CaBaCo$_4$O$_7$ +decreases with increasing the content of either Fe or Zn. The samples +CaBaCo$_3$ZnO$_7$ and CaBaCo$_{4-x}$Fe$_x$O$_7$ with $x \leq 1.5$ are +metrically hexagonal but much better refinements in the neutron diffraction +patterns are obtained using an orthorhombic unit cell. The two types of +substitution have opposite effects on the structural and magnetic properties. +Fe atoms preferentially occupy the sites at the triangular layer. Thus, the +replacement of Co by Fe supresses the ferrimagnetic ordering and +CaBaCo$_{4-x}$Fe$_x$O$_7$ samples are antiferromagnetically ordered with a new +propagation vector k=(1/3,0,0). However, the Zn atoms prefer occupying the +Kagome layer, which is very detrimental for the long range magnetic +interactions giving rise to a magnetic glass. The oxidation state of iron and +zinc is found to be 3+ and 2+, respectively, independently of the content. +Therefore, the average Co oxidation state changes accordingly with the +Fe$^{3+}$ or Zn$^{2+}$ doping. Also, x-ray absorption spectroscopy data +confirms the different preferential occupation for both Fe and Zn cations. The +combined information obtained by neutron diffraction and x-ray absorption +spectroscopy indicates that cobalt atoms can be either in a fluctuating +Co$^{2+}$/Co$^{3+}$ valence state or, alternatively, Co$^{2+}$ and Co$^{3+}$ +ions being randomly distributed in the lattice. These results explain the +occurrence of local disorder in the CoO$_4$ tetrahedra obtained by EXAFS. An +anomaly in the lattice parameters and an increase in the local disorder is +observed only at the ferrimagnetic transition for CaBaCo$_4$O$_7$ revealing the +occurrence of local magneto-elastic coupling.",2008.13649v1 +2020-09-29,Spin transfer torque in Mn$_3$Ga-based ferrimagnetic tunnel junctions from first principles,"We report on first-principles calculations of spin-transfer torque (STT) in +epitaxial magnetic tunnel junctions (MTJs) based on ferrimagnetic tetragonal +Mn$_3$Ga electrodes, both as analyzer in an Fe/MgO stack, and also in an +analogous stack with a second Mn$_3$Ga electrode (instead of Fe) as polarizer. +Solving the ballistic transport problem (NEGF + DFT) for the nonequilibrium +spin density in a scattering region extended to over 7.6 nm into the Mn$_3$Ga +electrode, we find long-range spatial oscillations of the STT decaying on a +length scale of a few tens of angstroms, both in the linear response regime and +for finite bias. The oscillatory behavior of the STT in Mn$_3$Ga is robust +against variations in the stack geometry and the applied bias voltage, which +may affect the phase and the amplitude of the spatial oscillation, but the wave +number is only responsive to variations in the longitudinal lattice constant of +Mn$_3$Ga (for fixed in-plane geometry) without being commensurate with the +lattice. Our interpretation of the long-range STT oscillations is based on the +bulk electronic structure of Mn$_3$Ga, taking also into account the +spin-filtering properties of the MgO barrier. Comparison to a fully +Mn$_3$Ga-based stack shows similar STT oscillations, but a significant +enhancement of both the TMR effect at the Fermi level and the STT at the +interface, due to resonant tunneling for the mirror-symmetric junction with +thinner barrier (three monoatomic layers). From the calculated energy +dependence of the spin-polarized transmissions at 0 V, we anticipate asymmetric +or symmetric TMR as a function of the applied bias voltage for the Fe-based and +the all-Mn$_3$Ga stacks, respectively, which also both exhibit a sign change +below 1 V. In the latter (symmetric) case we expect a TMR peak at zero, which +is larger for the thinner barriers because of a spin-polarized resonant +tunneling contribution.",2009.14095v2 +2020-10-15,Unconventional superparamagnetic behavior in the modified cubic spinel compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$,"Structural, electronic, and magnetic properties of modified cubic spinel +compound LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ are studied via x-ray diffraction, +resistivity, DC and AC magnetization, heat capacity, neutron diffraction, +$^7$Li nuclear magnetic resonance, magnetocaloric effect, magnetic relaxation, +and magnetic memory effect experiments. We stabilized this compound in a cubic +structure with space group $P4_{3}32$. It exhibits semiconducting character +with an electronic band gap of $\Delta/k_{\rm B} \simeq 0.4$ eV. The +interaction within each Mn$^{4+}$ and Ni$^{2+}$ sub-lattice and between +Mn$^{4+}$ and Ni$^{2+}$ sublattices is found to be ferromagnetic (FM) and +antiferromagnetic (AFM), respectively which leads to the onset of a +ferrimagnetic transition at $T_{\rm C} \simeq 125$~K. The reduced values of +frustration parameter ($f$) and ordered moments reflect magnetic frustration +due to competing FM and AFM interactions. From the $^7$Li NMR shift vs +susceptibility plot, the average hyperfine coupling between $^7$Li nuclei and +Ni$^{2+}$ and Mn$^{4+}$ spins is calculated to be $\sim 672.4$~Oe/$\mu_{\rm +B}$. A detailed critical behaviour study is done in the vicinity of $T_{\rm C}$ +using modified-Arrott plot, Kouvel-Fisher plot, and universal scaling of +magnetization isotherms. The estimated critical exponents correspond to the 3D +XY universality class. A large magneto-caloric effect is observed with a +maximum isothermal change in entropy $\Delta S_m \simeq - 11.3$~J/Kg-K and a +maximum relative cooling power $RCP \simeq 604$~J/Kg for 9~T magnetic field +change. The imaginary part of the AC susceptibility depicts a strong frequency +dependent hump at $T=T_{\rm f2}$ well below the blocking temperature $T_{\rm +b}\simeq120$~K. The Arrhenius behaviour of frequency dependent $T_{\rm f2}$ and +the absence of ZFC memory confirm the existence of superparamagnetism in the +ferrimagnetically ordered state.",2010.07709v1 +2021-04-14,Critical phenomena of the layered ferrimagnet Mn3Si2Te6 following proton irradiation,"We examine the magnetic properties of the quasi 2D ferrimagnetic single +crystal Mn3Si2Te6 (MST) through critical phenomena and magnetic entropy +analysis in the easy axis (H || ab) as a function of proton irradiance. +Employing a modified asymptotic analysis method, we find that upon proton +irradiation the critical exponents do not fall into any particular universality +class but lie close to mean field critical exponents ({\gamma} = 1, \b{eta} = +0.5). The presence of long-range interactions can be safely assumed for the +pristine and irradiated cases of MST examined in this work. Further analysis on +the effective spatial dimensionality reveal that MST remains at d = 3 under +proton irradiation transitioning from an n = 1 spin dimensionality to n = 2 and +n=3 for 1 x 10^15 and 5 x 10^15 H+/cm^2, indicating an XY interaction and a +Heisenberg interaction, respectively. The pair (spin-spin) correlation function +reveals an increase in magnetic correlations at the proton irradiance of 5 x +10^15 H+/cm^2. In conjunction, the maximum change in magnetic entropy obtained +from isothermal magnetization at 3 T is the largest for 5 x 10^15 H+/cm^2 with +a value of 2.45 J/kgK at T = 73.66 K, in comparison to 1.60 J/kgK for pristine +MST at T = 73 K. Magnetic entropy derived from zero-field heat capacity does +not show large deviations across the proton irradiated samples. This suggests +that the antiferromagnetic coupling between the Mn sites is stable even after +proton irradiation. Such result implies that magnetization is enhanced through +a strengthening of the super-exchange interaction between Mn atoms mediated +through Te rather than a weakening of the AFM component. Overall, our study +finds that the magnetic interactions are manipulated the greatest when MST is +irradiated at 5 x 10^15 H+/cm^2.",2104.06564v1 +2021-05-28,Monte Carlo calculations of Curie temperatures of Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ pseudobinary system,"The close-packed AB$_2$ structures called Laves phases constitute the largest +group of intermetallic compounds. In this paper we computationally investigated +the pseudo-binary Laves phase system Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ +spanning between the YFe$_2$, YCo$_2$, GdFe$_2$, and GdCo$_2$ vertices. While +the vast majority of the Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$ phase diagram is +the ferrimagnetic phase, YCo$_2$ along with a narrow range of concentrations +around it is the paramagnetic phase. We presented results obtained by Monte +Carlo simulations of the Heisenberg model with parameters derived from +first-principles calculations. For calculations, we used the Uppsala atomistic +spin dynamics (UppASD) code together with the spin-polarized relativistic +Korringa-Kohn-Rostoker (SPR-KKR) code. From first principles we calculated the +magnetic moments and exchange integrals for the considered pseudo-binary +system, together with spin-polarized densities of states for boundary +compositions. Furthermore, we showed how the compensation point with the +effective zero total moment depends on the concentration in the considered +ferrimagnetic phases. However, the main result of our study was the +determination of the Curie temperature dependence for the system +Y$_{1-x}$Gd$_x$(Fe$_{1-y}$Co$_y$)$_2$. Except for the paramagnetic region +around YCo$_2$, the predicted temperatures were in good qualitative and +quantitative agreement with experimental results, which confirmed the ability +of the method to predict magnetic transition temperatures for systems +containing up to three different magnetic elements (Fe, Co, and Gd) +simultaneously. For the Y(Fe$_{1-y}$Co$_y$)$_2$ and Gd(Fe$_{1-y}$Co$_y$)$_2$ +systems our calculations matched the experimentally-confirmed +Slater-Pauling-like behavior of T$_C$ dependence on the Co concentration.",2105.13844v1 +2021-10-11,Transition of laser-induced terahertz spin currents from torque- to conduction-electron-mediated transport,"Spin transport is crucial for future spintronic devices operating at +bandwidths up to the terahertz (THz) range. In F|N thin-film stacks made of a +ferro/ferrimagnetic layer F and a normal-metal layer N, spin transport is +mediated by (1) spin-polarized conduction electrons and/or (2) torque between +electron spins. To identify a cross-over from (1) to (2), we study laser-driven +spin currents in F|Pt stacks where F consists of model materials with different +degrees of electrical conductivity. For the magnetic insulators YIG, GIG and +maghemite, identical dynamics is observed. It arises from the THz interfacial +spin Seebeck effect (SSE), is fully determined by the relaxation of the +electrons in the metal layer and provides an estimate of the spin-mixing +conductance of the GIG/Pt interface. Remarkably, in the half-metallic +ferrimagnet Fe3O4 (magnetite), our measurements reveal two spin-current +components with opposite direction. The slower, positive component exhibits SSE +dynamics and is assigned to torque-type magnon excitation of the A- and B-spin +sublattices of Fe3O4. The faster, negative component arises from the +pyro-spintronic effect and can consistently be assigned to ultrafast +demagnetization of e-sublattice minority-spin hopping electrons. This +observation supports the magneto-electronic model of Fe3O4. In general, our +results provide a new route to the contact-free separation of torque- and +conduction-electron-mediated spin currents.",2110.05462v2 +2021-11-01,Localized-delocalized crossover of spin-carriers and magnetization reversal in Co$_{2}$VO$_{4}$,"Neutron diffraction, magnetization and muon spin relaxation measurements, +supplemented by density functional theory (DFT) calculations are employed to +unravel temperature-driven magnetization reversal (MR) in inverse spinel +Co$_2$VO$_4$. All measurements show a second-order magnetic phase transition at +$T_{\rm C} = 168$\,K to a collinear ferrimagnetic phase. The DFT results +suggest the moments in the ferrimagnetic phase are delocalized and undergo +gradual localization as the temperature is lowered below $T_{\rm C}$. The +delocalized-localized crossover gives rise to a maximum magnetization at +$T_{\rm NC} = 138$\,K and the continuous decrease in magnetization produces +sign-change at $T_{\rm MR} \sim 65$\,K. Muon spectroscopy results support the +DFT, as a strong $T_1$-relaxation is observed around $T_{\rm NC}$, indicating +highly delocalized spin-carriers gradually tend to localization upon cooling. +The magnetization reversal determined at zero field is found to be highly +sensitive to the applied magnetic field, such that above $B\sim 0.25$\,T +instead of a reversal a broad minimum in the magnetization is apparent at +$T_{\rm MR}$. Analysis of the neutron diffraction measurements shows two +antiparallel magnetic sub-lattice-structure, each belonging to magnetic ions on +two distinct crystal lattice sites. The relative balance of these two +structural components in essence determines the magnetization. Indeed, the +order parameter of the magnetic phase on one site develops moderately more than +that on the other site. Unusual tipping of the magnetic balance, caused by such +site-specific magnetic fluctuation, gives rise to a spontaneous flipping of the +magnetization as the temperature is lowered.",2111.00694v1 +2021-11-26,"Room temperature weak collinear ferrimagnet with symmetry driven, large intrinsic magneto-optic signatures","Here we present a magnetic thin film with a weak ferrimagnetic (FIM) phase +above the N\'eel temperature ($T_{N}$ = 240 K) and a non-collinear +antiferromagnetic (AFM) phase below, exhibiting a small net magnetisation due +to strain-associated canting of the magnetic moments. A long-range ordered FIM +phase has been predicted in related materials, but without symmetry analysis. +We now perform this analysis and use it to calculate the MOKE spectra in AFM +and FIM phases. From the good agreement between the form of the measured and +predicted MOKE spectra, we propose the AFM and FIM phases share the magnetic +space group C2'/m' and that the symmetry driven magneto-optic and +magneto-transport properties are maximised at room temperature in the FIM phase +due to the non-zero intrinsic Berry phase contribution present in these +materials. A room temperature FIM phase with large optical and transport +signatures, as well as sensitivity to lattice strain and magnetic field, has +useful prospects for high-speed spintronic applications.",2111.13498v4 +2022-04-24,Ground-state phase diagram and thermodynamics of coupled trimer chains,"The density matrix renormalization group and quantum Monte Carlo method are +used to describe coupled trimer chains in a magnetic field h. The Hamiltonian +contains exchange terms involving the intra-trimer coupling J1 (taken as the +unit of energy) and the inter-trimer coupling J2, plus the Zeeman interaction +for a magnetic field h along the z direction. Results for the magnetization per +trimer m are calculated in regimes of positive and negative values of the ratio +J = J2 / J1, from which the rich field-induced ground state phase diagram h vs. +J is derived, with the presence of Luttinger liquid, the 1/3-plateau (m = 1/2), +and the one of fully polarized magnetization (m = 3/2). Also, the zero-field +Lanczos calculation of spin-wave dispersion from the 1/3-plateau for $S^z = 1$ +is shown at the previous regimes of J values. In addition, we also report on +the decay of correlation functions of trimers along open chains, as well as the +average two-magnon distribution. The ground state is ferrimagnetic for $0$ 300 K and +the band gap less than 2 eV are obtained by DFT calculations, when 1/8 or 1/4 +Fe atoms in LaFeO$_3$ are replaced by the other 3d, 4d transition metal +elements. The large magneto-optical Kerr effect (MOKE) is obtained in these +LaFeO$_3$-based FIM semiconductors. In addition, the FIM semiconductors with +high $T_C$ are also obtained by spin-dependent doping in some other AFM +materials with high $T_N$, including BiFeO$_3$, SrTcO$_3$, CaTcO$_3$, etc. Our +theoretical results propose a way to obtain high $T_C$ FIM semiconductors by +spin-dependent doping in high $T_N$ AFM insulators and semiconductors.",2310.09061v1 +1998-11-03,"Microwave Emission by Dust: Mechanisms, Properties and Prospects for ISM Studies","I review my work with Bruce Draine on dust emissivity at microwave +frequencies (3 cm - 3 mm). This emissivity explains the recently detected +""anomalous"" component of the galactic foreground emission. Both small (a<0.001 +micron) and large grains contribute to this emission. Small grains have +electric dipole moments and emit while they rotate; the microwave emission of +large grains is mostly due to magneto-dipole radiation. Most efficient +magneto-dipole emitters are strongly magnetic, e.g. ferrimagnetic or +ferromagnetic, materials. The relative role of the two mechanisms can be +established through observations of microwave emissivity from dark clouds. New +microwave window is a window of opportunity for interstellar studies. Magnetic +fields inside dark clouds may be successfully studied via microwave +polarization. Microwave emissivity constrains the abundance of strongly +magnetic materials. For instance, the available data at 90 GHz indicate that +not more than 5% of interstellar Fe is in the form of metallic iron grains or +inclusions (e.g., in ``GEMS''). Future missions, e.g. MAP and PLANCK, will +bring a wealth of microwave data that can be successfully used to study ISM. +Such a study would be appreciated by cosmologists who franticly try to remove +all foregrounds from their data.",9811043v1 +1996-11-21,Blume-Emery-Griffiths model on the square lattice with repulsive biquadratic coupling,"Using a real-space renormalization group procedure with no adjustable +parameters, we investigate the Blume-Emery-Griffiths model on the square +lattice. The formalism respects sublattice symmetry, allowing the study of both +signs of K, the biquadratic exchange coupling. Our results for K>0 are compared +with other renormalization group calculations and with exact results, in order +to assess the magnitude of the errors introduced by our approximate +calculation. The quantitative agreement is excellent; values for critical +parameters differ, in some cases, by less than 1% from exact ones. For K<0, our +results lead to a rich phase diagram, with antiquadrupolar and ferromagnetic +ordered phases. Contrarily to Monte Carlo simulations, these two phases meet +only at zero temperature. Both antiquadrupolar-disordered and +ferromagnetic-disordered transitions are found to be continuous and no +ferrimagnetic phase is found.",9611159v1 +1997-02-05,Phase diagrams of the S=1/2 quantum antiferromagnetic XY model on the triangular lattice in magnetic fields,"We study the S=1/2 quantum antiferromagnetic XY model on finite triangular +lattices with N sites in both longitudinal and transverse magnetic fields. We +calculate physical quantities in the ground state using a diagonalization for +spins $N \leq 27$, and those at finite temperatures using a quantum transfer +Monte Carlo method for $N \leq 24$. In the longitudinal magnetic field, the +long-range chiral order parameter seems to have a finite, nonzero value at low +temperatures suggesting the occurrence of a classical umbrella-type phase. In +the transverse magnetic field, the 1/3-plateau of the magnetization curve +appears even at low temperatures, in contrast with the classical model. The +magnetic field dependences of the order parameters suggest that the +chiral-ordered, the ferrimagnetic, and the spin flop phases appear successively +as the magnetic field is increased. The transition temperatures are estimated +from the peak position of the specific heat, and the phase diagrams are +predicted in both longitudinal and transverse magnetic fields.",9702046v1 +1997-10-30,Elementary Excitations of Heisenberg Ferrimagnetic Spin Chains,"We numerically investigate elementary excitations of the Heisenberg +alternating-spin chains with two kinds of spins 1 and 1/2 antiferromagnetically +coupled to each other. Employing a recently developed efficient Monte Carlo +technique as well as an exact diagonalization method, we verify the spin-wave +argument that the model exhibits two distinct excitations from the ground state +which are gapless and gapped. The gapless branch shows a quadratic dispersion +in the small-momentum region, which is of ferromagnetic type. With the +intention of elucidating the physical mechanism of both excitations, we make a +perturbation approach from the decoupled-dimer limit. The gapless branch is +directly related to spin 1's, while the gapped branch originates from +cooperation of the two kinds of spins.",9710332v1 +1998-09-02,One-dimensional Ising model with long-range and random short-range interactions,"The one-dimensional Ising model in an external magnetic field with uniform +long-range interactions and random short-range interactions satisfying bimodal +annealed distributions is studied. This generalizes the random model discussed +by Paladin et al. (J. Phys. I France 4, 1994, p. 1597). Exact results are +obtained for the thermodynamic functions at arbitrary temperatures, and special +attention is given to the induced and spontaneous magnetization. At low +temperatures the system can exist in a ``ferrimagnetic'' phase with +magnetization 0x_c. The 180 +Ni-O-Ni inter-plane super-exchange coupling J_\perp \simeq -110K is confirmed +to be the predominant magnetic interaction. From the low temperature behavior, +we find a clear indication of a 90 Ni-O-Ni intra-plane antiferromagnetic +interaction $J_\parallel \simeq -1.5K$ which implies magnetic frustration.",9904194v1 +1999-12-09,Ab initio study of magnetic structure and chemical reactivity of Cr2O3 and its (0001) surface,"We present the first ab initio density functional theory study of the +oxygen-terminated Cr2O3 (0001) surface within the local spin-density +approximation (LSDA). We find that spin plays a critical role for even the most +basic properties of Cr2O3 such as the structure and mechanical response of the +bulk material. The surface exhibits strong relaxations and changes in +electronic and magnetic structure with important implications for the chemical +reactivity and unusual spin-dependent catalytic activity of the surface. Unlike +the bulk, the outermost chromium bilayer is ferromagnetically ordered, and the +surface oxygen layer exhibits appreciable net spin polarization in the opposite +sense. Surprisingly, despite this ferrimagnetic order, the chemically important +states near the Fermi level exhibit ferromagnetic order and thus favor +electronic spin alignment of species interacting with the surface. Finally, we +also find a high density of unoccupied electronic surface states available to +participate in the chemical reactivity of the surface.",9912154v1 +2000-01-27,Epitaxy and magnetotransport of Sr_2FeMoO_6 thin films,"By pulsed-laser deposition epitaxial thin films of Sr_2FeMoO_6 have been pre- +pared on (100) SrTiO_3 substrates. Already for a deposition temperature of 320 +C epitaxial growth is achieved. Depending on deposition parameters the films +show metallic or semiconducting behavior. At high (low) deposition temperature +the Fe,Mo sublattice has a rock-salt (random) structure. The metallic samples +have a large negative magnetoresistance which peaks at the Curie temperature. +The magnetic moment was determined to 4 mu_B per formula unit (f.u.), in +agreement with the expected value for an ideal ferrimagnetic arrangement. We +found an ordinary Hall coefficient of -6.01x10^{-10} m^3/As at 300 K, +corresponding to an electronlike charge-carrier density of 1.3 per Fe,Mo-pair. +In the semiconducting films the magnetic moment is reduced to 1 mu_B/f.u. due +to disorder in the Fe,Mo sublattice. In low fields an anomalous holelike +contribution dominates the Hall voltage, which vanishes at low temperatures for +the metallic films only.",0001398v1 +2000-04-18,"Metallic and nonmetallic double perovskites: A case study of A$_2$FeReO$_6$ (A= Ca, Sr, Ba)","We have investigated the structure and electronic properties of ferrimagnetic +double perovskites, A2FeReO6 (A= Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m) +and metallic, while the A=Ca phase is monoclinic (P21/n) and nonmetallic. + 57Fe Mossbauer spectroscopy shows that iron is present mainly in the +high-spin (S=5/2) Fe3+ state in the Ca compound, while it occurs in an +intermediate state between high-spin Fe2+ and Fe3+ in the Ba compound. It is +argued that a direct Re t2g - Re t2g interaction is the main cause for the +metallic character of the Ba compound; the high covalency of Ca-O bonds and the +monoclinic distortion (which lifts the degeneracy of t2g states) seem to +disrupt the Re-Re interaction in the case of the Ca compound, making it +non-metallic for the same electron count.",0004315v1 +2000-07-07,Dimerization of Ferrimagnets on Chains and Square Lattices,"A linear spin wave analysis of dimerization of alternating Heisenberg system +with spins $s_{1}$ and $s_{2}$ on linear chain as well as square lattice is +presented. Among the several possible dimerized configurations considered in +two dimensions the plaquette configuration is found to be energetically the +most favored one. Inclusion of a variable nearest neighbor exchange coupling +$J(a)=\frac{J}{a}$ leads to a uniform power law behavior: that is to say, the +same $\delta $-dependence is found (i) in chains as well as in square lattices; +(ii) in systems consisting of different pairs of spins $s_{1}$ and $s_{2}$; +(iii) for the magnetic energy gain, the energy gap, the energy of the gapped +magnetic excitation mode as well as for the sublattice magnetization; (iv) for +all the configurations of the square lattice; and (v) in the entire range of +$\delta :$ $(0\leq \delta <1)$. The variable exchange coupling also allows \ +the energy of the gapped excitation spectrum to be $\delta $-dependent even in +the linear spin wave theory.",0007133v1 +2000-10-27,Coexistent quantum and classical aspects of magnetization plateaux in alternating-spin chains,"Magnetization process of ferrimagnetic Heisenberg chains of alternating spins +are theoretically studied. The size scaling analysis with the exact +diagonalization of finite systems for ($S$,$s$)=(3/2,1) and (2,1) indicates a +multi-plateau structure in the ground-state magnetization curve for $S$ and $s$ +$>1/2$. The first plateau at the spontaneous magnetization can be explained by +a classical origin, that is the Ising gap. In contrast, the second or higher +one must be originated to the quantization of the magnetization. It is also +found that all the $2s$ plateaux, including the classical and quantum ones, +appear even in the isotropic case with no bond alternation.",0010446v1 +2000-10-29,Theory of Ferromagnetism in Diluted Magnetic Semiconductors,"Carrier-induced ferromagnetism has been observed in several (III,Mn)V +semiconductors. We review the theoretical picture of these ferromagnetic +semiconductors that emerges from a model with kinetic-exchange coupling between +localized Mn spins and valence-band carriers. We discuss the applicability of +this model, the validity of a mean-field approximation for its interaction term +widely used in the literature, and validity limits for the simpler RKKY model +in which only Mn spins appear explicitly. Our conclusions are based in part on +our analysis of the dependence of the system's elementary spin excitations on +carrier density and exchange-coupling strength. The analogy between this system +and spin-model ferrimagnets is explored. Finally, we list several extensions of +this model that can be important in realistic modeling of specific materials.",0010471v1 +2000-12-12,Low Energy Properties of Ferrimagnetic 2-leg Ladders: a Lanczos study,"We apply the Lanczos method to a 2-leg ladder with mixed spins of magnitudes +$(S_1,S_2)=(1,1/2)$ located at alternating positions along the ladder. The +effect of dimerization $\gamma$ is also considered according to two different +patterns. A Spin Wave Theory (SWT) is applied to this model predicting one +gapless branch with ferromagnetic properties and another gapful branch with +antiferromagnetic nature as low energy excitations of the model. We compute the +ground state energies, Ferro- and AF-excitation gaps, magnetizations and +correlation functions as a function of $J'$ and $\gamma$ which results into a +fine estimate of the phase diagram. The Lanczos results are compared with the +SWT analysis and a qualitative agreement is found but with numerical +discrepancies. We also study numerically the Spin-Peierls instability and find +that it is conditional for any value of $ J' \in (0, 2)$ and both dimerization +patterns.",0012209v1 +2000-12-15,Alternating-Spin Ladders in a Magnetic Field: New Magnetization Plateaux,"We study numerically the formation of magnetization plateaux with the Lanczos +method in 2-leg ladders with mixed spins of magnitudes $(S_1,S_2)=(1,1/2)$ +located at alternating positions along the ladder and with dimerization +$\gamma$. For interchain coupling $J'>0$ and $\gamma=0$, we find normalized +plateaux at $m=1/3$ starting at zero field and $m=1$ (saturation), while when +$\gamma \ne 0$ is columnar, another extra plateau at $m=2/3$ shows up. For +$J'<0$, when $\gamma<\gamma_c(J')$ we find no plateau while for +$\gamma>\gamma_c(J')$ we find four plateaux at $m=0,1/3,2/3,1$. We also apply +several approximate analytical methods (Spin Wave Theory, Low-Energy Effective +Hamiltonians and Bosonization) to understand these findings and to conjeture +the behaviour of ferrimagnetic ladders with a bigger number of legs.",0012278v1 +2001-06-12,Glauber slow dynamics of the magnetization in a molecular Ising chain,"The slow dynamics (10^-6 s - 10^4 s) of the magnetization in the paramagnetic +phase, predicted by Glauber for 1d Ising ferromagnets, has been observed with +ac susceptibility and SQUID magnetometry measurements in a molecular chain +comprising alternating Co{2+} spins and organic radical spins strongly +antiferromagnetically coupled. An Arrhenius behavior with activation energy +Delta=152 K has been observed for ten decades of relaxation time and found to +be consistent with the Glauber model. We have extended this model to take into +account the ferrimagnetic nature of the chain as well as its helicoidal +structure.",0106224v2 +2001-10-23,Effect of local Coulomb interactions on the electronic structure and exchange interactions in Mn12 magnetic molecules,"We have studied the effect of local Coulomb interactions on the electronic +structure of the molecular magnet Mn12-acetate within the LDA+U approach. The +account of the on-site repulsion results in a finite energy gap and an integer +value of the molecule's magnetic moment, both quantities being in a good +agreement with the experimental results. The resulting magnetic moments and +charge states of non-equivalent manganese ions agree very well with +experiments. The calculated values of the intramolecular exchange parameters +depend on the molecule's spin configuration, differing by 25-30% between the +ferrimagnetic ground state and the completely ferromagnetic configurations. The +values of the ground-state exchange coupling parameters are in reasonable +agreement with the recent data on the magnetization jumps in megagauss magnetic +fields. Simple estimates show that the obtained exchange parameters can be +applied, at least qualitatively, to the description of the spin excitations in +Mn12-acetate.",0110488v1 +2001-11-12,On the ground states of an array of magnetic dots in the vortex state and subject to a normal magnetic field,"Dipole-dipole interactions in a square planar array of sub-micron magnetic +disks (magnetic dots) have been studied theoretically. Under a normal magnetic +field the ground-state of the array undergoes many structural transitions +between the limiting chessboard antiferromagnetic state at zero field and the +ferromagnet at a threshold field. At intermediate fields, numerous +ferrimagnetic states having mean magnetic moments between zero and that of the +ferromagnetic state are favorable energetically. The structures and energies of +a selection of states are calculated and plotted, as are the fields required to +optimally reverse the magnetic moment of a single dot within them. Approximate +formulae for the dipolar energy and anhysteretic magnetization curve are +presented.",0111225v1 +2001-12-16,Magnetic phases of the mixed-spin $J_1-J_2$ Heisenberg model on a square lattice,"We study the zero-temperature phase diagram and the low-energy excitations of +a mixed-spin ($S_1>S_2$) $J_1-J_2$ Heisenberg model defined on a square lattice +by using a spin-wave analysis, the coupled cluster method, and the Lanczos +exact-diagonalization technique. As a function of the frustration parameter +$J_2/J_1$ ($ >0$), the phase diagram exhibits a quantized ferrimagnetic phase, +a canted spin phase, and a mixed-spin collinear phase. The presented results +point towards a strong disordering effect of the frustration and quantum spin +fluctuations in the vicinity of the classical spin-flop transition. In the +extreme quantum system $(S_1,S_2)=(1,{1/2})$, we find indications of a new +quantum spin state in the region $0.46< J_2/J_1<0.5$",0112295v2 +2002-04-22,"Magnetic ordering, electronic structure and magnetic anisotropy energy in the high-spin Mn$_{10}$ single molecule magnet","We report the electronic structure and magnetic ordering of the single +molecule magnet [Mn$_{10}$O$_{4}$(2,2'-biphenoxide)$_{4}$Br$_{12}$]$^{4-}$ +based on first-principles all-electron density-functional calculations. We find +that two of the ten core Mn atoms are coupled antiferromagnetically to the +remaining eight, resulting in a ferrimagnetic ground state with total spin +S=13. The calculated magnetic anisotropy barrier is found to be 9 K in good +agreement with experiment. The presence of the Br anions impact the electronic +structure and therefore the magnetic properties of the 10 Mn atoms. However, +the electric field due to the negative charges has no significant effect on the +magnetic anisotropy.",0204479v1 +2002-09-30,Investigation of a ring single molecular magnet Mn$_6$R$_6$ in megagauss fields,"The dependence of the magnetic susceptibility on the magnetic field is +investigated for the single molecular magnet [Mn(hfac)$_2$NITPh]$_6$. The +spikes of the susceptibility detected in a magnetic field ranging from 90 T to +285 T are interpreted as a manifestation of magnetic quantum jumps under spins +reorientation from ferrimagnetic to ferromagnetic structure. The characteristic +feature of the single molecular magnet Mn$_6$ R$_6$ is a deficiency of pair +Heisenberg exchange interactions for the description of its magnetic properties +in high magnetic fields. The comparison of the experimental data with the +results of theoretical calculations allows us to prove the existence of strong +three-spin interaction in this molecular cluster and to determine the values of +exchange constants. For the calculation of the ground state spin structure the +modified Lanczos method is used.",0209670v1 +2002-10-31,Magnetic Structure of Nano-Graphite Moebius Ribbon,"We consider the electronic and magnetic properties of nanographite ribbon +with zigzag edges under the periodic or Moebius boundary conditions. The zigzag +nano-graphite ribbons possess edge localized states at the Fermi level which +cause a ferrimagnetic spin polarization localized at the edge sites even in the +very weak Coulomb interaction. The imposition of the Moebius boundary condition +makes the system non-AB-bipartite lattice, and depress the spin polarization, +resulting in the formation of a magnetic domain wall. The width of the magnetic +domain depends on the Coulomb interaction and narrows with increasing U/t.",0210685v2 +2002-11-25,The Kagome-staircase lattice: Magnetic ordering in Ni3V2O8 and Co3V2O8,"Ni3V2O8 and Co3V2O8 have spin-1 and spin-3/2 magnetic lattices that are a new +anisotropic variant of the Kagome net, wherein edge-sharing MO6 octahedra form +the rises and rungs of a ""Kagome staircase"". The anisotropy largely relieves +the geometric frustration, but results in rich magnetic behavior. +Characterization of the magnetization of polycrystalline samples reveals that +the compounds are ferrimagnetic in character. Heat capacity measurements show +the presence of four magnetic phase transitions below 9 K for Ni3V2O8 and two +below 11 K for Co3V2O8. Comparison to the low temperature heat capacity of +isostructural nonmagnetic Zn3V2O8 provides an estimate of the magnetic entropy +involved with the phase transitions. The results suggest that Co3V2O8 may +display magnetic transitions below 2 K.",0211572v1 +2003-01-08,Ground-state phases in a system of two competing square-lattice Heisenberg antiferromagnets,"We study a two-dimensional (2D) spin-half Heisenberg model related to the +quasi 2D antiferromagnets (Ba,Sr)2Cu3O4Cl2 by means of exact diagonalization +and spin-wave theory. The model consists of two inequivalent interpenetrating +square-lattice Heisenberg antiferromagnets A and B. While the antiferromagnetic +interaction JAA within the A subsystem is strong the coupling JBB within the B +subsystem is much weaker. The coupling JAB between A and B subsystems is +competing giving rise for interesting frustration effects. In dependence of the +strength of JAB we find a collinear Neel phase, non-collinear states with zero +magnetizations as well as canted and collinear ferrimagnetic phases with +non-zero magnetizations. For not too large values of frustration JAB, which +correpond to the situation in (Ba,Sr)2Cu3O4Cl2, we have Neel ordering in both +subsystems A and B. In the classical limit these two Neel states are decoupled. +Quantum fluctuations lead to a fluctuational coupling between both subsystems +('order from disorder') and select the collinear structure. For stronger JAB we +find evidence for a novel spin state with coexisting Neel ordering in the A +subsystem and disorder in the B subsystem.",0301095v1 +2003-01-10,Phase diagram of a coupled tetrahedral Heisenberg model,"The phase diagram of a coupled tetrahedral Heisenberg model is obtained. The +quantum chain has a local gauge symmetry and its eigenspectrum is obtained by +the composition of the eigenspectra of spin-1/2 XXZ chains with arbitrary +distribution of spin-3/2 impurities. The phase diagram is quite rich with an +infinite number of phases with ferromagnetic, antiferromagnetic or +ferrimagnetic order. In some cases the ground state and the low lying +eigenlevels of the model can be exactly calculated since they coincide with the +eigenlevels of the exactly integrable XXZ chain. The thermodynamical properties +of the model at low temperatures is also studied through finite-size analysis.",0301162v2 +2003-02-26,Anomalous magnetotransport in (Y$_{1-x}$Gd$_{x}$)Co$_{2}$ alloys: interplay of disorder and itinerant metamagnetism,"New mechanism of magnetoresistivity in itinerant metamagnets with a +structural disorder is introduced basing on analysis of experimental results on +magnetoresistivity, susceptibility, and magnetization of structurally +disordered alloys (Y$_{1-x}$Gd$_{x}$)Co$_{2}$. In this series, YCo$_{2}$ is an +enhanced Pauli paramagnet, whereas GdCo$_{2}$ is a ferrimagnet (T$_{\rm c}$=400 +K) with Gd sublattice coupled antiferromagnetically to the itinerant Co-3d +electrons. The alloys are paramagnetic for $x < 0.12$. Large positive +magnetoresistivity has been observed in the alloys with magnetic ground state +at temperatures T$<$T$_{\rm c}$. We show that this unusual feature is linked to +a combination of structural disorder and metamagnetic instability of itinerant +Co-3d electrons. This new mechanism of the magnetoresistivity is common for a +broad class of materials featuring a static magnetic disorder and itinerant +metamagnetism.",0302539v2 +2003-07-21,Study of an Antiferromagnetic Sawtooth Chain with Spin-1/2 and Spin-1 sites,"We study the low-energy properties of a sawtooth chain with spin-1's at the +bases of the triangles and spin-1/2's at the vertices of the triangles. The +spins have Heisenberg antiferromagnetic interactions between nearest neighbors, +with a coupling J_2 between a spin-1 and a spin-1/2, and a coupling J_1 = 1 +between two spin-1's. Analysis of the exact diagonalization data for periodic +chains containing up to N=12 unit cells shows that the ground state is a +singlet for exchange couplings up to approximately J_2 = 3.8, whereas for +larger J_2, the system exhibits a ferrimagnetic ground state characterized by a +net ferromagnetic moment per unit cell of 1/2. In the region of small +interactions J_2, the mixed spin sawtooth chain maps on to an effective +isotropic spin model representing two weakly interacting and frustrated +spin-1/2 Heisenberg chains composed of spin-1/2 sites at odd and even vertices +respectively. Finally, we study the phenomenon of a macroscopic magnetization +jump which occurs if a magnetic field is applied with a value close to the +saturation field for J_2 = 2.",0307492v1 +2003-07-21,Does a surface spin-flop occur in antiferromagnetically coupled multilayers? Magnetic states and reorientation transitions in antiferromagnetic superlattices,"Equilibrium spin configurations and their stability limits have been +calculated for models of magnetic superlattices with a finite number of thin +ferromagnetic layers coupled antiferromagnetically through (non-magnetic) +spacers as Fe/Cr and Co/Ru multilayers. Depending on values of applied magnetic +field and unaxial anisotropy, the system assumes collinear(antiferromagnetic, +ferromagnetic, various ""ferrimagnetic"") phases, or spatially inhomogeneous +(symmetric spin-flop phase and asymmetric, canted and twisted, phases)via +series of field induced continuous and discontinuous transitions. Contrary to +semi-infinite systems a surface phase transition, so-called ""surface +spin-flop"", does not occur in the models with a finite number of layers. It is +shown that ""discrete jumps"" observed in some Fe/Cr superlattices and +interpreted as ""surface spin-flop"" transition are first-order ""volume"" +transitions between different canted phases. Depending on the system several of +these collinear and canted phases can exist as metastable states in broad +ranges of the magnetic fields, which may cause severe hysteresis effects. The +results explain magnetization processes in recent experiments on +antiferromagnetic Fe/Cr superlattices.",0307494v1 +2003-07-23,Role of surface disorder on the magnetic properties and hysteresis of nanoparticles,"We present the results of Monte Carlo simulations of a model of a single +maghemite ferrimagnetic nanoparticle including radial surface anisotropy +distinct from that in the core with the aim to clarify what is its role on the +magnetization processes at low temperatures. The low temperature equilibrium +states are analized and compared to those of a ferromagnetic particle with the +same lattice structure. We have found that the formation of hedgehog-like +structures due to increased surface anisotropy is responsible for a change in +the reversal mechanism of the particles.",0307584v1 +2003-12-19,Field-Induced Disorder Point in Non-Collinear Ising Spin Chains,"We perform a theoretical study of a non-collinear Ising ferrimagnetic spin +chain inspired by the compound Co(hfac)2NITPhOMe. The basic building block of +its structure contains one Cobalt ion and one organic radical each with a spin +1/2. The exchange interaction is strongly anisotropic and the corresponding +axes of anisotropy have a period three helical structure. We introduce and +solve a model Hamiltonian for this spin chain. We show that the present +compound is very close to a so-called disorder point at which there is a +massive ground state degeneracy. We predict the equilibrium magnetization +process and discuss the impact of the degeneracy on the dynamical properties by +using arguments based on the Glauber dynamics.",0312528v1 +2004-01-15,Ferrimagnetic mixed-spin ladders in weak and strong coupling limits,"We study two similar spin ladder systems with the ferromagnetic leg coupling. +First model includes two sorts of spins, s= 1/2 and s= 1, and the second model +comprises only s=1/2 legs coupled by a ""triangular"" rung exchange. The +antiferromagnetic (AF) rung coupling destroys the long-range order and +eventually makes the systems equivalent to the AF s=1/2 Heisenberg chain. We +investigate the situation by different methods in weak and strong rung coupling +limits. Particularly we compare the spin-wave theory and the bosonization +method in the weak coupling regime of the second model. We analyze the spectra +and correlations, and discuss the order parameter of these ladder systems.",0401264v2 +2004-03-30,"Finite-Size effects in ""Single Chain Magnets"": an experimental and theoretical study","The problem of finite size effects in s=1/2 Ising systems showing slow +dynamics of the magnetization is investigated introducing diamagnetic +impurities in a Co$^{2+}$-radical chain. The static magnetic properties have +been measured and analyzed considering the peculiarities induced by the +ferrimagnetic character of the compound. The dynamic susceptibility shows that +an Arrhenius law is observed with the same energy barrier for the pure and the +doped compounds while the prefactor decreases, as theoretically predicted. +Multiple spins reversal has also been investigated.",0403731v1 +2004-05-31,Orbital order and ferrimagnetic properties of the new compound $Sr_8 Ca Re_3 Cu_4 O_{24}$,"By means of the LSDA+U method and the Green function method, we investigate +the electronic and magnetic properties of the new material of +Sr$_8$CaRe$_3$Cu$_4$O$_{24}$. Our LSDA+U calculation shows that this system is +an insulator with a net magnetic moment of 1.01 $\mu_{\rm B}$/f.u., which is in +good agreement with the experiment. Magnetic moments are mainly located at Cu +atoms, and the magnetic moments of neighboring Cu sites align anti-parallel. It +is the non-magnetic Re atoms that induce an orbital order of $d$ electrons of +Cu atoms, which is responsible for the strong exchange interaction and the high +magnetic transition temperature. Based on the LSDA+U results, we introduce an +effective model for the spin degrees of freedom, and investigate the +finite-temperature properties by the Green function method. The obtained +results are consistent with the experimental results, indicating that the +spin-alternating Heisenberg model is suitable for this compound.",0405684v1 +2004-06-11,"Electronic structures of Cr$_{1-δ}$X (X=S, Te) studied by Cr 2p soft x-ray magnetic circular dichroism","Cr 2p core excited XAS and XMCD spectra of ferromagnetic Cr$_{1-\delta}$Te +with several concentrations of $\delta$=0.11-0.33 and ferrimagnetic +Cr$_{5}$S$_{6}$ have been measured. The observed XMCD lineshapes are found to +very weakly depend on $\delta$ for Cr$_{1-\delta}$Te. The experimental results +are analyzed by means of a configuration-interaction cluster model calculation +with consideration of hybridization and electron correlation effects. The +obtained values of the spin magnetic moment by the cluster model analyses are +in agreement with the results of the band structure calculation.The calculated +result shows that the doped holes created by the Cr deficiency exist mainly in +the Te 5porbital of Cr$_{1-\delta}$Te, whereas the holes are likely to be in Cr +3d state for Cr$_{5}$S$_{6}$.",0406283v1 +2004-07-01,Orbital Glass in FeCr2S4,"Low-temperature heat-capacity investigations on the spinel FeCr2S4 with +ferrimagnetic spin order and orbitally degenerated Jahn-Teller active Fe2+ ions +in a tetrahedral crystal field, provide experimental evidence of an orbital +liquid state above 10 K. We demonstrate that the low-temperature transition at +10 K arises from orbital order and is very sensitive to fine tuning of the +stoichiometry in polycrystals. In single crystals the orbital order is fully +suppressed resulting in an orbital glass state with the heat capacity following +a strict T^2 dependence as temperature approaches zero.",0407026v1 +2004-12-10,Thermodynamic properties of tetrameric bond-alternating spin chains,"Thermodynamic properties of a tetrameric bond-alternating Heisenberg spin +chain with ferromagnetic-ferromagnetic-antiferromagnetic-antiferromagnetic +exchange interactions are studied using the transfer-matrix renormalization +group and compared to experimental measurements. The temperature dependence of +the uniform susceptibility exhibits typical ferrimagnetic features. Both the +uniform and staggered magnetic susceptibilities diverge in the limit $T\to 0$, +indicating that the ground state has both ferromagnetic and antiferromagnetic +long-range orders. A double-peak structure appears in the temperature +dependence of the specific heat. Our numerical calculation gives a good account +for the temperature and field dependence of the susceptibility, the +magnetization, and the specific heat for Cu(3-Clpy)$_{2}$(N$_{3}$)$_{2}$ +(3-Clpy=3-Chloroyridine).",0412275v2 +2004-12-29,Spin wave analysis of Heisenberg magnets in restricted geometries,"In the last decade it has been proven that the standard spin wave theory was +able to provide accurate zero-temperature results for a number of +low-dimensional Heisenberg spin systems. In this chapter we introduce the main +ingredients of the spin-wave technique using as a working model the two-leg +mixed-spin ferrimagnetic ladder and the Dyson--Maleev boson formalism up to +second order in the spin-wave interaction. In the remainder, we survey typical +applications in low-space dimensionality as well as some recent modifications +of the theory admitting a quantitative analysis in magnetically disordered +phases. The presented spin-wave results are compared with available numerical +estimates.",0412742v1 +2005-02-23,Charge order in Fe2OBO3: An LSDA+U study,"Charge ordering in the low-temperature monoclinic structure of iron oxoborate +(Fe2OBO3) is investigated using the local spin density approximation (LSDA)+U +method. While the difference between t_{2g} minority occupancies of Fe^{2+} and +Fe^{3+} cations is large and gives direct evidence for charge ordering, the +static ""screening"" is so effective that the total 3d charge separation is +rather small. The occupied Fe^{2+} and Fe^{3+} cations are ordered alternately +within the chain which is infinite along the a-direction. The charge order +obtained by LSDA+U is consistent with observed enlargement of the \beta angle. +An analysis of the exchange interaction parameters demonstrates the +predominance of the interribbon exchange interactions which determine the whole +L-type ferrimagnetic spin structure.",0502555v1 +2005-02-23,Enhanced magnetic moment and conductive behavior in NiFe2O4 spinel ultrathin films,"Bulk NiFe2O4 is an insulating ferrimagnet. Here, we report on the epitaxial +growth of spinel NiFe2O4 ultrathin films onto SrTiO3 single-crystals. We will +show that - under appropriate growth conditions - epitaxial stabilization leads +to the formation of a spinel phase with magnetic and electrical properties that +radically differ from those of the bulk material : an enhanced magnetic moment +(Ms) - about 250% larger - and a metallic character. A systematic study of the +thickness dependence of Ms allows to conclude that its enhanced value is due to +an anomalous distribution of the Fe and Ni cations among the A and B sites of +the spinel structure resulting from the off-equilibrium growth conditions and +to interface effects. The relevance of these findings for spinel- and, more +generally, oxide-based heterostructures is discussed. We will argue that this +novel material could be an alternative ferromagetic-metallic electrode in +magnetic tunnel junctions.",0502558v1 +2005-03-26,On effects of regular S=1 dilution of S=1/2 antiferromagnetic Heisenberg chains by a quantum Monte Carlo simulation,"The effects of regular S=1 dilution of S=1/2 isotropic antiferromagnetic +chain are investigated by the quantum Monte Carlo loop/cluster algorithm. Our +numerical results show that there are two kinds of ground-state phases which +alternate with the variation of $S^1=1$ concentration. When the effective spin +of a unit cell is half-integer, the ground state is ferrimagnetic with gapless +energy spectrum and the magnetism becomes weaker with decreasing of the $S^1$ +concentration $\rho = 1/M$. While it is integer, a non-magnetic ground state +with gaped spectrum emerges and the gap gradually becomes narrowed as fitted by +a relation of $\Delta \approx 1.25\sqrt{\rho}$.",0503624v3 +2005-05-17,Robust Half-Metallic Character and Large Oxygen Magnetism in a Perovskite Cuprate,"The new perovskite cuprate material Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$, which +behaves ferrimagnetically and shows an unusually high Curie temperature ($T_c +\sim$ 440 K), is found from density-functional theory calculation to display +several surprising properties after hole doping or chemical substitution: (1) +Half metal (HM) is realized by replacing Re with W or Mo while $T_c$ remains +high; (2) hole-doped Sr$_{8}$CaRe$_{3}$Cu$_{4}$O$_{24}$ is also HM with high +$T_c$. Moreover, we find that the O atoms will carry a large magnetic moment +after hole doping, which is in sharp contrast with the generally accepted +concept that magnetism in solid requires partially filled shells of $d$ or $f$ +electrons in cations. The material Sr$_8$CaRe$_3$Cu$_4$O$_{24}$ is therefore +expected to provide a very useful platform for material design and development.",0505408v1 +2005-05-30,Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles,"We have studied the magnetic behavior of dextran-coated magnetite +(Fe$_3$O$_4$) nanoparticles with median particle size $\left=8$ $nm$. +Magnetization curves and in-field M\""ossbauer spectroscopy measurements showed +that the magnetic moment $M_S$ of the particles was much smaller than the bulk +material. However, we found no evidence of magnetic irreversibility or +non-saturating behavior at high fields, usually associated to spin canting. The +values of magnetic anisotropy $K_{eff}$ from different techniques indicate that +surface or shape contributions are negligible. It is proposed that these +particles have bulk-like ferrimagnetic structure with ordered A and B +sublattices, but nearly compensated magnetic moments. The dependence of the +blocking temperature with frequency and applied fields, $T_B(H,\omega)$, +suggests that the observed non-monotonic behavior is governed by the strength +of interparticle interactions.",0505682v5 +2005-06-02,Magnetic moments of W 5d in Ca2CrWO6 and Sr2CrWO6 double perovskites,"We have investigated the magnetic moment of the W ion in the ferrimagnetic +double perovskites Sr2CrWO6 and Ca2CrWO6 by X-ray magnetic circular dichroism +(XMCD) at the W L(2,3) edges. In both compounds a finite negative spin and +positive orbital magnetic moment was detected. The experimental results are in +good agreement with band-structure calculations for (Sr/Ca)2CrWO6 using the +full-potential linear muffin-tin orbital method. It is remarkable, that the +magnetic ordering temperature, TC, is correlated with the magnetic moment at +the 'non-magnetic' W atom.",0506048v2 +2005-06-16,Phase diagrams in the Blume-Emery-Griffiths Ising films,"We study the spin-1 Ising model with bilinear and biquadratic exchange +interactions and single-ion crystal field. In addition to the four usual +phases: disordered DIS, ferromagnetic FER, antiquadrupolar AQU and +ferrimagnetic FRI, we found three new phases in the case of a thin magnetic +film, namely: the sublattice A non magnetic phase NMA, the sublattice B non +magnetic phase NMB and the global non magnetic phase NMG. These phases are +studied, for each layer of the film, either in the temperature-crystal field +plane $(T,\Delta)$ or in the biquadratic coupling-crystal field plane +$(d,\Delta)$, for diferent film thicknesses. On the other hand, the thermal +behaviour of the layer quadrupolar moments $q_{A}, q_{B}$ and layer +magnetisations $m_{A}, m_{B}$ are investigated for negative values of the +biquadratic coupling and crystal field. It is also found that for fixed values +of the biquadratic coupling, the temperature and the crystal field, each layer +of the film can belong to a differnt phase. To illustrate this situation, an +example is given for $d=-3.0$, $\Delta =-3.0$ and $T=1.3$.",0506413v2 +2005-07-14,Ground states of the generalized Falicov-Kimball model in one and two dimensions,"A combination of small-cluster exact-diagonalization calculations and a +well-controlled approximative method is used to study the ground-state phase +diagram of the spin-one-half Falicov-Kimball model extended by the +spin-dependent on-site interaction between localized ($f$) and itinerant ($d$) +electrons. Both the magnetic and charge ordering are analysed as functions of +the spin-dependent on-site interaction ($J$) and the total number of itinerant +($N_d$) and localized ($N_f$) electrons at selected $U$ (the spin-independent +interaction between the $f$ and $d$ electrons). It is shown that the +spin-dependent interaction (for $N_f=L$, where $L$ is the number of lattice +sites) stabilizes the ferromagnetic (F) and ferrimagnetic (FI) state, while the +stability region of the antiferromagnetic (AF) phase is gradually reduced. The +precisely opposite effect on the stability of F, FI and AF phases has a +reduction of $N_f$. Moreover, the strong coupling between the $f$ and +$d$-electron subsystems is found for both $N_f=L$ as well as $N_f < L$.",0507342v1 +2005-07-15,Reentrant transitions of a mixed-spin Ising model on the diced lattice,"Magnetic behaviour of a mixed spin-1/2 and spin-1 Ising model on the diced +lattice is studied by the use of an exact star-triangle mapping transformation. +It is found that the uniaxial as well as biaxial single-ion anisotropy acting +on the spin-1 sites may potentially cause a reentrant transition with two +consecutive critical points. Contrary to this, the effect of +next-nearest-neighbour interaction between the spin-1/2 sites possibly leads to +a reentrant transition with three critical temperatures in addition to the one +with two critical points only. The shape of the total magnetization versus +temperature dependence is particularly investigated for the case of +ferrimagnetically ordered system.",0507367v2 +2005-09-28,"Switching of sub-micrometer sized, antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers","This work reports on the magnetic reversal of sub-micrometer sized elements +consisting of an CoFeB/Ru/CoFeB artificial ferrimagnet (AFi). The elements were +patterned into ellipses having a width of approximately 250 to 270nm and a +varying aspect ratio between 1.3 and 8. The coercivity was found to decrease +with an increasing imbalance of the magnetic moment of the two +antiferromagnetically coupled layers and is therefore strongly affected by an +increase of effective anisotropy due to the antiferromagnetic coupling of the +two layers. With respect to a single layer of amorphous CoFeB, patterned in +comparable elements, the AFi has an increased coercivity. Switching asteroids +comparable to single layers were only observed for samples with a high net +moment.",0509750v3 +2006-01-17,Electron Correlations and the Minority-Spin Band Gap in Half-Metallic Heusler Alloys,"Electron-electron correlations affect the band gap of half-metallic +ferromagnets by introducing non-quasiparticle states just above the Fermi +level. In contrast to the spin-orbit coupling, a large asymmetric +non-quasiparticle spectral weight is present in the minority-spin channel, +leading to a peculiar finite-temperature spin depolarization effects. Using +recently developed first-principle dynamical mean field theory, we investigate +these effects for the half-metallic ferrimagnetic Heusler compound FeMnSb. We +discuss depolarization effects in terms of strength of local Coulomb +interaction $U$ and temperature in FeMnSb. We propose Ni$_{1-x}$Fe$_{x}$MnSb +alloys as a perspective materials to be used in spin-valve structures and for +experimental search of non-quasiparticle states in half-metallic materials.",0601376v1 +2006-02-26,Strong temperature dependence of antiferromagnetic coupling in CoFeB/Ru/CoFeB,"The temperature dependence of saturation and spin-flop fields for artificial +ferrimagnets (AFi) based on antiparallel coupled CoFeB/Ru/CoFeB trilayers has +been investigated in a temperature range between 80K and 600K. The results +presented in this paper are relevant for magnetic devices using this system, +e.g. magnetic-random access memory based on spin-flop switching. In good +accordance to the theory, the saturation field Hsat behaves like Hsat ~ H_0 +(T/T_0)/sinh(T/T_0) with a characteristic temperature of T_0 = 150K. Within +this model, the Fermi velocity for the Ru layer is of the order of 10^5m/s, +therefore, explaining the strong variation of the coupling strength with the +temperature in Ru based AFi. Furthermore, a strong uniaxial anisotropy of K_u = +2x10^3 J/m^3 with a small angular distribution of the anisotropy axes is +observed for the AFi trilayers based on amorphous CoFeB alloys.",0602609v2 +2006-03-08,Magnetic and Electronic Properties of the New Ferrimagnet Sr8CaRe3Cu4O24,"Magnetic and electronic properties of the recently-discovered material +Sr8CaRe3Cu4O24 were investigated by means of a quantum Monte Carlo simulation, +the Green function method and the LSDA+U (local spin-density approximation plus +the Hubbard-U term) method. The LSDA+U calculation shows that the ground state +is an insulator with magnetic moment M=1.01\muB/f.u., which is consistent with +experimental results. The magnetic sites were specified and an effective model +for the magnetic properties of this compound derived. The resultant effective +model is a three-dimensional Heisenberg model with spin-alternation. +Finite-temperature properties of this effective model are investigated by the +quantum Monte Carlo method (continuous-time loop algorithm) and the Green +function method. The numerical results are consistent with experimental +results, indicating that the model is suitable for this material. Using the +analysis of the effective model, some predictions for the material are made.",0603194v1 +2006-04-28,High and low-temperature crystal and magnetic structures of epsilon-Fe2O3 and their correlation to its magnetic properties,"The crystal and magnetic structures of the orthorhombic e-Fe2O3 have been +studied by simultaneous Rietveld refinement of X-ray and neutron powder +diffraction data in combination with Mossbauer spectroscopy, as well as +magnetisation and heat capacity measurements. It has been found that above 150 +K the e-Fe2O3 polymorph is a collinear ferrimagnet with the magnetic moments +directed along the a axis, while the magnetic ordering below 80 K is +characterised by a square-wave incommensurate structure. The transformation +between these two states is a second order phase transition and involves subtle +structural changes mostly affecting the coordination of the tetrahedral and one +of the octahedral Fe sites. The temperature dependence of the e-Fe2O3 magnetic +properties is discussed in the light of these results.",0604677v1 +2006-06-16,Unravelling the origin of the controversial magnetic properties of BiFeO3 thin films,"Single phase (001)-oriented BiFeO3 (BFO) thin films grown by pulsed laser +deposition can only be obtained in a narrow window of deposition pressure and +temperature and have a low magnetic moment. Out of the stability window Fe- or +Bi-rich impurity phases form, which has a strong impact on the physical and +structural properties of the films, even for impurity concentrations hardly +detectable by standard X-ray diffraction measurements. By using more sensitive +tools such as X-Ray absorption spectroscopy and X-ray magnetic circular +dichroism and performing advanced X-ray diffraction characterization, we show +that in non-optimal conditions Fe forms ferrimagnetic gamma-Fe2O3 precipitates +that are responsible for virtually all the ferromagnetic signal measured on +such BFO films by standard magnetometry. This confirms that the BFO phase has a +very low intrinsic moment that does not depend on strain. We also study the +influence of film thickness on the nucleation of parasitic phases and find that +epitaxial strain can stabilize the pure BFO phase in slightly over-oxidizing +growth conditions.",0606441v1 +2006-06-20,Giant tunnel magnetoresistance and high annealing stability in CoFeB/MgO/CoFeB magnetic tunnel junctions with synthetic pinned layer,"We investigated the relationship between tunnel magnetoresistance (TMR) ratio +and the crystallization of CoFeB layers through annealing in magnetic tunnel +junctions (MTJs) with MgO barriers that had CoFe/Ru/CoFeB synthetic ferrimagnet +pinned layers with varying Ru spacer thickness (tRu). The TMR ratio increased +with increasing annealing temperature (Ta) and tRu, reaching 361% at Ta = 425C, +whereas the TMR ratio of the MTJs with pinned layers without Ru spacers +decreased at Ta over 325C. Ruthenium spacers play an important role in forming +an (001)-oriented bcc CoFeB pinned layer, resulting in a high TMR ratio through +annealing at high temperatures.",0606503v1 +2006-07-03,A surprising relation between double exchange and Heisenberg model spectra: Application to half-doped manganites,"The Zener polarons recently found in half-doped manganites are usually seen +as mixed valence entities ruled by a double exchange Hamiltonian involving only +correlated electrons of the metals. They can however be considered as +ferrimagnetic local units if the holes are localized on the bridging oxygen +atoms as implicitely suggested by recent mean-field it ab initio calculations. +In the latter case, the physics is ruled by a Heisenberg Hamiltonian involving +magnetic oxygen bridges. This paper shows that the spectra resulting from the +resolution of both models are analytically identical. This single resulting +model spectrum accurately reproduces the spectrum of Zener polarons in +Pr0.6Ca0.4MnO3 manganite studied by means of explicitely correlated ab initio +calculations. Since the physics supported by each model are different, the +analysis of the exact Hamiltonian ground state wave function should a priori +enables one to determine the most appropriate model. It will be shown that +neither the spectrum nor the wavefunction analysis bring any decisive arguments +to settle the question. Such undecidability would probably be encountered in +experimental information.",0607048v1 +2006-07-18,Magnetic properties of Fe/Dy multilayers: a Monte Carlo investigation,"We investigate the magnetic properties of a Heisenberg ferrimagnetic +multilayer by using Monte Carlo simulations. The aim of this work is to study +the local structural anisotropy model which is a possible origin of the +perpendicular magnetic anisotropy in transition metal/rare earth amorphous +multilayers. We have considered a face centered cubic lattice where each site +is occupied by a classical Heisenberg spin. We have introduced in our model of +amorphous multilayers a small fraction of crystallized Fe-Dy nanoclusters with +a mean anisotropy axis along the deposition direction. We show that a +competition in the energy terms takes place between the mean uniaxial +anisotropy of the Dy atoms in the nanoclusters and the random anisotropy of the +Dy atoms in the matrix.",0607437v1 +2006-07-27,Magnetic anisotropy and geometrical frustration in the Ising spin-chain system Sr5Rh4O12,"A structural and thermodynamic study of the newly synthesized single crystal +Sr5Rh4O12 is reported. Sr5Rh4O12 consists of a triangular lattice of spin +chains running along the c-axis. It is antiferromagnetically ordered below 23 K +with the intrachain and interchain coupling being ferromagnetic (FM) and +antiferromagnetic (AFM), respectively. There is strong evidence for an Ising +character in the interaction and geometrical frustration that causes incomplete +long-range AFM order. The isothermal magnetization exhibits two step-like +transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T, +respectively. Sr5Rh4O12 is a unique frustrated spin-chain system ever found in +4d and 5d based materials without a presence of an incomplete 3d-electron +shell.",0607732v1 +2006-08-17,Spatially anisotropic Heisenberg Kagome antiferromagnet,"In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite +has recently been the subject of experimental studies [Hiroi et al.,2001]. It +has been suggested that the magnetic properties of this material are described +by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic +exchange couplings. We report on investigations of the Sp(N) symmetric +generalisation of this model in the large N limit. We obtain a detailed +description of the dependence of possible ground states on the anisotropy and +on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, +incommensurate phases with and without long range order and a decoupled chain +phase emerges.",0608393v1 +2006-10-30,Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first-principles,"Half-metallic Heusler alloys are amongst the most promising materials for +future magnetoelectronic applications. We review some recent results on the +electronic properties of these compounds. The origin of the gap in these +half-metallic alloys and its connection to the magnetic properties are well +understood. Changing the lattice parameter shifts slightly the Fermi level. +Spin-orbit coupling induces states within the gap but the alloys keep a very +high degree of spin-polarization at the Fermi level. Small degrees of doping +and disorder as well as defects with low formation energy have little effect on +the properties of the gap, while temperature effects can lead to a quick loss +of half-metallicity. Finally we discuss two special issues; the case of +quaternary Heusler alloys and the half-metallic ferrimagnets.",0610827v1 +2006-11-23,Quantum dissipation theory of slow magnetic relaxation mediated by domain-wall motion in one-dimensional chain compound [Mn(hfac)_{2}BNO_{H}}],"Based on a quantum dissipation theory of open systems, we present a +theoretical study of slow dynamics of magnetization for the ordered state of +the new molecule-based magnetic complex [Mn(hfac)_{2}BNO_{H}] composed from +antiferromagnetically coupled ferrimagnetic (5/2,1) spin chains. Experimental +investigations of the magnetization process in pulsed fields have shown that +this compound exhibits a metamagnetic AF-FI transition at a critical field in +the order of the interchain coupling. A strong frequency dependence for the +ac-susceptibility has been revealed in the vicinity of the AF-FI transition and +was associated with an AF-FI interface kink motion. We model these processes by +a field-driven domain-wall motion along the field-unfavorable chains correlated +with a dissipation effect due to a magnetic system-bath coupling. The +calculated longitudinal magnetization has a two-step relaxation after the field +is switched off and are found in good agreement with the experiment. The +relaxation time determined from the imaginary part of the model +ac-susceptibility agrees qualitatively with that found from the remanent +magnetization data.",0611610v1 +2006-12-01,Antiferromagnetic Ising Model on Inverse Perovskite Lattice,"We study thermodynamic properties of an antiferromagnetic Ising model on the +inverse perovskite lattice by using Monte Carlo simulations. The lattice +structure is composed of corner-sharing octahedra and contains +three-dimensional geometrical frustration in terms of magnetic interactions. +The system with the nearest-neighbor interactions alone does not exhibit any +phase transition, leading to a degenerate ground state with large residual +entropy. The degeneracy is lifted by an external magnetic field or by an +anisotropy in the interactions. Depending on the anisotropy, they stabilize +either a 3D ferrimagnetic state or a partially-disordered antiferromagnetic +(PDAF) state with a dimensionality reduction to 2D. By the degeneracy-lifting +perturbations, all the transition temperatures of these different ordered +states continuously grow from zero, leaving an unusual zero-temperature +critical point at the unperturbed point. Such a zero-temperature +multicriticality is not observed in other frustrated structures such as +face-centered cubic and pyrochlore. The transition to the PDAF state is +represented by either the first- or second-order boundaries separated by +tricritical lines, whereas the PDAF phase shows 1/3 magnetization plateaus.",0612016v1 +2006-12-20,Spin transitions induced by a magnetic field in quantum dot molecules,"We present a theoretical study of magnetic field driven spin transitions of +electrons in coupled lateral quantum dot molecules. A detailed numerical study +of spin phases of artificial molecules composed of two laterally coupled +quantum dots with N=8 electrons is presented as a function of magnetic field, +Zeeman energy, and the detuning using real space Hartree-Fock Configuration +Interaction (HF-CI) technique. A microscopic picture of quantum Hall +ferromagnetic phases corresponding to zero and full spin polarization at +filling factors $\nu=2$ and $\nu=1$, and ferrimagnetic phases resulting from +coupling of the two dots, is presented.",0612529v2 +2006-12-27,"Partial antiferromagnetism in spin-chain Sr5Rh4O12, Ca5Ir3O12 and Ca4IrO6 single crystals","We report a structural, thermodynamic and transport study of the newly +synthesized Sr5Rh4O12, Ca5Ir3O12 and Ca4IrO6 single crystals. These +quasi-one-dimensional insulators consist of a triangular lattice of spin chains +running along the c-axis, and are commonly characterized by a partial +antiferromagnetic (AFM) order, a small entropy removal associated with the +phase transitions and a sizable low-temperature specific heat linearly +proportional to temperature. Sr5Rh4O12 is defined by an AFM order below 23 K +with strong evidence for an Ising character and two step-like transitions in +isothermal magnetization leading to a ferrimagnetic state at 2.4 T and a +ferromagnetic state at 4.8 T, respectively. Ca5Ir3O12 and Ca4IrO6 are also +antiferromagnetically ordered below 7.8 K and 12 K, respectively, and show an +unusually large ratio of the Curie-Weiss temperature to the Neel temperature. +In particular, Ca5Ir3O12, which includes both Ir4+ and Ir5+ ions, reveals that +only S=1/2 spins of the Ir4+ ions are involved in the magnetic ordering whereas +S=3/2 spins of the Ir5+ ions remain disordered. All results suggest the +presence of the geometrical frustration that causes incomplete long-range AFM +order in these quasi-one-dimensional compounds.",0612642v1 +2007-01-01,Size dependence of the photoinduced magnetism and long-range ordering in Prussian blue analog nanoparticles of rubidium cobalt hexacyanoferrate,"Nanoparticles of rubidium cobalt hexacyanoferrate +(Rb$_j$Co$_k$[Fe(CN)$_6$]$_l \cdot n$H$_2$O) were synthesized using different +concentrations of the polyvinylpyrrolidone (PVP) to produce four different +batches of particles with characteristic diameters ranging from 3 to 13 nm. +Upon illumination with white light at 5 K, the magnetization of these particles +increases. The long-range ferrimagnetic ordering temperatures and the coercive +fields evolve with nanoparticle size. At 2 K, particles with diameters less +than approximately 10 nm provide a Curie-like magnetic signal.",0701027v2 +2007-01-25,Doping of Mn$_2$VAl and Mn$_2$VSi Heusler alloys as a route to half-metallic antiferromagnetism,"Half-metallic antiferromagnets are the ideal materials for spintronic +applications since their zero magnetization leads to lower stray fields and +thus tiny energy losses. Starting from the Mn$_2$VAl and Mn$_2$VSi alloys we +substitute Co or Fe for Mn and we show by means of first-principle electronic +structure calculations that the resulting compounds are ferrimagnets. When the +total number of valence electrons reaches the magic number of 24 the Fe-doped +compounds are semi-metals and thus non-magnetic while the Co-doped ones show +the desirable half-metallic antiferromagnetic character. The compounds are very +likely to be synthesized experimentally since the parent compounds, Mn$_2$VAl +and Co$_2$VAl, have been already grown in the Heusler $L2_1$ lattice structure.",0701611v1 +2007-03-26,Magnetodielectric coupling in Mn3O4,"We have investigated the dielectric anomalies associated with spin ordering +transitions in the tetragonal spinel Mn$_3$O$_4$, using thermodynamic, +magnetic, and dielectric measurements. We find that two of the three magnetic +ordering transitions in Mn$_3$O$_4$ lead to decreases in the temperature +dependent dielectric constant at zero applied field. Applying a magnetic field +to the polycrystalline sample leaves these two dielectric anomalies practically +unchanged, but leads to an increase in the dielectric constant at the +intermediate spin-ordering transition. We discuss possible origins for this +magnetodielectric behavior in terms of spin-phonon coupling. Band structure +calculations suggest that in its ferrimagnetic state, Mn$_3$O$_4$ corresponds +to a semiconductor with no orbital degeneracy due to strong Jahn-Teller +distortion.",0703685v1 +1993-09-02,On a mean field approximation for Higgs-Yukawa systems,"We discuss the phase structure of a lattice Higgs-Yukawa system in the +variational mean field approximation with contributions of fermionic +determinant being calculated in a ladder approximation. In particular, we +demonstrate that in this approximation the ferrimagnetic phase in the $Z_2$ +model with naive fermions can appear as an artifact of a finite lattice and +that the phase diagram for this model on infinite lattice changes qualitatively +at space-time dimension $D = 4$ compared with those at $D > 4$.",9309001v2 +1994-02-03,Phase Diagram of An SU(2)xSU(2) Scalar-Fermion Model with Massless Decoupled Doublers,"We present the phase structure of the chiral SU(2)xSU(2) scalar-fermion model +on the lattice using the Zaragoza proposal for chiral fermions. The numerical +result agrees with an analytic study based on the use of weak and strong Yukawa +coupling expansions combined with the mean field approach. The phase diagram +consits of four phases: paramagnetic(PM), ferromagnetic(FM), +antiferromagnetic(AFM) and ferrimagnetic (FI). The transition lines separating +these four phases intersect at one quadruple point.",9402001v2 +2006-04-13,Exchange Bias and Vertical Shift in CoFe2O4 nanoparticles,"Magnetic properties of core-shell cobalt ferrite nanoparticles 15 to 48nm +prepared by a sol-gel route have been studied. It is shown that the coercivity +follows non-monotonic size dependence varying as 1/d above the maximum (d is +the particle size). Field cooled magnetization exhibited both horizontal +(exchange bias) and vertical shifts. The exchange bias is understood as +originating at the interface between a surface region with structural and spin +disorder and a core ferrimagnetic region. The dependence of the exchange bias +and vertical shifts on the particle sizes and cooling fields are found to have +significant differences and the differences are explained in the light of +recent results which suggest that both weakly and strongly pinned spins are +present at the interface. It is suggested that the exchange bias is dominated +by the weakly pinned spins while the vertical shift is affected by the strongly +pinned ones.",0604027v1 +2000-09-04,Test of Cosmic Spatial Isotropy for Polarized Electrons Using a Rotatable Torsion Balance,"To test the cosmic spatial isotropy, we use a rotatable torsion balance +carrying a transversely spin-polarized ferrimagnetic Dy_{6}Fe_{23} mass. With a +rotation period of one hour, the period of anisotropy signal is reduced from +one sidereal day by about 24 times, and hence the 1/f noise is greatly reduced. +Our present experimental results constrain the cosmic anisotropy Hamiltonian H += C_{1} sigma_{1} + C_{2} sigma_{2} + C_{3} sigma_{3} (sigma_{3} is in the axis +of earth rotation) to (C_{1}^{2} +C_{2}^{2})^{1/2} = (1.8 +- 5.3) X 10^{-21} eV +and | C_{3} | = (1.2 +- 3.5) X 10^{-19} eV. This improves the previous limits +on (C_{1},C_{2}) by 120 times and C_{3} by a factor of 800.",0009012v1 +2005-03-01,Large Magnetic Moments of Arsenic-Doped Mn Clusters and their Relevance to Mn-Doped III-V Semiconductor Ferromagnetism,"We report electronic and magnetic structure of arsenic-doped manganese +clusters from density-functional theory using generalized gradient +approximation for the exchange-correlation energy. We find that arsenic +stabilizes manganese clusters, though the ferromagnetic coupling between Mn +atoms are found only in Mn$_2$As and Mn$_4$As clusters with magnetic moments 9 +$\mu_B$ and 17 $\mu_B$, respectively. For all other sizes, $x=$ 3, 5-10, +Mn$_x$As clusters show ferrimagnetic coupling. It is suggested that, if grown +during the low temperature MBE, the giant magnetic moments due to ferromagnetic +coupling in Mn$_2$As and Mn$_4$As clusters could play a role on the +ferromagnetism and on the variation observed in the Curie temperature of +Mn-doped III-V semiconductors.",0503009v1 +2007-03-31,Formation of quasi-solitons in transverse confined ferromagnetic film media,"The formation of quasi-2D spin-wave waveforms in longitudinally magnetized +stripes of ferrimagnetic film was observed by using time- and space-resolved +Brillouin light scattering technique. In the linear regime it was found that +the confinement decreases the amplitude of dynamic magnetization near the +lateral stripe edges. Thus, the so-called effective dipolar pinning of dynamic +magnetization takes place at the edges. + In the nonlinear regime a new stable spin wave packet propagating along a +waveguide structure, for which both transversal instability and interaction +with the side walls of the waveguide are important was observed. The +experiments and a numerical simulation of the pulse evolution show that the +shape of the formed waveforms and their behavior are strongly influenced by the +confinement.",0704.0024v1 +2007-06-29,AC susceptibility and $^{51}$V NMR study of MnV$_2$O$_4$,"We report $^{51}$V zero-field NMR of manganese vanadate spinel of +MnV$_2$O$_4$, together with both ac and dc magnetization measurements. The +field and temperature dependence of ac susceptibilities show a +reentrant-spin-glass-like behavior below the ferrimagnetic(FEM) ordering +temperature. The zero-field NMR spectrum consists of multiple lines ranging +from 240 MHz to 320 MHz. Its temperature dependence reveals that the ground +state is given by the simultaneous formation of a long-range FEM order and a +short-range order component. We attribute the spin-glass-like anomalies to +freezing and fluctuations of the short-range ordered state caused by the +competition between spin and orbital ordering of the V site.",0707.0018v1 +2007-07-05,"Supersolidity, entropy and frustration","We study the properties of t-t'-V model of hard-core bosons on the triangular +lattice that can be realized in optical lattices. By mapping to the spin-1/2 +XXZ model in a field, we determine the phase diagram of the t-V model where the +supersolid characterized by the ordering pattern (x,x,-2x') (""ferrimagnetic"" or +SS A) is a ground state for chemical potential \mu >3V. By turning on either +temperature or t' at half-filling \mu =3V, we find a first order transition +from SS A to the elusive supersolid characterized by the (x,-x,0) ordering +pattern (""antiferromagnetic"" or SS C). In addition, we find a large region +where a superfluid phase becomes a solid upon raising temperature at fixed +chemical potential. This is an analog of the Pomeranchuk effect driven by the +large entropic effects associated with geometric frustration on the triangular +lattice.",0707.0866v1 +2007-07-26,The phase structure of a chirally invariant lattice Higgs-Yukawa model - numerical simulations,"The phase diagram of a chirally invariant lattice Higgs-Yukawa model is +explored by means of numerical simulations. The results revealing a rich phase +structure are compared to analytical large Nf calculations which we performed +earlier. The analytical and numerical results are in excellent agreement at +large values of Nf. In the opposite case the large Nf computation still gives a +good qualitative description of the phase diagram. In particular we find +numerical evidence for the predicted ferrimagnetic phase at intermediate values +of the Yukawa coupling constant and for the symmetric phase at strong Yukawa +couplings. Emphasis is put on the finite size effects which can hide the +existence of the latter symmetric phase.",0707.3849v1 +2007-09-26,Role of defects and disorder in the half-metallic full-Heusler compounds,"Half-metallic ferromagnets and especially the full-Heusler alloys containing +Co are at the center of scientific research due to their potential applications +in spintronics. For realistic devices it is important to control accurately the +creation of defects in these alloys. We review some of our late results on the +role of defects and impurities in these compounds. More precisely we present +results for the following cases (i) doping and disorder in Co$_2$Cr(Mn)Al(Si) +alloys, (ii) half-metallic ferrimagnetism appeared due to the creation of +Cr(Mn) antisites in these alloys, (iii) Co-doping in Mn$_2$VAl(Si) alloys +leading to half-metallic antiferromagnetism, and finally (iv) the occurrence of +vacancies in the full-Heusler alloys containing Co and Mn. These results are +susceptible of encouraging further theoretical and experimental research in the +properties of these compounds.",0709.4183v2 +2007-10-19,Intrinsic avalanches and collective phenomena in a Mn(II)-free radical ferrimagnetic chain,"Magnetic hysteresis loops below 300 mK on single crystals of the Mn(II) - +nitronyl nitroxide free radical chain (Mn(hfac)_2({\it R})-3MLNN) present +abrupt reversals of the magnetization, or avalanches. We show that, below 200 +mK, the avalanches occur at a constant field, independent of the sample and so +propose that this avalanche field is an intrinsic property. We compare this +field to the energy barrier existing in the sample and conclude that the +avalanches are provoked by multiple nucleation of domain-walls along the +chains. The different avalanche field observed in the zero field cooled +magnetization curves suggests that the avalanche mechanisms are related to the +competition between ferromagnetic and antiferromagnetic order in this compound.",0710.3707v2 +2007-11-02,Origin of ferromagnetic response in diluted magnetic semiconductors and oxides,"This paper reviews the present understanding of the origin of ferromagnetic +response of diluted magnetic semiconductors and diluted magnetic oxides as well +as in some nominally magnetically undoped materials. It is argued that these +systems can be grouped into four classes. To the first belong composite +materials in which precipitations of a known ferromagnetic, ferrimagnetic or +antiferromagnetic compound account for magnetic characteristics at high +temperatures. The second class forms alloys showing chemical nano-scale phase +separation into the regions with small and large concentrations of the magnetic +constituent. To the third class belong (Ga,Mn)As, heavily doped p-(Zn,Mn)Te, +and related semiconductors. In these solid solutions the theory built on p-d +Zener's model of hole-mediated ferromagnetism and on either the Kohn-Luttinger +kp theory or the multi-orbital tight-binding approach describes qualitatively, +and often quantitatively many relevant properties. Finally, in a number of +carrier-doped DMS and DMO a competition between long-range ferromagnetic and +short-range antiferromagnetic interactions and/or the proximity of the +localisation boundary lead to an electronic nano-scale phase separation.",0711.0340v1 +2007-11-12,Magnetic and orbital ordering in the spinel MnV2O4,"Neutron inelastic scattering and diffraction techniques have been used to +study the MnV2O4 spinel system. Our measurements show the existence of two +transitions to long-range ordered ferrimagnetic states; the first collinear and +the second noncollinear. The lower temperature transition, characterized by +development of antiferromagnetic components in the basal plane, is accompanied +by a tetragonal distortion and the appearance of a gap in the magnetic +excitation spectrum. The low-temperature noncollinear magnetic structure has +been definitively resolved. Taken together, the crystal and magnetic structures +indicate a staggered ordering of the V d orbitals. The anisotropy gap is a +consequence of unquenched V orbital angular momentum.",0711.1844v1 +2007-11-22,Three Dimensional Magnetic Correlations in Multiferroic LuFe2O4,"We present single-crystal neutron diffraction measurements on multiferroic +LuFe2O4 showing phase transitions at 240 and 175 K. Magnetic reflections are +observed below each transition indicating that the magnetic interactions in +LuFe2O4 are 3-dimensional (3D) in character. The magnetic structure is refined +as a ferrimagnetic spin configuration below the 240 K transition. While 3D +magnetic correlations persists below 175 K, a significant broadening of the +magnetic peaks is observed along with the build up of a diffuse component to +the magnetic scattering.",0711.3560v4 +2007-12-10,Fractional magnetization plateaus and magnetic order in the Shastry Sutherland magnet TmB4,"We investigate the phase diagram of TmB4, an Ising magnet on a frustrated +Shastry-Sutherland lattice by neutron diffraction and magnetization +experiments. At low temperature we find Neel order at low field, ferrimagnetic +order at high field and an intermediate phase with magnetization plateaus at +fractional values M/Msat = 1/7, 1/8, 1/9 ... and spatial stripe structures. +Using an effective S = 1/2 model and its equivalent two-dimensional (2D) +fermion gas we suggest that the magnetic properties of TmB4 are related to the +fractional quantum Hall effect of a 2D electron gas.",0712.1537v2 +2007-12-12,Reentrant spin glass transition in LuFe2O4,"We have carried out a comprehensive investigation of magnetic properties of +LuFe$_2$O$_4$, using AC susceptibility, DC magnetization and specific heat. A +magnetic phase transition around $\sim$236 K was observed with DC magnetization +and specific heat measurements, which is identified as a paramagnetic to +ferrimagnetic transition based on the nonlinear susceptibility data. Upon +further cooling below this temperature, we also observed highly relaxational +magnetic behavior: the DC magnetization exhibits history and time dependence, +and the real and imaginary part of the AC susceptibility shows large frequency +dependence. Dynamic scaling of the AC susceptibility data suggests that this +low temperature phase can be described as a reentrant spin glass phase. We also +discuss magnetic field dependence of the spin glass transition and aging, +memory and rejuvenation effect below the glass transition temperature around +228 K.",0712.1975v1 +2008-01-09,Magnetic coupling in highly-ordered NiO/Fe3O4(110): Ultrasharp magnetic interfaces vs. long-range magnetoelastic interactions,"We present a laterally resolved X-ray magnetic dichroism study of the +magnetic proximity effect in a highly ordered oxide system, i.e. NiO films on +Fe3O4(110). We found that the magnetic interface shows an ultrasharp +electronic, magnetic and structural transition from the ferrimagnet to the +antiferromagnet. The monolayer which forms the interface reconstructs to +NiFe2O4 and exhibits an enhanced Fe and Ni orbital moment, possibly caused by +bonding anisotropy or electronic interaction between Fe and Ni cations. The +absence of spin-flop coupling for this crystallographic orientation can be +explained by a structurally uncompensated interface and additional +magnetoelastic effects.",0801.1468v1 +2008-01-28,Magnetism as a mass term of the edge states in graphene,"The magnetism by the edge states in graphene is investigated theoretically. +An instability of the pseudo-spin order of the edge states induces +ferrimagnetic order in the presence of the Coulomb interaction. Although the +next nearest-neighbor hopping can stabilize the pseudo-spin order, a strong +Coulomb interaction makes the pseudo-spin unpolarized and real spin polarized. +The magnetism of the edge states makes two peaks of the density of states in +the conduction and valence energy bands near the Fermi point. Using a +continuous model of the Weyl equation, we show that the edge-induced gauge +field and the spin dependent mass terms are keys to make the magnetism of the +edge states. A relationship between the magnetism of the edge states and the +parity anomaly is discussed.",0801.4170v1 +2008-02-19,Jahn-Teller Distortion in Bimetallic Oxalates,"A C$_3$-symmetric crystal-field potential in the Fe(II)Fe(III) bimetallic +oxalates splits the L=2 Fe(II) multiplet into two doublets and a singlet. In +compounds that exhibit magnetic compensation, one of the doublets was predicted +to lie lowest in energy and carry a non-quenched orbital angular momentum $\pm +\ld $, where $\ld $ exceeds a threshold value. In a range of $\ld $, a +Jahn-Teller (JT) distortion increases the energy splitting of the low-lying +doublet and breaks the C$_3$ symmetry of the bimetallic planes around the +ferrimagnetic transition temperature. At low temperatures, the JT distortion +disappears in compounds that display magnetic compensation due to the +competition with the spin-orbit coupling. A comparison with recent measurements +provides strong evidence for this re-entrant, low-temperature JT transition and +a prediction for the normal, high-temperature JT transition. The size of the JT +distortion is estimated using first-principles calculations, which suggest that +the long-range ordering of smaller, non-C$_3$-symmetric organic cations can +eliminate magnetic compensation.",0802.2678v1 +2008-02-22,Microwave spectral analysis by means of non-resonant parametric recovery of spin-wave signals in a thin magnetic film,"We report on the storage and non-resonant parametric recovery of microwave +signals carried by a dipolar surface spin-wave pulse in a thin ferrimagnetic +film. The information about the intensity of the spectral components of the +signal within a narrow frequency band is saved due to the excitation of a +dipolar-exchange standing spin-wave mode across the film thickness and is +afterwards restored by means of parametric amplification of this mode. The +intensity of the restored signal measured for varying shifts between the signal +carrier frequency and half of the pumping frequency, which is equal to the +frequency of the standing mode, reveals information about the entire frequency +spectrum of the input microwave signal.",0802.3302v1 +2008-03-29,Misfit Strain Induced Giant Magnetoelectric Coupling in Thin Ferroic Films,"We show that misfit strain originated from the film-substrate lattice +mismatch strongly increases the value of the quadratic magnetoelectric +coupling. The giant magnetoelectric coupling, size effects and misfit strain +cause strong changes of ferroic films phase diagrams at zero external magnetic +and electric fields, in particular, the transformation of antiferromagnetic +phase into ferromagnetic or ferrimagnetic ones for compressive or tensile +misfit strains correspondingly as well as thickness induced paramagnetic or/and +paraelectric phases appearance. Ferromagnetism appearance and magnetoelectric +coupling increase in thin ferroelectric-antiferromagnetic films is in agreement +with available experimental data and opens the way for tailoring of ferroic +films magnetic and electric properties.",0803.4246v2 +2008-05-29,"Microscopic Evidence of Spin State Order and Spin State Phase Separation in Layered Cobaltites RBaCo2O5.5 with R=Y, Tb, Dy, and Ho","We report muon spin relaxation measurements on the magnetic structures of +RBaCo_2O_5.5 with R=Y, Tb, Dy, and Ho. Three different phases, one +ferrimagnetic and two antiferromagnetic, are identified below 300 K. They +consist of different ordered spin state arrangements of high-, intermediate-, +and low-spin Co^3+ of CoO_6 octahedra. Phase separation into well separated +regions with different spin state order is observed in the antiferromagnetic +phases. The unusual strongly anisotropic magnetoresistance and its onset at the +FM-AFM phase boundary is explained.",0805.4509v1 +2008-08-11,Monitoring of band gap and magnetic state of graphene nanoribbons through vacancies,"Using first-principles plane wave calculations we predict that electronic and +magnetic properties of graphene nanoribbons can be affected by defect-induced +itinerant states. The band gaps of armchair nanoribbons can be modified by +hydrogen saturated holes. Defects due to periodically repeating vacancy or +divacancies induce metallization, as well as magnetization in non-magnetic +semiconducting nanoribbons due to the spin-polarization of local defect states. +Antiferromagnetic ground state of semiconducting zigzag ribbons can change to +ferrimagnetic state upon creation of vacancy defects, which reconstruct and +interact with edge states. Even more remarkable is that all these effects of +vacancy defects are found to depend on their geometry and position relative to +edges. It is shown that these effects can, in fact, be realized without really +creating defects.",0808.1468v1 +2008-08-12,Magnetism Driven by Anion Vacancies in Superconducting $α$--FeSe$_{1-x}$,"To study the microscopic electronic and magnetic interactions in the +substoichiometric iron chalcogenide FeSe$_{1-x}$ which is observed to +superconduct at x~1/8 up to $T_c$=27 K, we use first principles methods to +study the Se vacancy in this nearly magnetic FeSe system. The vacancy forms a +ferrimagnetic cluster of eight Fe atoms, which for the ordered x=1/8 alloy +leads to half metallic conduction. Similar magnetic clusters are obtained for +FeTe$_{1-x}$ and for BaFe$_2$As$_2$ with an As vacancy, although neither of +these are half metallic. Based on fixed spin density results, we suggest the +low energy excitations in FeSe$_{1-x}$ are antiparamagnon-like with short +correlation length.",0808.1733v2 +2008-09-11,Two dimensional XXZ-Ising model on square-hexagon lattice,"We study a two dimensional XXZ-Ising on square-hexagon (4-6) lattice with +spin-1/2. The phase diagram of the ground state energy is discussed, shown two +different ferrimagnetic states and two type of antiferromagnetic states, beside +of a ferromagnetic state. To solve this model, it could be mapped into the +eight-vertex model with union jack interaction term. Imposing exact solution +condition we find the region where the XXZ-Ising model on 4-6 lattice have +exact solutions with one free parameter, for symmetric eight-vertex model +condition. In this sense we explore the properties of the system and analyze +the competition of the interaction parameters providing the region where it has +an exact solution. However the present model does not satisfy the \textit{free +fermion} condition, unless for a trivial situation. Even so we are able to +discuss their critical points region, when the exactly solvable condition is +ignored.",0809.2015v2 +2008-09-25,Magnetic Behavior of Single Crystalline Pr_{5}Ge_{3} and Tb_{5}Ge_{3}Compounds,"The results of the magnetization studies on Pr_{5}Ge_{3}and Tb_{5}Ge_{3} +single crystals are reported. Single Crystals of Pr_{5}Ge_{3} and Tb_{5}Ge_{3} +compounds were successfully grown by Czochralski method. These compounds +crystallize in a Mn_{5}Si_{3} type hexagonal structure with space group +P6_{3}/mcm. Ferromagnetic correlations set in at around 36 K in Pr_{5}Ge_{3} in +the ab plane followed by an antiferromagnetic transition at 13 K. Along the +c-axis the magnetization shows a ferromagnetic transition around 13 K with an +overall ferrimagnetic behavior. At 2K, the magnetic isotherm of the compound +along [0001] direction is typical for a ferromagnet, while a field induced +ferromagnetic type response is observed along the [10\overline{\mathit{1}}0] +direction. Hexagonal ab plane or [10\overline{\mathit{1}}0] direction was found +to be the easy axis of magnetization. Tb_{5}Ge_{3} orders antiferromagneticaly +at 85 K with the hexagonal ab plane as easy axis of magnetization. The compound +shows a field induced ferromagnetic behavior in its magnetic isotherm at 2 K.",0809.4467v2 +2008-10-15,Vacancy-induced magnetism in SnO$_{2}$: A density functional study,"We study the magnetic and electronic properties of defects in SnO$_{2}$ using +pseudopotential and all electron methods. Our calculations show that bulk +SnO$_{2}$ is non-magnetic, but it shows magnetism with a magnetic moment around +4.00 $\mu_{B}$ due to Sn vacancy (V$_\mathrm{Sn}$). The magnetic moment comes +mainly from O atoms surrounding V$_\mathrm{Sn}$ and Sn atoms, which couple +antiferromagnetically with the O atoms in the presence of V$_\mathrm{Sn}$. The +coupling between different Sn vacancies is also studied and we find that these +defects not only couple ferromagnetically but also antiferromagnetically and +ferrimagnetically. Our calculations demonstrate that the experimentally +observed giant magnetic moment of transition metal doped SnO$_{2}$ can be +attributed to V$_\mathrm{Sn}$.",0810.2720v1 +2008-10-27,Hybrid resonant phenomenon in a metamaterial structure with integrated resonant magnetic material,"We explore the hybridization of fundamental material resonances with the +artificial resonances of metamaterials. A hybrid structure is presented in the +waveguide environment that consists of a resonant magnetic material with a +characteristic tuneable gyromagnetic response that is integrated into a +complementary split ring resonator (CSRR) metamaterial structure. The combined +structure exhibits a distinct hybrid resonance in which each natural resonance +of the CSRR is split into a lower and upper resonance that straddle the +frequency for which the magnetic material's permeability is zero. We provide an +analytical understanding of this hybrid resonance and define an effective +medium theory for the combined structure that demonstrates good agreement with +numerical electromagnetic simulations. The designed structure demonstrates the +potential for using a ferrimagnetic or ferromagnetic material as a means of +creating a tunable metamaterial structure.",0810.4871v1 +2008-11-11,Even-odd effects in finite Heisenberg spin chains,"Magnetic superlattices and nanowires may be described as Heisenberg spin +chains of finite length N, where N is the number of magnetic units (films or +atoms, respectively). We study antiferromagnetically coupled spins which are +also coupled to an external field H (superlattices) or to a ferromagnetic +substrate (nanowires). The model is analyzed through a two-dimensional map +which allows fast and reliable numerical calculations. Both open and closed +chains have different properties for even and odd N (parity effect). Open +chains with odd N are known [S.Lounis et al., Phys. Rev. Lett. 101, 107204 +(2008)] to have a ferrimagnetic state for small N and a noncollinear state for +large N. In the present paper, the transition length N_c is found analytically. +Finally, we show that closed chains arrange themselves in the uniform bulk +spin-flop state for even N and in nonuniform states for odd N.",0811.1687v2 +2008-11-12,Disorder Effects in La substituted ferrimagnetic Ca2FeMoO6 double perovskite,"Ca2-xLaxFeMoO6 double perovskite with La concentration x = 0 to 0.6 was +synthesized using solid state sintering route. The standard techniques of XRD, +SEM and EDX were applied to characterize the material. Crystal structure of the +samples was stabilized in monoclinic phase with space group P2I/n and lattice +expansion was indicated with the increase of x. The increase of La +concentration gradually suppressed the coexisting minor secondary phase in the +material and simultaneously, EDX results indicated the accommodation of more Mo +atoms in the crystal structure. A significant modification in the surface +morphology of the material was noted from adhesive type surface for x = 0 to +brittle type surface with more grain boundary contributions for La doped +samples. We understand a significant change in magnetic properties (appearance +of cluster glass component, reduction of magnetic moment and indication of +higher TC) and in electrical properties (reduction of metallic character) in +terms of enhanced internal disorder in the material, introduced due to La +doping in double perovskite structure.",0811.1876v2 +2008-11-21,Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles,"In the present work, we investigate the magnetic properties of ferrimagnetic +and noninteracting maghemite (g-Fe2O3) hollow nanoparticles obtained by the +Kirkendall effect. From the experimental characterization of their magnetic +behavior, we find that polycrystalline hollow maghemite nanoparticles are +characterized by low superparamagnetic-to-ferromagnetic transition +temperatures, small magnetic moments, significant coercivities and +irreversibility fields, and no magnetic saturation on external magnetic fields +up to 5 T. These results are interpreted in terms of the microstructural +parameters characterizing the maghemite shells by means of an atomistic Monte +Carlo simulation of an individual spherical shell model. The model comprises +strongly interacting crystallographic domains arranged in a spherical shell +with random orientations and anisotropy axis. The Monte Carlo simulation allows +discernment between the influence of the structure polycrystalline and its +hollow geometry, while revealing the magnetic domain arrangement in the +different temperature regimes.",0811.3592v2 +2009-01-28,Epitaxial growth and magnetic properties of Sr2CrReO6 thin films,"The double perovskite Sr2CrReO6 is an interesting material for spintronics, +showing ferrimagnetism up to 635 K with a predicted high spin polarization of +about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition +on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum +crystallographic and magnetic properties were obtained by growing at a +substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films +are c-axis oriented, coherently strained, and show less than 20% anti-site +defects. The magnetization curves reveal high saturation magnetization of 0.8 +muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic +anisotropy.",0901.4499v1 +2009-03-11,Structure and Properties of Epitaxial Thin Films of Bi2fecro6: A Multiferroic Material Postulated by Ab-Initio Computation,"Experimental results on Bi2FeCrO6 (BFCO) epitaxial films deposited by laser +ablation on SrTiO3 substrates are presented. It has been theoretically +predicted using first-principles density functional theory that BFCO is +ferrimagnetic (with a magnetic moment of 2muB per formula unit) and +ferroelectric (with a polarization of ~80 microC/cm2 at 0K). The crystal +structure investigated using X-ray diffraction shows that the films are +epitaxial with a high degree of crystallinity. Chemical analysis carried out by +X-ray Microanalysis and X-ray Photoelectron Spectroscopy indicates the correct +cationic stoichiometry in the BFCO layer, namely (Bi:Fe:Cr = 2:1:1). +Cross-section high-resolution transmission electron microscopy images together +with selected area electron diffraction confirm the crystalline quality of the +epitaxial BFCO films with no identifiable foreign phase or inclusion. The +multiferroic character of BFCO is proven by piezoresponse force microscopy +(PFM) and magnetic measurements showing that the films exhibit ferroelectric +and magnetic hysteresis at room temperature. The local piezoelectric +measurements show the presence of ferroelectric domains and their switching at +the sub-micron scale.",0903.1995v1 +2009-03-17,Observation of a Griffiths-like phase in the paramagnetic regime of ErCo_2,"A systematic x-ray magnetic circular dichroism study of the paramagnetic +phase of ErCo2 has recently allowed to identify the inversion of the net +magnetization of the Co net moment with respect to the applied field well above +the ferrimagnetic ordering temperature, Tc. The study of small angle neutron +scattering measurements has also shown the presence of short range order +correlations in the same temperature region. This phenomenon, which we have +denoted parimagnetism, may be related with the onset of a Griffiths-like phase +in paramagnetic ErCo2. We have measured ac susceptibility on ErCo2 as a +function of temperature, applied field, and excitation frequency. Several +characteristics shared by systems showing a Griffiths phase are present in +ErCo2, namely the formation of ferromagnetic clusters in the disordered phase, +the loss of analyticity of the magnetic susceptibility and its extreme +sensitivity to an applied magnetic field. The paramagnetic susceptibility +allows to establish that the magnetic clusters are only formed by Co moments as +well as the intrinsic nature of those Co moments.",0903.2931v1 +2009-04-15,Order--disorder induced magnetic structures of FeMnP$_{0.75}$Si$_{0.25}$,"We report on the synthesis and structural characterization of the +magnetocaloric FeMnP$_{0.75}$Si$_{0.25}$ compound. Two types of samples (as +quenched and annealed) were synthesized and characterized structurally and +magnetically. We have found that minute changes in the degree of +crystallographic order causes a large change in the magnetic properties. The +annealed sample, with higher degree of order is antiferromagnetic with a zero +net moment. The as-quenched sample has a net moment of 1.26 $\mu_B$/f.u. and +ferrimagnetic-like behavior. Theoretical calculations give rather large values +for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and +pyramidal lattice site. The largest being the Mn moment for the pyramidal site +reaches values as high as 2.8 $\mu_B$/atom.",0904.2256v1 +2009-04-23,Magnetic order induced crystal symmetry lowering in ACr$_2$O$_4$ ferrimagnetic spinels,"We demonstrate that the onset of complex spin orders in ACr$_2$O$_4$ spinels +with magnetic A$=$Co, Fe and Cu ions lowers the lattice symmetry. This is +clearly indicated by the emergence of anisotropic lattice dynamics -- as +evidenced by the pronounced phonon splittings -- even when experiments probing +static distortions fail. We show that the crystal symmetry in the magnetic +phase is reduced from tetragonal to orthorhombic for FeCr$_2$O$_4$ and +CuCr$_2$O$_4$ with Jahn-Teller active A-site ions. The conical spin structure +in FeCr$_2$O$_4$ is also manifested in the phonon frequencies. In contrast, the +multiferroic CoCr$_2$O$_4$ with no orbital degrees of freedom remains nearly +cubic in its ground state.",0904.3712v1 +2009-05-12,Large magnetic entropy change near room temperature in antipervoskite SnCMn3,"We report the observation of large magnetocaloric effect near room +temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at +the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is +about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 +kOe, respectively. These values are close to those of typical magnetocaloric +materials. The large magnetocaloric effect is associated with the sharp change +of lattice, resistivity and magnetization in the vicinity of TC. Through the +measurements of Seebeck coefficient and normal Hall effect, the title system is +found to undergo a reconstruction of electronic structure at TC. Considering +its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are +suggested to be appropriate for pursuing new materials with larger +magnetocaloric effect.",0905.1773v1 +2009-06-08,"The observation of a positive magnetoresistance and close correlation among lattice, spin and charge around TC in antipervoskite SnCMn3","The temperature dependences of magnetization, electrical transport, and +thermal transport properties of antiperovskite compound SnCMn3 have been +investigated systematically. A positive magnetoresistance (~11%) is observed +around the ferrimagnetic-paramagnetic transition (TC ~ 280 K) in the field of +50 kOe, which can be attributed to the field-induced magnetic phase transition. +The abnormalities of resistivity, Seebeck coefficient, normal Hall effect and +thermal conductivity near TC are suggested to be associated with an abrupt +reconstruction of electronic structure. Further, our results indicate an +essential interaction among lattice, spin and charge degrees of freedom around +TC. Such an interaction among various degrees of freedom associated with sudden +phase transition is suggested to be characteristic of Mn-based antiperovskite +compounds.",0906.1511v1 +2009-07-29,Analysis of optical magnetoelectric effect in GaFeO_3,"We study the optical absorption spectra in a polar ferrimagnet GaFeO_3. We +consider the E1, E2 and M1 processes on Fe atoms. It is shown that the +magnetoelectric effect on the absorption spectra arises from the E1-M1 +interference process through the hybridization between the 4p and 3d states in +the noncentrosymmetry environment of Fe atoms. We perform a microscopic +calculation of the spectra on a cluster model of FeO_6 consisting of an +octahedron of O atoms and an Fe atom displaced from the center with reasonable +values for Coulomb interaction and hybridization. We obtain the magnetoelectric +spectra, which depend on the direction of magnetization, as a function of +photon energy in the optical region 1.0-2.5 eV, in agreement with the +experiment.",0907.5070v1 +2009-08-20,Phase transitions in exactly solvable decorated model of localized Ising spins and itinerant electrons,"A hybrid lattice-statistical model of doubly decorated two-dimensional +lattices, which have localized Ising spins at its nodal sites and itinerant +electrons delocalized over decorating sites, is exactly solved with the help of +a generalized decoration-iteration transformation. Under the assumption of a +quarter filling of each couple of the decorating sites, the ground state +constitutes either spontaneously long-range ordered ferromagnetic or +ferrimagnetic phase in dependence on whether the ferromagnetic or +antiferromagnetic interaction between the localized Ising spins and itinerant +electrons is considered. The critical temperature of the spontaneously +long-range ordered phases monotonically increases upon strengthening the ratio +between the kinetic term and the Ising-type exchange interaction.",0908.2880v1 +2009-08-24,"Spinel ferrite nanocrystals embedded inside ZnO: magnetic, electronic and magneto-transport properties","In this paper we show that spinel ferrite nanocrystals (NiFe2O4, and CoFe2O4) +can be texturally embedded inside a ZnO matrix by ion implantation and +post-annealing. The two kinds of ferrites show different magnetic properties, +e.g. coercivity and magnetization. Anomalous Hall effect and positive +magnetoresistance have been observed. Our study suggests a +ferrimagnet/semiconductor hybrid system for potential applications in +magneto-electronics. This hybrid system can be tuned by selecting different +transition metal ions (from Mn to Zn) to obtain various magnetic and electronic +properties.",0908.3488v1 +2009-09-19,Cooperative order and excitation spectra in the bicomponent spin networks,"A ferrimagnetic spin model composed of $S=1/2$ spin-dimers and $S=5/2$ +spin-chains is studied by combining the bond-operator representation (for +$S=1/2$ spin-dimers) and Holstein-Primakoff transformation (for $S=5/2$ spins). +A finite interaction $J_{\rm DF}$ between the spin-dimer and the spin chain +makes the spin chains ordered antiferromagnetically and the spin dimers +polarized. The effective interaction between the spin chains, mediated by the +spin dimers, is calculated up to the third order. The staggered magnetization +in the spin dimer is shown proportional to $J_{\rm DF}$. It presents an +effective staggered field reacting on the spin chains. The degeneracy of the +triplons is lifted due to the chain magnetization and a mode with longitudinal +polarization is identified. Due to the triplon-magnon interaction, the +hybridized triplon-like excitations show different behaviors near the vanishing +$J_{\rm DF}$. On the other hand, the hybridized magnon-like excitations open a +gap $\Delta_A\sim J_{\rm DF}$. These results consist well with the experiments +on Cu$_{2}$Fe$_{2}$Ge$_{4}$O$_{13}$.",0909.3576v2 +2010-01-18,The missing atom as a source of carbon magnetism,"Atomic vacancies have a strong impact in the mechanical, electronic and +magnetic properties of graphene-like materials. By artificially generating +isolated vacancies on a graphite surface and measuring their local density of +states on the atomic scale, we have shown how single vacancies modify the +electronic properties of this graphene-like system. Our scanning tunneling +microscopy experiments, complemented by tight binding calculations, reveal the +presence of a sharp electronic resonance at the Fermi energy around each single +graphite vacancy, which can be associated with the formation of local magnetic +moments and implies a dramatic reduction of the charge carriers' mobility. +While vacancies in single layer graphene naturally lead to magnetic couplings +of arbitrary sign, our results show the possibility of inducing a macroscopic +ferrimagnetic state in multilayered graphene samples just by randomly removing +single C atoms.",1001.3081v2 +2010-02-25,Ferromagnetic Resonance of Co/Gd and Co/Tb Multilayers,"The in-plane dynamics of ferrimagnetic Co/Gd multilayers are investigated by +means of ferromagnetic resonance, magneto-optical Kerr effect and SQUID +magnetometry. The power absorbed from these multilayers is strongly temperature +dependent. For example, the resonant peak for a (Co 40 A /Gd 40 A)8 multilayer +vanishes approximately 50 K below room temperature. We have further +investigated Gd/Co/Gd and Tb/Co/Tb trilayers with different thicknesses of Gd +(5-7 A), Tb (1-7 A) and Co (30-40 A). At room temperature, these Co-based +trilayers show a shift of approximately 600 Oe at 24 GHz in the uniform +ferromagnetic resonance field, compared to pure Co film, indicating the +exchange coupling between the Co and Gd. The shift in the field for the +resonance increases as the temperature is decreased. Furthermore the resonance +linewidth increases as the temperature is decreased. The experimental results +are in good agreement with our theoretical calculations.",1002.4889v1 +2010-04-07,Magnetization plateau and incommensurate spin modulation in Ca3Co2O6,"The magnetic properties of a trigonal prism unit of the spin-2 frustrated +compound Ca3Co2O6 are studied by means of the density-matrix renormalization +group method. A magnetization plateau at $ms/3$ ($ms$ is the saturation +magnetization) with ferrimagnetic structure is observed. By fitting the +experimental data of magnetic curve, an estimation of the couplings gives +J1=-26.84K, J_{2}=0.39K, and J_{3}=0.52K. The local magnetic moments are +unveiled to exhibit an incommensurate sinusoidally modulation along the three +chains of the trigonal prism, which gives a strong theoretical support to the +experimentally observed incommensurate partially disordered antiferromagnetic +state for Ca3Co2O6. The present result suggests that the modulation indeed +originates from the competition of antiferromagnetic and ferromagnetic +couplings.",1004.1031v1 +2010-04-08,Divergent effects of static disorder and hole doping in geometrically frustrated b-CaCr2O4,"The gallium substituted and calcium deficient variants of geometrically +frustrated b-CaCr2O4, b-CaCr2-2xGa2xO4 (0.02<= x<= 0.25) and b-Ca1-yCr2O4 +(0.075<= y<= 0.15), have been investigated by x-ray powder diffraction, +magnetization and specific heat measurements. This allows for a direct +comparison of the effects, in a geometrically frustrated magnet, of the static +disorder that arises from non-magnetic substitution and the dynamic disorder +that arises from hole doping. In both cases, disturbing the Cr3+ lattice +results in a reduction in the degree of magnetic frustration. On substitution +of Ga, which introduces disorder without creating holes, a gradual release of +spins from ordered antiferromagnetic states is observed. In contrast, in the +calcium deficient compounds the introduction of holes induces static +ferrimagnetic ordering and much stronger perturbations of the b-CaCr2O4 host.",1004.1390v1 +2010-06-24,Magnetodielectric coupling of infrared phonons in single crystal Cu$_{2}$OSeO$_{3}$,"Reflection and transmission as a function of temperature have been measured +on a single crystal of the magnetoelectric ferrimagnetic compound +Cu$_{2}$OSeO$_{3}$ utilizing light spanning the far infrared to the visible +portions of the electromagnetic spectrum. The complex dielectric function and +optical properties were obtained via Kramers-Kronig analysis and by fits to a +Drude-Lortentz model. The fits of the infrared phonons show a magnetodielectric +effect near the transition temperature ($T_{c}\sim 60$~K). Assignments to +strong far infrared phonon modes have been made, especially those exhibiting +anomalous behavior around the transition temperature.",1006.4676v1 +2010-08-23,Self-magnetic compensation and Exchange Bias in ferromagnetic Samarium systems,"For Sm(3+) ions in a vast majority of metallic systems, the following +interesting scenario has been conjured up for long, namely, a magnetic lattice +of tiny self (spin-orbital) compensated 4f-moments exchange coupled (and phase +reversed) to the polarization in the conduction band. We report here the +identification of a self-compensation behavior in a variety of ferromagnetic Sm +intermetallics via the fingerprint of a shift in the magnetic hysteresis (M-H) +loop from the origin. Such an attribute, designated as exchange bias in the +context of ferromagnetic/antiferromagnetic multilayers, accords these compounds +a potential for niche applications in spintronics. We also present results on +magnetic compensation behavior on small Gd doping (2.5 atomic percent) in one +of the Sm ferromagnets (viz. SmCu(4)Pd). The doped system responds like a +pseudo-ferrimagnet and it displays a characteristic left-shifted linear M-H +plot for an antiferromagnet.",1008.3779v1 +2010-10-09,Superparamagnetism in Nanocrystalline Copper Ferrite Thin Films,"The rf sputtered copper ferrite films contain nanocrystalline grains. In +these films, the magnetization does not saturate even in high magnetic fields. +This phenomenon of high field susceptibility is attributed to the defects +and/or superparamagnetic grains in the films. A simple model is developed to +describe the observed high field magnetization behavior of these films. The +model is found to fit well to the high field part for all the studied films. An +attempt is also made to explain the temperature variation of the ferrimagnetic +contribution on the basis of reported exchange constants.",1010.1877v1 +2010-10-26,Phase transitions and thermodynamics of the two-dimensional Ising model on a distorted Kagomé lattice,"The two-dimensional Ising model on a distorted Kagom\'{e} lattice is studied +by means of exact solutions and the tensor renormalisation group (TRG) method. +The zero-field phase diagrams are obtained, where three phases such as +ferromagnetic, ferrimagnetic and paramagnetic phases, along with the +second-order phase transitions, have been identified. The TRG results are quite +accurate and reliable in comparison to the exact solutions. In a magnetic +field, the magnetization ($m$), susceptibility and specific heat are studied by +the TRG algorithm, where the $m=1/3$ plateaux are observed in the magnetization +curves for some couplings. The experimental data of susceptibility for the +complex Co(N$_3$)$_2$(bpg)$\cdot$ DMF$_{4/3}$ are fitted with the TRG results, +giving the couplings of the complex $J=22K$ and $J'=33K$.",1010.5297v1 +2010-10-27,Electronic structure of fully epitaxial Co2TiSn thin films,"In this article we report on the properties of thin films of the full Heusler +compound Co2TiSn prepared by DC magnetron co-sputtering. Fully epitaxial, +stoichiometric films were obtained by deposition on MgO (001) substrates at +substrate temperatures above 600{\deg}C. The films are well ordered in the L21 +structure, and the Curie temperature exceeds slightly the bulk value. They show +a significant, isotropic magnetoresistance and the resistivity becomes strongly +anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with +nearly 1 \mu_B on the Co atoms, and a small antiparallel Ti moment, in +agreement with theoretical expectations. From comparison of x-ray absorption +spectra on the Co L3/L2 edges, including circular and linear magnetic +dichroism, with ab initio calculations of the x-ray absorption and circular +dichroism spectra we infer that the electronic structure of Co2TiSn has +essentially non-localized character. Spectral features that have not been +explained in detail before, are explained here in terms of the final state band +structure.",1010.5754v1 +2010-12-15,Exchange interactions and Curie temperatures in Mn2CoZ compounds,"The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb) +with the Hg2CuTi structure are of large interest due to their half-metallic +ferrimagnetism. The complex magnetic interactions between the constituents are +studied by first principles calculations of the Heisenberg exchange coupling +parameters, and Curie temperatures are calculated from those. Due to the direct +Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while +the total moment increases when changing Z from one group to another. The +exchange interactions are dominated by a strong direct exchange between Co and +its nearest neighbor Mn on the B site, which is nearly constant. The coupling +between the nearest-neighbor Mn atoms scales with the magnetic moment of the Mn +atom on the C site. Calculations with different lattice parameters suggest a +negative pressure dependence of the Curie temperature, which follows from +decreasing magnetic moments. Curie temperatures of more than 800 K are +predicted for Mn2CoAl (890 K), Mn2CoGa (886 K), and Mn2CoIn (845 K).",1012.3261v1 +2011-01-10,Radiation of caustic beams from a collapsing bullet,"Collapse of an intense (2+1)-dimensional wave packet in a medium with cubic +nonlinearity and a two-dimensional dispersion of an order higher than parabolic +is studied both theoretically and experimentally. The carrier waves are +microwave backward volume spin waves which propagate in a stripe made from a +thin ferrimagnetic film and the packet is a spin-wave bullet. We show that +before being self-destroyed the bullet irradiates untrapped dispersive waves, +which is in agreement with a previous theoretical prediction. Since, in +addition, the ferromagnetic medium is characterized by an induced uniaxial +anisotropy, this radiation takes the form of narrow beams of continuous waves +at very specific angles to its propagation direction. Based on our theoretical +calculations we find that these beams are caustic beams and the angles are the +characteristic spin-wave caustic angles modified by the motion of the source.",1101.1696v2 +2011-02-25,Origin and tailoring of the antiferromagnetic domain structure in $α$-Fe$_2$O$_3$ thin films unraveled by statistical analysis of dichroic spectro-microscopy (X-PEEM) images,"The magnetic microstructure and domain wall distribution of antiferromagnetic +$\alpha$-Fe$_2$O$_3$ epitaxial layers is determined by statistical image +analyses. Using dichroic spectro-microscopy images, we demonstrate that the +domain structure is statistically invariant with thickness and that the +antiferromagnetic domain structure of the thin films is inherited from the +ferrimagnetic precursor layer one, even after complete transformation into +antiferromagnetic $\alpha$-Fe$_2$O$_3$. We show that modifying the magnetic +domain structure of the precursor layer is a genuine way to tune the magnetic +domain structure and domain walls of the antiferromagnetic layers.",1102.5177v1 +2011-03-11,Spin pumping by parametrically excited exchange magnons,"We experimentally show that exchange magnons can be detected using a +combination of spin pumping and inverse spin-Hall effect (iSHE) proving its +wavelength integrating capability down to the sub-micrometer scale. The magnons +were injected in a ferrimagnetic yttrium iron garnet film by parametric pumping +and the iSHE-induced voltage was detected in an attached Pt layer. The role of +the density, wavelength, and spatial localization of the magnons for the spin +pumping efficiency is revealed. This study opens the field of the magnon-based +information processing to magnons with nano-scale wavelengths.",1103.2229v2 +2011-03-15,"Structural, Superconducting and Magnetic Properties of La(3-x)R(x)Ni2B2N3 (R = Ce, Pr, Nd)","We report on structural and superconducting properties of La(3-x)R(x)Ni2B2N3 +where La is substituted by the magnetic rare-earth elements Ce, Pr, Nd. The +compounds Pr3Ni2B2N3 and Nd3Ni2B2N3 are characterized for the first time. +Powder X-ray diffraction confirmed all samples R3Ni2B2N3 with R = La, Ce, Pr, +Nd and their solid solutions to crystallize in the body centered tetragonal +La3Ni2B2N3 structure type. Superconducting and magnetic properties of +La(3-x)R(x)Ni2B2N3 were studied by resistivity, specific heat and +susceptibility measurements. While La3Ni2B2N3 has a superconducting transition +temperature Tc ~ 14 K, substitution of La by Ce, Pr, and Nd leads to magnetic +pair breaking and, thus, to a gradual suppression of superconductivity. +Pr3Ni2B2N3 exibits no long range magnetic order down to 2 K, Nd3Ni2B2N3 shows +ferrimagnetic ordering below T_C = 17 K and a spin reorientation transition to +a nearly antiferromagnetic state at 10 K.",1103.2947v1 +2011-03-15,FFLO oscillations and magnetic domains in the Hubbard model with off-diagonal Coulomb repulsion,"We observe the effect of non-zero magnetization m onto the superconducting +ground state of the one dimensional repulsive Hubbard model with correlated +hopping X. For t/2 < X < 2t/3, the system first manifests +Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) oscillations in the pair-pair +correlations. For m = m1 a kinetic energy driven macroscopic phase separation +into low-density superconducting domains and high-density polarized walls takes +place. For m > m2 the domains fully localize, and the system eventually becomes +a ferrimagnetic insulator.",1103.2962v3 +2011-05-05,muSR investigation of magnetism and magnetoelectric coupling in Cu2OSeO3,"A detailed zero and transverse field (ZF&TF) muon spin rotation (muSR) +investigation of magnetism and the magneto-electric coupling in Cu2OSeO3 is +reported. An internal magnetic field B_int(T=0) = 85.37(25) mT was found, in +agreement with a ferrimagnetic state below Tc = 57.0(1) K. The temperature +dependence of the magnetic order parameter is well described by the relation +B_int = B(0)(1-(T/Tc)^2)^b with an effective exponent b = 0.39(1) which is +close to the critical exponent B ~ 1/3 for a three dimensional (3D) magnetic +system. Just above Tc the muon relaxation rate follows the power low \lambda +(T)\propto (T/Tc - 1)^\omega with \omega = 1.06(9), which is characteristic for +3D ferromagnets. Measurements of B_int(T) with and without an applied +electrostatic field E = 1.66 x 10^5 V/m suggest a possible electric field +effect of magnitude \Delta Bv = Bv(0 V)-Bv(500 V) = - 0.4(4) mT.",1105.1083v1 +2011-05-25,Frustrated Ising model on the Cairo pentagonal lattice,"Through the direct decoration transformation approach, we obtain a general +solution for the pentagonal Ising model, showing its equivalence to the +isotropic free-fermion eight-vertex model. We study the ground-state phase +diagram, in which one ferromagnetic (FM) state, one ferrimagnetic (FIM) state, +and one frustrated state are found. Using the exact solution of the pentagonal +Ising model, we discuss the finite-temperature phase diagrams and find a phase +transition between the FIM state and the disordered state as well as a phase +transition between the disordered state and the FM state. We also discuss some +additional remarkable properties of the model, such as the magnetization, +entropy, and specific heat, at finite temperature and at its low-temperature +asymptotic limit. Because of the influence of the second-order phase transition +between the frustrated and ferromagnetic phases, we obtain surprisingly low +values of the entropy and the specific heat until the critical temperature is +reached.",1105.5130v3 +2011-06-27,Crystal Structure and Magnetic Properties of the New Zn1.5Co1.5B7O13Br Boracite,"New Zn1.5Co1.5B7O13Br boracite crystals were grown by chemical transport +reactions in quartz ampoules, at a temperature of 1173 K. The crystal structure +was characterized by X-ray diffraction. The crystals present an orthorhombic +structure with space group Pca21, (No. 29). The determined cell parameters +were: a = 8.5705(3){\AA}, b = 8.5629(3) {\AA}, and c = 12.1198(4){\AA}, and +cell volume, V = 889.45(5) {\AA}3 with Z = 4. Magnetic properties in single +crystals of the new boracite, were determined. The Susceptibility-Temperature +(X -T) behavior at different magnetic intensities was studied. The inverse of +the magnetic susceptibility X-1(T) shows a Curie-Weiss characteristic with spin +s = 3/2 and a small orbital contribution, l. At low temperatures, below 10 K, +X(T) shows irreversibility that is strongly dependent on the applied magnetic +field. This boracite is ferrimagnetic up to a maximum temperature of about 16 +K, as shows the coercive field. The reduction of the irreversibility by the +influence of the magnetic field, may be related to a metamagnetic phase +transition.",1106.5446v1 +2011-07-05,Itinerant and local magnetic moments in ferrimagnetic Mn2CoGa thin films probed by x-ray magnetic linear dichroism: experiment and ab initio theory,"Epitaxial thin films of the half-metallic Xa-compound Mn2CoGa (Hg2CuTi +prototype) were prepared by dc magnetron co-sputtering with different heat +treatments on MgO (001) substrates. High-quality films with a bulk +magnetization of 1.95(5)\mu_B per unit cell were obtained. The L3,2 x-ray +magnetic circular dichroism spectra agree with calculations based on density +functional theory (DFT) and reveal the antiparallel alignment of the two +inequivalent Mn moments. X-ray magnetic linear dichroism, in good agreement +with theory as well, allows to distinguish between itinerant and local Mn +moments. Based on non-collinear spin DFT it is shown that one of the two Mn +moments has local character, whereas the other Mn moment and the Co moment are +itinerant.",1107.0887v2 +2011-07-07,Correlations in the Ising antiferromagnet on the anisotropic kagome lattice,"We study the correlation function of middle spins, i. e. of spins on +intermediate sites between two adjacent parallel lattice axes, of the spatially +anisotropic Ising antiferromagnet on the kagome lattice. It is given rigorously +by a Toeplitz determinant. The large-distance behaviour of this correlation +function is obtained by analytic methods. For shorter distances we evaluate the +Toeplitz determinant numerically. The correlation function is found to vanish +exactly on a line J_d(T) in the T-J (temperature vs. coupling constant) phase +diagram. This disorder line divides the phase diagram into two regions. For J +less than J_d(T) the correlations display the features of an unfrustrated +two-dimensional Ising magnet, whereas for J greater than J_d(T) the +correlations between the middle spins are seen to be strongly influenced by the +short-range antiferromagnetic order that prevails among the spins of the +adjacent lattice axes. While for J less than J_d(T) there is a region with +ferrimagnetic long-range order, the model remains disordered for J greater than +J_d(T) down to T=0.",1107.1368v2 +2011-07-12,Pressure- and Field-Tuning the Magnetostructural Phases of Mn3O4: Raman Scattering and X-Ray Diffraction Studies,"We present temperature-, magnetic-field-, and pressure-dependent Raman +scattering studies of single crystal Mn3O4, combined with temperature- and +field-dependent x-ray diffraction studies, revealing the novel +magnetostructural phases in Mn3O4. Our temperature-dependent studies showed +that the commensurate magnetic transition at T2=33K in the binary spinel Mn3O4 +is associated with a structural transition from tetragonal to orthorhombic +structures. Field-dependent studies showed that the onset and nature of this +structural transition can be controlled with an applied magnetic field, and +revealed evidence for a field-tuned quantum phase transition to a tetragonal +spin-disordered phase for H||[1-10]. Pressure-dependent Raman measurements +showed that the magnetic easy axis direction in Mn3O4 can be controlled---and +the ferrimagnetic transition temperature increased---with applied pressure. +Finally, combined pressure- and magnetic-field-tuned Raman measurements +revealed a rich magnetostructural phase diagram---including a pressure- and +field-induced magnetically frustrated tetragonal phase in the PH phase +diagram---that can be generated in Mn3O4 with applied pressure and magnetic +field.",1107.2329v2 +2011-08-13,First Principle Study of Magnetism and Magneto-structural Coupling in Gallium Ferrite,"We report a first-principles study of the magnetic properties, site disorder +and magneto-structural coupling in multiferroic gallium ferrite (GFO) using +local spin density approximation (LSDA+U) of density functional theory. The +calculations of the ground state A-type antiferromagnetic structure predict +magnetic moments consistent with the experiments whilst consideration of +spin-orbit coupling yields a net orbital moment of ~ 0.025 Bohr magneton/Fe +site also in good accordance with the experiments. We find that though site +disorder is not spontaneous in the ground state, interchange between Fe2 and +Ga2 sites is most favored in the disordered state. The results show that +ferrimagnetism in GFO is due to Ga-Fe site disordering such that Fe spins at +Ga1 and Ga2 sites are antiferromagnetically aligned while maintaining +ferromagnetic coupling between Fe spins at Ga1 and Fe1 sites as well as between +Fe spins at Ga2 and Fe2 sites. The effect of spin configuration on the +structural distortion clearly indicates presence of magneto-structural coupling +in GFO.",1108.2773v1 +2011-08-31,Interplay between charge and magnetic orderings in the zero-bandwidth limit of the extended Hubbard model for strong on-site repulsion,"A simple effective model of charge ordered and (or) magnetically ordered +insulators is studied. The tight binding Hamiltonian analyzed consists of (i) +the effective on-site interaction U, (ii) the intersite density-density +interaction W and (iii) intersite magnetic exchange interaction Jz (or Jxy) +between nearest-neighbors. The intersite interaction are treated within the +mean-field approximation. One shows that the systems considered can exhibit +very interesting multicritical behaviors, including among others bicritical, +tricritical, tetracritical and critical end points. The analysis of the model +has been performed for an arbitrary electron concentration as well as an +arbitrary chemical potential in the limit of strong on-site repulsion. The +phase diagrams obtained in such a case are shown to consist of at least 9 +different states, including four homogenous phases: nonordered (NO), +ferromagnetic (F), charge ordered (CO), ferrimagnetic (intermediate, I) and +five types of phase separation: NO-NO, F-NO, F-F, CO-F, CO-I.",1108.6181v1 +2011-09-02,Symmetry Theory of the Flexomagnetoelectric Effect in the Bloch Lines,"It was shown, that there are 48 magnetic point groups of the Bloch lines +including 22 (11 time-invariant and 11 time-noninvariant) enantimorphic and 26 +non-enantiomorphic groups. The Bloch lines with the time-noninvariant +enantiomorphism have identical types (parities) of the magnetization and +polarization dependences. The soliton like Bloch lines are derived from the +symmetry classification. The tip electrode method of the creation of these +Bloch lines is suggested for the potential applications in the magnetoelectric +memory devices. The method of the experimental determination of the +flexomagnetoelectric properties of the Bloch lines carried by the Bloch domain +walls has been suggested. New type of the flexomagnetoelectric coupling, +determined by the spatial derivatives of the electric polarization can be found +in the vicinity of the Curie temperature or compensation point of the +ferrimagnets. The multiple states Bloch line based magnetoelectric/multiferroic +memory is proposed. It can be considered as a concept of the magnetoelectric +enhancement of existing Bloch line memory invention.",1109.0531v1 +2011-10-04,Zero and finite temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7,"We investigate the spin-induced polarization in the multiferroic compound +Ba2CuGe2O7 using variarional and finite temperature mean field approaches. The +compound is described by a spin-3/2 Heisenberg model extended with easy plane +anisotropy and Dzyaloshinskii-Moriya (DM) interaction. Applying magnetic field +parallel to the [110] axis, three phases can be distinguished: (i) At high +magnetic field we find a partially magnetized phase with spins parallel to the +fields and uniform polarization; (ii) Below a critical field the ground state +is a twofold degenerate canted antiferromagnet, where the degeneracy can be +lifted by a finite DM interaction; (iii) At zero field a U(1) symmetry breaking +phase takes place, exhibiting a Goldstone-mode. To reproduce the magnetization +and polarization measurements reported in Murakawa et al. [Phys. Rev. Lett. +105, 137202 (2010)], we introduce an additional term in the Hamiltonian that +couples the polarizations on neighboring tetrahedra. This results in the +appearance of a canted ferrimagnetic phase for h < 1 T, characterized by a +finite staggered polarization, as well as by a finite magnetization along the +[-1,1,0] axis that leads to torque anomalies.",1110.0788v1 +2011-10-05,Skyrmion quantum numbers and quantized pumping in two dimensional topological chiral magnets,"We investigate the general conditions to achieve the adiabatic charge and +spin polarizations and quantized pumping in 2D magnetic insulators possessing +inhomogeneous spin structures. In particular, we focus on the chiral +ferrimagnetic insulators which are generated via spontaneous symmetry breaking +from correlated two dimensional topological insulators. Adiabatic deformation +of the inhomogeneous spin structure generates the spin gauge flux, which +induces adiabatic charge and spin polarization currents. The unit pumped +charge/spin are determined by the product of two topological invariants which +are defined in momentum and real spaces, respectively. The same topological +invariants determine the charge and spin quantum numbers of skyrmion textures. +It is found that in noncentrosymmetric systems, a new topological phase, dubbed +the topological chiral magnetic insulator, exists in which a skyrmion defect is +a spin-1/2 fermion with electric charge $e$. Considering the adiabatic current +responses of generic inhomogeneous systems, it is shown that the quantized +topological response of chiral magnetic insulators is endowed with the second +Chern number.",1110.0946v2 +2011-10-10,Magnetic order and frustrated dynamics in Li(Ni0.8Co0.1Mn0.1)O2: a study by μ+SR and SQUID magnetometry,"Recently, the mixed transition metal oxides of the form Li(Ni1-y-zCoyMnz)O2, +have become the center of attention as promising candidates for novel battery +material. These materials have also revealed very interesting magnetic +properties due to the alternate stacking of planes of metal oxides on a 2D +triangular lattice and the Li-layers. The title compound, +Li(Ni0.8Co0.1Mn0.1)O2, has been investigated by both magnetometry and +measurements and {\mu}+SR. We find the evolution of localized magnetic moments +with decreasing temperature below 70 K. The magnetic ground state (T = 2 K) is, +however, shown to be a frustrated system in 3D, followed by a transition into a +possible 2D spinglass above 22 K. With further increasing temperature the +compound show the presence of remaining correlations with increasing effective +dimensionality all the way up to the ferrimagnetic transition at TC = 70 K.",1110.2071v1 +2011-10-17,Investigation of the magnetic phase transition and magnetocaloric properties of the Mn$_2$FeSbO$_6$ ilmenite,"The magnetic phase transition and magnetocaloric properties of mineral and +synthetic melanostibite Mn$_2$FeSbO$_6$ with ilmenite-type structure have been +studied. Mn$_2$FeSbO$_6$ orders ferrimagnetically below 270 K and is found to +undergo a second-order magnetic phase transition. The associated magnetic +entropy change amounts to 1.7 J/kgK for the mineral and 1.8 J/kgK synthetic +melanostibite for 5 T field change. For the synthetic Mn$_2$FeSbO$_6$ the +adiabatic temperature change was estimated from magnetic- and specific heat +measurements and amounts to 0.2 K in 1 T field change. Perspectives of the +promising functional properties of Mn$_2$FeSbO$_6$-based materials are +discussed.",1110.3624v2 +2011-12-26,Surface properties of the clean and Au/Pd covered Fe$_3$O$_4$(111): a DFT and DFT+$U$ study,"The spin-density functional theory (DFT) and DFT+$U$ with Hubbard $U$ term +accounting for on-site Coulomb interactions were applied to investigate +structure, stability, and electronic properties of different terminations of +the Fe$_3$O$_4$(111) surface. All terminations of the ferrimagnetic +Fe$_3$O$_4$(111) surface exhibit very large (up to 90%) relaxations of the +first four interlayer distances, decreasing with the oxide layer depth. Our +calculations predict the iron terminated surface to be most stable in a wide +range of the accessible values of the oxygen chemical potential. The adsorption +of Au and Pd on two stable Fe- and O-terminated surfaces is studied. Our +results show that Pd binds stronger than Au both to the Fe- and O-terminated +surface. DFT+$U$ gives stronger bonding than DFT. The bonding of both +adsorbates to the O-terminated magnetite surface is by 1.5-2.5 eV stronger than +to the Fe-terminated surface.",1112.5827v1 +2011-12-26,"Multiferroic and magnetoelectric nature of GaFeO3, AlFeO3 and related oxides","GaFeO3, AlFeO3 and related oxides are ferrimagnetic exhibiting +magnetodielectric effect. There has been no evidence to date for +ferroelectricity and hence multiferroicity in these oxides. We have +investigated these oxides as well as oxides of the composition +Al1-x-yGaxFe1+yO3 (x = 0.2, y = 0.2) for possible ferroelectricity by carrying +out pyroelectric measurements. These measurements establish the occurrence of +ferroelectricity at low temperatures below the N\`eel temperature in these +oxides. They also exhibit significant magnetoelectric effect. We have tried to +understand the origin of ferroelectricity based on non-centrosymmetric magnetic +ordering and disorder by carrying out first-principles calculations.",1112.5848v2 +2011-12-27,Effective Soft-Mode Theory of Strongly Interacting Fermions,"An effective field theory for clean electron systems is developed in analogy +to the generalized nonlinear sigma-model for disordered interacting electrons. +The physical goal is to separate the soft or massless electronic degrees of +freedom from the massive ones and integrate out the latter to obtain a field +theory in terms of the soft degrees of freedom only. The resulting theory is +not perturbative with respect to the electron-electron interaction. It is +controlled by means of a systematic loop expansion and allows for a +renormalization-group analysis in a natural way. It is applicable to universal +phenomena within phases, and to transitions between phases, with order +parameters in arbitrary angular-momentum channels, and in the spin-singlet, +spin-triplet, particle-hole, and particle-particle channels. Applications +include ferromagnetic and ferrimagnetic ordering, non-s-wave ferromagnetic +order (magnetic nematics), Fermi-liquid to non-Fermi-liquid transitions, and +universal phenomena within a Fermi-liquid phase.",1112.5916v3 +2012-02-26,Quantum Anomalous Hall Effect in Flat Band Ferromagnet,"We proposed a theory of quantum anomalous Hall effect in a flat-band +ferromagnet on a two-dimensional (2D) decorated lattice with spin-orbit +coupling. Free electrons on the lattice have dispersionless flat bands, and the +ground state is highly degenerate when each lattice site is occupied averagely +by one electron, i.e., the system is at half filling. The on-site Coulomb +interaction can remove the degeneracy and give rise to the ferrimagnetism, +which is the coexistence of the ferromagnetic and antiferromagnetic long-range +orders. On the other hand the spin-orbit coupling makes the band structure +topologically non-trivial, and produces the quantum spin Hall effect with a +pair of helical edge states around the system boundary. Based on the rigorous +results for the Hubbard model, we found that the Coulomb interaction can +provide an effective staggered potential and turn the quantum spin Hall phase +into a quantum anomalous Hall phase.",1202.5747v1 +2012-06-07,Observation of different spin behavior with temperature variation and Cr substitution in a multiferroic compound YMn$_2$O$_5$,"In this article, the collective response of the spins is explored through low +field bulk magnetic measurement for the series YMn$_{2-x}$Cr$_x$O$_5$ (x= 0.0, +0.05). Low field ac susceptibility and dc magnetization of YMn$_2$O$_5$ shows +multiple transition in analogy to those observed in electrical measurement of +the compound. Using various time dependent magnetization protocols it has been +observed that the behavior of spins in commensurate and incommensurate phase +are drastically different. YMn$_{1.95}$Cr$_{0.05}$O$_5$ undergoes a +ferrimagnetic ordering with an enhanced magnetic ordering temperature as +compared to the parent, which undergoes an antiferromagnetic ordering. +Appearance of spontaneous magnetization without any major change in the atomic +structure is rather significant since the parent compound is an important +multiferroic material. In addition, magnetic memory effect is observed in the +Cr substituted compound whereas it is absent in the parent compound.",1206.1446v1 +2012-06-21,Strong Dzyaloshinskii-Moriya Interaction and Origin of Ferroelectricity in Cu2OSeO3,"By performing density functional calculations, we investigate the origin of +the skyrmion state and ferroelectricity in Cu2OSeO3. We find that the +Dzyaloshinskii-Moriya interactions between the two different kinds of Cu ions +are extremely strong and induce the helical ground state and the skyrmion state +in the absence and presence of magnetic field, respectively. On the basis of +the general model for the spin-order induced polarization, we propose that the +ferroelectric polarization of Cu2OSeO3 in the collinear ferrimagnetic state +arises from an unusual mechanism, i.e., the single-spin-site contribution due +to the spin-orbit coupling.",1206.4792v2 +2012-06-22,Investigation of bond dilution effects on the magnetic properties of a cylindrical Ising nanowire,"A cylindrical magnetic nanowire system composed of ferromagnetic core and +shell layers has been investigated by using effective field theory with +correlations. Both ferromagnetic and antiferromagnetic exchange couplings at +the core-shell interface have been considered. Main attention has been focused +on the effects of the quenched disordered shell bonds, as well as interface +bonds on the magnetic properties of the system. A complete picture of the phase +diagrams and magnetization profiles has been represented. It has been shown +that for the antiferromagnetic nanowire system, the magnetization curves can be +classified according to N\'{e}el theory of ferrimagnetism and it has been found +that under certain conditions, the magnetization profiles may exhibit Q-type, +P-type, N-type and L-type behaviors. The observed L-type behavior has not been +reported in the literature before for the equilibrium properties of nanoscaled +magnets. As another interesting feature of the system, it has been found that a +compensation point can be induced by a bond dilution process in the surface. +Furthermore, we have not found any evidence of neither the first order phase +transition characteristics, nor the reentrance phenomena.",1206.5326v1 +2012-06-29,Light-induced magnetization reversal of high-anisotropy TbCo alloy films,"Magnetization reversal using circularly polarized light provides a new way to +control magnetization without any external magnetic field and has the potential +to revolutionize magnetic data storage. However, in order to reach ultra-high +density data storage, high anisotropy media providing thermal stability are +needed. Here, we evidence all-optical magnetization switching for different +TbxCo1-x ferrimagnetic alloy composition and demonstrate all-optical switching +for films with anisotropy fields reaching 6 T corresponding to anisotropy +constants of 3x106 ergs/cm3. Optical magnetization switching is observed only +for alloys which compensation temperature can be reached through sample +heating.",1206.6978v1 +2012-07-11,Photoinduced Perturbations of the Magnetic Superexchange in Core-Shell Prussian Blue Analogues,"Cubic heterostructured (BA) particles of Prussian blue analogues, composed of +a shell of ferromagnetic K_{0.3}Ni[Cr(CN)_6]_{0.8} \cdot 1.3H_2O (A), Tc ~ 70 +K, surrounding a bulk core of photoactive ferrimagnetic +Rb_{0.4}Co[Fe(CN)_6]_{0.8} \cdot 1.2H_2O (B), Tc ~20 K, have been studied. +Below Tc ~ 70 K, these samples exhibit a persistent photoinduced decrease in +low-field magnetization, and these results resemble data from other core-shell +particles and analogous ABA heterostructured films. This net decrease suggests +that the photoinduced lattice expansion in the B layer generates a +strain-induced decrease in the magnetization of the A layer, similar to a +pressure-induced decrease observed by others in a pure A-like material and by +us in our BA cubes. Upon further examination, the data also reveal a +significant portion of the A material whose superexchange, J, is perturbed by +the photoinduced strain from the B constituent.",1207.2623v1 +2012-07-25,High cooperativity in coupled microwave resonator ferrimagnetic insulator hybrids,"We report the observation of strong coupling between the exchange-coupled +spins in gallium-doped yttrium iron garnet and a superconducting coplanar +microwave resonator made from Nb. The measured coupling rate of 450 MHz is +proportional to the square-root of the number of exchange-coupled spins and +well exceeds the loss rate of 50 MHz of the spin system. This demonstrates that +exchange coupled systems are suitable for cavity quantum electrodynamics +experiments, while allowing high integration densities due to their +extraordinary high spin densities. Our results furthermore show, that +experiments with multiple exchange-coupled spin systems interacting via a +single resonator are within reach.",1207.6039v2 +2012-09-12,Modeling of the magnetic properties of nanomaterials with different crystalline structure,"We propose a method for modeling the magnetic properties of nanomaterials +with different structures. The method is based on the Ising model and the +approximation of the random field interaction. It is shown that in this +approximation, the magnetization of the nanocrystal depends only on the number +of nearest neighbors of the lattice atoms and the values of exchange integrals +between them. This gives a good algorithmic problem of calculating the +magnetization of any nano-object, whether it is ultrathin film or nanoparticle +of any shape and structure, managing only a rule of selection of nearest +neighbors. By setting different values of exchange integrals, it is easy to +describe ferromagnets, antiferromagnets, and ferrimagnets in a unified +formalism. Having obtained the magnetization curve of the sample it is possible +to find the Curie temperature as a function of, for example, the thickness of +ultrathin film. Afterwards one can obtain the numerical values for critical +exponents of the phase transition ""ferromagnet -- paramagnet"". Good agreement +between the results of calculations and the experimental data proves the +correctness of the method.",1209.3256v2 +2012-09-17,Magnetism in MoS2 induced by MeV proton irradiation,"Molybdenum disulphide, a diamagnetic layered dichalcogenide solid, is found +to show magnetic ordering at room temperature when exposed to a 2 MeV proton +beam. The temperature dependence of magnetization displays ferrimagnetic +behavior with a Curie temperature of 895 K. A disorder mode corresponding to a +zone-edge phonon and a Mo valence higher than +4, have been detected in the +irradiated samples using Raman and X-ray photoelectron spectroscopy, +respectively. The possible origins of long-range magnetic ordering in +irradiated MoS2 samples are discussed.",1209.3569v1 +2012-09-29,Realization of spin gapless semiconductors: the Heusler compound Mn2CoAl,"Recent studies have reported an interesting class of semiconductor materials +that bridge the gap between semiconductors and halfmetallic ferromagnets. These +materials, called spin gapless semiconductors, exhibit a bandgap in one of the +spin channels and a zero bandgap in the other and thus allow for tunable spin +transport. Here, a theoretical and experimental study of the spin gapless +Heusler compound Mn2CoAl is presented. It turns out that Mn2CoAl is a very +peculiar ferrimagnetic semiconductor with a magnetic moment of 2 {\mu}B and a +high Curie temperature of 720 K. Below 300 K, the compound exhibits nearly +temperature-independent conductivity, very low, temperature-independent carrier +concentration, and a vanishing Seebeck coefficient. The magnetoresistance +changes sign with temperature. In high fields, it is positive and +non-saturating at low temperatures, but negative and saturating at high +temperatures. The anomalous Hall effect is comparatively low, which is +explained by the close antisymmetry of the Berry curvature for kz of opposite +sign.",1210.0148v1 +2012-10-05,Thermodynamics of Ising Spins on the Star Lattice,"There is a new class of two-dimensional magnetic materials polymeric iron +(III) acetate fabricated recently in which Fe ions form a star lattice. We +study the thermodynamics of Ising spins on the star lattice with exact analytic +method and Monte Carlo simulations. Mapping the star lattice to the honeycomb +lattice, we obtain the partition function for the system with asymmetric +interactions. The free energy, internal energy, specific heat, entropy and +susceptibility are presented, which can be used to determine the sign of the +interactions in the real materials. Moreover, we find the rich phase diagrams +of the system as a function of interactions, temperature and external magnetic +field. For frustrated interactions without external field, the ground state is +disordered (spin liquid) with residual entropy 1.522 per unit cell. When a weak +field is applied, the system enters a ferrimagnetic phase with residual entropy +ln4 per unit cell.",1210.1675v1 +2012-10-10,Negative spin polarization of Mn2VGa probed by tunnel magnetoresistance,"The ferrimagnetic Heusler compound Mn2VGa is predicted to have a pseudogap in +the majority spin channel, which should lead to a negative tunnel +magnetoresistance. We synthesized epitaxial Mn2VGa thin films on MgO(001) +substrates by dc and rf magnetron co-sputtering, resulting in nearly +stoichiometric films. XRD analysis revealed a mostly B2-ordered structure for +the films deposited at substrate temperatures of 350{\deg}C, 450{\deg}C, and +550{\deg}C. Magnetic tunnel junctions with MgO barrier and CoFe +counter-electrodes were fabricated. After post-annealing at up to +T_a=425{\deg}C negative TMR was obtained around zero bias, providing evidence +for the inverted spin-polarization. Band structures of both electrodes were +computed within the coherent potential approximation and used to calculate the +TMR(V) characteristics, which are in good agreement with our experimental +findings.",1210.2966v1 +2012-10-18,Parity effect in ground state localization of antiferromagnetic chains coupled to a ferromagnet,"We investigate the ground states of antiferromagnetic Mn nanochains on +Ni(110) by spin-polarized scanning tunneling microscopy in combination with +theory. While the ferrimagnetic linear trimer experimentally shows the +predicted collinear classical ground state, no magnetic contrast was observed +for dimers and tetramers where non-collinear structures were expected based on +ab-initio theory. This striking observation can be explained by zero-point +energy motion for even numbered chains derived within a classical equation of +motion leading to non classical ground states. Thus, depending on the parity of +the chain length, the system shows a classical or a quantum behavior.",1210.5220v1 +2012-10-24,Theory of Half-Metallic Double Perovskites II: Effective Spin Hamiltonian and Disorder Effects,"Double perovskites like Sr$_2$FeMoO$_6$ are materials with half-metallic +ground states and ferrimagnetic T$_{\rm{c}}$'s well above room temperature. +This paper is the second of our comprehensive theory for half metallic double +perovskites. Here we derive an effective Hamiltonian for the Fe core spins by +""integrating out"" the itinerant Mo electrons and obtain an unusual double +square-root form of the spin-spin interaction. We validate the classical spin +Hamiltonian by comparing its results with those of the full quantum treatment +presented in the companion paper ""Theory of Half-Metallic Double Perovskites I: +Double Exchange Mechanism"". We then use the effective Hamiltonian to compute +magnetic properties as a function of temperature and disorder and discuss the +effect of excess Mo, excess Fe, and anti-site disorder on the magnetization and +T$_{\rm{c}}$. We conclude with a proposal to increase T$_{\rm{c}}$ without +sacrificing carrier polarization.",1210.6689v2 +2012-11-05,Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers,"Using X-ray magnetic circular dichroism (XMCD) measurements, we explore the +possible existence of induced magnetic moments in thin Pt films deposited onto +the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12). Such a magnetic +proximity effect is well established for Pt/ferromagnetic metal +heterostructures. Indeed, we observe a clear XMCD signal at the Pt L3 edge in +Pt/Fe bilayers, while no such signal can be discerned in XMCD traces of +Pt/Y3Fe5O12 bilayers. Integrating the XMCD signals allows to estimate an upper +limit for the induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers.",1211.0916v1 +2012-12-19,Spontaneous atomic ordering and magnetism in epitaxially stabilized double perovskites,"We have studied the atomic ordering of B-site transition metals and magnetic +properties in the pulsed-laser deposited films of La2CrFeO6 (LCFO) and La2VMnO6 +(LVMO), whose bulk materials are known to be single perovskites with random +distribution of the B-site cations. Despite similar ionic characters of +constituent transition metals in each compound, the maximum B-site order +attained was surprisingly high, ~90% for LCFO and ~80% for LVMO, suggesting a +significant role of epitaxial stabilization in the spontaneous ordering +process. Magnetization and valence state characterizations revealed that the +magnetic ground state of both compounds was coincidently ferrimagnetic with +saturation magnetization of ~2myuB per formula unit, unlike those predicted +theoretically. In addition, they were found to be insulating with optical band +gaps of 1.6 eV and 0.9 eV for LCFO and LVMO, respectively. Our results present +a wide opportunity to explore novel magnetic properties of binary +transition-metal perovskites upon epitaxial stabilization of the ordered phase.",1212.4622v1 +2013-01-02,Spin-orbital locked magnetic excitations in a half-metallic double perovskite Ba2FeReO6,"We present a powder inelastic neutron scattering study of magnetic +excitations in Ba$_2$FeReO$_6$, a member of the double perovskite family of +materials which exhibit half-metallic behavior and high Curie temperatures. We +find clear evidence of two well-defined dispersing magnetic modes in its low +temperature ferrimagnetic state. We develop a local moment model, which +incorporates the interaction of Fe spins with spin-orbit locked magnetic +moments on Re, and show that this captures our experimental observations. Our +study further opens up double perovskites as model systems to explore the +interplay of strong correlations and spin-orbit coupling in 5d transition metal +oxides.",1301.0327v1 +2013-01-08,Magnetic phases of mass- and population-imbalanced ultracold fermionic mixtures in optical lattices,"We study magnetic phases of two-component mixtures of ultracold fermions with +repulsive interactions in optical lattices in the presence of both hopping and +population imbalance by means of dynamical mean-field theory (DMFT). It is +shown that these mixtures can have easy-axis antiferromagnetic, ferrimagnetic, +charge-density wave, and canted-antiferromagnetic order or be unordered +depending on parameters of the system. We study the resulting phase diagram in +detail and investigate the stability of the different phases with respect to +thermal fluctuations. We also perform a quantitative analysis for a gas +confined in a harmonic trap, both within the local density approximation and +using a full real-space generalization of DMFT.",1301.1691v2 +2013-01-09,High coercivity induced by mechanical milling in cobalt ferrite powders,"In this work we report a study of the magnetic behavior of ferrimagnetic +oxide CoFe2O4 treated by mechanical milling with different grinding balls. The +cobalt ferrite nanoparticles were prepared using a simple hydrothermal method +and annealed at 500oC. The non-milled sample presented coercivity of about 1.9 +kOe, saturation magnetization of 69.5 emu/g, and a remanence ratio of 0.42. +After milling, two samples attained coercivity of 4.2 and 4.1 kOe, and +saturation magnetization of 67.0 and 71.4 emu/g respectively. The remanence +ratio MR/MS for these samples increase to 0.49 and 0.51, respectively. To +investigate the influence of the microstructure on the magnetic behavior of +these samples, we used X-ray powder diffraction (XPD), transmission electron +microscopy (TEM), and vibrating sample magnetometry (VSM). The XPD analysis by +the Williamson-Hall plot was used to estimate the average crystallite size and +strain induced by mechanical milling in the samples.",1301.1945v1 +2013-01-21,Role of critical spin fluctuations in ultrafast demagnetization of transition-metal rare-earth alloys,"Ultrafast magnetization dynamics induced by femtosecond laser pulses have +been measured in ferrimagnetic Co0.8Gd0.2, Co.74Tb.26 and Co.86Tb.14 alloys. +Using element sensitivity of X-ray magnetic circular dichroism at the Co L3, Tb +M5 and Gd M5 edges we evidence that the demagnetization dynamics is element +dependent. We show that a thermalization time as fast as 280 fs is observed for +the rare-earth in the alloy, when the laser excited state temperature is below +the compensation temperature. It is limited to 500 fs when the laser excited +state temperature is below the Curie temperature (Tc). We propose critical spin +fluctuations in the vicinity of TC as the mechanism which reduces the +demagnetization rates of the 4f electrons in transition-metal rare-earth alloys +whereas at any different temperature the limited demagnetization rates could be +avoided.",1301.4885v3 +2013-02-04,"Parimagnetism in RCo$_2$ series (R=Dy, Ho, and Tm)","X-ray circular magnetic dichroism (XMCD), longitudinal ($\chi_{ac}$) and +transverse (TS) ac magnetic susceptibility have been measured in several +members of the $R$Co$_2$ series ($R$ = Dy, Ho, and Tm) as a function of +temperature and applied magnetic field. We show that parimagnetism is a general +behavior along the $R$Co$_2$ ferrimagnetic series ($R$ being a heavy rare earth +ion). XMCD results evidence the presence of two compensation temperatures, +defining two different parimagnetic configurations, which is a fully unexpected +result. The inverse $\chi_{ac}$ curve exhibits a deviation from Curie-Weiss +behavior which is recovered under applied magnetic field. The large excess of +polarizability above the critical temperature proves the existence of an +enhanced effective moment due to the presence of short range magnetic +correlations, which are also observed in TS measurements. The combination of TS +and XMCD measurements allows to depict new magnetic phase diagrams for the +$R$Co$_2$ series. A new scenario allowing to understand the observed +phenomenology as a Griffiths phase-like behavior is proposed, where the +amorphous $R$Co$_2$ represents the undiluted system case.",1302.0775v1 +2013-02-16,Room Temperature Nanoscale Ferroelectricity in Magnetoelectric GaFeO3 Epitaxial Thin Films,"We demonstrate room temperature ferroelectricity in the epitaxial thin films +of magnetoelectric GaFeO3. Piezo-force measurements show a 180o phase shift of +piezoresponse upon switching the electric field indicating nanoscale +ferroelectricity in epitaxial thin films of gallium ferrite. Further, +temperature dependent impedance analysis with and without the presence of an +external magnetic field clearly reveals a pronounced magneto-dielectric effect +across the magnetic transition temperature. In addition, our first principles +calculations show that Fe ions are not only responsible for ferrimagnetism as +observed earlier, but also give rise to the observed ferroelectricity, making +GFO an unique single phase multiferroic.",1302.3983v2 +2013-02-27,Specific heat and thermal conductivity of ferromagnetic magnons in Yttrium Iron Garnet,"The specific heat and thermal conductivity of the insulating ferrimagnet +Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured +down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a +characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward +deviation is observed, which is attributed to the magnetic dipole-dipole +interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon +thermal conductivity $\kappa_m$ does not show the characteristic $T^2$ +dependence below 0.8 K. To fit the $\kappa_m$ data, both magnetic defect +scattering effect and dipole-dipole interaction are taken into account. These +results complete our understanding of the thermodynamic and thermal transport +properties of the low-lying ferromagnetic magnons.",1302.6739v1 +2013-03-07,"Magnetic properties of the double perovskites LaPbMSbO6 (M = Mn, Co and Ni)","New double perovskites LaPbMSbO6, where M2+ = Mn2+, Co2+, and Ni2+, were +synthesized as polycrystals by an aqueous synthetic route at temperatures below +1000 oC. All samples are monoclinic, space group P21/n, as obtained from +Rietveld analysis of X-ray powder diffraction patterns. The distribution of M2+ +and Sb5+ among the two octahedral sites have 3% of disorder for M2+ = Ni2+, +whereas for M2+ = Mn2+ and Co2+ less disorder is found. The three samples have +an antiferromagnetic transition, due to the antiferromagnetic coupling between +M2+ through super-superexchange paths M2+ - O2- - Sb5+ - O2- - M2+. Transition +temperatures are low: 8, 10 and 17 K for Mn2+, Co2+, and Ni2+ respectively, as +a consequence of the relatively long distances between the magnetic ions M2+. +Besides, for LaPbMnSbO6 a small transition at 45 K was found, with +ferrimagnetic characteristics, possibly as a consequence of a small disorder +between Mn2+ and Sb5+. This disorder would give additional and shorter +interaction paths: superexchange Mn2+ - O2- - Mn2+.",1303.1834v1 +2013-04-04,The effect of Al doping on the structure and magnetism in cobaltite CaBaCo4O7,"We report the effects of Al-doping on the structure and magnetic properties +in CaBa(Co$_{1-x}$Al$_{x}$)$_4$O$_7$ (0$\leq$x$\leq$0.25). The system exhibits +a structural transition from an orthorhombic symmetry to a hexagonal symmetry +when the Al content exceeds $x =$ 0.1. The Curie temperature and the value of +the magnetization decrease with increasing Al doping level, indicating that the +ferrimagnetic ground state is gradually suppressed. The ground state eventually +transits into a spin-glass state for $x >$ 0.1. Moreover, the short-range +magnetic correlations, which occur at high temperatures in CaBaCo$_4$O$_7$, are +found to be gradually suppressed with increasing Al content and eventually +disappear for $x =$ 0.25. By comparing our results with other Co-site doping +cases, we suggest that the lattice and the spin degrees of freedom are +relatively decoupled in CaBaCo$_4$O$_7$.",1304.1387v1 +2013-04-05,Laser-Induced Magnetic Nanostructures with Tunable Topological Properties,"We report the creation and real-space observation of magnetic structures with +well-defined topological properties and a lateral size as low as about 150 nm. +They are generated in a thin ferrimagnetic film by ultrashort single optical +laser pulses. Thanks to their topological properties, such structures can be +classified as Skyrmions of a particular type that does not require an +externally applied magnetic field for stabilization. Besides Skyrmions, we are +able to generate magnetic features with topological characteristics that can be +tuned by changing the laser fluence. The stability of such features is +accounted for by an analytical model based on the interplay between the +exchange and the magnetic dipole-dipole interactions",1304.1754v1 +2013-04-08,YIG thickness and frequency dependence of the spin-charge current conversion in YIG/Pt systems,"We report the frequency dependence of the spin current emission in a hybrid +ferrimagnetic insulator/normal metal system as function of the insulating layer +thickness. The system is based on a yttrium iron garnet (YIG) film [0.2, 1, and +3 \mu m] grown by liquid-phase-epitaxy coupled with a spin current detector of +platinum [6 nm]. A strong YIG thickness dependence of the efficiency of the +spin pumping has been observed. The highest conversion factor \Delta V/P_{abs} +has been demonstrated for the thinner YIG (1.79 and 0.55 mV/mW^{-1} at 2.5 and +10 GHz, respectively) which presents an interest for the realisation of +YIG-based devices. A strong YIG thickness dependence of the efficiency of the +spin pumping has been also observed and we demonstrate the threshold frequency +dependence of the three-magnon splitting process.",1304.2190v1 +2013-04-23,Converse Magnetoelectric Effects in Fe3O4/BaTiO3 Multiferroic Hybrids,"The quantitative understanding of converse magnetoelectric effects, i.e., the +variation of the magnetization as a function of an applied electric field, in +extrinsic multiferroic hybrids is a key prerequisite for the development of +future spintronic devices. We present a detailed study of the strain-mediated +converse magnetoelectric effect in ferrimagnetic Fe3O4 thin films on +ferroelectric BaTiO3 substrates at room temperature. The experimental results +are in excellent agreement with numerical simulation based on a two-region +model. This demonstrates that the electric field induced changes of the +magnetic state in the Fe3O4 thin film can be well described by the presence of +two different ferroelastic domains in the BaTiO3 substrate, resulting in two +differently strained regions in the Fe3O4 film with different magnetic +properties. The two-region model allows to predict the converse magnetoelectric +effects in multiferroic hybrid structures consisting of ferromagnetic thin +films on ferroelastic substrates.",1304.6315v1 +2013-04-24,Observation of an inter-sublattice exchange magnon in CoCr$_2$O$_4$ and analysis of magnetic ordering,"We report on an investigation of optical properties of multiferroic +CoCr$_{2}$O$_{4}$ at terahertz frequencies in magnetic fields up to 30 T. Below +the ferrimagnetic transition (94 K), the terahertz response of +CoCr$_{2}$O$_{4}$ is dominated by a magnon mode, which shows a steep +magnetic-field dependence. We ascribe this mode to an exchange resonance +between two magnetic sublattices with different $g$-factors. In the framework +of a simple two-sublattice model (the sublattices are formed by Co$^{2+}$ and +Cr$^{3+}$ ions), we find the inter-sublattice coupling constant, $\lambda = - +(18 \pm 1)$ K, and trace the magnetization for each sublattice as a function of +field. We show that the Curie temperature of the Cr$^{3+}$ sublattice, +$\Theta_{2}$ = $(49 \pm 2)$ K, coincides with the temperature range, where +anomalies of the dielectric and magnetic properties of CoCr$_{2}$O$_{4}$ have +been reported in literature.",1304.6525v1 +2013-05-03,Design of Magnetic Textures of Ad-Nanocorrals with an Extra Adatom,"It is shown that in antiferromagnetic open or closed corrals of magnetic +adatoms grown on surfaces, the attachment of a single extra adatom anywhere in +the corral impacts on the geometrical topology of the nanosystem and generates +complex magnetic structures when a magnetic field is applied or a magnetic +coupling to a ferromagnetic substrate exists. The spin configuration of the +corral can be tuned to a non-planar state or a planar non-collinear or +ferrimagnetic state by adjusting its number of sites, the location of the extra +adatom or the strength of the coupling to the ferromagnetic substrate. This +shows the possibility to generate non-trivial magnetic textures with atom by +atom engineering anywhere in the corral and not only at the edges.",1305.0706v1 +2013-05-22,Field-induced spin-structural transition and giant magnetostriction in Ising chain $α$-CoV$_2$O$_6$,"We have investigated the temperature and magnetic field dependence of +magnetization, specific heat ($C_p$), and relative sample length change +($\Delta L/L_0$) for understanding the field-induced spin-structural change in +quasi-one-dimensional spin chain $\alpha$-CoV$_2$O$_6$ which undergoes +antiferromagnetic (AFM) transition below $T_N$$=$15 K. Analysis of $C_p$($T$) +shows that an effective $S$$=$1/2 Ising state is realized below 20 K, though +the magnetic fluctuations persist well above $T_N$. $C_p$ and the coefficient +of linear thermal expansion ($\alpha$) exhibit strong $H$ dependence in the AFM +state. We also observe a huge positive magnetostriction [$\Delta L$($H$)/$L_0$] +below 20 K which does not show any tendency of saturation up to 9 T. With +increasing field, a sharp and symmetric peak emerges below $T_N$ in both +$C_p$($T$) and $\alpha$($T$) due to field-induced first order +ferrimagnetic/ferromagnetic-paramagnetic transitions. The large value of +magnetostriction below $T_N$ suggests strong spin-lattice coupling in +$\alpha$-CoV$_2$O$_6$.",1305.5027v2 +2013-06-29,Strain-induced enhancement of coercivity in amorphous TbFeCo films,"We report a strong size dependence of coercivity in amorphous ferrimagnetic +TbFeCo films. The as-deposited film exhibited a low saturation magnetization +(Ms=100 emu/cc) and a high perpendicular anisotropy (Ku=10^6 erg/cc). Hall-bar +devices were fabricated for characterizing the magneto-transport behaviors. A +significant increase in coercivity (up to 300 %) was observed at room +temperature as the width of Hall bar was reduced. The large coercivity +enhancement was attributed to the relaxation of film stress. The effect of +strain and dimensionality on the coercivity in TbFeCo makes it attractive for +tunable coercivity and the magnetization reversal in future nanoscale devices.",1307.0057v1 +2013-07-04,Spin Hall magnetoresistance at Pt/CoFe2O4 interfaces and texture effects,"We report magnetoresistance measurements on thin Pt bars grown on epitaxial +(001) and (111) CoFe2O4 (CFO) ferrimagnetic insulating films. The results can +be described in terms of the recently discovered spin Hall magnetoresistance +(SMR). The magnitude of the SMR depends on the interface preparation +conditions, being optimal when Pt/CFO samples are prepared in situ, in a single +process. The spin-mixing interface conductance, the key parameter governing SMR +and other relevant spin-dependent phenomena such as spin pumping or spin +Seebeck effect, is found to be different depending on the crystallographic +orientation of CFO, highlighting the role of the composition and density of +magnetic ions at the interface on spin mixing.",1307.1267v3 +2013-07-09,Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6,"The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of +spin structures that differ in the spin sequence of ferrimagnetic iron - osmium +layers along the tetragonal c-axis. Neutron powder diffraction experiments, +57Fe M\""ossbauer spectra, and density-functional theory calculations suggest +that this behavior arises because a lattice instability resulting in +alternating iron-osmium distances fine-tunes the balance of competing exchange +interactions. Thus, Sr2FeOsO6 is an example for a double perovskite, in which +the electronic phases are controlled by the interplay of spin, orbital, and +lattice degrees of freedom.",1307.2587v2 +2013-07-10,Doping a correlated band insulator: A new route to half metallic behaviour,"We demonstrate in a simple model the surprising result that turning on an +on-site Coulomb interaction U in a doped band insulator leads to the formation +of a half-metallic state. In the undoped system, we show that increasing U +leads to a first order transition between a paramagnetic, band insulator and an +antiferomagnetic Mott insulator at a finite value U_{AF}. Upon doping, the +system exhibits half metallic ferrimagnetism over a wide range of doping and +interaction strengths on either side of U_{AF}. Our results, based on dynamical +mean field theory, suggest a novel route to half-metallic behavior and provide +motivation for experiments on new materials for spintronics.",1307.2693v1 +2013-10-02,Full Control of Magnetism in Manganite Bilayer by Ferroelectric Polarization,"An oxide heterostructure made of manganite bilayers and ferroelectric +perovskites is predicted to lead to the full control of magnetism when +switching the ferroelectric polarizations. By using asymmetric polar interfaces +in the superlattices, more electrons occupy the Mn layer at the $n$-type +interface side than at the $p$-type side. This charge disproportionation can be +enhanced or suppressed by the ferroelectric polarization. Quantum model and +density functional theory calculations reach the same conclusion: a +ferromagnetic-ferrimagnetic phase transition with maximal change $>90%$ of the +total magnetization can be achieved by switching the polarization's direction. +This function is robust and provides full control of the magnetization's +magnitude, not only its direction, via electrical methods.",1310.0811v1 +2013-10-05,Ferrimagnetism in the Heisenberg-Ising Bilayer with Magnetically Non-equivalent Planes,"The Pair Approximation method is applied to the antiferromagnetic +Heisenberg-Ising spin-1/2 bilayer with a simple cubic crystalline structure. +The method allows for self-consistent calculations of thermodynamic quantities, +based on the determination of Gibbs free-energy. In the paper the phase +diagrams and planar magnetizations are calculated for the system in question. +Special attention is paid to the case of magnetically non-equivalent planes, +one of which is additionally randomly diluted. The occurrence of a compensation +phenomenon is found and the compensation temperature is discussed for such a +system. The characteristic concentration of magnetic atoms $p^{\star}$, below +which the compensation phenomenon vanishes, is examined as a function of the +Hamiltonian parameters.",1310.1457v2 +2013-10-11,Phase boundaries of a spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice,"The spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice is studied by +Monte Carlo simulations with the goal to determine phase diagrams for a range +of the model parameters and to investigate the nature of the phase transitions +between the respective phases. For positive values of the biquadratic to +bilinear interaction ratio $\alpha$, we find two ferromagnetically ordered +phases, F1 and F2, with the sublattice magnetizations (1/2,1/2) and (3/2,3/2), +respectively, and our results confirm the discontinuous character of the +order-disorder critical line as a function of the single-ion anisotropy +strength, predicted by the effective-field theory (EFT). For negative values of +$\alpha$, there is another ferrimagnetic (FRM) phase of the type (1/2,3/2), +located between F1 and F2. However, the step-like variation of the +order-disorder critical frontier obtained from EFT for large negative $\alpha$ +is not reproduced and thus deemed artifact of the EFT approximation. +Finite-size scaling analysis performed at various points between the respective +identified phases gave the ratio of critical exponents $\gamma/\nu$ consistent +with the 2D Ising universality class, except in the vicinity of the boundary +intersection, where the results deviated from the standard values beyond the +measurement errors.",1310.3296v1 +2013-10-13,Jahn-Teller distortion induced magnetic phase transition in cubic BaFeO$_{3}$,"Using density functional theory (DFT) with local density approximation (LDA) +and generalized gradient approximation (GGA) correlation functionals, the +electronic and magnetic structures of cubic BaFeO$_{3}$ in the ferromagnetic +(FM) and antiferromagnetic (AFM) states are studied. Our LDA/GGA and +LDA$+U$/GGA$+U$ results show that cubic BFO has a FM ground state, in agreement +with recent experimental works. Two types of Jahn-Teller (JT) distortions, +denoted as JT1 and JT2, are considered. We find FM to ferrimagnetic (FIM) and +FM to AFM magnetic phase transitionn in the JT1 and JT2 type of distortions, +respectively. Larger strains are required for the FM-AFM transition as compared +to the FM-FIM. DFT$+U$ calculations also show that the magnetic moments +dramatically decrease at large strains due to strong overlapping between the Fe +and O atoms. The origins of these transitions is discussed in terms of a +competition between double exchange and superexchange interactions. Oxygen and +Fe displacements are therefore responsible for the magnetic phase transitions +and the reduction of the magnetic moments.",1310.3502v1 +2013-11-02,Interface-induced magnetism in perovskite quantum wells,"We investigate the angular dependence of the magnetoresistance of thin (< 1 +nm), metallic SrTiO3 quantum wells epitaxially embedded in insulating, +ferrimagnetic GdTiO3 and insulating, antiferromagnetic SmTiO3, respectively. +The SrTiO3 quantum wells contain a high density of mobile electrons (~7x10^14 +cm^-2). We show that the longitudinal and transverse magnetoresistance in the +structures with GdTiO3 are consistent with anisotropic magnetoresistance, and +thus indicative of induced ferromagnetism in the SrTiO3, rather than a +nonequilibrium proximity effect. Comparison with the structures with +antiferromagnetic SmTiO3 shows that the properties of thin SrTiO3 quantum wells +can be tuned to obtain magnetic states that do not exist in the bulk material.",1311.0337v1 +2013-11-19,Observation of the spin Peltier effect,"We report the observation of the spin Peltier effect (SPE) in the +ferrimagnetic insulator Yttrium Iron Garnet (YIG), i.e. a heat current +generated by a spin current flowing through a Platinum (Pt)|YIG interface. The +effect can be explained by the spin torque that transforms the spin current in +the Pt into a magnon current in the YIG. Via magnon-phonon interactions the +magnetic fluctuations modulate the phonon temperature that is detected by a +thermopile close to the interface. By finite-element modelling we verify the +reciprocity between the spin Peltier and spin Seebeck effect. The observed +strong coupling between thermal magnons and phonons in YIG is attractive for +nanoscale cooling techniques.",1311.4772v1 +2013-12-04,Physical characteristics and cation distribution of NiFe2O4 thin films with high resistivity prepared by reactive co-sputtering,"We fabricated NiFe2O thin films on MgAl2O4 (001) substrates by reactive dc +magnetron co-sputtering in a pure oxygen atmosphere at different substrate +temperatures. The film properties were investigated by various techniques with +a focus on their structure, surface topography, magnetic characteristics, and +transport properties. Structural analysis revealed a good crystallization with +epitaxial growth and low roughness and a similar quality as in films grown by +pulsed laser deposition. Electrical conductivity measurements showed high room +temperature resistivity (12 Ohmm), but low activation energy, indicating an +extrinsic transport mechanism. A band gap of about 1.55 eV was found by optical +spectroscopy. Detailed x-ray spectroscopy studies confirmed the samples to be +ferrimagnetic with fully compensated Fe moments. By comparison with multiplet +calculations of the spectra we found that the cation valencies are to a large +extent Ni2+ and Fe3+.",1312.1086v1 +2013-12-27,Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field,"The magnetic phase diagram of a ground state is studied theoretically for +graphene nanoflakes of bow-tie shape and various size in external in-plane +magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is +used to model the electronic structure of the systems in question. The +existence of the antiferromagnetic phase with magnetic moments localized at the +sides of the bow-tie is found for low field and a field-induced spin-flip +transition to ferromagnetic state is predicted to occur in charge-undoped +structures. For small nanoflake doped with a single charge carrier the +low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic +ordering can be forced by the field. The critical field is found to decrease +with increasing size of the nanoflake. The influence of diagonal and +off-diagonal disorder on the mentioned magnetic properties is studied. The +effect of off-diagonal disorder is found to be more important than this of +diagonal disorder, leading to significantly widened distribution of critical +fields for disordered population of nanoflakes.",1312.7298v1 +2014-01-18,"Magnetic Moment and Band Structure Analysis of Fe, Co, Ni-modified Graphene-nano- ribbon","Magnetic properties and band characteristics of graphene-nano-ribbon (GNR) +modified by Fe, Co, and Ni were analyzed by the first principles DFT +calculation. Typical unit cell is [C32H2Fe1], [C32H2Co1] and [C32H2Ni1] +respectively. The most stable spin state was Sz=4/2 for Fe-modified GNR, +whereas Sz=3/2 for Co-case and Sz=2/2 for Ni-case. Atomic magnetic moment of +Fe, Co and Ni were 3.63, 2.49 and 1.26 {\mu}B, which were reduced values than +that of atomic Hund-rule due to magnetic coupling with graphene network. There +is a possibility for a ferromagnetic Fe, Co and Ni spin array through an +interaction with carbon pi-conjugated spin system. By expanding a unit cell of +Co-modified case as [C96H6Co3], ferromagnetic like spin state and ferrimagnetic +like one were compared. It was concluded that ferromagnetic state was more +stable magnetic state. Band calculations of Co-modified case show half-metal +like structure with relatively large band gap (0.55eV) for up-spin, whereas +small gap (0.05eV) for down-spin. This suggested a capability of spintronics +application like a spin fiter.",1401.4504v1 +2014-01-27,Prospects for electron spin-dependent short-range force experiments with rare earth iron garnet test masses,"A study of the possible interactions between fermions assuming only +rotational invariance has revealed 15 forms for the potential involving the +fermion spins. We review the experimental constraints on unobserved +macroscopic, spin-dependent interactions between electrons in the range below 1 +cm. An existing experiment, using 1 kHz mechanical oscillators as test masses, +has been used to constrain mass-coupled forces in this range. With suitable +modifications, including spin-polarized test masses, this experiment can be +used to explore all 15 possible spin-dependent interactions between electrons +in this range with unprecedented sensitivity. Samples of ferrimagnetic +dysprosium iron garnet have been fabricated in the suitable test mass geometry +and shown to have high spin density with very low intrinsic magnetism.",1401.6730v2 +2014-01-30,Temperature dependent spin transport properties of Platinum inferred from spin Hall magnetoresistance measurements,"We study the temperature dependence of the spin Hall magnetoresistance (SMR) +in yttrium iron garnet/platinum hybrid structures via magnetization orientation +dependent magnetoresistance measurements. Our experiments show a decrease of +the SMR magnitude with decreasing temperature. Using the sensitivity of the SMR +to the spin transport properties of the normal metal, we interpret our data in +terms of a decrease of the spin Hall angle in platinum from 0.11 at room +temperature to 0.075 at 10K, while the spin diffusion length and the spin +mixing conductance of the ferrimagnetic insulator/normal metal interface remain +almost constant.",1401.7787v4 +2014-02-07,Effects of Structural Distortion Induced by Sc Substitution in LuFe$_2$O$_4$,"We have studied the correlation between the structural distortion and the +electronic/magnetic properties in single-crystalline (Lu,Sc)Fe$_2$O$_4$ +(Sc=0.05 and 0.3) by using X-ray diffraction (XRD), magnetic susceptibility, +and X-ray absorption spectroscopy (XAS)/x-ray magnetic circular dichroism +(XMCD)measurements. The Rietveld structure analysis of the XRD patterns +revealed that the Sc substitution induced an elongation of the FeO$_5$ +bipyramidal cages in LuFe$_2$O$_4$ and increased the Fe$_2$O$_4$ bilayer +thickness. A non-negligible decrease in the ferrimagnetic transition +temperature T$_C$ is observed in the magnetic susceptibility curve of the +Sc=0.3 sample, but the XAS/XMCD spectra do not show any difference except for a +small reduction of dichroism signals at the Fe$^{3+}$ absorption edge. We +interpret this suppression of T$_C$ to be the result of a decreased spin-orbit +coupling effect in the Fe$^{2+}$ $e_{1g}$ doublet under $D_{3h}$ symmetry, +which is induced by the weakened structural asymmetry of the FeO$_5$ +bipyramids.",1402.1685v3 +2014-04-07,Co-existence of ferromagnetic and antiferromagnetic interactions in Mn$_3$Ga$ _{(1-x)} $Sn$_x$C,"The magnetic properties of the Mn$_3$Ga$_{(1-x)}$Sn$_x$C, 0 $\le$ x $\le$ 1 +antiperovskite compounds have been investigated in detail. Though all compounds +of this series crystallize in a cubic structure, the Ga rich (x $\le$ 0.2) +compounds transform, via a first order transformation, to an antiferromagnetic +ground state and the Sn rich (x $\ge$ 0.8) compounds exhibit dominant +ferromagnetic interactions at low temperature. In the intermediate range (0.4 +$\le$ x $\le$ 0.7) co-existence of ferromagnetic and antiferromagnetic +interactions can be seen. The results have been explained to be due to growth +of ferromagnetic sub-lattice at the expense of antiferromagnetic sub-lattice +with increasing Sn concentration in Mn$_3$Ga$_{(1-x)}$Sn$_x$C. This growth +occurs to a point where the first-order transition is altered from a +ferromagnetic - antiferromagnetic type in Ga rich compounds to a paramagnetic - +ferrimagnetic type in Mn$_3$SnC.",1404.1753v1 +2014-04-07,Fingerprints of Galactic Loop I on the Cosmic Microwave Background,"We investigate possible imprints of galactic foreground structures such as +the ""radio loops"" in the derived maps of the cosmic microwave background. +Surprisingly there is evidence for these not only at radio frequencies through +their synchrotron radiation, but also at microwave frequencies where emission +by dust dominates. This suggests the mechanism is magnetic dipole radiation +from dust grains enriched by metallic iron or ferrimagnetic materials. This new +foreground we have identified is present at high galactic latitudes, and +potentially dominates over the expected $B$-mode polarization signal due to +primordial gravitational waves from inflation.",1404.1899v3 +2014-04-28,Electronic structure and magnetic properties of L1_0 binary alloys,"We present a systematic study of the magnetic properties of L1$_0$ binary +alloys FeNi, CoNi, MnAl and MnGa via two different density functional theory +approaches. Our calculations show large magnetocrystalline anisotropies in the +order $1~\text{MJ/m}^3$ or higher for CoNi, MnAl and MnGa while FeNi shows a +somewhat lower value in the range $0.48 - 0.77 ~\text{MJ/m}^3$. Saturation +magnetization values of $1.3~\text{MA/m}$, $1.0~\text{MA/m}$, $0.8~\text{MA/m}$ +and $0.9~\text{MA/m}$ are obtained for FeNi, CoNi, MnAl and MnGa respectively. +Curie temperatures are evaluated via Monte Carlo simulations and show +$T_\text{C}=916~\text{K}$ and $T_\text{C}=1130~\text{K}$ for FeNi and CoNi +respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions +are found to be important for the stability of a ferro or ferrimagnetic ground +state with $T_\text{C}$ greater than $600~\text{K}$. The effect of +substitutional disorder is studied and found to decrease both +magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.",1404.7097v2 +2014-07-12,Possible Half Metallic Antiferromagnetism in a Double Perovskite Material with Strong Spin-Orbit Couplings,"Using the first-principles density functional approach, we investigate a +material Pr$_2$MgIrO$_6$ (PMIO) of double perovskite structure synthesized +recently. According to the calculations, PMIO is a magnetic Mott-Hubbard +insulator influenced by the cooperative effect of spin-orbit coupling (SOC) and +Coulomb interactions of Ir-5$d$ and Pr-4$f$ electrons, as well as the crystal +field. When Pr is replaced with Sr gradually, the system exhibits half metallic +(HM) states desirable for spintronics applications. In +[Pr$_{2-x}$Sr$_x$MgIrO$_6$]$_2$, HM antiferromagnetism (HMAFM) with zero spin +magnetization in the unit cell is obtained for $x=1$, whereas for $x=0.5$ and +1.5 HM ferrimagnetism (HMFiM) is observed with $\mu_{\rm tot}=3\mu_{\rm B}$ and +$\mu_{\rm tot}=-3\mu_{\rm B}$ per unit cell respectively. It is emphasized that +the large exchange splitting between spin-up and spin-down bands at the Fermi +level makes the half metallicity possible even with strong SOC.",1407.3408v1 +2014-07-17,Ferroelectric and Magnetic Domains in LuFe2O4 Observed by Scanning Probe Microscopy,"LuFe2O4 is a multiferroic system which exhibits ferroelectricity, charge +order, and ferrimagnetic order simultaneously below ~230 K. The ferroelectric +domains of LuFe2O4 are imaged with both piezoresponse force microscopy (PFM) +and electrostatic force microscopy (EFM), while the magnetic domains are +characterized by magnetic force microscopy (MFM). Comparison of PFM and EFM +results lead to a conclusion that the ferroelectricity is of electronic origin +as opposed to the usual displacive one. Simultaneous characterization of +ferroelectric and magnetic domains by EFM and MFM, respectively, on the same +surface of LuFe2O4 reveals that both domains have irregular patterns of similar +shape, but the length scales are quite different. The domain size is +approximately 100 nm for the ferroelectric domains while the magnetic domain +size is much larger and gets as large as 1{\mu}m. We also demonstrate that the +origin of the formation of irregular domains in LuFe2O4 is not extrinsic but +intrinsic.",1407.4536v1 +2014-08-10,Thermodynamic curvature for a two-parameter spin model with frustration,"Microscopic models of realistic thermodynamic systems usually involve a +number of parameters, not all of equal macroscopic relevance. We examine a +decorated $(1+3)$ Ising spin chain containing two microscopic parameters: a +""stiff"" $K$ mediating the long-range interactions, and a ""sloppy"" $J$ operating +within local spin groups. $K$ dominates the macroscopic behavior, and varying +$J$ has weak effect except in regions where $J$ brings about transitions +between phases through its conditioning of the local spin groups with which $K$ +interacts. We calculate the heat capacity $C_H$, the magnetic susceptibility +$\chi_T$, and the thermodynamic curvature $R$. For large $|J/K|$, we identify +four magnetic phases: ferromagnetic, antiferromagnetic, and two ferrimagnetic +ones, according to the signs of $K$ and $J$. We argue that for characterizing +these phases, the strongest picture is offered by the thermodynamic geometric +invariant $R$, proportional to the correlation length $\xi$. This picture has +correspondences to other cases, such as fluids.",1408.2236v1 +2014-08-26,Exotic magnetic phases in an Ising-spin Kondo lattice model on a kagome lattice,"Magnetic and electronic states of an Ising-spin Kondo lattice model on a +kagome lattice are investigated by a Monte Carlo simulation. In addition to the +conventional ferromagnetic and ferrimagnetic orders, we show that this model +exhibits several thermally-induced phases, such as partially disordered, +Kosteritz-Thouless-like, and loop-liquid states. In the partially disordered +state, we show that the magnetic transition is associated with the charge-gap +formation. We find that the density of state shows characteristic peaks +reflecting the underlying spin texture. In the loop-liquid state, we also find +a peak in a different manner in the density of states as well as in the optical +conductivity. This is a consequence of the formation of closed loops of the +same spin sites in the loop-liquid state. Our results elucidates the peculiar +cooperation between thermal fluctuations and the spin-charge interplay in this +frustrated itinerant electron system.",1408.5998v2 +2014-09-15,Frustration and Dzyaloshinsky-Moriya anisotropy in the kagome francisites Cu$_3$Bi(SeO$_3)_2$O$_2$X,"We investigate the antiferromagnetic canting instability of the spin-1/2 +kagome ferromagnet, as realized in the layered cuprates +Cu$_3$Bi(SeO$_3)_2$O$_2$X (X=Br, Cl, and I). While the local canting can be +explained in terms of competing exchange interactions, the direction of the +ferrimagnetic order parameter fluctuates strongly even at short distances on +account of frustration which gives rise to an infinite ground state degeneracy +at the classical level. In analogy with the kagome antiferromagnet, the +accidental degeneracy is fully lifted only by non-linear 1/S corrections, +rendering the selected uniform canted phase very fragile even for spins-1/2, as +shown explicitly by coupled-cluster calculations. To account for the observed +ordering, we show that the minimal description of these systems must include +the microscopic Dzyaloshinsky-Moriya interactions, which we obtain from +density-functional band-structure calculations. The model explains all +qualitative properties of the kagome francisites, including the detailed nature +of the ground state and the anisotropic response under a magnetic field. The +predicted magnon excitation spectrum and quantitative features of the +magnetization process call for further experimental investigations of these +compounds.",1409.4335v1 +2014-11-10,Temperature evolution of the effective magnetic anisotropy in the MnCr$_2$O$_4$ spinel,"In this work we present a study of the low temperature magnetic phases of +polycrystalline MnCr$_2$O$_4$ spinel through dc magnetization and ferromagnetic +resonance spectroscopy (FMR). Through these experiments we determined the main +characteristic temperatures: T$_C$ $\sim$41 K and T$_H$ $\sim$18 K +corresponding, respectively, to the ferrimagnetic order and to the low +temperature helicoidal transitions. The temperature evolution of the system is +described by a phenomenological approach that considers the different terms +that contribute to the free energy density. Below the Curie temperature the FMR +spectra were modeled by a cubic magnetocrystalline anisotropy to the second +order, with $K_1$ and $K_2$ anisotropy constants that define the easy +magnetization axis along the <110> direction. At lower temperatures, the +formation of a helicoidal phase was considered by including uniaxial anisotropy +axis along the [1-10] propagation direction of the spiral arrange, with a $K_u$ +anisotropy constant. The values obtained from the fittings at 5 K are +$K_1$=-2.3x10$^4$ erg/cm$^3$, $K^2$=6.4x10$^4$ erg/cm$^3$ and $K_u$=7.5x10$^4$ +erg/cm$^3$.",1411.2461v1 +2015-01-06,Microstructural Effects of Chemical Island Templating in Patterned Matrix-Pillar Oxide Nanocomposites,"The ability to pattern the location of pillars in epitaxial matrix-pillar +nanocomposites is a key challenge to develop future technologies using these +intriguing materials. One such model system employs a ferrimagnetic +CoFe$_{2}$O$_{4}$ (CFO) pillar embedded in a ferroelectric BiFeO$_{3}$ (BFO) +matrix, which has been proposed as a possible memory or logic system. These +composites self-assemble spontaneously with pillars forming through nucleation +at a random location when grown via physical vapor deposition. Recent results +have shown that if an island of the pillar material is pre-patterned on the +substrate, it is possible to control the nucleation process and determine the +locations where pillars form. In this work, we employ electron microscopy and +x-ray diffraction to examine the chemical composition and microstructure of +patterned CFO-BFO nanocomposites. Cross-sectional transmission electron +microscopy is used to examine the nucleation effects at the interface between +the template island and resulting pillar.Evidence of grain boundaries and +lattice tilting in the templated pillars is also presented and attributed to +the microstructure of the seed island.",1501.01061v2 +2015-01-12,Anomalous Hall effect in YIG$|$Pt bilayers,"We measure the ordinary and the anomalous Hall effect in a set of yttrium +iron garnet$|$platinum (YIG$|$Pt) bilayers via magnetization orientation +dependent magnetoresistance experiments. Our data show that the presence of the +ferrimagnetic insulator YIG leads to an anomalous Hall like signature in Pt, +sensitive to both Pt thickness and temperature. Interpretation of the +experimental findings in terms of the spin Hall anomalous Hall effect indicates +that the imaginary part of the spin mixing interface conductance +$G_{\mathrm{i}}$ plays a crucial role in YIG$|$Pt bilayers. In particular, our +data suggest a sign change in $G_{\mathrm{i}}$ between $10\,\mathrm{K}$ and +$300\,\mathrm{K}$. Additionally, we report a higher order Hall effect, which +appears in thin Pt films on YIG at low temperatures.",1501.02574v3 +2015-01-28,Spin Seebeck devices using local on-chip heating,"A micro-patterned spin Seebeck device is fabricated using an on-chip heater. +Current is driven through a Au heater layer electrically isolated from a +bilayer consisting of Fe$_3$O$_4$ (insulating ferrimagnet) and a spin detector +layer. It is shown that through this method it is possible to measure the +longitudinal spin Seebeck effect (SSE) for small area magnetic devices, +equivalent to traditional macroscopic SSE experiments. Using a lock-in +detection technique it is possible to more sensitively characterize both the +SSE and the anomalous Nernst effect (ANE), as well as the inverse spin Hall +effect in various spin detector materials. By using the spin detector layer as +a thermometer, we can obtain a value for the temperature gradient across the +device. These results are well matched to values obtained through +electromagnetic/thermal modeling of the device structure and with large area +spin Seebeck measurements.",1501.07599v1 +2015-01-30,Fragility of ferromagnetic double exchange interactions and pressure tuning of magnetism in 3d-5d double perovskite Sr2FeOsO6,"The ability to tune exchange (magnetic) interactions between 3d transition +metals in perovskite structures has proven to be a powerful route to discovery +of novel properties. Here we demonstrate that the introduction of 3d-5d +exchange pathways in double perovskites enables additional tunability, a result +of the large spatial extent of 5d wave functions. Using x-ray probes of +magnetism and structure at high pressure, we show that compression of Sr2FeOsO6 +drives an unexpected continuous change in the sign of Fe-Os exchange +interactions and a transition from antiferromagnetic to ferrimagnetic order. We +analyze the relevant electron-electron interactions, shedding light into +fundamental differences with the more thoroughly studied 3d-3d systems.",1501.07889v2 +2015-02-22,Excitation and detection of propagating spin waves at the single magnon level,"Ferro- and ferrimagnets play host to small-signal, microwave-frequency +magnetic excitations called spin waves, the quanta of which are known as +magnons. Over the last decade, the field of spin-wave dynamics has contributed +much to our understanding of fundamental magnetism. To date, experiments have +focussed overwhelmingly on the study of room-temperature systems within +classical limits. Here we demonstrate, for the first time, the excitation and +detection of propagating spin waves at the single magnon level. Our results +allow us to project that coupling of propagating spin-wave excitations to +quantum circuits is achievable, enabling fundamental quantum-level studies of +magnon systems and potentially opening doors to novel hybrid quantum +measurement and information processing devices.",1502.06263v1 +2015-03-01,"A combined first-principles and thermodynamic approach to M-Nitronyl Nitroxide (M=Co, Mn) spin helices","The properties of two molecular-based magnetic helices, composed of 3$d$ +metal Co and Mn ions bridged by Nitronyl Nitroxide radicals, are investigated +by density functional calculations. Their peculiar and distinctive magnetic +behavior is here elucidated by a thorough description of their magnetic, +electronic, and anisotropy properties. Metal ions are antiferromagnetically +coupled with the radicals, leading to a ferrimagnetically ordered ground state. +A strong metal-radical exchange coupling is found, about 44 meV and 48 meV for +Co- and Mn-helices, respectively. The latter have also relevant +next-nearest-neighbor Mn-Mn antiferromagnetic interactions (of $\sim$ 6 meV). +Co-sites are characterized by non-collinear uniaxial anisotropies, whereas +Mn-sites are rather isotropic. A key result pertains to the Co-helix: the +microscopic picture resulting from density-functional calculations allows us to +propose a spin Hamiltonian of increased complexity with respect to the commonly +employed Ising Hamiltonian, suitable for the study of finite-temperature +behavior, and that seems to clarify the puzzling scenario of multiple +characteristic energy scales observed in experiments.",1503.00292v1 +2015-04-16,Experimental Observation of Large Chern numbers in Photonic Crystals,"Despite great interest in the quantum anomalous Hall phase and its analogs, +all experimental studies in electronic and bosonic systems have been limited to +a Chern number of one. Here, we perform microwave transmission measurements in +the bulk and at the edge of ferrimagnetic photonic crystals. Bandgaps with +large Chern numbers of 2, 3, and 4 are present in the experimental results +which show excellent agreement with theory. We measure the mode profiles and +Fourier transform them to produce dispersion relations of the edge modes, whose +number and direction match our Chern number calculations.",1504.04399v2 +2015-05-01,"Half-metallic state and magnetic properties versus the lattice constant in Zr2RhZ (Z = Al, Ga, In) Heusler alloys","The half metallic and magnetic properties of Zr2RhZ (Z = Al, Ga, In) alloys +with an Hg2CuTi-type structure were systematically investigated using the +first-principle calculations. Zr2RhZ (Z = Al, Ga, In) alloys are predicted to +be half-metallic ferrimagnets at their equilibrium lattice constants. The +Zr2Rh-based alloys have Mt (the total magnetic moment per unit cell) and Zt +(the valence concentration) values that in agreement with Slater-Pauling rule +Mt = Zt -18. The half-metallic properties and the magnetic properties at +different lattice constants are discussed in detail. We expect that our results +may trigger Zr2RhZ (Z = Al, Ga, In) applying in the future spintronics field.",1505.00203v1 +2015-05-08,Nonreciprocal magnon propagation in a noncentrosymmetric ferromagnet,"Relativistic spin-orbit interaction drastically modifies electronic band and +endows emergent functionalities. One of the example is the Rashba effect. In +noncentrosymmetric systems such as interface and polar materials, the +electronic band is spin-splitted depending on the momentum direction owing to +the spin-orbit interaction, which is useful for the electric manipulation of +spin current. Similar relativistic band-modification is also emergent for spin +wave (magnon) in magnetic materials. The asymmetric magnon band dispersion +induced by the Dzyaloshinskii-Moriya interaction, which is antisymmetric +exchange interaction originating from the spin-orbit interaction, is +theoretically expected, and experimentally observed recently in +noncentrosymmetric ferromagnets. Here, we demonstrate that the nonreciprocal +microwave response can be induced by the asymmetric magnon band in a +noncentrosymmetric ferrimagnet LiFe$_5$O$_8$. This result may pave a new path +to designing magnonic device based on the relativistic band engineering.",1505.01942v1 +2015-05-19,"An orbital glass state of a nearly metallic spinel, CoV$_2$O$_4$","Strain, magnetization, and unpolarized and polarized neutron diffraction +measurements were performed to study the magnetic and structural properties of +spinel CoV$_{2}$O$_{4}$. Magnetostriction measurements indicate that a subtle +distortion of the crystal along the direction of magnetization, $\Delta L/L +\sim 10^{-4}$, exists and varies from elongation to contraction in a second +order fashion upon cooling. Unpolarized and polarized single-crystal neutron +experiments indicate that upon cooling the ferrimagnetic structure changes from +collinear to noncollinear at $T \sim 90$ K, where the elongation of the crystal +is maximized. These results imply the existence of an orbital glassy state in +the nearly metallic frustrated magnet CoV$_{2}$O$_{4}$.",1505.04864v1 +2015-07-01,Three-dimensional topological photonic crystal with a single surface Dirac cone,"A single Dirac cone on the surface is the hallmark of three-dimensional (3D) +topological insulators, where the double degeneracy at the Dirac point is +protected by time-reversal symmetry and the spin-splitting away from the point +is provided by the spin-orbital coupling. Here we predict a single Dirac-cone +surface state in a 3D photonic crystal, where the degeneracy at the Dirac point +is protected by a nonsymmorphic glide reflection and the linear splitting away +from it is enabled by breaking time-reversal symmetry. Such a gapless surface +state is fully robust against random disorder of any type. This bosonic +topological band structure is achieved by applying alternating magnetization to +gap out the 3D ""generalized Dirac points"" discovered in the bulk of our +crystal. The $Z_2$ bulk invariant is characterized through the evolution of +Wannier centers. Our proposal--readily realizable using ferrimagnetic materials +at microwave frequencies--can also be regarded as the photonic analog of +topological crystalline insulators, providing the first 3D bosonic +symmetry-protected topological system.",1507.00337v1 +2015-07-06,Spin-Hall magnetoresistance and spin Seebeck effect in spin-spiral and paramagnetic phases of multiferroic CoCr2O4 films,"We report on the spin-Hall magnetoresistance (SMR) and spin Seebeck effect +(SSE) in multiferroic CoCr2O4 (CCO) spinel thin films with Pt contacts. We +observe a large enhancement of both signals below the spin-spiral (Ts = 28 K) +and the spin lock-in transitions (T_{lock_in} = 14 K). The SMR and SSE response +in the spin lock-in phase are one order of magnitude larger than those observed +at the ferrimagnetic transition temperature (Tc = 94 K), which indicates that +the interaction between spins at the Pt|CCO interface is more efficient in the +non-collinear magnetic state below Ts and T_{lock-in}. At T > Tc, magnetic +field-induced SMR and SSE signals are observed, which can be explained by a +high interface susceptibility. Our results show that the spin transport at the +Pt|CCO interface is sensitive to the magnetic phases but cannot be explained +solely by the bulk magnetization.",1507.01352v1 +2015-07-09,Structural transition and orbital glass physics in near itinerant CoV2O4,"The ferrimagnetic spinel $\mathrm{CoV_2O_4}$ has been a topic of intense +recent interest, both as a frustrated insulator with unquenched orbital +degeneracy and as a near-itinerant magnet which can be driven metallic with +moderate applied pressure. Here, we report on our recent neutron diffraction +and inelastic scattering measurements on powders with minimal cation site +disorder. Our main new result is the identification of a weak ($\frac{\Delta +a}{a} \sim 10^{-4}$), first order structural phase transition at $T^*$ = 90 K, +the same temperature where spin canting was seen in recent single crystal +measurements. This transition is characterized by a short-range distortion of +oxygen octahedral positions, and inelastic data further establish a weak +$\Delta\sim 1.25 meV$ spin gap at low temperature. Together, these findings +provide strong support for the local orbital picture and the existence of an +orbital glass state at temperatures below $T^*$.",1507.02572v2 +2015-07-12,On a mechanism of high-temperature superconductivity: Spin-electron acoustic wave as a mechanism for the Cooper pair formation,"We have found the mechanism of the electron Cooper pair formation via the +electron interaction by means of the spin-electron acoustic waves. This +mechanism takes place in metals with rather high spin polarization, like +ferromagnetic, ferrimagnetic and antiferromagnetic materials. The spin-electron +acoustic wave mechanism leads to transition temperatures 100 times higher than +the transition temperature allowed by the electron-phonon interaction. +Therefore, spin-electron acoustic waves give the explanation for the +high-temperature superconductivity. We find that the transition temperature has +strong dependence on the electron concentration and the spin polarization of +the electrons.",1507.03295v2 +2015-07-30,"First principle investigations of the structural, electronic and magnetic properties of the new zirconium based full-Heusler compounds, Zr2MnZ (Z = Al, Ga and In)","The crystal structure, electronic and magnetic properties of the new +full-Heusler compounds Zr2MnZ (Z=Al, Ga, In), were studied within the Density +Functional Theory (DFT) framework. The materials exhibit unique properties that +connect the spin gapless semiconducting character with the completely +compensated ferrimagnetism. In magnetic configurations, Zr2MnZ (Z=Al, Ga, In) +crystallize in inverse Heusler structure, are stable against decomposition and +have zero magnetic moment per formula unit properties, in agreement with +Slater-Pauling rule. The Zr2MnAl compound presents spin gapless semiconducting +properties with a energy band gap of 0.41 eV in the majority spin channel and a +zero band gap in the minority spin channel. By substituting Ga or In elements, +for Al in Zr2MnAl, semiconducting pseudo band gaps are formed in the majority +spin channels due to the different neighborhood around the manganese atoms, +which decreases the energy of Mn's triple degenerated anti-bonding states.",1507.08605v2 +2015-08-10,Field induced metamagnetic transitions in quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$,"We have investigated the temperature and magnetic field dependence of +magnetization ($M$), specific heat ($C_p$), and relative sample length change +($\Delta L/L_0$) for understanding the field-induced metamagnetic transitions +in quasi-one-dimensional monoclinic ($\alpha$ phase) and triclinic ($\gamma$ +phase) CoV$_2$O$_6$ spin chains. With the application of external magnetic +field, a sharp peak emerges in $C_p$($T$) below $T_N$$=$15 K in $\alpha$ phase +and a hump-like feature appears above $T_N$$=$6.5 K in $\gamma$ phase due to +the field-induced ferrimagnetic and ferromagnetic transitions, respectively. +Strong field dependence of linear thermal expansion and large positive +magnetostriction have been observed in $\alpha$ phase. Though magnetization +data indicate strong spin-orbit coupling for both phases, other measurements +show that this effect is very weak for the $\gamma$ phase.",1508.02269v1 +2015-08-12,Kinetic Arrest of Field-Temperature Induced First Order Phase Transition in Quasi- One Dimensional Spin System Ca3Co2O6,"We have found that the geometrically frustrated spin chain compound Ca3Co2O6 +belonging to Ising like universality class with uniaxial anisotropy shows +kinetic arrest of first order intermediate phase (IP) to ferrimagnetic (FIM) +transition. In this system, dc magnetization measurements followed by different +protocols suggest the coexistence of high temperature IP with equilibrium FIM +phase in low temperature. Formation of metastable state due to hindered first +order transition has also been probed through cooling and heating in unequal +field (CHUF) protocol. Kinetically arrested high temperature IP appears to +persist down to almost the spin freezing temperature in this system.",1508.02894v1 +2015-09-04,Origin of lowered magnetic moments in epitaxially strained thin films of multiferroic Bi$_2$FeCrO$_6$,"We have investigated the effect of epitaxial strain on the magnetic +properties and $B$-site cation ordering in multiferroic Bi$_2$FeCrO$_6$ (001) +thin films using a density-functional theory approach. We find that in thin +films with rock-salt ordering of Fe and Cr the ground state is characterised by +C-type anti-ferromagnetic (AFM) order. This is in contrast to the bulk form of +the material which was predicted to be a ferrimagnet with G-type AFM order. +Furthermore, the cation ordered thin-films undergo a transition with epitaxial +strain from C to A-type AFM order. Other magnetic orders appear as thermally +accessible excited states. We also find that $B$-site cation disordered +structures are more stable in coherent epitaxial strains thereby explaining the +lowered magnetic moments observed in these samples at room temperature. Strain +varies both the sign as well as strength of the Fe-Cr superexchange coupling +resulting in a very interesting phase diagram for Bi$_2$FeCrO$_6$ thin films.",1509.01563v2 +2015-09-04,Spin frustration and fermionic entanglement in an exactly solved hybrid diamond chain with the localized Ising spins and mobile electrons,"The strongly correlated spin-electron system on a diamond chain containing +localized Ising spins on its nodal lattice sites and mobile electrons on its +interstitial sites is exactly solved in a magnetic field using the +transfer-matrix method. We have investigated in detail all available ground +states, the magnetization processes, the spin-spin correlation functions around +an elementary plaquette, fermionic quantum concurrence and spin frustration. It +is shown that the fermionic entanglement between mobile electrons hopping on +interstitial sites and the kinetically-induced spin frustration are closely +related yet independent phenomena. In the ground state, quantum entanglement +only appears within a frustrated unsaturated paramagnetic phase, while thermal +fluctuations can promote some degree of quantum entanglement above the +non-frustrated ground states with saturated paramagnetic or classical +ferrimagnetic spin arrangements.",1509.01639v1 +2015-09-05,Magnetic and magnetocaloric properties of quasi-one-dimensional Ising spin chain CoV$_{2}$O$_{6}$,"We have investigated the magnetic and magnetocaloric properties of +antiferromagnetic Ising spin chain CoV$_{2}$O$_{6}$ by magnetization and heat +capacity measurements. Both monoclinic $\alpha$-CoV$_{2}$O$_{6}$ and triclinic +$\gamma$-CoV$_{2}$O$_{6}$ exhibit field-induced metamagnetic transition from +antiferromagnetic to ferromagnetic state via an intermediate ferrimagnetic +state with 1/3 magnetization plateau. Due to this field-induced metamagnetic +transition, these systems show large conventional as well as inverse +magnetocaloric effects. In $\alpha$-CoV$_{2}$O$_{6}$, we observe field-induced +complex magnetic phases and multiple magnetization plateaux at low temperature +when the field is applied along $c$ axis. Several critical temperatures and +fields have been identified from the temperature and field dependence of +magnetization, magnetic entropy change and heat capacity to construct the +$H$-$T$ phase diagram. As compared to $\alpha$-CoV$_{2}$O$_{6}$, +$\gamma$-CoV$_{2}$O$_{6}$ displays a relatively simple magnetic phase diagram. +Due to the large magnetic entropy change and adiabatic temperature change at +low or moderate applied magnetic field, $\gamma$-CoV$_{2}$O$_{6}$ may be +considered as a magnetic refrigerant in the low-temperature region.",1509.01690v2 +2015-09-09,"Large magneto-optical Kerr effect in noncollinear antiferromagnets Mn$_{3}X$ ($X$ = Rh, Ir, or Pt)","Magneto-optical Kerr effect, normally found in magnetic materials with +nonzero magnetization such as ferromagnets and ferrimagnets, has been known for +more than a century. Here, using first-principles density functional theory, we +demonstrate large magneto-optical Kerr effect in high temperature noncollinear +antiferromagnets Mn$_{3}X$ ($X$ = Rh, Ir, or Pt), in contrast to usual wisdom. +The calculated Kerr rotation angles are large, being comparable to that of +transition metal magnets such as bcc Fe. The large Kerr rotation angles and +ellipticities are found to originate from the lifting of the band +double-degeneracy due to the absence of spatial symmetry in the Mn$_{3}X$ +noncollinear antiferromagnets which together with the time-reversal symmetry +would preserve the Kramers theorem. Our results indicate that Mn$_{3}X$ would +provide a rare material platform for exploration of subtle magneto-optical +phenomena in noncollinear magnetic materials without net magnetization.",1509.02865v1 +2015-09-14,Competing Magnetic Orderings and Tunable Topological States in Two-Dimensional Hexagonal Organometallic Lattices,"The exploration of topological states is of significant fundamental and +practical importance in contemporary condensed matter physics, for which the +extension to two-dimensional (2D) organometallic systems is particularly +attractive. Using first-principles calculations, we show that a 2D hexagonal +triphenyl-lead lattice composed of only main group elements is susceptible to a +magnetic instability, characterized by a considerably more stable +antiferromagnetic (AFM) insulating state rather than the topologically +nontrivial quantum spin Hall state proposed recently. Even though this AFM +phase is topologically trivial, it possesses an intricate emergent degree of +freedom, defined by the product of spin and valley indices, leading to Berry +curvature-induced spin and valley currents under electron or hole doping. +Furthermore, such a trivial band insulator can be tuned into a topologically +nontrivial matter by the application of an out-of-plane electric field, which +destroys the AFM order, favoring instead ferrimagnetic spin ordering and a +quantum anomalous Hall state with a non-zero topological invariant. These +findings further enrich our understanding of 2D hexagonal organometallic +lattices for potential applications in spintronics and valleytronics.",1509.03921v1 +2015-10-13,Optomagnonic whispering gallery microresonators,"Magnons in ferrimagnetic insulators such as yttrium iron garnet (YIG) have +recently emerged as promising candidates for coherent information processing in +microwave circuits. Here we demonstrate optical whispering gallery modes of a +YIG sphere interrogated by a silicon nitride photonic waveguide, with quality +factors approaching $10^6$ in the telecom c-band after surface treatments. +Moreover, in contrast to conventional Faraday setup, this implementation allows +input photon polarized colinearly to the magnetization to be scattered to a +sideband mode of orthogonal polarization. This Brillouin scattering process is +enhanced through triply resonant magnon, pump and signal photon modes - all of +whispering gallery nature - within an ""optomagnonic cavity"". Our results show +the potential use of magnons for mediating microwave-to-optical carrier +conversion.",1510.03545v1 +2015-10-19,Ferroelectric polarization switching with a remarkably high activation-energy in orthorhombic GaFeO3 thin films,"Orthorhombic GaFeO3 (o-GFO) with the polar Pna21 space group is a prominent +ferrite by virtue of its piezoelectricity and ferrimagnetism, coupled with +magneto-electric effects. Herein, we unequivocally demonstrate a large +ferroelectric remanent polarization in undoped o-GFO thin films by adopting +either a hexagonal strontium titanate (STO) or a cubic yttrium-stabilized +zirconia (YSZ) substrate. The polarization-electric-field hysteresis curves of +the polar c-axis-grown o-GFO film on a SrTiO3/STO substrate show the net +switching polarization of ~35 {\mu}C/cm2 with an unusually high coercive field +of +-1400 kV/cm at room temperature. The PUND measurement also demonstrates the +switching polarization of ~26 {\mu}C/cm2. The activation energy for the +polarization switching, as obtained by density-functional theory calculations, +is remarkably high, 1.05 eV per formula unit. This high value accounts for the +observed stability of the polar Pna21 phase over a wide range of temperature up +to 1368 K.",1510.05359v1 +2015-11-11,Cavity magnomechanics,"A dielectric body couples with electromagnetic fields through radiation +pressure and electrostrictive forces, which mediate phonon-photon coupling in +cavity optomechanics. In a magnetic medium, according to Korteweg-Helmholtz +formula, magnetostrictive forces should arise and lead to phonon-magnon +interaction. Here we report such a coupled phonon-magnon system based on +ferrimagnetic spheres, which we term as cavity magnomechanics, by analogy to +cavity optomechanics. Coherent phonon-magnon interactions, including +electromagnetically induced transparency and absorption, are demonstrated. +Excitingly, due to strong hybridization of magnon and microwave photon modes +and their high tunability, our platform exhibits new features including +parametric amplification of magnons and phonons, triply resonant +photon-magnon-phonon coupling and phonon lasing. Our work demonstrates the +fundamental principle of cavity magnomechanics and its application as a new +information transduction platform based on coherent coupling between photons, +phonons and magnons.",1511.03680v2 +2016-01-03,Detection of DC currents and resistance measurements in longitudinal spin Seebeck effect experiments on Pt/YIG and Pt/NFO,"In this work we investigated thin films of the ferrimagnetic insulators YIG +and NFO capped with thin Pt layers in terms of the longitudinal spin Seebeck +effect (LSSE). The electric response detected in the Pt layer under an +out-of-plane temperature gradient can be interpreted as a pure spin current +converted into a charge current via the inverse spin Hall effect. Typically, +the transverse voltage is the quantity investigated in LSSE measurements (in +the range of \mu V). Here, we present the directly detected DC current (in the +range of nA) as an alternative quantity. Furthermore, we investigate the +resistance of the Pt layer in the LSSE configuration. We found an influence of +the test current on the resistance. The typical shape of the LSSE curve varies +for increasing test currents.",1601.00304v1 +2016-01-04,Unidirectional terahertz light absorption in the pyroelectric ferrimagnet CaBaCo4O7,"Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which +is a type-I multiferroic compound with the largest magnetic-order induced +ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed +two optical magnon branches: a solely electric dipole allowed one and a mixed +magnetoelectric resonance. The entangled magnetization and polarization +dynamics of the magnetoelectric resonance gives rise to unidirectional light +absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one +propagation direction but not for the opposite direction. Our systematic study +of the magnetic field and temperature dependence of magnon modes provides +information about the energies and symmetries of spin excitations, which is +required to develop a microscopic spin model of CaBaCo4O7.",1601.00444v1 +2016-01-20,Alternating-spin S=3/2 and sigma=1/2 Heisenberg chain with three-body exchange interactions,"The promotion of collinear classical spin configurations as well as the +enhanced tendency towards nearest-neighbor clustering of the quantum spins are +typical features of the frustrating isotropic three-body exchange interactions +in Heisenberg spin systems. Based on numerical density-matrix renormalization +group calculations, we demonstrate that these extra interactions in the +Heisenberg chain constructed from alternating S=3/2 and sigma=1/2 site spins +can generate numerous specific quantum spin states, including some +partially-polarized ferrimagnetic states as well as a doubly-degenerate +non-magnetic gapped phase. In the non-magnetic region of the phase diagram, the +model describes a crossover between the spin-1 and spin-2 Haldane-type states.",1601.05319v1 +2016-02-12,Transport and spin conversion of multi-carriers in semimetal bismuth,"In this paper, we report on the investigation of (1) the transport properties +of multi-carriers in semi-metal Bi and (2) the spin conversion physics in this +semimetal system in a ferrimagnetic insulator, yttrium-iron-garnet. Hall +measurements reveal that electrons and holes co-exist in the Bi, with electrons +being the dominant carrier. The results of a spin conversion experiment +corroborate the results of the Hall measurement; in addition, the inverse spin +Hall effect governs the spin conversion in the semimetal/insulator system. This +study provides further insights into spin conversion physics in semimetal +systems.",1602.03953v1 +2016-02-12,Thermal generation of spin current in a helimagnetic multiferroic hexaferrite,"We report the experimental observation of longitudinal spin Seebeck effect in +a multiferroic helimagnet Ba0.5Sr1.5Zn2Fe12O22. Temperature gradient applied +normal to Ba0.5Sr1.5Zn2Fe12O22/Pt interface generates inverse spin Hall voltage +of spin current origin in Pt, whose magnitude was found to be proportional to +bulk magnetization of Ba0.5Sr1.5Zn2Fe12O22 even through the successive magnetic +transitions among various helimagnetic and ferrimagnetic phases. This finding +demonstrates that the helimagnetic spin wave can be an effective carrier of +spin current. By controlling the population ratio of spin-helicity domains +characterized by clockwise/counter-clockwise manner of spin rotation with use +of poling electric field in the ferroelectric helimagnetic phase, we found that +spin-helicity domain distribution does not affect the magnitude of spin current +injected into Pt. The results suggest that the spin-wave spin current is rather +robust against the spin-helicity domain wall, unlike the case with the +conventional ferromagnetic domain wall.",1602.04011v1 +2016-02-17,Quantum Rotors on the AB$_2$ Chain with Competing Interactions,"We present the ground state phase diagram of $q = 1/2$ quantum-rotor chains +with competing interactions (frustration) calculated through cluster +variational mean field approaches. We consider two interaction patterns, named +F$_1$ and F$_2$ models, between the quantum-rotor momentum and position +operators, which follow exchange patterns of known one-dimensional spin-1/2 +systems with a ferrimagnetic state in their phase diagrams. The spin-1/2 F$_1$ +model is known as the diamond chain and is related to the azurite compound, +while the spin-1/2 F$_2$ model was recently shown to present a +frustration-induced condensation of magnons. We provide a detailed comparison +between the quantum-rotor phase diagrams, in single- and multi-site mean-field +approaches, and known results for the spin-1/2 models, including exact +diagonalization and density matrix renormalization group data for these +systems, as well as phase diagrams of the associated classical models.",1602.05383v1 +2016-02-25,Study of the ultrafast dynamics of ferromagnetic materials with a Quantum Monte Carlo atomistic model,"We study of the ultrafast dynamics of the atomic angular momentum in +ferrimagnets irradiated by laser pulses. My apply a quantum atomistic spin +approach based on the Monte Carlo technique. Our model describes the coherent +transfer of angular momentum between the spin and the orbital momentum as well +as the quenching of the orbital momentum induced by the lattice field. The +Elliott-Yafet collision mechanism is also included. We focus on elementary +mechanisms that lead to the dissipation of the total angular momentum in a rare +earth-transition metal (RE-TM) alloy in which the two sublattices have opposite +spin orientation. Our model shows that the observed ultrafast quenching of the +magnetization can be explained microscopically by the transfer of spin between +the sublattices and by the quenching of the localized orbital angular momentum.",1602.07950v1 +2016-03-10,Engineering charge ordering into multiferroicity,"Multiferroic materials have attracted great interests but are rare in nature. +In many transitional metal oxides, charge ordering and magnetic ordering +coexist, so that a method of engineering charge-ordered materials into +ferroelectric materials would lead to a large class of multiferroic materials. +We propose a strategy for designing new ferroelectric or even multiferroic +materials by inserting a spacing layer into each two layers of charge-ordered +materials and artificially making a superlattice. One example of the model +demonstrated here is the perovskite (LaFeO$_3$)$_2$/LaTiO$_3$ (111) +superlattice, in which the LaTiO$_3$ layer acts as the donor and the spacing +layer, and the LaFeO$_3$ layer is half doped and performs charge ordering. The +collaboration of the charge ordering and the spacing layer breaks the space +inversion symmetry, resulting in a large ferroelectric polarization. As the +charge ordering also leads to a ferrimagnetic structure, the +(LaFeO$_3$)$_2$/LaTiO$_3$ is multiferroic. It is expected that this work can +encourage the designing and experimentally implementation of a large class of +multiferroic structures with novel properties.",1603.03253v1 +2016-03-22,Contributions to the Monte Carlo study of the magnetic properties of nanomaterials such as graphyne and graphone,"Attracted by the importance of new materials in nanotechnology area, this +thesis develops this research field while deepening results. We started by +introducing the more sophisticated simulation and calculation methods, such as +the Monte Carlo method, the mean field theory, the effectif field theory and +the transfer matrix. Subsequently, we studied the magnetic and hysteretic +properties of the materials. Then we have detailed some of our contributions +related to the materials based on graphene and ferrimagnetic nanomaterials with +different morphologies. We discussed the effect of defects on the thermodynamic +properties of these novel materials. Particular attention was paid to the +physical parameters that influence the compensation behavior that is of crucial +importance for technological applications such as thermo-optical recording. +With all these elements, we are opened ourselves up to the latest developments +in physics of new materials. Finally, we finished with the conclusion and +perspectives.",1603.06766v1 +2016-03-28,"Ab initio Studies on Electronic and Magnetic Properties of X$_{2}$PtGa (X = Cr, Mn, Fe, Co) Heusler Alloys","Using first-principles calculations based on density functional theory, we +probe the electronic and magnetic properties of X$_{2}$PtGa (X being Cr, Mn, +Fe, Co) Heusler alloys. Our calculations predict that all these systems possess +inverse Heusler alloy structure in their respective ground states. Application +of tetragonal distortion leads to lowering of energy with respect to the cubic +phase for all the materials. The equilibrium volumes of both the phases are +nearly the same. These results of our calculations indicate that all these +materials are prone to undergo martensite transition, as has been recently +shown theoretically for Mn$_{2}$PtGa in the literature. Ground state with a +tetragonal symmetry of these materials is supported by the observation of soft +tetragonal shear constants in their cubic phase. By comparing the energies of +various types of magnetic configurations of these alloys we predict that +Cr$_{2}$PtGa and Mn$_{2}$PtGa possess ferrimagnetic configuration whereas +Fe$_{2}$PtGa and Co$_{2}$PtGa possess ferromagneic configuration in their +respective ground states.",1603.08350v2 +2016-03-31,Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states,"Spin-momentum locking in protected surface states enables efficient +electrical detection of magnon decay at a +magnetic-insulator/topological-insulator heterojunction. Here we demonstrate +this property using the spin Seebeck effect, i.e. measuring the transverse +thermoelectric response to a temperature gradient across a thin film of yttrium +iron garnet, an insulating ferrimagnet, and forming a heterojunction with +(BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population +established at the interface can decay in part by interactions of magnons with +electrons near the Fermi energy of the topological insulator. When this decay +channel is made active by tuning (BixSb1-x)2Te3 to a bulk insulator, a large +electromotive force emerges in the direction perpendicular to the in-plane +magnetization of yttrium iron garnet. The enhanced, tunable spin Seebeck effect +which occurs when the Fermi level lies in the bulk gap offers unique advantages +over the usual spin Seebeck effect in metals and therefore opens up exciting +possibilities in spintronics.",1603.09427v1 +2016-04-08,Gate-tunable spin-charge conversion and a role of spin-orbit interaction in graphene,"The small spin-orbit interaction of carbon atoms in graphene promises a long +spin diffusion length and potential to create a spin field-effect transistor. +However, for this reason, graphene was largely overlooked as a possible +spin-charge conversion material. We report electric gate tuning of the +spin-charge conversion voltage signal in a single-layer graphene. Using spin +pumping from yttrium iron garnet ferrimagnetic insulator and ionic liquid top +gate we determined that the inverse spin Hall effect is the dominant +spin-charge conversion mechanism in a single-layer graphene. From the gate +dependence of the electromotive force we showed dominance of the intrinsic over +Rashba spin-orbit interaction: a long-standing question in graphene research.",1604.02222v1 +2016-04-25,Magnon based logic in a multi-terminal YIG/Pt nanostructure,"Boolean logic is the foundation of modern digital information processing. +Recently, there has been a growing interest in phenomena based on pure spin +currents, which allow to move from charge to spin based logic gates. We study a +proof-of-principle logic device based on the ferrimagnetic insulator Yttrium +Iron Garnet (YIG), with Pt strips acting as injectors and detectors for +nonequilibrium magnons. We experimentally observe incoherent superposition of +magnons generated by different injectors. This allows to implement a fully +functional majority gate, enabling multiple logic operations (AND and OR) in +one and the same device. Clocking frequencies of the order of several GHz and +straightforward down-scaling make our device promising for applications.",1604.07262v1 +2016-05-21,Magnetic shielding and exotic spin-dependent interactions,"Experiments searching for exotic spin-dependent interactions typically employ +magnetic shielding between the source of the exotic field and the interrogated +spins. We explore the question of what effect magnetic shielding has on +detectable signals induced by exotic fields. Our general conclusion is that for +common experimental geometries and conditions, magnetic shields should not +significantly reduce sensitivity to exotic spin-dependent interactions, +especially when the technique of comagnetometry is used. However, exotic fields +that couple to electron spin can induce magnetic fields in the interior of +shields made of a soft ferro- or ferrimagnetic material. This induced magnetic +field must be taken into account in the interpretation of experiments searching +for new spin-dependent interactions and raises the possibility of using a flux +concentrator inside magnetic shields to amplify exotic spin-dependent signals.",1606.00696v1 +2016-06-06,Switching field distribution of exchange coupled ferri-/ferromagnetic composite bit patterned media,"We investigate the switching field distribution and the resulting bit error +rate of exchange coupled ferri-/ferromagnetic bilayer island arrays by +micromagnetic simulations. Using islands with varying microstructure and +anisotropic properties, the intrinsic switching field distribution is computed. +The dipolar contribution to the switching field distribution is obtained +separately by using a model of a triangular patterned island array resembling +$1.4\,\mathrm{Tb/in}^2$ bit patterned media. Both contributions are computed +for different thickness of the soft exchange coupled ferrimagnet and also for +ferromagnetic single phase FePt islands. A bit patterned media with a bilayer +structure of FeGd($5\,\mathrm{nm}$)/FePt($5\,\mathrm{nm}$) shows a bit error +rate of $10^{-4}$ with a write field of $1.16\,\mathrm{T}$.",1606.01874v2 +2016-06-23,Inversion of ferrimagnetic magnetization by ferroelectric switching via a novel magnetoelectric coupling,"Although several multiferroic materials/heterostructures have been +extensively studied, finding strong magnetoelectric couplings for the electric +field control of the magnetization remains challenging. Here, a novel +interfacial magnetoelectric coupling based on three components (ferroelectric +dipole, magnetic moment, and antiferromagnetic order) is analytically +formulated. As an extension of carrier-mediated magnetoelectricity, the new +coupling is shown to induce an electric-magnetic hysteresis loop. Realizations +employing BiFeO$_3$ bilayers grown along the [$111$] axis are proposed. Without +involving magnetic phase transitions, the magnetization orientation can be +switched by the carrier modulation driven by the field effect, as confirmed +using first-principles calculations.",1606.07203v1 +2016-07-08,Control of magnon-photon coupling strength in a planar resonator/YIG thin film configuration,"A systematic study of the coupling at room temperature between ferromagnetic +resonance (FMR) and a planar resonator is presented. The chosen magnetic +material is a ferrimagnetic insulator (Yttrium Iron Garnet: YIG) which is +positioned on top of a stop band (notch) filter based on a stub line +capacitively coupled to a 50 $\Omega$ microstrip line resonating at 4.731 GHz. +Control of the magnon-photon coupling strength is discussed in terms of the +microwave excitation configuration and the YIG thickness from 0.2 to 41 $\mu$m. +From the latter dependence, we extract a single spin-photon coupling of +g$_{0}$/2$\pi$=162$\pm$6 mHz and a maximum of an effective coupling of 290 MHz.",1607.02358v3 +2016-07-18,Monte Carlo simulations of an Ising bilayer with non-equivalent planes,"We study the thermodynamic and magnetic properties of an Ising bilayer +ferrimagnet. The system is composed of two interacting non-equivalent planes in +which the intralayer couplings are ferromagnetic while the interlayer +interactions are antiferromagnetic. Moreover, one of the planes is randomly +diluted. The study is carried out within a Monte Carlo approach employing the +multiple histogram reweighting method and finite-size scaling tools. The +occurrence of a compensation phenomenon is verified and the compensation +temperature, as well as the critical temperature for the model, are obtained as +functions of the Hamiltonian parameters. We present a detailed discussion of +the regions of the parameter space where the compensation effect is present or +absent. Our results are then compared to a mean-field-like approximation +applied to the same model by Balcerzak and Sza{\l}owski (2014). Although the +Monte Carlo and mean-field results agree qualitatively, our quantitative +results are significantly different.",1607.05221v2 +2016-09-15,Low-damping sub-10-nm thin films of lutetium iron garnet grown by molecular-beam epitaxy,"We analyze the structural and magnetic characteristics of (111)-oriented +lutetium iron garnet (Lu$_3$Fe$_5$O$_{12}$) films grown by molecular-beam +epitaxy, for films as thin as 2.8 nm. Thickness-dependent measurements of the +in- and out-of-plane ferromagnetic resonance allow us to quantify the effects +of two-magnon scattering, along with the surface anisotropy and the saturation +magnetization. We achieve effective damping coefficients of $11.1(9) \times +10^{-4}$ for 5.3 nm films and $32(3) \times 10^{-4}$ for 2.8 nm films, among +the lowest values reported to date for any insulating ferrimagnetic sample of +comparable thickness.",1609.04753v1 +2016-08-07,Ultrafast photo-magnetic recording in transparent medium,"Finding a conceptually new way to control the magnetic state of media with +the lowest possible production of heat and simultaneously at the fastest +possible time-scale is a new challenge in fundamental magnetism [1-4] as well +as an increasingly important issue in modern information technology [5]. Recent +results demonstrate that exclusively in metals it is possible to switch +magnetization between metastable states by femtosecond circularly polarized +laser pulses [6-8]. However, despite the record breaking speed of the +switching, the mechanisms in these materials are directly related to strong +optical absorption and laser-induced heating close to the Curie temperature +[9-12]. Here we report about ultrafast all-optical photo-magnetic recording in +transparent dielectrics. In ferrimagnetic garnet film a single linearly +polarized femtosecond laser pulse breaks the degeneracy between metastable +magnetic states and promotes switching of spins between them. Changing the +polarization of the laser pulse we deterministically steer the net +magnetization in the garnet, write ""0"" and ""1"" magnetic bits at will. This +mechanism operates at room temperature and allows ever fastest write-read +magnetic recording event (< 20 ps) accompanied by unprecedentedly low heat load +(< 6 J/cm3).",1609.05223v1 +2016-09-20,Anomalous Hall hysteresis in Tm3Fe5O12/Pt with strain-induced perpendicular magnetic anisotropy,"We demonstrate robust interface strain-induced perpendicular magnetic +anisotropy in atomically flat ferrimagnetic insulator Tm3Fe5O12 films grown +with pulsed laser deposition on substituted-Gd3Ga5O12 substrate which maximizes +the tensile strain at the interface. In bilayers consisting of Pt and TIG, we +observe large squared Hall hysteresis loops over a wide range of thicknesses of +Pt at room temperature. When a thin Cu layer is inserted between Pt and TIG, +the Hall hysteresis magnitude decays but stays finite as the thickness of Cu +increases up to 5 nm. However, if the Cu layer is placed atop Pt instead, the +Hall hysteresis magnitude is consistently larger than when the Cu layer with +the same thickness is inserted in between for all Cu thicknesses. These results +suggest that both the proximity-induced ferromagnetism and spin current +contribute to the anomalous Hall effect.",1609.06367v1 +2016-09-23,Electromagnon resonance in a collinear spin state of a polar antiferromagnet Fe2Mo3O8,"Magnetic excitations are investigated for a hexagonal polar magnet Fe2Mo3O8 +by terahertz spectroscopy. We observed magnon modes including an electric-field +active magnon, electromagnon, in the collinear antiferromagnetic phase with +spins parallel to the c axis. We unravel the nature of these excitations by +investigating the correlation between the evolution of the mode profile and the +magnetic transition from antiferromagnetic to ferrimagnetic order induced by +magnetic field or Zn-doping. We propose that the observed electromagnon mode +involves the collective precession of the spins with oscillating in-plane +electric polarization through the mechanism of the linear magnetoelectric +effect.",1609.07230v2 +2016-09-25,Quantum Spin Hall Effect in Twisted Bilayer Graphene,"Motivated by a recent experiment (Sanchez-Yamagishi et.al, arXiv:1602.06815) +reporting evidence of helical spin-polarized edge states in layer-biased +twisted bilayer graphene under a magnetic flux, we study the possibility of +stabilising a Quantum Spin Hall (QSH) phase in such a system, without Zeeman or +spin-orbit couplings, and with a QSH gap induced instead by electronic +interactions. We analyse how magnetic flux, electric field, interlayer rotation +angle, and interactions (treated at a mean field level) combine to produce a +pseudo-QSH with broken time-reversal symmetry, and spin-polarized helical edge +states. The effect is a consequence of a robust interaction-induced +ferrimagnetic ordering of the Quantum Hall ground state under an interlayer +bias, provided the two rotated layers are effectively decoupled at low +energies. We discuss in detail the electronic structure, and the constraints on +system parameters, such as the angle, interactions and magnetic flux, required +to reach the pseudo-QSH phase. We find, in particular, that purely local +electronic interactions are not sufficient to account for the experimental +observations, which demand at least nearest-neighbour interactions to be +included.",1609.07734v1 +2016-09-27,Steady State and Dynamics of Joule Heating in Magnetic Tunnel Junctions Observed via the Temperature Dependence of RKKY Coupling,"Understanding quantitatively the heating dynamics in magnetic tunnel +junctions (MTJ) submitted to current pulses is very important in the context of +spin-transfer-torque magnetic random access memory development. Here we provide +a method to probe the heating of MTJ using the RKKY coupling of a synthetic +ferrimagnetic storage layer as a thermal sensor. The temperature increase +versus applied bias voltage is measured thanks to the decrease of the spin-flop +field with temperature. This method allows distinguishing spin transfer torque +(STT) effects from the influence of temperature on the switching field. The +heating dynamics is then studied in real-time by probing the conductance +variation due to spin-flop rotation during heating. This approach provides a +new method for measuring fast heating in spintronic devices, particularly +magnetic random access memory (MRAM) using thermally assisted or spin transfer +torque writing.",1609.08385v1 +2016-09-29,"On the rich magnetic phase diagram of (Ni, Co)-Mn-Sn Heusler alloys","We put a spotlight on the exceptional magnetic properties of the metamagnetic +Heusler alloy (Ni,Co)-Mn-Sn by means of first principles simulations. + In the energy landscape we find a multitude of local minima, which belong to +different ferrimagnetic states and are close in total magnetization and energy. +All these magnetic states correspond to the local high spin state of the Mn +atoms with different spin alignments and are related to the magnetic properties +of Mn. Compared to pure Mn, the magneto-volume coupling is reduced by Ni, Co, +and Sn atoms in the lattice and no local low-spin Mn states appear. For the +cubic phase we find a ferromagnetic ground state whereas the global energy +minimum is a tetragonal state with complicated spin structure and vanishing +magnetization which so far has been overlooked in simulations.",1609.09399v1 +2016-09-30,The Tricritical Point of the f-electron Antiferromagnet USb2 Driven by High Magnetic Fields,"In pulsed magnetic fields up to 65T and at temperatures below the N\'eel +transition, our magnetization and magnetostriction measurements reveal a +field-induced metamagnetic-like transition that is suggestive of an +antiferromagnetic to polarized paramagnetic or ferrimagnetic ordering. Our data +also suggests a change in the nature of this metamagnetic-like transition from +second- to first-order-like near a tricritical point at T_{tc} ~145K and +H_{c}~52T. At high fields for H>H_{c} we found a decreased magnetic moment +roughly half of the moment reported in low field measurements. We propose that +\mathit{f-p} hybridization effects and magnetoelastic interactions drive the +decreased moment, lack of saturation at high fields, and the decreased phase +boundary.",1609.09845v1 +2016-10-11,Magnetic gap opening in rhombohedral-stacked multilayer graphene from first principles,"We investigate the occurrence of magnetic and charge density wave +instabilities in rhombohedral-stacked multilayer (three to eight layers) +graphene by first principles calculations including exact exchange. Neglecting +spin-polarization, an extremely flat surface band centered at the special point +${\bf K}$ of the Brillouin zone occurs at the Fermi level. Spin polarization +opens a gap in the surface state by stabilizing an antiferromagnetic state. The +top and the bottom surface layers are weakly ferrimagnetic in-plane (net +magnetization smaller than $10^{-3}\mu_B$), and are antiferromagnetic coupled +to each other. This coupling is propagated by the out-of-plane +antiferromagnetic coupling between the nearest neighbors. The gap is very small +in a spin-polarized generalized gradient approximation, while it is +proportional to the amount of exact exchange in hybrid functionals. For +trilayer rhombohedral graphene it is $38.6$ meV in PBE0, in agreement with the +$42$ meV gap found in experiments. We study the temperature and doping +dependence of the magnetic gap. At electron doping of $n \sim 7 \times 10^{11}$ +cm$^{-2}$ the gap closes. Charge density wave instabilities with +$\sqrt{3}\times\sqrt{3}$ periodicity do not occur.",1610.03445v2 +2016-10-18,Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy,"Recently, theorists have predicted many materials with a low magnetic moment +and large spin-polarization for spintronic applications. These compounds are +predicted to form in the inverse Heusler structure, however, many of these +compounds have been found to phase segregate. In this study, ordered Cr2CoGa +thin films were synthesized without phase segregation using molecular beam +epitaxy. The present as-grown films exhibit a low magnetic moment from +antiferromagnetically coupled Cr and Co atoms as measured with SQUID +magnetometry and soft X-ray magnetic circular dichroism. Electrical +measurements demonstrated a thermally-activated semiconductor-like resistivity +with an activation energy of 87 meV. These results confirm spin gapless +semiconducting behavior, which makes these thin films well positioned for +future devices.",1610.05808v1 +2016-10-29,Tailoring magnetic insulator proximity effects in graphene: First-principles calculations,"We report a systematic first-principles investigation of the influence of +different magnetic insulators on the magnetic proximity effect induced in +graphene. Four different magnetic insulators are considered: two ferromagnetic +europium chalcogenides namely EuO and EuS and two ferrimagnetic insulators +yttrium iron garnet (YIG) and cobalt ferrite (CFO). The obtained +exchange-splitting varies from tens to hundreds of meV. We also find an +electron doping induced by YIG and europium chalcogenides substrates, that +shift the Fermi level up to 0.78 eV and 1.3 eV respectively, whereas hole +doping up to 0.5 eV is generated by CFO. Furthermore, we study the variation of +the extracted exchange and tight binding parameters as a function of the EuO +and EuS thicknesses. We show that those parameters are robust to thickness +variation such that a single monolayer of magnetic insulator can induce a large +magnetic proximity effect on graphene. Those findings pave the way towards +possible engineering of graphene spin-gating by proximity effect especially in +view of recent experiments advancement.",1610.09554v1 +2017-02-03,Quantitative investigation of the inverse Rashba-Edelstein effect in Bi/Ag and Ag/Bi on YIG,"The inverse Rashba-Edelstein effect (IREE) is a spin conversion mechanism +that recently attracts attention in spintronics and condensed matter physics. +In this letter, we report an investigation of the IREE in Bi/Ag by using +ferrimagnetic insulator yttrium iron garnet (YIG). We prepared two types of +samples with opposite directions of the Rashba field by changing a stacking +order of Bi and Ag. An electric current generated by the IREE was observed from +both stacks, and an efficiency of spin conversion -characterized by the IREE +length- was estimated by taking into account a number of contributions left out +in previous studies. This study provides a further insight into the IREE spin +conversion mechanism: important step towards achieving efficient spin-charge +conversion devices.",1702.00890v1 +2017-02-13,Magnetic properties and spin structure of MnO single crystal and powder,"Zero field cooled (ZFC)/Field Cooled (FC) magnetization curves of a bulk MnO +single crystal show a peculiar peak at low temperatures (~40K) similar to the +low temperature peak observed in MnO nanoparticles. In order to investigate the +origin of this peak, the spin structure of a MnO single crystal has been +studied and compared with a single phase powder sample using magnetometry and +polarized neutron scattering. Both magnetometry and polarized neutron +diffraction results confirm the antiferromagnetic (AF) phase transition at the +N\'eel temperature T_N of 118K, in both powder and single crystal form. +However, the low temperature peak in the ZFC/FC magnetization curves is not +observed in single phase MnO powder. To better understand the observed +behavior, ac susceptibility measurements have been employed. We conclude that +the clear peak in the magnetic signal from the single crystal originates from a +small amount of ferrimagnetic (FiM) Mn2O3 or Mn3O4 impurities, which is grown +at the interfaces between MnO crystal twins.",1702.03879v1 +2017-02-13,Kagome-like chains with anisotropic ferromagnetic and antiferromagnetic interactions,"We consider a spin-$\frac{1}{2}$ kagome-like chain with competing ferro- and +antiferromagnetic anisotropic exchange interactions. The ground state phase +diagram of this model consists of the ferromagnetic and ferrimagnetic phases. +We study the ground state and the low-temperature properties on the phase +boundary between these phases. The ground state on this phase boundary is +macroscopically degenerate and consists of localized magnon states. We +calculate the ground state degeneracy and corresponding residual entropy. The +spontaneous magnetization has a jump on the phase boundary confirming the +first-order type of the phase transition. In the limit of a strong anisotropy +the spectrum of the low-energy excitations has multi-scale structure governing +the peculiar features of the specific heat behavior.",1702.03915v1 +2017-02-20,Effect of annealing on the magnetic properties of zinc ferrite thin films,"We report on the magnetic properties of zinc ferrite thin film deposited on +SrTiO$_3$ single crystal using pulsed laser deposition. X-ray diffraction +result indicates the highly oriented single phase growth of the film along with +the presence of the strain. In comparison to the bulk antiferromagnetic order, +the as-deposited film has been found to exhibit ferrimagnetic ordering with a +coercive field of 1140~Oe at 5~K. A broad maximum, at $\approx$105~K, observed +in zero-field cooled magnetization curve indicates the wide grain size +distribution for the as-deposited film. Reduction in magnetization and blocking +temperature has been observed after annealing in both argon as well as oxygen +atmospheres, where the variation was found to be dependent on the annealing +temperature.",1702.06033v1 +2017-02-20,Parametric pumping of spin waves by acoustic waves,"The linear and nonlinear interactions between spin waves (magnons) and +acoustic waves (phonons) in magnetostrictive materials provide an exciting +opportunity for realizing novel microwave signal processing devices and +spintronic circuits. Here we demonstrate the parametric pumping of spin waves +by acoustic waves, the possibility of which has long been theoretically +anticipated but never experimentally realized. Spin waves propagating in a thin +film of yttrium iron garnet (YIG), a magnetostrictive ferrimagnet with low spin +and acoustic wave damping, are pumped using an acoustic resonator driven at +frequencies near twice the spin wave frequency. The observation of a +counter-propagating idler wave and a distinct pump threshold that increases +quadratically with frequency non-degeneracy are evidence of a nonlinear +parametric pumping process consistent with classical theory. This demonstration +of acoustic parametric pumping lays the groundwork for developing new +spintronic and microwave signal processing devices based on amplification and +manipulation of spin waves by efficient, spatially localized acoustic +transducers.",1702.06038v1 +2017-02-21,Topological staggered field-electric effect with bipartite magnets,"We study the interface physics of bipartite magnetic materials deposited on a +topological insulator. This comprises antiferromagnets as well as ferrimagnets +and ferromagnets with multiple magnetic moments per unit cell. If an energy gap +is induced in the Dirac states on the topological surface, a topological +magnetoelectric effect has been predicted. Here, we show that this effect can +act in opposite directions on the two components of the magnet in certain +parameter regions. Consequently, an electric field will mainly generate a +staggered field rather than a net magnetization in the plane. This is relevant +for the current attempts to detect the magnetoelectric effect experimentally, +as well as for possible applications. We take a field-theoretic approach that +includes the quantum fluctuations of both the Dirac fermions on the topological +surface as well as the fermions in the surface layer of the magnet in an +analytically solvable model. The effective Lagrangian and the Landau-Lifshitz +equation describing the interfacial magnetization dynamics are derived.",1702.06483v2 +2017-02-26,Magnon-photon coupling in antiferromagnets,"Magnon-photon coupling in antiferromagnets has many attractive features that +do not exist in ferro- or ferrimagnets. We show quantum-mechanically that, in +the absence of an external field, one of the two degenerated spin wave bands +couples with photons while the other does not. The photon mode anticrosses with +the coupled spin waves when their frequencies are close to each other. Similar +to its ferromagnetic counterpart, the magnon-photon coupling strength is +proportional to the square root of number of spins $\sqrt{N}$ in +antiferromagnets. An external field removes the spin wave degeneracy and both +spin wave bands couple to the photons, resulting in two anticrossings between +the magnons and photons. Two transmission peaks were observed near the +anticrossing frequency. The maximum damping that allows clear discrimination of +the two transmission peaks is proportional to $\sqrt{N}$ and it's well below +the damping of antiferromagnetic insulators. Therefore the strong magnon-photon +coupling can be realized in antiferromagnets and the coherent information +transfer between the photons and magnons is possible.",1702.07977v1 +2017-03-01,Thickness Dependence of Spin-Orbit Torques in Ferrimagnetic GdFeCo Alloys,"So far, studies of spin-orbit torques (SOT) in ferromagnets with +perpendicular magnetic anisotropy (PMA) have been restricted to ultra thin +samples, while a systematic study of its thickness dependence is still lacking +in literature. In this article we discuss the thickness dependence of SOT in +GdFeCo samples with bulk PMA. We show that the effective SOT fields are +decreasing inversely as a function of thickness while the spin-Hall angle stays +constant, as expected from angular momentum conservation. Further we show that +even 30nm thick GdFeCo samples can be switched with SOT. This has important +technological implications as the switching efficiency does not depend on the +thickness. Finally, we investigate the composition dependence of SOT in 30nm +thick GdFeCo samples and find that the spin torque effective field diverges at +the magnetization compensation point.",1703.00146v1 +2017-03-08,Spin dynamics of antiferromagnets in the presence of a homogeneous magnetization,"We use general hydrodynamic equations to determine the long-wavelength spin +excitations in isotropic antiferromagnets in the presence of a homogeneous +magnetization. The latter may be induced, such as in antiferromagnets in an +external magnetic field, or spontaneous, such as in ferrimagnetic or canted +phases that are characterized by the coexistence of antiferromagnetic and +ferromagnetic order. Depending on the physical situation, we find propagating +spin waves that are gapped in some cases and gapless in others, diffusive +modes, or relaxational modes. The excitation spectra turn out to be +qualitatively different depending on whether or not the homogeneous +magnetization is a conserved quantity. The results lay the foundation for a +description of a variety of quantum phase transitions, including the transition +from a ferromagnetic metal to an antiferromagnetic one, and the spin-flop +transitions that are observed in some antiferromagnets. They also are crucial +for incorporating weak-localization and Altshuler-Aronov effects into the +descriptions of quantum phases in both clean and disordered magnetic metals.",1703.03009v1 +2017-03-11,Generalized Boundary Conditions for Spin Transfer,"We develop a comprehensive description of static and dynamic spin-transfer +torque at interfaces between a normal metal and a magnetic material. Specific +examples of the latter include ferromagnets, collinear and noncollinear +antiferromagnets, general ferrimagnets, and spin glasses. We study the limit of +the exchange-dominated interactions, so that the full system is isotropic in +spin space, apart from a possible symmetry-breaking order. A general such +interface yields three coefficients (corresponding to three independent +generators of rotations) generalizing the well-established notion of the +spin-mixing conductance, which pertains to the collinear case. We develop a +nonequilibrium thermodynamic description of the emerging interfacial spin +transfer and its effect on the collective spin dynamics, while circumventing +the usual discussion of spin currents and net spin dynamics. Instead, our focus +is on the dissipation and work effectuated by the interface. Microscopic +scattering-matrix based expressions are derived for the generalized +spin-transfer coefficients.",1703.04020v2 +2017-03-31,(LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ as a model system for unconventional charge transfer and polar metallicity,"At interfaces between oxide materials, lattice and electronic reconstructions +always play important roles in exotic phenomena. In this study, the density +functional theory and maximally localized Wannier functions are employed to +investigate the (LaTiO$_3$)$_n$/(LaVO$_3$)$_n$ magnetic superlattices. The +electron transfer from Ti$^{3+}$ to V$^{3+}$ is predicted, which violates the +intuitive band alignment based on the electronic structures of LaTiO$_3$ and +LaVO$_3$. Such unconventional charge transfer quenches the magnetism of +LaTiO$_3$ layer mostly and leads to metal-insulator transition in the $n=1$ +superlattice when the stacking orientation is altered. In addition, the +compatibility among the polar structure, ferrimagnetism, and metallicity is +predicted in the $n=2$ superlattice.",1703.10748v1 +2017-03-31,Spin Seebeck effect in Y-type hexagonal ferrite thin films,"Spin Seebeck effect (SSE) has been investigated in thin films of two +Y-hexagonal ferrites Ba$_2$Zn$_{2}$Fe$_{12}$O$_{22}$ (Zn2Y) and +Ba$_2$Co$_{2}$Fe$_{12}$O$_{22}$ (Co2Y) deposited by a spin-coating method on +SrTiO$_3$(111) substrate. The selected hexagonal ferrites are both +ferrimagnetic with similar magnetic moments at room temperature and both +exhibit easy magnetization plane normal to $c$-axis. Despite that, SSE signal +was only observed for Zn2Y, whereas no significant SSE signal was detected for +Co2Y. We tentatively explain this different behavior by a presence of two +different magnetic ions in Co2Y, whose random distribution over octahedral +sites interferes the long range ordering and enhances the Gilbert damping +constant. The temperature dependence of SSE for Zn2Y was measured and analyzed +with regard to the heat flux and temperature gradient relevant to the SSE +signal.",1703.10903v1 +2017-08-02,Realistic finite temperature simulations of magnetic systems using quantum statistics,"We have performed realistic atomistic simulations at finite temperatures +using Monte Carlo and atomistic spin dynamics simulations incorporating quantum +(Bose-Einstein) statistics. The description is much improved at low +temperatures compared to classical (Boltzmann) statistics normally used in +these kind of simulations, while at higher temperatures the classical +statistics are recovered. This corrected low-temperature description is +reflected in both magnetization and the magnetic specific heat, the latter +allowing for improved modeling of the magnetic contribution to free energies. A +central property in the method is the magnon density of states at finite +temperatures and we have compared several different implementations for +obtaining it. The method has no restrictions regarding chemical and magnetic +order of the considered materials. This is demonstrated by applying the method +to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co +random alloys and the ferrimagnetic system GdFe$_3$ .",1708.00709v1 +2017-08-08,Observation of Giant Exchange Bias and Topological Hall Effect in Manganese Nitride Films,"Magnetic and magneto-transport properties of manganese nitride films grown by +molecular beam epitaxy have been investigated. Due to the mixed ferrimagnetic +(FI) phase (${\epsilon}$-phase with TFI ~ 738 K) and the antiferromagnetic +phase (${\zeta}$-phase with TN ~ 273 K), we observe magnetization hysteresis +loops with non-zero exchange bias below TN, reaching ~ 0.22 T at 5 K. This +indicates that noncollinear spins exist at the interfaces between two phases, +creating a competition between interfacial Dzyaloshinskii-Moriya (DM) and +exchange interactions. Strikingly, in addition to the normal Hall effect by +Lorentz force and anomalous Hall effect by magnetization, we observe new +contribution namely topological Hall effect below 75 K. This verifies the +existence of topological spin texture, which is the consequence of competing +interactions controlled by both applied field and temperature. Our work +demonstrates that spintronic devices may be fabricated exploiting rich magnetic +properties of different phases.",1708.02540v1 +2017-08-14,Terahertz frequency magnetoelectric effect in Ni doped CaBaCo$_4$O$_7$,"We present a study of terahertz frequency magnetoelectric effect in +ferrimagnetic pyroelectric CaBaCo$_4$O$_7$ and its Ni-doped variants. The +terahertz absorption spectrum of these materials consists of spin excitations +and low-frequency infrared-active phonons. We studied the +magnetic-field-induced changes in the terahertz refractive index and absorption +in magnetic fields up to 17 T. We find that the magnetic field modulates the +strength of infrared-active optical phonons near 1.2 and 1.6 THz. We use the +Lorentz model of the dielectric function to analyze the measured magnetic-field +dependence of the refractive index and absorption. We propose that most of the +magnetoelectric effect is contributed by the optical phonons near 1.6 THz and +higher-frequency resonances. Our experimental results can be used to construct +and validate more detailed theoretical descriptions of magnetoelectricity in +CaBaCo$_{4-x}$Ni$_x$O$_7$.",1708.04345v1 +2017-08-29,"Structural, magnetic, and electronic properties of GdTiO3 Mott insulator thin films grown by pulsed laser deposition","We report on the optimization process to synthesize epitaxial thin films of +GdTiO3 on SrLaGaO4 substrates by pulsed laser deposition. Optimized films are +free of impurity phases and are fully strained. They possess a magnetic Curie +temperature TC = 31.8 K with a saturation magnetization of 4.2 muB per formula +unit at 10 K. Transport measurements reveal an insulating response, as +expected. Optical spectroscopy indicates a band gap of 0.7 eV, comparable to +the bulk value. Our work adds ferrimagnetic orthotitanates to the palette of +perovskite materials for the design of emergent strongly correlated states at +oxide interfaces using a versatile growth technique such as pulsed laser +deposition.",1708.08785v1 +2017-08-29,Element-resolved ultrafast demagnetization rates in ferrimagnetic CoDy,"Femtosecond laser induced ultrafast magnetization dynamics have been studied +in multisublattice CoxDy1-x alloys. By performing element and time-resolved +X-ray spectroscopy, we distinguish the ultrafast quenching of Co3d and Dy4f +magnetic order when the initial temperatures are below (T=150K) or above +(T=270K) the temperature of magnetic compensation (Tcomp). In accordance with +former element-resolved investigations and theoretical calculations, we observe +different dynamics for Co3d and Dy4f spins. In addition we observe that, for a +given laser fluence, the demagnetization amplitudes and demagnetization times +are not affected by the existence of a temperature of magnetic compensation. +However, our experiment reveals a twofold increase of the ultrafast +demagnetization rates for the Dy sublattice at low temperature. In parallel, we +measure a constant demagnetization rate of the Co3d sublattice above and below +Tcomp. This intriguing difference between the Dy4f and Co3d sublattices calls +for further theoretical and experimental investigations.",1708.08918v2 +2018-11-12,Current direction anisotropy of the spin Hall magnetoresistance in nickel ferrite thin films with bulk-like magnetic properties,"We utilize spin Hall magnetoresistance (SMR) measurements to experimentally +investigate the pure spin current transport and magnetic properties of nickel +ferrite (NiFe2O4,NFO)/normal metal (NM) thin film heterostructures. We use +(001)-oriented NFO thin films grown on lattice-matched magnesium gallate +substrates by pulsed laser deposition, which significantly improves the +magnetic and structural properties of the ferrimagnetic insulator. The NM in +our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude +for charge currents applied in the [100]- and [110]-direction of NFO yields a +change of 50% for Pt at room temperature. We also investigated the temperature +dependence of this current direction anisotropy and find that it is +qualitatively different for the conductivity and the SMR magnitude. From our +results we conclude that the observed current direction anisotropy may +originate from an anisotropy of the spin mixing conductance or of the spin Hall +effect in these Pt and Ta layers, and/or additional spin-galvanic contributions +from the NFO/NM interface.",1811.04696v1 +2018-11-14,Anomalous Hall-like transverse magnetoresistance in Au thin films on Y$_3$Fe$_5$O$_{12}$,"Anomalous Hall-like signals in platinum in contact with magnetic insulators +are common observations that could be explained by either proximity +magnetization or spin Hall magnetoresistance. In this work, longitudinal and +transverse magnetoresistances are measured in a pure gold thin film on the +ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG). We show +that both the longitudinal and transverse magnetoresistances have +quantitatively consistent scaling in YIG/Au and in a YIG/Pt reference system +when applying the Spin Hall magnetoresistance framework. No contribution of an +anomalous Hall effect due to the magnetic proximity effect is evident.",1811.05848v1 +2018-11-30,Magnetic and mechanical effects of Mn substitutions in AlFe2B2,"The mechanical and magnetic properties of the newly discovered MAB-phase +class of materials based upon AlFe2B2 were investigated. The samples were +synthesised from stoichiometric amounts of all constituent elements. X-ray +diffraction shows that the main phase is orthorhombic with an elongated b-axis, +similar to AlFe2B2. The low hardness and visual inspection of the samples after +deformation indicate that these compounds are deformed via a delamination +process. When substituting iron in AlFe2B2 with manganese, the magnetism in the +system goes from being ferro- to antiferromagnetic via a disordered +ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory +calculations indicate a weakening of the magnetic interactions among the +transitions metal ions as iron is substituted by manganese in AlFe2B2. The +Mn-Mn exchange interactions in AlMn2 B2 are found to be very small.",1811.12720v1 +2019-05-09,A Novel ground state in a new dimer iridate Ba13Ir6O30 with Ir6+(5d3) Ions,"We have synthesized and studied a new iridate, Ba13Ir6O30, with unusual Ir +oxidation states: 2/3 Ir6+(5d3) ions and 1/3 Ir5+(5d4) ions. Its crystal +structure features dimers of face-sharing IrO6 octahedra, and IrO6 monomers, +that are linked via long, zigzag Ir-O-Ba-O-Ir pathways. Nevertheless, +Ba13Ir6O30 exhibits two transitions at TN1 = 4.7 K and TN2 = 1.6 K. This +magnetic order is accompanied by a huge Sommerfeld coefficient 200 mJ/mole K +below TN2, signaling a coexisting frustrated/disordered state persisting down +to at least 0.05 K. This iridate hosts unusually large Jeff=3/2 degrees of +freedom, which is enabled by strong spin-orbit interactions (SOI) in the +monomers with Ir6+ ions and a joint effect of molecular orbitals and SOI in the +dimers occupied by Ir5+ and Ir6+ ions. Features displayed by the magnetization +and heat capacity suggest that the combination of covalency, SOI and large +effective spins leads to highly frustrated ferrimagnetic ordering, possibly +into a skyrmion crystal, a novelty of this new high-spin iridate.",1905.03891v1 +2019-05-18,"The New Nitrides: Layered, Ferroelectric, Magnetic, Metallic and Superconducting Nitrides to Boost the GaN Photonics and Electronics Eco-System","The nitride semiconductor materials GaN, AlN, and InN, and their alloys and +heterostructures have been investigated extensively in the last 3 decades, +leading to several technologically successful photonic and electronic devices. +Just over the past few years, a number of new nitride materials have emerged +with exciting photonic, electronic, and magnetic properties. Some examples are +2D and layered hBN and the III-V diamond analog cBN, the transition metal +nitrides ScN, YN, and their alloys (e.g. ferroelectric ScAlN), piezomagnetic +GaMnN, ferrimagnetic Mn4N, and epitaxial superconductor/semiconductor NbN/GaN +heterojunctions. This article reviews the fascinating and emerging physics and +science of these new nitride materials. It also discusses their potential +applications in future generations of devices that take advantage of the +photonic and electronic devices eco-system based on transistors, light-emitting +diodes, and lasers that have already been created by the nitride +semiconductors.",1905.07627v1 +2019-05-23,"Thermodynamic and Thermoelectric Properties of CoFeYGe (Y= Ti, Cr) Quaternary Heusler Alloys: First Principle Calculations","Utilizing a material in thermoelectric applications requires a mechanical, +thermal, and lattice stability as well a high figure of merit (ZT). In this +work, we present the structural, electronic, magnetic, mechanical, +thermodynamic, dynamic, and thermoelectric properties of CoFeYGe (Y = Ti, Cr) +quaternary Heusler compounds using the density functional theory (DFT). The +calculated mechanical properties and phonon dispersions reveal that the +structures of these compounds are stable. Both CoFeCrGe and CoFeTiGe compounds +show a ferromagnetic and ferrimagnetic half-metallic behavior with band gaps of +0.41 and 0.38 eV, respectively. The lattice thermal conductivity (\k{appa}L) +exhibits low values that reach 3.01 W/(m.K) (3.47 W/(m.K)) for CoFeCrGe +(CoFeTiGe) at 1100 K. The optical phonon modes have a large contribution of +60.2% (70.9 %) to \k{appa}L value for CoFeCrGe (CoFeTiGe). High ZT values of +0.71 and 0.65 were obtained for CoFeCrGe and CoFeTiGe, respectively. Based on +our calculations, CoFeCrGe and CoFeTiGe combine both good spintronic and +thermoelectric behaviors that may be used in spin injection applications.",1905.09854v1 +2020-07-07,Unconventional superconductivity in a strongly correlated band-insulator without doping,"We present a novel route for attaining unconventional superconductivity (SC) +in a strongly correlated system without doping. In a simple model of a +correlated band insulator (BI) at half-filling we demonstrate, based on a +generalization of the projected wavefunctions method, that SC emerges when e-e +interactions and the bare band-gap are both much larger than the kinetic +energy, provided the system has sufficient frustration against the magnetic +order. As the interactions are tuned, SC appears sandwiched between the +correlated BI followed by a paramagnetic metal on one side, and a ferrimagnetic +metal, antiferromagnetic (AF) half-metal, and AF Mott insulator phases on the +other side.",2007.03739v2 +2020-07-13,Intra-chain collinear magnetism and inter-chain magnetic phases in Cr3As3-K-based materials,"We perform a comparative study of the KCr3As3 and the K2Cr3As3 quasi 1D +compounds, and show that the strong interplay between the lattice and the spin +degrees of freedom promotes a new collinear ferrimagnetic ground state within +the chains in presence of intrachain antiferromagnetic couplings. We propose +that the interchain antiferromagnetic coupling in KCr3As3 plays a crucial role +for the experimentally observed spin-glass phase with low critical temperature. +In the same region of the parameter space, we predict K2Cr3As3 to be +non-magnetic but on the verge of the magnetism, sustaining interchain +ferromagnetic spin fluctuations while the intrachain spin fluctuations are +antiferromagnetic.",2007.06337v4 +2013-08-06,Two magnon bound state causes ultrafast thermally induced magnetisation switching,"There has been much interest recently in the discovery of thermally induced +magnetisation switching, where a ferrimagnetic system can be switched +deterministically without and applied magnetic field. Experimental results +suggest that the reversal occurs due to intrinsic material properties, but so +far the microscopic mechanism responsible for reversal has not been identified. +Using computational and analytic methods we show that the switching is caused +by the excitation of two magnon bound states, the properties of which are +dependent on material factors. This discovery allows us to accurately predict +the switching behaviour and the identification of this mechanism will allow new +classes of materials to be identified or designed to use this switching in +memory devices in the THz regime.",1308.1314v1 +2013-08-13,Interface states in CoFe2O4 spin-filter tunnel junctions,"Spin-filter tunneling is a promising way to generate highly spin-polarized +current, a key component for spintronics applications. In this work we explore +the tunneling conductance across the spin-filter material CoFe2O4 interfaced +with Au electrodes, a geometry which provides nearly perfect lattice matching +at the CoFe2O4/Au(001) interface. Using density functional theory calculations +we demonstrate that interface states play a decisive role in controlling the +transport spin polarization in this tunnel junction. For a realistic CoFe2O4 +barrier thickness, we predict a tunneling spin polarization of about -60%. We +show that this value is lower than what is expected based solely on +considerations of the spin-polarized band structure of CoFe2O4, and therefore +that these interface states can play a detrimental role. We argue this is a +rather general feature of ferrimagnetic ferrites and could make an important +impact on spin-filter tunneling applications.",1308.3461v1 +2014-03-04,Off-Resonant Manipulation of Spins in Diamond via Precessing Magnetization of a Proximal Ferromagnet,"We report the manipulation of nitrogen vacancy (NV) spins in diamond when +nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession. +The change in NV spin polarization, as measured by changes in +photoluminescence, is comparable in magnitude to that from conventional +optically detected magnetic resonance, but relies on a distinct mechanism as it +occurs at a microwave frequency far removed from the magnetic resonance +frequency of the NV spin. This observation presents a new approach to +transferring ferromagnetic spin information into a paramagnet and then +transducing the response into a robust optical signal. It also opens new +avenues for studying ferromagnetism and spin transport at the nanoscale.",1403.0656v1 +2014-03-04,All-optical control of ferromagnetic thin films and nanostructures,"The interplay of light and magnetism has been a topic of interest since the +original observations of Faraday and Kerr where magnetic materials affect the +light polarization. While these effects have historically been exploited to use +light as a probe of magnetic materials there is increasing research on using +polarized light to alter or manipulate magnetism. For instance deterministic +magnetic switching without any applied magnetic fields using laser pulses of +the circular polarized light has been observed for specific ferrimagnetic +materials. Here we demonstrate, for the first time, optical control of +ferromagnetic materials ranging from magnetic thin films to multilayers and +even granular films being explored for ultra-high-density magnetic recording. +Our finding shows that optical control of magnetic materials is a much more +general phenomenon than previously assumed. These results challenge the current +theoretical understanding and will have a major impact on data memory and +storage industries via the integration of optical control of ferromagnetic +bits.",1403.0784v1 +2014-03-21,Colloidal Assemblies of Oriented Maghemite Nanocrystals and their NMR Relaxometric Properties,"Elevated-temperature polyol-based colloidal-chemistry approach allows for the +development of size-tunable (50 and 86 nm) assemblies of maghemite iso-oriented +nanocrystals, with enhanced magnetization. 1H-Nuclear Magnetic Resonance (NMR) +relaxometric experiments show that the ferrimagnetic cluster-like colloidal +entities exhibit a remarkable enhancement (4 to 5 times) in the transverse +relaxivity, if compared to that of the superparamagnetic contrast agent +Endorem, over an extended frequency range (1-60 MHz). The marked increase of +the transverse relaxivity r2 at a clinical magnetic field strength (1.41 T), +which is 405.1 and 508.3 mM-1 s-1 for small and large assemblies respectively, +allows to relate the observed response to the raised intra-aggregate magnetic +material volume fraction. Furthermore, cell tests with murine fibroblast +culture medium confirmed the cell viability in presence of the clusters. We +discuss the NMR dispersion profiles on the basis of relaxivity models to +highlight the magneto-structural characteristics of the materials for improved +T2-weighted magnetic resonance images.",1403.5450v1 +2017-01-10,Temperature dependence of the non-local spin Seebeck effect in YIG/Pt nanostructures,"We study the transport of thermally excited non-equilibrium magnons through +the ferrimagnetic insulator YIG using two electrically isolated Pt strips as +injector and detector. The diffusing magnons induce a non- local inverse spin +Hall voltage in the detector corresponding to the so-called non-local spin +Seebeck effect (SSE). We measure the non-local SSE as a function of temperature +and strip separation. In experiments at room temperature we observe a sign +change of the non-local SSE voltage at a characteristic strip separation d0, in +agreement with previous investigations. At lower temperatures however, we find +a strong temperature dependence of d0. This suggests that both the angular +momentum transfer across the YIG/Pt interface as well as the transport +mechanism of the magnons in YIG as a function of temperature must be taken into +account to describe the non-local spin Seebeck effect.",1701.02635v1 +2017-04-20,Ferrimagnetism in the Spin-1/2 Heisenberg Antiferromagnet on a Distorted Triangular Lattice,"The ground state of the spin-$1/2$ Heisenberg antiferromagnet on a distorted +triangular lattice is studied using a numerical-diagonalization method. The +network of interactions is the $\sqrt{3}\times\sqrt{3}$ type; the interactions +are continuously controlled between the undistorted triangular lattice and the +dice lattice. We find new states between the nonmagnetic 120-degree-structured +state of the undistorted triangular case and the up-up-down state of the dice +case. The intermediate states show spontaneous magnetizations that are smaller +than one third of the saturated magntization corresponding to the up-up-down +state.",1704.06013v2 +2017-04-25,Probing length-scale separation of thermal and spin currents by nanostructuring YIG,"We have fabricated bulk nanostructured ferrimagnetic materials with different +grain sizes by sintering ball-milled Y3Fe5O12 (YIG) nanoparticles and measured +the grain-size dependence of the thermal conductivity and spin Seebeck +thermopower. The nanostructuring reduces both thermal conductivity and +thermopower, but the reduction of the latter was found to be considerably +stronger despite the moderate difference in magnetization, which suggests that +the length scales of transport of magnons and phonons contributing to the spin +Seebeck effect are significantly larger than that of phonons carrying thermal +current. This is consistent with the measurements of high-magnetic-field +response of the spin Seebeck thermopower and low-temperature thermal +conductivity, where the quenching of magnons seen in single-crystalline YIG was +not observed in nanostructured YIG due to scattering of long-range low +frequency magnons.",1704.07568v1 +2017-04-28,Thermal Control of the Magnon-Photon Coupling in a Notch Filter coupled to a Yttrium-Iron-Garnet/Platinum System,"We report thermal control of mode hybridization between the ferromagnetic +resonance (FMR) and a planar resonator (notch filter) working at 4.74 GHz. The +chosen magnetic material is a ferrimagnetic insulator (Yttrium Iron Garnet: +YIG) covered by 6 nm of platinum (Pt). A current induced heating method has +been used in order to enhance the temperature of the YIG/Pt system. The device +permits us to control the transmission spectra and the magnon-photon coupling +strength at room temperature. These experimental findings reveal potentially +applicable tunable microwave filtering function.",1704.08896v3 +2018-05-07,Single-shot multi-level all-optical magnetization switching mediated by spin-polarized hot electron transport,"All-optical ultrafast magnetization switching in magnetic material thin film +without the assistance of an applied external magnetic field is being explored +for future ultrafast and energy-efficient magnetic storage and memories. It has +been shown that femto-second light pulses induce magnetization reversal in a +large variety of magnetic materials. However, so far, only GdFeCo-based +ferrimagnetic thin films exhibit magnetization switching via a single optical +pulse. Here we demonstrate the single-pulse switching of Co/Pt multilayers +within a magnetic spin-valve structure ([Co/Pt] / Cu / GdFeCo) and further show +that the four possible magnetic configurations of the spin valve can be +accessed using a sequence of single femto-second light pulses. Our experimental +study reveals that the magnetization final state of the ferromagnetic [Co/Pt] +layer is determined by spin-polarized hot electrons generated by the light +pulse interactions with the GdFeCo layer. This work provides a new approach to +deterministically switch ferromagnetic layers and a pathway to engineering +materials for opto-magnetic multi-bit recording.",1805.02432v1 +2018-05-09,Nature of the Magnetic Interactions in Sr$_3$NiIrO$_6$,"Iridates abound with interesting magnetic behaviours because of their strong +spin-orbit coupling. Sr$_3$NiIrO$_6$ brings together the spin-orbital +entanglement of the Ir$^{4+}$ ion with a 3$d$ Ni cation and a one-dimensional +crystal structure. It has a ferrimagnetic ground state with a 55 T coercive +field. We perform a theoretical study of the magnetic interactions in this +compound, and elucidate the role of anisotropic symmetric exchange as the +source of its strong magnetic anisotropy. Our first-principles calculations +reproduce the magnon spectra of this compound and predict a signature in the +cross sections that can differentiate the anisotropic exchange from single-ion +anisotopy.",1805.03733v2 +2018-05-26,Observation of gyromagnetic reversal,"We report direct observation of gyromagnetic reversal, which is the sign +change of gyromagnetic ratio in a ferrimagnet Ho$_3$Fe$_5$O$_{12}$, by using +the Barnett effect measurement technique at low temperatures. The Barnett +effect is a phenomenon in which magnetization is induced by mechanical rotation +through the coupling between rotation and total angular momentum $J$ of +electrons. The magnetization of Ho$_3$Fe$_5$O$_{12}$ induced by mechanical +rotation disappears at 135~K and 240~K. The temperatures correspond to the +magnetization compensation temperature $T_{\rm M}$ and the angular momentum +compensation temperature $T_{\rm A}$, respectively. Between $T_{\rm M}$ and +$T_{\rm A}$, the magnetization flips over to be parallel against the angular +momentum due to the sign change of gyromagnetic ratio. This study provides an +unprecedented technique to explore the gyromagnetic properties.",1805.10426v3 +2009-12-05,Electrical and magnetic transport properties of Fe3O4 thin films on GaAs (100) substrate,"Thin films of magnetite (Fe3O4) are grown on single crystal GaAs (100) +substrate by pulsed laser deposition. X ray diffraction (XRD) result shows the +(111) preferred orientation of the Fe3O4 film and x-ray photoelectron +spectroscopy confirm the presence of single phase Fe3O4 in the film. The +electrical transport property of the film shows the characteristic Verwey +transition at 122 K and below 110 K, the transport follows variable range +hopping type conduction mechanism. The film shows room temperature +magnetization hysteresis loop suggesting the ferrimagnetic behavior of the film +with saturation magnetization value close to 470 emu/cc.",0912.0979v1 +2011-11-03,Competing Ferri- and Antiferromagnetic Phases in Geometrically Frustrated LuFe2O4,"We present a detailed study of magnetism in LuFe2O4, combining magnetization +measurements with neutron and soft x-ray diffraction. The magnetic phase +diagram in the vicinity of T_N involves a metamagnetic transition separating an +antiferro- and a ferrimagnetic phase. For both phases the spin structure is +refined by neutron diffraction. Observed diffuse magnetic scattering far above +T_N is explained in terms of near degeneracy of the magnetic phases.",1111.0746v1 +2011-11-18,Exchange Bias Induced by the Fe3O4 Verwey transition,"We present a study of the exchange bias in different configurations of V2O3 +thin films with ferromagnetic layers. The exchange bias is accompanied by a +large vertical shift in the magnetization. These effects are only observed when +V2O3 is grown on top of Ni80Fe20 permalloy. The magnitude of the vertical shift +is as large as 60% of the total magnetization which has never been reported in +any system. X-Ray diffraction studies show that the growth conditions promote +the formation of a ferrimagnetic Fe3O4 interlayer. The change in the easy +magnetization axis of Fe3O4 across the Verwey transition at 120 K is correlated +with the appearance of exchange bias and vertical shift in magnetization. Both +phenomena disappear above 120 K, indicating for the first time a direct +relationship between the magnetic signature of the Verwey transition and +exchange bias.",1111.4255v2 +2012-04-12,Magnetic order and ice rules in the multiferroic spinel FeV2O4,"We present a neutron diffraction study of FeV2O4, which is rare in exhibiting +spin and orbital degrees of freedom on both cation sublattices of the spinel +structure. Our data confirm the existence of three structural phase transitions +previously identified with x-ray powder diffraction, and reveal that the lower +two transitions are associated with sequential collinear and canted +ferrimagnetic transitions involving both cation sites. Through consideration of +local crystal and spin symmetry, we further conclude that Fe2+ cations are +ferro-orbitally ordered below 135K and V3+ orbitals order at 60K in accordance +with predictions for vanadium spinels with large trigonal distortions and +strong spin-orbit coupling. Intriguingly, the direction of ordered vanadium +spins at low temperatures obey `ice rules' more commonly associated with the +frustrated rare-earth pyrochlore systems.",1204.2812v3 +2012-04-14,"Evaluation of Half-metallic Antiferromagnetism in ${\cal A}_2$CrFeO$_6$ ({$\cal A$}=La, Sr","The nearly well-ordered double perovskite La$_2$CrFeO$_6$ has been +synthesized recently. Contrary to previous theoretical predictions, but in +agreement with experimental observations, our first principle calculations +indicate an insulating ferrimagnet La$_2$CrFeO$_6$ with antialigned S=3/2 +Cr$^{3+}$ and S=5/2 Fe$^{3+}$ ions,using the local spin density approximation +(LSDA), a correlated band theory LDA+U, and a semilocal functional modified +Becke-Johnson method. Additionally, we investigated the double perovskite +Sr$_2$CrFeO$_6$, which is as yet unsynthesized. In LSDA calculations, this +system shows formally tetravalent Cr and Fe ions both having antialigned $S$=1 +moments, but is a simple metal. Once applying on-site Coulomb repulsion U on +both Cr and Fe ions, this system becomes half-metallic and the moment of Fe is +substantially reduced, resulting in zero net moment. These results are +consistent with our fixed spin moment studies. Our results suggest a precisely +compensated half-metallic Sr$_2$CrFeO$_6$.",1204.3150v2 +2012-04-16,Long wavelength helimagnetic order and skyrmion lattice phase in Cu2OSeO3,"We report a long-wavelength helimagnetic superstructure in bulk samples of +the ferrimagnetic insulator Cu2OSeO3. The magnetic phase diagram associated +with the helimagnetic modulation inferred from small angle neutron scattering +and magnetisation measurements includes a skyrmion lattice phase and is +strongly reminiscent of MnSi, FeGe and Fe1-xCoxSi, i.e., binary isostructural +siblings of Cu2OSeO3 that order helimagnetically. The temperature dependence of +the specific heat of Cu2OSeO3 is characteristic of nearly critical spin +fluctuations at the helimagnetic transition. This provides putative evidence +for effective spin currents as the origin of enhancements of the +magneto-dielectric response instead of atomic displacements considered so far.",1204.3597v1 +2013-08-30,Magnetocapacitance as a sensitive probe of magnetostructural changes in NiCr$_2$O$_4$,"The spinel NiCr$_2$O$_4$ is characterized using dielectric and high magnetic +field measurements. The trends in the magnetodielectric response fall into +three clear temperature regimes corresponding to known magnetic and structural +transitions. Above 65\,K, weak magnetic field dependence of the dielectric +constant is observed with no hysteresis. When 30\,K\,$\leq\,T\,\leq$\,65\,K, a +strong dependence of the dielectric constant on the magnetic field is observed +and hysteresis develops resulting in so called butterfly loops. Below 30\,K, +magnetodielectric hysteresis is enhanced. Magnetodielectric hysteresis mirrors +magnetic hysteresis suggesting that spin-spin interactions are the mechanism +for the magnetoelectric effect in NiCr$_2$O$_4$. At high fields however, the +magnetization continues to increase while the dielectric constant saturates. +Magnetodielectric measurements of NiCr$_2$O$_4$ suggest an additional, +previously unobserved transition at 20\,K. Subtle changes in magnetism and +structure suggest that this 20\,K anomaly corresponds to the completion of +ferrimagnetic ordering and the spin driven structural distortion. We +demonstrate that magnetocapacitance is a sensitive probe of magnetostructural +distortion.",1309.0016v1 +2013-09-06,"Magnetism and local structure in low-dimensional, Mott insulating GdTiO3","Cation displacements, oxygen octahedral tilts, and magnetism of epitaxial, +ferrimagnetic, insulating GdTiO3 films sandwiched between cubic SrTiO3 layers +are studied using scanning transmission electron microscopy and magnetization +measurements. With decreasing GdTiO3 film thickness, structural (GdFeO3-type) +distortions are reduced, concomitant with a reduction in the Curie temperature. +Ferromagnetism persists to smaller deviations from the cubic perovskite +structure than is the case for the bulk rare earth titanates. The results +indicate that the FM ground state is controlled by the narrow bandwidth, +exchange and orbital ordering, and only to second order depends on amount of +the GdFeO3-type distortion.",1309.1531v1 +2013-09-13,Thermodynamic properties of a diluted triangular Ising antiferromagnet in a field,"Within the framework of the effective-field theory with correlations we +investigate effects of an external magnetic field and random site dilution on +basic thermodynamic quantities, such as the magnetization and the magnetic +susceptibility, of the geometrically frustrated triangular lattice Ising +antiferromagnet. Behavior of these quantities is presented in the +temperaturefield parameter space for selected mild degrees of dilution. It is +found that, besides the anomalies associated with phase transitions from the +ferrimagnetic to the paramagnetic state, in some regions of the parameter space +these functions display some more anomalies and peculiarities, as a result of +joint effects of the geometrical frustration, magnetic dilution, thermal +fluctuations and the applied magnetic field.",1309.3592v3 +2013-09-25,Ab-initio calculation of the effective on-site Coulomb interaction parameters for half-metallic magnets,"Correlation effects play an important role in the electronic structure of +half-metallic (HM) magnets. In particular, they give rise to non-quasiparticle +states above (or below) the Fermi energy at finite temperatures that reduce the +spin polarization and, as a consequence, the efficiency of spintronics devices. +Employing the constrained random-phase approximation (cRPA) within the +full-potential linearized augmented-plane-wave (FLAPW) method using maximally +localized Wannier functions, we calculate the strength of the effective on-site +Coulomb interaction (Hubbard $U$ and Hund exchange $J$) between localized +electrons in different classes of HM magnets considering: (i) +\emph{sp}-electron ferromagnets in rock-salt structure, (ii) zincblende +3\emph{d} binary ferromagnets, as well as (iii) ferromagnetic and ferrimagnetic +semi- and full-Heusler compounds.",1309.6657v1 +2014-05-02,Spin-Polarized-Current State of Electrons in Bilayer Graphene,"We propose a model of spin-polarized-current state for electrons in bilayer +graphene. The model resolves the puzzles as revealed by experiments that (a) +the energy gap $E_{\rm gap}$ of the insulating ground state at the charge +neutrality point (CNP) can be closed by a perpendicular electric field of +either polarity, (b) $E_{\rm gap}$ increases significantly with increasing the +magnetic field $B$, (c) the particle-hole spectrum is asymmetric in the +presence of $B$, (d) there is a peak structure in the electric conductivity at +small $B$ at the CNP, and (e) there are quantum Hall states stemming from +lifting of degeneracy in the lowest Landau level. The model predicts that the +ground state of the system close to the CNP is a ferrimagnet at finite $B$ and +the Hall current is spin polarized.",1405.0335v1 +2014-05-09,Magnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model,"We present a microscopic calculation of magnetization damping for a magnetic +""toy model."" The magnetic system consists of itinerant carriers coupled +antiferromagnetically to a dispersionless band of localized spins, and the +magnetization damping is due to coupling of the itinerant carriers to a phonon +bath in the presence of spin-orbit coupling. Using a mean-field approximation +for the kinetic exchange model and assuming the spin-orbit coupling to be of +the Rashba form, we derive Boltzmann scattering integrals for the distributions +and spin coherences in the case of an antiferromagnetic exchange splitting, +including a careful analysis of the connection between lifetime broadening and +the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract +dephasing and magnetization times T_1 and T_2 from initial conditions +corresponding to a tilt of the magnetization vector, and draw a comparison to +phenomenological equations such as the Landau-Lifshitz or the Gilbert damping. +We also analyze magnetization precession and damping for this system including +an anisotropy field and find a carrier mediated dephasing of the localized spin +via the mean-field coupling.",1405.2347v1 +2014-05-19,Multiferroic Iron Oxide Thin Films at Room-Temperature,"In spite of being highly relevant for the development of a new generation of +information storage devices, not many single-phase materials displaying +magnetic and ferroelectric orders above room temperature are known. Moreover, +these uncommon materials typically display insignificant values of the remanent +moment in one of the ferroic orders or are complex multicomponent oxides which +will be very challenging to integrate in devices. Here we report on the +strategy to stabilize the metastable epsilon-Fe2O3 in thin film form, and we +show that besides its already known ferrimagnetic nature, the films are also +ferroelectric at 300 K with a remanent polarization of 1 microC/cm2. The film +polarization shows long retention times and can be switched under small applied +voltages. These characteristics make of epsilon-Fe2O3 the first single-ion +transition-metal oxide which is ferro(ferri)magnetic and ferroelectric at room +temperature. The simple composition of this new multiferroic oxide and the +discovery of a robust path for its thin film growth may boost the exploitation +of epsilon-Fe2O3 in novel devices.",1405.4909v1 +2014-05-27,"Non-d$^0$ Electric Dipole in FeO$_5$ bipyramid: a New Resource for Quantum Paraelectrics, Ferroelectrics and Multiferroics","Electric polarization in conventional ferroelectric oxides usually involves +nonmagnetic transition-metal ions with an empty d shell (the d$^0$ rule). Here +we unravel a new mechanism for local electric dipoles based on magnetic +Fe$^{3+}$ (3d$^5$) ion violating the d$^0$ rule. The competition between the +long-range Coulomb interaction and short-range Pauli repulsion in a FeO$_5$ +bipyramid with proper lattice parameters would favor an off-center displacement +of Fe$^{3+}$ that induces a local electric dipole. The manipulation of this +kind of non-d$^0$ electric dipoles opens up a new route for generating +unconventional dielectrics, ferroelectrics, and multiferroics. As a prototype +example, we show that the non-d$^0$ electric dipoles in ferrimagnetic +hexaferrites (Ba,Sr)Fe$_{12}$O$_{19}$ lead to a new family of magnetic quantum +paraelectrics.",1405.6806v1 +2014-06-02,Electronic and magnetic properties of (1 1 1)-oriented CoCr2O4 epitaxial thin film,"We report on the fabrication of high quality (1 1 1)-oriented ferrimagnetic +normal spinel CoCr2O4 epitaxial thin films on single crystal Al2O3 substrates. +The structural, electronic and magnetic properties were characterized by +in-situ reflection high energy electron diffraction, atomic force microscopy, +X-ray diffraction, X-ray photoemission spectroscopy, SQUID magnetometry and +element resolved resonant X-ray magnetic scattering. The comprehensive +characterization reveals that no disorder in the cation distribution or +multivalency issue is present in the samples. As a result, Kagome and +triangular layers are naturally formed via this specific growth approach. These +findings offer a pathway to fabricate two dimensional Kagome heterostructures +with novel quantum many-body phenomena by means of geometrical design.",1406.0523v1 +2014-06-05,Magnetic properties of epitaxial Fe$_3$O$_4$ films with various crystal orientations and TMR effect in room temperature,"Fe$_3$O$_4$ is a ferrimagnetic spinel ferrite that exhibits electric +conductivity at room temperature (RT). Although the material has been predicted +to be a half metal according to ab-initio calculations, magnetic tunnel +junctions (MTJs) with Fe$_3$O$_4$ electrodes have demonstrated a small tunnel +magnetoresistance effect. Not even the sign of the TMR ratio has been +experimentally established. Here, we report on the magnetic properties of +epitaxial Fe$_3$O$_4$ films with various crystal orientations. The films +exhibited apparent crystal orientation dependence on hysteresis curves. In +particular, Fe$_3$O$_4$(110) films exhibited in-plane uniaxial magnetic +anisotropy. With respect to the squareness of hysteresis, Fe$_3$O$_4$ (111) +demonstrated the largest squareness. Furthermore, we fabricated MTJs with +Fe$_3$O$_4$(110) electrodes, and obtained an TMR effect of -12\% at RT. The +negative TMR ratio corresponded to the negative spin polarization of +Fe$_3$O$_4$ predicted from band calculations.",1406.1296v1 +2014-06-05,Designing Asymmetric Multiferroics with Strong Magnetoelectric Coupling,"Multiferroics offer exciting opportunities for electric-field control of +magnetism. Unfortunately, single-phase multiferroics suitable for such +applications at room temperature has not been discovered. Here, we propose the +concept of a new type of multiferroics, namely, ""asymmetric multiferroic"". In +asymmetric multiferroics, two locally stable ferroelectric states are not +symmetrically equivalent, leading to different magnetic properties between +these two states. Furthermore, we predict from first-principles that a Fe-Cr-Mo +superlattice with the LiNbO3-type structure is such an asymmetric multiferroic. +The strong ferrimagnetism, high ferroelectric polarization, and significant +dependence of the magnetic transition temperature on polarization make this +asymmetric multiferroic an ideal candidate for realizing electric-field control +of magnetism at room temperature. Our study suggests that asymmetric +multiferroic may provide a new playground for voltage control of magnetism and +find its applications in spintronics and quantum computing.",1406.1318v1 +2014-06-12,First-principles modelling of magnetic excitations in Mn12,"We have developed a fully microscopic theory of magnetic properties of the +prototype molecular magnet Mn12. First, the intra-molecular magnetic properties +have been studied by means of first-principles density functional-based +methods, with local correlation effects being taken into account within the +local density approximation plus U (LDA+U) approach. Using the magnetic force +theorem, we have calculated the interatomic isotropic and anisotropic exchange +interactions and full tensors of single-ion anisotropy for each Mn ion. +Dzyaloshinskii-Moriya (DM) interaction parameters turned out to be unusually +large, reflecting a low symmetry of magnetic pairs in molecules, in comparison +with bulk crystals. Based on these results we predict a distortion of +ferrimagnetic ordering due to DM interactions. Further, we use an exact +diagonalization approach allowing to work with as large Hilbert space dimension +as 10^8 without any particular symmetry (the case of the constructed magnetic +model). Based on the computational results for the excitation spectrum, we +propose a distinct interpretation of the experimental inelastic neutron +scattering spectra.",1406.3116v1 +2014-06-28,Effects of Strain and Buffer Layer on Interfacial Magnetization in Sr$_2$CrReO$_6$ Films Determined by Polarized Neutron Reflectometry,"We have determined the depth-resolved magnetization structures of a series of +highly ordered Sr$_{2}$CrReO$_{6}$ (SCRO) ferrimagnetic epitaxial films via +combined studies of x-ray reflectometry, polarized neutron reflectometry and +SQUID magnetometry. The SCRO films deposited directly on +(LaAlO$_3$)$_{0.3}$(Sr$_2$AlTaO$_6$)$_{0.7}$ or SrTiO$_{3}$ substrates show +reduced magnetization of similar width near the interfaces with the substrates, +despite having different degrees of strain. When the SCRO film is deposited on +a Sr$_{2}$CrNbO$_{6}$ (SCNO) double perovskite buffer layer, the width the +interfacial region with reduced magnetization is reduced, agreeing with an +improved Cr/Re ordering. However, the relative reduction of the magnetization +averaged over the interfacial regions are comparable among the three samples. +Interestingly, we found that the magnetization suppression region is wider than +the Cr/Re antisite disorder region at the interface between SCRO and SCNO.",1406.7351v2 +2015-12-02,Bose-Einstein Condensation of Magnons Pumped by the Bulk Spin Seebeck Effect,"We propose inducing Bose-Einstein condensation of magnons in a magnetic +insulator by a heat flow oriented toward its boundary. At a critical heat flux, +the oversaturated thermal gas of magnons accumulated at the boundary +precipitates the condensate, which then grows gradually as the thermal bias is +dialed up further. The thermal magnons thus pumped by the magnonic bulk (spin) +Seebeck effect must generally overcome both the local Gilbert damping +associated with the coherent magnetic dynamics as well as the radiative +spin-wave losses toward the magnetic bulk, in order to achieve the threshold of +condensation. We quantitatively estimate the requisite bias in the case of the +ferrimagnetic yttrium iron garnet, discuss different physical regimes of +condensation, and contrast it with the competing (so-called Doppler-shift) bulk +instability.",1512.00557v1 +2015-12-11,Possible ferrimagnetism and ferroelectricity of half-substituted rare-earth titanate: a first-principles study on Y$_{0.5}$La$_{0.5}$TiO$_3$,"Titanates with the perovskite structure, including ferroelectrics (e.g., +BaTiO$_3$) and ferromagnetic ones (e.g., YTiO$_3$), are important functional +materials. Recent theoretical studies predicted multiferroic states in strained +EuTiO$_3$ and titanate superlattices, the former of which has already been +experimental confirmed. Here, a first-principles calculation is performed to +investigate the structural, magnetic, and electronic properties of Y +half-substituted LaTiO3. Our results reveal that the magnetism of +Y$_{0.5}$La$_{0.5}$TiO$_3$ sensitively depends on its structural details +because of the inherent phase competition. The lowest energy state is the +ferromagnetic state, resulting in 0.25 $\mu_{\rm B}$/Ti. Furthermore, some +configurations of Y$_{0.5}$La$_{0.5}$TiO$_3$ exhibit hybrid improper +polarizations, which can be significantly affected by magnetism, resulting in +the multiferroic properties. Because of the quenching disorder of substitution, +the real Y$_{0.5}$La$_{0.5}$TiO3 material with random A-site ions may exhibit +interesting relaxor behaviors.",1512.03616v1 +2016-05-24,Roles of heating and helicity in ultrafast all-optical magnetization switching in TbFeCo,"Using time-resolved magneto-optical Kerr effect (TR-MOKE) method, +helicity-dependent all-optical magnetization switching (HD-AOS) is observed in +ferrimagnetic TbFeCo films. The thermal effect and opto-magneto effects are +separately justified after single circularly polarized laser pulse. The +integral evolution of this ultrafast switching is characterized on different +time scales and the defined magnetization reversal time of 460 fs is the +fastest ever observed. Combining the heat effect and inverse Faraday effect +(IFE), micromagnetic simulations based on a single macro-spin model are +performed that reproduce HD-AOS following a linear reversal mechanism.",1605.07448v3 +2016-05-30,"An integrated approach to doped thin films with strain tunable magnetic anisotropy: Powder synthesis, target preparation and pulsed laser deposition of Bi:YIG","We present a synthesis/processing method for fabricating ferrimagnetic +insulator (Bi-doped yttrium iron garnet) thin films with tunable magnetic +anisotropy. Since the desired magnetic properties rely on controllable +thickness and successful doping, we pay attention to the entire +synthesis/processing procedure (nanopowder synthesis, nanocrystalline target +preparation and pulsed laser deposition (PLD)). Atomically flat films were +deposited by PLD on (111)-orientated yttrium aluminum garnet. We show a +significant enhancement of perpendicular anisotropy in the films, caused by +strain-induced anisotropy. In addition, the perpendicular anisotropy is tunable +by decreasing the film thickness and overwhelms the shape anisotropy at a +critical thickness of 3.5 nm.",1605.09084v2 +2016-05-31,The role of electron and phonon temperatures in the helicity-independent all-optical switching of GdFeCo,"Ultrafast optical heating of the electrons in ferrimagnetic metals can result +in all-optical switching (AOS) of the magnetization. Here we report +quantitative measurements of the temperature rise of GdFeCo thin films during +helicity-independent AOS. Critical switching fluences are obtained as a +function of the initial temperature of the sample and for laser pulse durations +from 55 fs to 15 ps. We conclude that non-equilibrium phenomena are necessary +for helicity-independent AOS, although the peak electron temperature does not +play a critical role. Pump-probe time-resolved experiments show that the +switching time increases as the pulse duration increases, with 10 ps pulses +resulting in switching times of ~sim 13 ps. These results raise new questions +about the fundamental mechanism of helicity-independent AOS.",1605.09764v3 +2016-08-05,On supercurrents in Bose-Einstein magnon condensates in YIG ferrimagnet,"Recently E. Sonin commented [1] on our preprint ""Supercurrent in a room +temperature Bose-Einstein magnon condensate"" [2,3], arguing that our ""claim of +detection of spin supercurrent is premature and has not been sufficiently +supported by presented experimental results and their theoretical +interpretation."" We consider the appearance of this Comment as a sign of +significant interest into the problem of supercurrents in Bose-Einstein magnon +condensates. Here, we explicitly address E. Sonin's comments and show that our +interpretation of our experimental results as a detection of a magnon +supercurrent is fully supported not only by the experimental results +themselves, but also by independent theoretical analysis [4].",1608.01813v2 +2016-08-25,Ferroelectricity-induced asymmetrical two-dimensional electron gas in superlattices consisteing of insulating GdTiO3 and ferroelectric BaTiO3,"Two-dimensional electron gas due to semiconductor interfaces can have high +mobility and exhibits superconductivity, magnetism, and other exotic properties +that are unexpected in constituent bulk materials. We study crystal structures, +electronic states, and magnetism of short-period (BTO)$_m$/(GTO)$_2$ ($m$=2 and +4) superlattices consisting of ferroelectric BaTiO$_3$ (BTO) and ferrimagnetic +insulating polar GdTiO$_3$ (GTO) by first principles calculations. Our +investigation shows that the middle Ti-O monolayer in the GTO layer becomes +metallic because the ferroelectricity in the insulating BTO layer induces an +inhomogeneous electric field against the polarity-produced electric field in +the GTO layer and thus differentially changes the d energy levels of the three +Ti-O monolayers related with the GTO layer. Through avoiding electron +reconstruction, the ferroelectric polarization also makes the electronic states +and magnetism of two interfacial Ti-O monolayers become substantially different +from those in the GTO/SrTiO$_3$ superlattices without ferroelectricity. Such +superlattices are interesting for potential spintronics applications because of +their unique asymmetrical two-dimensional electron-gas properties and possible +useful spin-orbit effects.",1608.07140v2 +2016-12-20,Discovery of room temperature multiferroicity and magneto-electric coupling in Fe3Se4 nanorods,"We report for the first time, that Fe3Se4 is a room temperature, type-II +multiferroic with magnetoelectric coupling. We observed the coexistence of +coupled ferrimagnetic and ferroelectric ordering in Fe3Se4nanorods well above +room temperature, which is a hard magnet with large magnetocrystalline +anisotropy. For the first time, we observed spontaneous, reversible +ferroelectric polarization in Fe3Se4 nanorods below the magnetic Curie +temperature. The coupling is manifested by an anomaly in the dielectric +constant and Raman shift at Tc. We do not completely understand the origin of +the ferroelectric ordering at this point however the simultaneous presence of +magnetic and ferroelectric ordering at room temperature in Fe3Se4 along with +hard magnetic properties will open new research areas for devices.",1612.06512v2 +2016-12-21,Giant ferroelectric polarization and electric reversal of strong spontaneous magnetization in multiferroic Bi2FeMoO6,"BiFeO$_3$ is the most famous multiferroic material, but it has no strong +spontaneous magnetization due to its antiferromagnetism. Here we show that +giant ferroelectric polarization and strong spontaneous magnetization can be +both realized in double perovskite Bi$_2$FeMoO$_6$ with R3 (\#146) space group +based on BiFeO$_3$. Our first-principles phonon spectra establishes that this +multiferroic R3 phase is stable. Our systematic calculations show that it is a +spin-polarized semiconductor with gap reaching to 0.54 eV and has a strong +ferroelectric polarization of 85$\mu$C/cm$^2$. This ferroelctricity is +comparable with that of BiFeO$_3$, but here obtained is a strong ferrimagnetism +with net magnetic moment of 2$\mu_B$ per formula unit and Curie temperature of +650 K. Both ferroelectric polarization and magnetic easy axis are shown to be +in pseudocubic [111] orientation. Our further analysis shows that the +macroscopic spontaneous magnetization can be deterministically reversed through +a three-step path by external electric field. Therefore, we believe that this +Bi$_2$FeMoO$_6$ material can be used to design new multifunctional materials +and achieve high-performance devices.",1612.07124v1 +2016-12-28,"Magnetic structure of Cu2MnBO5 ludwigite: thermodynamic, magnetic properties and neutron diffraction study","We report on the thermodynamic, magnetic properties and the magnetic +structure of ludwigite-type Cu2MnBO5. The specific heat, the low-field +magnetization and the paramagnetic susceptibility were studied on a single +crystal and combined with powder neutron diffraction data. The temperature +dependence of the specific heat and the neutron diffraction pattern reveal a +single magnetic phase transition at T=92 K, which corresponds to the magnetic +ordering into a ferromagnetic phase. The cation distribution and the values and +directions of magnetic moments of ions in different crystallographic sites are +established. The magnetic moments of Cu2+ and Mn3+ ions occupying different +magnetic sites in the ferrimagnetic phase are pairwise antiparallel and their +directions do not coincide with the directions of the principal +crystallographic axes.The small value of the magnetic moment of copper ions +occupying site 2a is indicative of partial disordering of the magnetic moments +on this site. The magnetization measurements show a strong temperature +hysteresis of magnetization, which evidences for field-dependent transitions +below the phase transition temperature.",1612.08805v1 +2016-12-29,Manipulating exchange bias using all-optical helicity-dependent switching,"Deterministic all-optical control of magnetization without an applied +magnetic field has been reported for different materials such as ferrimagnetic +and ferromagnetic thin films and granular recording media. These findings have +challenged the understanding of all-optical helicity-dependent switching of +magnetization and opened many potential applications for future magnetic +information, memory and storage technologies. Here we demonstrate optical +control of an antiferromagnetic layer through the exchange bias interaction +using the helicity of a femtosecond pulsed laser on IrMn/[Co/Pt]xN +antiferromagnetic/ ferromagnetic heterostructures. We show controlled switching +of the sign of the exchange bias field without any applied field, only by +changing the helicity of the light, and quantify the influence of the laser +fluence and the number of light pulses on the exchange bias control. We also +present the combined effect of laser pulses and applied magnetic field. This +study opens applications in spintronic devices where the exchange bias +phenomenon is routinely used to fix the magnetization orientation of a magnetic +layer in one direction.",1612.09338v1 +2017-06-19,Spin Hall effect from hybridized 3$d$-4$p$ orbitals,"Electrical manipulation of magnetization by spin-orbit torque (SOT) has shown +promise for realizing reliable magnetic memories and oscillators. To date, the +generation of transverse spin current and SOT, whether it is of spin Hall +effect (SHE), Rashba-Edelstein effect or spin-momentum locking origin, relies +primarily on materials or heterostructures containing 5$d$ or 6$p$ heavy +elements with strong spin-orbit coupling. Here we show that a paramagnetic CoGa +compound possesses large enough spin Hall angle to allow robust SOT switching +of perpendicularly-magnetized ferrimagnetic MnGa films in CoGa/MnGa/Oxide +heterostructures. The spin Hall efficiency estimated via spin Hall +magnetoresistance and harmonic Hall measurements is +0.05$\pm$0.01, which is +surprisingly large for a system that does not contain any heavy metal element. +First-principles calculations corroborate our experimental observations and +suggest that the hybridized Co 3$d$ - Ga 4$p$ orbitals along R-X in the +Brillouin zone is responsible for the intrinsic SHE. Our results suggest that +efficient spin current generation can be realized in intermetallic by alloying +a transition metal with a $p$-orbital element and by Fermi level tuning.",1706.05846v1 +2017-06-23,Detection of induced paramagnetic moments in Pt on Y$_3$Fe$_5$O$_{12}$ via x-ray magnetic circular dichroism,"Magnetic moments in an ultra-thin Pt film on a ferrimagnetic insulator +Y$_3$Fe$_5$O$_{12}$ (YIG) have been investigated at high magnetic fields and +low temperatures by means of X-ray magnetic circular dichroism (XMCD). We +observed an XMCD signal due to the magnetic moments in a Pt film at the Pt +$L_{3}$- and $L_{2}$-edges. By means of the element-specific magnetometry, we +found that the XMCD signal at the Pt $L_{3}$-edge gradually increases with +increasing the magnetic field even when the field is much greater than the +saturation field of YIG. Importantly, the observed XMCD intensity was found to +be much greater than the intensity expected from the Pauli paramagnetism of Pt +when the Pt film is attached to YIG. These results imply the emergence of +induced paramagnetic moments in Pt on YIG and explain the characteristics of +the unconventional Hall effect in Pt/YIG systems.",1706.07559v1 +2017-06-26,Perpendicular magnetic anisotropy in insulating ferrimagnetic gadolinium iron garnet thin films,"We present experimental control of the magnetic anisotropy in a gadolinium +iron garnet (GdIG) thin film from in-plane to perpendicular anisotropy by +simply changing the sample temperature. The magnetic hysteresis loops obtained +by SQUID magnetometry measurements unambiguously reveal a change of the +magnetically easy axis from out-of-plane to in-plane depending on the sample +temperature. Additionally, we confirm these findings by the use of temperature +dependent broadband ferromagnetic resonance spectroscopy (FMR). In order to +determine the effective magnetization, we utilize the intrinsic advantage of +FMR spectroscopy which allows to determine the magnetic anisotropy independent +of the paramagnetic substrate, while magnetometry determines the combined +magnetic moment from film and substrate. This enables us to quantitatively +evaluate the anisotropy and the smooth transition from in-plane to +perpendicular magnetic anisotropy. Furthermore, we derive the temperature +dependent $g$-factor and the Gilbert damping of the GdIG thin film.",1706.08488v1 +2017-07-07,Magnetoelectric antiferromagnets as platforms for the manipulation of solitons,"We study the magnetic dynamics of magnetoelectric antiferromagnetic thin +films, where an unconventional boundary ferromagnetism coexists with the bulk +N\'{e}el phase below the N\'{e}el temperature. The spin exchange between the +two order parameters yields an effective low-energy theory that is formally +equivalent to that of a ferrimagnet. Dynamics of domain walls and skyrmions are +analyzed within the collective variable approach, from which we conclude that +they behave as massive particles moving in a viscous medium subjected to a +gyrotropic force. We find that the film thickness can be used as a control +parameter for the motion of these solitons. In this regard, it is shown that an +external magnetic field can drive the dynamics of domain walls, whose terminal +velocity is tunable with the sample thickness. Furthermore, the classification +of the skyrmion dynamics is sensitive to the spatial modulation of the sample +thickness, which can be easily engineered with the present (thin-film) +deposition techniques. Current-driven spin transfer can trigger drifting orbits +of skyrmions, which can be utilized as racetracks for these magnetic textures.",1707.02374v1 +2017-07-12,Broad line-width of antiferromagnetic spinwave due to electrons correlation,"We study magnetic excitations in a bilayer of an antiferromagnetic (AF) +insulator and a correlated metal, in which double occupancy is forbidden. The +effective action of the AF spin wave in the AF insulator is derived by using +the path integral formula within the second order of interplane coupling. The +electron correlation in the correlated metal is treated by the Gutzwiller +approximation, which renormalizes the hopping integrals by g_t as proportional +to the hole density. The linewidth of the AF spin wave excitations originates +from particle-hole excitations in the correlated metal. By increasing the +correlation effect, i.e., by decreasing g_t, it is found that the linewidth at +low energies increases inversely proportional to g_t. The present results will +also be useful for bilayers of a metal and ferrimagnet.",1707.03523v2 +2017-07-21,Mn$_2$VAl Heusler alloy thin films: Appearance of antiferromagnetism and an exchange bias in a layered structure with Fe,"Mn$_2$VAl Heusler alloy films were epitaxially grown on MgO(100) single +crystal substrates by means of ultra-high-vacuum magnetron sputtering. A2 and +L2$_1$ type Mn$_2$VAl order was controlled by the deposition temperatures. +A2-type Mn$_2$VAl films showed no spontaneous magnetization and L2$_1$-type +Mn$_2$VAl films showed ferrimagnetic behavior with a maximum saturation +magnetization of 220 emu/cm$^3$ at room temperature. An antiferromagnetic +reflection was observed with neutron diffraction at room temperature for an +A2-type Mn$_2$VAl film deposited at 400$^\circ$C. A bilayer sample of the +antiferromagnetic A2 Mn$_2$VAl and Fe showed an exchange bias of 120 Oe at 10 +K.",1707.06731v1 +2017-07-23,A core-shell-surface layer model to explain the size dependence of effective magnetic anisotropy in magnetic nanoparticles,"The particle size (D) dependence of the effective magnetic anisotropy Keff of +magnetic nanoparticles (NPs) usually shows Keff increasing with decreasing D. +This dependence is often interpreted using the Eq.: Keff = Kb + (6Ks/D) where +Kb and Ks are the anisotropy constants of the spins in the bulk-like core and +surface layer, respectively. Here, we show that this model is inadequate to +explain the observed size-dependency of Keff for smaller nanoparticles with D < +5 nm. Instead the results in NPs of maghemite ({\gamma}-Fe2O3), NiO and Ni are +best described by an extension of the above model leading to the variation +given by Keff = Kb + (6Ks/D) +Ksh{[1-(2d/D)]^(-3) -1}, where the last term is +due to the spins in a shell of thickness d with anisotropy Ksh. The validation +of this core-shell-surface layer (CSSL) model for three different magnetic NPs +systems viz. ferrimagnetic {\gamma}-Fe2O3, ferromagnetic Ni and +antiferromagnetic NiO suggests its possible applicability for all magnetic +nanoparticles.",1707.07241v1 +2017-10-05,First-principles and model simulation of all-optical spin reversal,"All-optical spin switching is a potential trailblazer for information storage +and communication at an unprecedented fast rate and free of magnetic fields. +However, the current wisdom is largely based on semiempirical models of +effective magnetic fields and heat pulses, so it is difficult to provide +high-speed design protocols for actual devices. Here, we carry out a massively +parallel first-principles and model calculation for thirteen spin systems and +magnetic layers, free of any effective field, to establish a simpler and +alternative paradigm of laser-induced ultrafast spin reversal and to point out +a path to a full-integrated photospintronic device. It is the interplay of the +optical selection rule and sublattice spin orderings that underlines seemingly +irreconcilable helicity-dependent/independent switchings. Using realistic +experimental parameters, we predict that strong ferrimagnets, in particular, +Laves phase C15 rare-earth alloys, meet the telecommunication energy +requirement of 10 fJ, thus allowing a cost-effective subpicosecond laser to +switch spin in the GHz region.",1710.01834v1 +2017-10-11,Approaching quantum anomalous Hall effect in proximity-coupled YIG/graphene/h-BN sandwich structure,"Quantum anomalous Hall state is expected to emerge in Dirac electron systems +such as graphene under both sufficiently strong exchange and spin-orbit +interactions. In pristine graphene, neither interaction exists; however, both +interactions can be acquired by coupling graphene to a magnetic insulator (MI) +as revealed by the anomalous Hall effect. Here, we show enhanced magnetic +proximity coupling by sandwiching graphene between a ferrimagnetic insulator +yttrium iron garnet (YIG) and hexagonal-boron nitride (h-BN) which also serves +as a top gate dielectric. By sweeping the top-gate voltage, we observe Fermi +level-dependent anomalous Hall conductance. As the Dirac point is approached +from both electron and hole sides, the anomalous Hall conductance reaches 1/4 +of the quantum anomalous Hall conductance 2e2/h. The exchange coupling strength +is determined to be as high as 27 meV from the transition temperature of the +induced magnetic phase. YIG/graphene/h-BN is an excellent heterostructure for +demonstrating proximity-induced interactions in two-dimensional electron +systems.",1710.04179v1 +2017-12-12,Substitution- and Strain-induced Magnetic Phase Transition in Iron Carbide,"Cementite-type carbides are of interest for magnetocaloric applications owing +to their temperature- or pressure-induced magnetic phase transition. Here, +using first-principles calculations, we investigate the magnetism and the +magnetic phase transition in iron carbide (Fe3C) with the substitution of Cr +atoms at Fe sites with the strain effect. The presence of Cr atoms is found to +give rise to a second-order magnetic phase transition from a ferromagnetic +phase for Fe3C to a nonmagnetic phase in chromium carbide (Cr3C).While the +ternary Fe2CrC and Cr2FeC compounds prefer the ferrimagnetic ground state, the +magnitudes of both the Fe and Cr spin moments, which are antiparallel in +orientation, decrease as x increases in Fe3-xCrxC (x = 0, 1, 2, and 3). +Furthermore, the fixed spin-moment calculations indicate that the magnetization +of Fe3-xCrxC compounds can be delicately altered via the strain effect and that +the magnetic-nonmagnetic phase transition occurs at an early stage of Cr +substitution, x = 2.",1712.04128v1 +2017-12-13,High-temperature terahertz optical diode effect without magnetic order in polar FeZnMo$_3$O$_8$,"We present a terahertz spectroscopic study of polar ferrimagnet +FeZnMo$_3$O$_8$. Our main finding is a giant high-temperature optical diode +effect, or nonreciprocal directional dichroism, where the transmitted light +intensity in one direction is over 100 times lower than intensity transmitted +in the opposite direction. The effect takes place in the paramagnetic phase +with no long-range magnetic order in the crystal, which contrasts sharply with +all existing reports of the terahertz optical diode effect in other +magnetoelectric materials, where the long-range magnetic ordering is a +necessary prerequisite. In \fzmo, the effect occurs resonantly with a strong +magnetic dipole active transition centered at 1.27 THz and assigned as electron +spin resonance between the eigenstates of the single-ion anisotropy +Hamiltonian. We propose that the optical diode effect in paramagnetic +FeZnMo$_3$O$_8$ is driven by signle-ion terms in magnetoelectric free energy.",1712.04972v2 +2017-12-14,Theoretical prediction of a two-dimensional intrinsic double-metal ferromagnetic semiconductor MnCoO4,"A two-dimensional double-metal oxide MnCoO4 was predicted to be an intrinsic +ferromagnetic semiconductor by using density functional theory. The low +cleavage energy 0.36 Jm-2, which is similar to that of graphene, indicates that +it can be easily exfoliated. The bulk structure has an antiferromagnetic ground +state while the ferromagnetic configuration is the ground state against two +antiferromagnetic and three ferrimagnetic configurations in the two-dimensional +structure. The spin flip gaps for valence and conduction bands are 0.41 and +0.10 eV calculated with the HSE06 density functional, which are much larger +than the thermal energy at room temperature. The Curie temperature obtained +from the Monte Carlo simulation is 40 K. Under 9% tensile strain, the spin flip +gaps increase largely so that the spin flip can be suppressed. The direct +antiferromagnetic coupling between the Mn and Co atoms reduces largely while +the indirect ferromagnetic couplings between two Mn or two Co atoms mediated by +the O atoms do not decrease much in the stretched structure. The Curie +temperature increases to 230 K, higher than the dry ice temperature. Moreover, +phonon dispersion indicates that the MnCoO4 is also stable under the tensile +stain. Therefore, two-dimensional MnCoO4 could be a good candidate for +low-dimensional spintronics.",1712.05071v1 +2017-12-31,Proper dissipative torques in antiferromagnetic dynamics,"There is little doubt that the magnetization dynamics of ferromagnetic +systems is governed by the Landau-Lifshitz-Gilbert equation or its +generalization with various spin torques. In contrast, there are several sets +of dynamic equations for two-sublattice antiferromagnets (AFMs) in literature +that have different forms of dissipative torques and no proper dynamic +equations for multi-sublattice AFMs and ferrimagnets in general. Here we +introduce the general Rayleigh dissipation functional into the Lagrange +equation and derive the proper form of the dissipative torques in the +phenomenological equations for the AFMs with multiple sublattices. A new type +of dissipative torque arising from inter-sublattice drag effect is discovered +that has important influences on magnon lifetime and domain wall motion. In +particular, our theory unifies different dynamic equations of AFMs in +literature.",1801.00217v1 +2018-01-24,Quantization of magnetoelectric fields,"The effect of quantum coherence involving macroscopic degree of freedom, and +occurring in systems far larger than individual atoms are one of the topical +fields in modern physics. Because of material dispersion, a phenomenological +approach to macroscopic quantum electrodynamics, where no canonical formulation +is attempted, is used. The problem becomes more complicated when geometrical +forms of a material structure have to be taken into consideration. Magnetic +dipolar mode (MDM) oscillations in a magnetically saturated quasi 2D ferrite +disk are macroscopically quantized states. In this ferrimagnetic structure, +long range dipole dipole correlation in positions of electron spins can be +treated in terms of collective excitations of a system as a whole. The near +fields in the proximity of a MDM ferrite disk have space and time symmetry +breakings. Such MDM-originated fields, called magnetoelectric (ME) fields,carry +both spin and orbital angular momentums. By virtue of unique topology, ME +fields are different from free space electromagnetic (EM) fields. The ME fields +are quantum fluctuations in vacuum. We call these quantized states ME photons. +There are not virtual EM photons. We show that energy, spin and orbital angular +momenta of MDM oscillations constitute the key physical quantities that +characterize the ME field configurations. We show that vacuum can induce a +Casimir torque between a MDM ferrite disk, metal walls, and dielectric samples.",1801.08042v1 +2018-01-30,Engineering Surface Critical Behavior of (2+1)-Dimensional O(3) Quantum Critical Points,"Surface critical behavior (SCB) refers to the singularities of physical +quantities on the surface at the bulk phase transition. It is closely related +to and even richer than the bulk critical behavior. In this work, we show that +three types of SCB universality are realized in the dimerized Heisenberg models +at the (2+1)-dimensional O(3) quantum critical points by engineering the +surface configurations. The ordinary transition happens if the surface is +gapped in the bulk disordered phase, while the gapless surface state generally +leads to the multicritical special transition, even though the latter is +precluded in classical phase transitions because the surface is in the lower +critical dimension. An extraordinary transition is induced by the ferrimagnetic +order on the surface of the staggered Heisenberg model, in which the surface +critical exponents violate the results of the scaling theory and thus seriously +challenge our current understanding of extraordinary transitions.",1801.10035v2 +2018-09-07,Integrating all-optical switching with spintronics,"All-optical switching (AOS) of magnetic materials describes the reversal of +the magnetization using short (femtosecond) laser pulses, and has been observed +in a variety of materials. In the past decade it received extensive attention +due to its high potential for fast and energy-efficient data writing in future +spintronic memory applications. Unfortunately, the AOS mechanism in the +ferromagnetic multilayers commonly used in spintronics needs multiple pulses +for the magnetization reversal, losing its speed and energy efficiency. Here, +we experimentally demonstrate `on-the-fly' single-pulse AOS in combination with +spin Hall effect (SHE) driven motion of magnetic domains in Pt/Co/Gd +synthetic-ferrimagnetic racetracks. Moreover, using field-driven-SHE-assisted +domain wall (DW) motion measurements, both the SHE efficiency in the racetrack +is determined and the chirality of the optically written DW's is verified. Our +experiments demonstrate that Pt/Co/Gd racetracks facilitate both single-pulse +AOS as well as efficient SHE induced domain wall motion, which might ultimately +pave the way towards integrated photonic memory devices.",1809.02347v1 +2018-10-02,Spin-dependent (inverse) spin Hall effect in Co$_{60}$Fe$_{20}$B$_{20}$,"In ferromagnetic metals, the interconversion of spin and charge currents via +the spin Hall effect and its inverse can depend on the angle between the +ferromagnets magnetization and the spin current polarization direction. Here, +such a spin-dependent (inverse) spin Hall effect is found in the ferromagnetic +alloy Co$_{60}$Fe$_{20}$B$_{20}$. In a nonlocal magnon transport experiment, +Co$_{60}$Fe$_{20}$B$_{20}$ is used to both excite and detect magnonic spin +currents flowing in the ferrimagnetic insulator Y$_{3}$Fe$_{5}$O$_{12}$. We +find that the signal amplitude is significantly modulated by tuning the +direction of the Co$_{60}$Fe$_{20}$B$_{20}$ magnetization. We design a sample +structure that completely prevents direct magnonic coupling between the +ferromagnets. Thus, we can identify unambiguously an intrinsic electronic +origin of the observed effect.",1810.01227v3 +2018-10-17,Conventional magnon BEC in YIG film,"The conventional magnon Bose-Einstein condensation (BEC of magnons with k = +0) is a coherent state of excited magnons described by a common wave function. +It was observed first in antiferromagnetic superfluid states of 3He. Here we +report on the discovery of a very similar magnon BEC in ferrimagnetic film at +room temperature. The experiments were performed in Yttrium Iron Garnet (YIG) +films at a magnetic field oriented perpendicular to the film. The high-density +quasiequilibrium state of excited magnon was formed by methods of pulse and/or +Continuous Waves (CW) magnetic resonance. We have observed a Long Lived +Induction Decay Signals (LLIDS), well known as a signature of spin +superfluidity. We demonstrate that the BEC state may maintain permanently by +continuous replenishment of magnons with a small radiofrequency (RF) field. Our +finding opens the way for development of potential supermagnonic applications +at an ambient conditions.",1810.08051v2 +2018-10-31,Millimeter-sized magnetic domains in perpendicularly magnetized ferrimagnetic Mn4N thin films grown on SrTiO3,"The use of epitaxial layers for domain wall-based spintronic applications is +often hampered by the presence of pinning sites. Here, we show that when +depositing Mn4N(10 nm) epitaxial films, the replacement of MgO(001) by +SrTiO3(001) substrates allows minimizing the misfit, and to obtain an improved +crystalline quality, a sharper switching, a full remanence, a high anisotropy +and remarkable millimeter-sized magnetic domains, with straight and smooth +domain walls. In a context of rising interest for current-induced domain wall +motion in rare",1810.13184v1 +2019-06-03,Oxygen-vacancy induced magnetic phase transitions in multiferroic thin films,"Multiferroics in which giant ferroelectric polarization and magnetism coexist +are of tremendous potential for engineering disruptive applications in +information storage and energy conversion. Yet the functional properties of +multiferroics are thought to be affected detrimentally by the presence of point +defects, which may be abundant due to the volatile nature of some constituent +atoms and high temperatures involved in materials preparation. Here, we +demonstrate with theoretical methods that oxygen vacancies may enhance the +functionality of multiferroics by radically changing their magnetic +interactions in thin films. Specifically, oxygen vacancies may restore missing +magnetic super-exchange interactions in large axial ratio phases, leading to +full antiferromagnetic spin ordering, and induce the stabilization of +ferrimagnetic states with a significant net magnetization of 0.5 uB per formula +unit. Our theoretical study should help to clarify the origins of long-standing +controversies in bismuth ferrite and improve the design of technological +applications based on multiferroics.",1906.01117v1 +2019-06-04,Thickness dependence of spin Peltier effect visualized by thermal imaging technique,"Magnon propagation length in a ferrimagnetic insulator yttrium iron garnet +(YIG) has been investigated by measuring and analyzing the YIG-thickness t_YIG +dependence of the spin Peltier effect (SPE) in a Pt/YIG junction system. By +means of the lock-in thermography technique, we measured the spatial +distribution of the SPE-induced temperature modulation in the Pt/YIG system +with the t_YIG gradation, allowing us to obtain the accurate t_YIG dependence +of SPE with high t_YIG resolution. Based on the t_YIG dependence of SPE, we +verified the applicability of several phenomenological models to estimate the +magnon diffusion length in YIG.",1906.01560v3 +2019-06-20,Purely magnetic logic based on polarized spin waves,"Spin wave, the precession of magnetic order in magnetic materials, is a +collective excitation that carries spin angular momentum. Similar to the +acoustic or optical waves, the spin wave also possesses the polarization degree +of freedom. Although such polarization degrees of freedom are frozen in +ferromagnets, they are fully unlocked in antiferromagnets or ferrimagnets. Here +we introduce the concept of magnetic gating and demonstrate a spin wave analog +of the Datta-Das spin transistor in antiferromagnet. Utilizing the interplay +between polarized spin wave and the antiferromagnetic domain walls, we propose +a universal logic gate of pure magnetic nature, which realizes all Boolean +operations in one single magnetic structure. We further construct a full +functional 4-bit Arithmetic Logic Unit using only sixteen spin wave universal +logic gates, operating in a weaving fashion as a Jacquard loom machine. The +spin wave-based architecture proposed here also sets a model for the future +energy efficient non-volatile computing, the distributed processing-in-memory +computing, and the evolvable neuromorphic computing.",1906.08702v1 +2019-06-24,Electrical and magnetic properties of thin films of the spin-filter material CrVTiAl,"The spin-filter material CrVTiAl is a promising candidate for producing +highly spin-polarized currents at room temperature in a nonmagnetic +architecture. Thin films of compensated-ferrimagnetic CrVTiAl have been grown +and their electrical and magnetic properties have been studied. The resistivity +shows two-channel semiconducting behavior with one disordered gapless channel +and a gapped channel with activation energy $\Delta E$=~0.1~-~0.2~eV. +Magnetoresistance measurements to B~=~35~T provide values for the mobilities of +the gapless channel, leading to an order of magnitude difference in the carrier +effective masses, which are in reasonable accord with our +density-functional-theory based results. The density of states and electronic +band structure is computed for permutations of the four sublattices arranged +differently along the (111) body diagonal, yielding metallic (Cr-V-Al-Ti), +spin-gapless (Cr-V-Ti-Al) and spin-filtering (Cr-Ti-V-Al) phases. Robustness of +the spin-gapless phase to substitutional disorder is also considered.",1906.10222v1 +2019-06-26,Fermi Level Dependent Spin Pumping from a Magnetic Insulator into a Topological Insulator,"Topological spintronics aims to exploit the spin-momentum locking in the +helical surface states of topological insulators for spin-orbit torque devices. +We address a fundamental question that still remains unresolved in this +context: does the topological surface state alone produce the largest values of +spin-charge conversion efficiency or can the strongly spin-orbit coupled bulk +states also contribute significantly? By studying the Fermi level dependence of +spin pumping in topological insulator/ferrimagnetic insulator bilayers, we show +that the spin Hall conductivity is constant when the Fermi level is tuned +across the bulk band gap, consistent with a full bulk band calculation. The +results suggest a new perspective, wherein ""bulk-surface correspondence"" allows +spin-charge conversion to be simultaneously viewed either as coming from the +full bulk band, or from spin-momentum locking of the surface state.",1906.11116v1 +2019-07-02,Entanglement entropy in low-energy field theories at finite chemical potential,"We investigate the leading area-law contribution to entanglement entropy in a +system described by a general Lagrangian with O(2) symmetry containing first- +and second-order time derivatives, namely breaking the Lorentz-invariance. We +establish a connection between the Higgs gap present in a symmetry-broken phase +and the area-law term for the entanglement entropy in the general, +non-relativistic case. Our predictions for the entanglement entropy and +correlation length are successfully compared to numerical results in two +paradigmatic systems: the Mott insulator to superfluid transition for ultracold +lattice bosons, and the ground state of ferrimagnetic systems.",1907.01204v2 +2019-07-05,Supraferromagnetic correlations in clusters of magnetic nanoflowers,"Magnetic nanoflowers are densely packed aggregates of superferromagnetically +coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia +experiments. Here, we investigate the nature of the moment coupling within a +powder of such nanoflowers using spin-resolved small-angle neutron scattering. +Within the powder the nanoparticles are agglomerated to clusters, and we can +show that the moments of neighboring nanoflowers tend to align parallel to each +other. Thus, the whole system resembles a hierarchical magnetic nanostructure +consisting of three distinct levels, i.e. (i) the ferrimagnetic +nanocrystallites as building blocks, (ii) the superferromagnetic nanoflowers, +and (iii) the \textit{supra}ferromagnetic clusters of nanoflowers. We surmise +that such a supraferromagnetic coupling explains the enhanced magnetic +hyperthermia performance in case of interacting nanoflowers.",1907.02752v2 +2019-07-10,Mechanism for a Chemical Potential of Nonequilibrium Magnons in Parametric Parallel Pumping,"We demonstrate how a magnon chemical potential is generated in parametric +parallel pumping. We study how a time-periodic magnetic field of this pumping +affects magnon properties of a ferrimagnet in a nonequilibrium steady state. We +show that the magnon distribution function of our nonequilibrium steady state +becomes the Bose distribution function with $\mu=\omega_{\textrm{p}}/2$, where +$\mu$ is the magnon chemical potential and $\omega_{\textrm{p}}$ is the pumping +frequency. This result is distinct from the absence of the magnon chemical +potential in the standard theory and can qualitatively explain its generation +in experiments. We believe our result is a first theoretical demonstration of +the generation of the magnon chemical potential in the parametric parallel +pumping, providing an important step towards a thorough understanding of +properties of nonequilibrium magnons.",1907.04552v1 +2019-07-12,Electrical current switching of the noncollinear antiferromagnet Mn$_3$GaN,"We report electrical current switching of noncollinear antiferromagnetic +(AFM) Mn$_3$GaN/Pt bilayers at room temperature. The Hall resistance of these +bilayers can be manipulated by applying a pulse current of +$1.5\times10^6$~A/cm$^2$, whereas no significant change is observed up to +$\sim10^8$~A/cm$^2$ in Mn$_3$GaN single films, indicating that the Pt layer +plays an important role. In comparison with ferrimagnetic Mn$_3$GaN/Pt +bilayers, a lower electrical current switching of noncollinear AFM Mn$_3$GaN is +demonstrated, with a critical current density two orders of magnitude smaller. +Our results highlight that a combination of a noncollinear AFM antiperovskite +nitride and a spin-torque technique is a good platform of AFM spintronics.",1907.05544v1 +2019-07-18,Compensation in the spin-1/2 site diluted Ising ferrimagnet: A Monte Carlo study,"A two-dimensional spin-1/2 trilayer magnetic system with quenched +non-magnetic impurity is studied. The lattice is formed by alternate layers of +two different theoretical atoms A and B arranged in a particular fashion A-B-A. +The compensation point appears below the critical temperature, for which total +magnetization of the system becomes zero even though the sublattice +magnetization has a nonzero value. For a range of values of the relative +interaction strength in the Hamiltonian, a compensation point is observed. We +considered the Ising mechanics and employed the Monte Carlo method to determine +the compensation point and critical temperature of the system. However, the +effects of impurity in such systems are still not well studied. With that in +mind, we address the effects of random non-magnetic impurity in the trilayer +system. We also investigate the lattice morphologies in the presence of +compensation and dilution and finally obtain the three-dimensional phase +diagram for selected Hamiltonian parameters and impurity concentration.",1907.07879v5 +2019-07-24,Electron doping induced magnetic glassy state in phase separated YBaCo$_2$O$_{5.5-δ}$,"The structural, magnetic and transport properties of the layered +RBaCo$_2$O$_{5.5}$ cobaltites are sensitive to the oxygen stoichiometry. In +this present study, we report the presence of a low-temperature magnetic glassy +state in electron-doped polycrystalline YBaCo$_2$O$_{5.5}$ cobaltite. The ac +magnetization studies show the absence of conventional spin glass features, +while the various dc magnetization studies demonstrate the presence of +non-equilibrium magnetic glassy state at low temperature. The magnetic glassy +state of this sample results from the kinetic arrest of the first order ferro +(or ferri) to antiferromagnetic transition. The role of electron doping in the +occurrence of magnetic glassy phenomena is discussed in terms of magnetic phase +separation involving the Co3+/Co2+ clusters of the ferrimagnetic phase in the +Co3+/Co3+ antiferromagnetic matrix.",1907.10248v1 +2019-07-31,Large spin Hall magnetoresistance in antiferromagnetic α-Fe2O3/Pt heterostructures,"We investigate the spin Hall magnetoresistance (SMR) at room temperature in +thin film heterostructures of antiferromagnetic, insulating, (0001)-oriented +alpha-Fe2O3 (hematite) and Pt. We measure their longitudinal and transverse +resistivities while rotating an applied magnetic field of up to 17T in three +orthogonal planes. For out-of-plane magnetotransport measurements, we find +indications for a multidomain antiferromagnetic configuration whenever the +field is aligned along the film normal. For in-plane field rotations, we +clearly observe a sinusoidal resistivity oscillation characteristic for the SMR +due to a coherent rotation of the Neel vector. The maximum SMR amplitude of +0.25% is, surprisingly, twice as high as for prototypical ferrimagnetic +Y3Fe5O12/Pt heterostructures. The SMR effect saturates at much smaller magnetic +fields than in comparable antiferromagnets, making the alpha-Fe2O3/Pt system +particularly interesting for room-temperature antiferromagnetic spintronic +applications.",1907.13393v4 +2019-10-01,Weyl nodes and magnetostructural instability in antiperovskite Mn$_3$ZnC,"The ferromagnetic phase of the cubic antiperovskite Mn$_3$ZnC is suggested +from first-principles calculation to be a nodal line Weyl semimetal. Features +in the electronic structure that are the hallmark of a nodal line Weyl state, a +large density of linear band crossings near the Fermi level, can also be +interpreted as signatures of a structural and/or magnetic instability. Indeed, +it is known that Mn$_3$ZnC undergoes transitions upon cooling from a +paramagnetic to a cubic ferromagnetic state under ambient conditions and then +further into a non-collinear ferrimagnetic tetragonal phase at a temperature +between 250$\,$K and 200$\,$K. The existence of Weyl nodes and their +destruction via structural and magnetic ordering is likely to be relevant to a +range of magnetostructurally coupled materials.",1910.00184v2 +2019-10-02,Phase diagrams and critical behaviours of the mixed spin-5/2 and spin-7/2 Ising system,"We used mean-field theory based on the Bogoliubov inequality for the Gibbs +free energy to examine the magnetic properties of a mixed spin-5/2 and spin-7/2 +Blume-Capel ferrimagnetic system. The thermal behaviours of the system +magnetization are classified according to the extended N\'eel nomenclature. The +system exhibits compensation phenomena where a complete cancellation of +sublattice magnetizations is observed below the critical temperature. +Temperature-dependent phase diagrams are constructed for the case of unequal +sublattice crystal field interactions. Under appropriate conditions, our +calculations reveal first-order transitions in addition to second-order ones +previously observed in Monte Carlo simulations.",1910.00908v1 +2019-10-24,Zero Field Cooled Exchange Bias Effect in Nano-Crystalline Mg-Ferrite Thin Film,"I report, Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase +nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz +substrate using pulsed laser ablation technique. The film showed a high ZFC EB +shift (HE~ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing +temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite +thin film also showed Conventional Exchange Bias (CEB) effect, but unlike many +CEB systems, the film showed decrease in the coercivity (HC) under the Field +Cooled (FC) measurements. The film also showed training effect in ZFC +measurements which followed the frozen spin relaxation behaviour. The observed +exchange bias could be attributed to the pinning effect of the surface spins of +frozen glassy states at the interface of large ferrimagnetic grains.",1910.10948v1 +2019-10-25,Local magnetic anisotropy by polarized neutron powder diffraction: application of magnetically induced preferred crystallite orientation,"Polarized neutron diffraction allows to determine the local susceptibility +tensor on the magnetic site both in single crystals and powders. It is widely +used in the studies of single crystals, but it is still hardly applicable to a +number of highly interesting powder materials, like molecular magnets or +nanoscale systems because of the low luminosity of existing instruments and the +absence of an appropriate data analysis software. We show that these +difficulties can be overcome by using a large area detector in combination with +the two-dimensional Rietveld method and powder samples with magnetically +induced preferred crystallite orientation. This is demonstrated by revisiting +two test powder compounds, namely, low anisotropy (soft) ferrimagnetic compound +Fe3O4 and spin-ice compound Ho2Ti2O7 with high local anisotropy. The values of +magnetic moments in Fe3O4 and the susceptibility tensors of Ho2Ti2O7 at various +temperatures and fields were found in perfect agreement with these found +earlier in single crystal experiments. The magnetically induced preferred +crystallite orientation was used to study the local susceptibility of a +single-molecule magnet Co([(CH3)2N]2CS)2Cl2. Hence, the studies of local +magnetic anisotropy in powder systems might now become accessible.",1910.11822v1 +2020-01-09,"High temperature thermal cycling effect on the irreversible responses of lattice structure, magnetic properties and electrical conductivity in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide","We report high temperature synchrotron X-ray diffraction (SXRD), dc +magnetization and current-voltage (I-V) characteristics for the samples of +Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical +reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing +at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by +cycling the temperature from 300 K to high temperature (warming mode) and +return back to 300 K (cooling mode). The SXRD patterns indicated a fine +bi-phased cubic spinel structure in the highly Co rich spinel oxide. +Magnetization curves showed intrinsic ferrimagnetic features and defect induced +additional ferromagnetic phase at higher temperatures. Electrical conductivity +showed thermal hysteresis loop between warming and cooling modes of temperature +variation. The samples exhibited new information on the irreversibility +phenomena of lattice structure, magnetization and electrical conductivity on +cycling the measurement temperatures.",2001.02829v2 +2020-02-23,"Generating lightwave-photon-and-magnon entanglement with a mechanical oscillator as a ""cold reservoir""","We present a scheme to implement a steady lightwave-photon-and-magnon +entanglement in a hybrid photon-magnon system by adiabatically eliminating the +auxiliary microwave cavity and effectively laser cooling a delocalized +Bogoliubov mode. The system consists of magnons, lightwave and microwave +photons, and phonons. The magnons are embodied by a collective motion of a +large number of spins in a macroscopic ferrimagnet. To achieve an entangling +interaction between magnons and lightwave photons, we drive optical cavity and +magnon at the red and blue sideband associated with the mechanical resonator. +In particular, optimizing the relative ratio of effect couplings, rather than +simply increasing their magnitudes, is essential for achieving strong +entanglement. Unlike typical dissipative entanglement schemes, our results +cannot be described by treating the effects of the entangling reservoir via a +Linblad master equation.",2002.10877v2 +2020-04-04,Lattice distortion in TmCo$_2$: a poly- and single- crystal study,"Within the RCo$_2$ family of compounds, a structural distortion linked with +the onset of magnetic ordering around the critical temperature can be observed. +One of the less explored RCo$_2$ compounds is TmCo$_2$ probably due to its low +Curie temperature. Exceptionally this compound, given its position at the end +of the ferrimagnetic series, shows discrepancies in the ordering of the Co +sub-lattice because of a weak Weiss molecular field. In this paper we focus on +the structural distortion in TmCo$_2$, which appears together with the magnetic +ordering around the critical temperature of $T_{C}\sim3.6$~K. Poly-crystals as +well as single-crystals of TmCo$_2$ were used in our experiments. For both +kinds of samples we observed the same type of the rhombohedral distortion along +the [111] direction from the cubic Fd$\bar{3}$m to R$\bar{3}$m space group. The +relation between observed magnetic and structural properties in this compound +is discussed.",2004.01938v1 +2020-04-07,Optomagnonic Barnett effect,"Combining the technologies of quantum optics and magnonics, we find that the +circularly polarized laser can dynamically realize the quasiequilibrium magnon +Bose-Einstein condensates (BEC). The Zeeman coupling between the laser and +spins generates the optical Barnett field, and its direction is controllable by +switching the laser chirality. We show that the optical Barnett field develops +the total magnetization in insulating ferrimagnets with reversing the local +magnetization, which leads to the quasiequilibrium magnon BEC. This +laser-induced magnon BEC transition through optical Barnett effect, dubbed the +optomagnonic Barnett effect, provides an access to coherent magnons in the high +frequency regime of the order of terahertz. We also propose a realistic +experimental setup to observe the optomagnonic Barnett effect using current +device and measurement technologies as well as the laser chirping. The +optomagnonic Barnett effect is a key ingredient for the application to +ultrafast spin transport.",2004.03353v2 +2020-04-11,Brillouin Light Scattering of Spin Waves Inaccessible with Free-Space Light,"Micro-focus Brillouin light scattering is a powerful technique for the +spectroscopic and spatial characterization of elementary excitations in +materials. However, the small momentum of light limits the accessible +excitations to the center of the Brillouin zone. Here, we utilize a metallic +nanoantenna fabricated on the archetypal ferrimagnet yttrium iron garnet to +demonstrate the possibility of Brillouin light scattering from +large-wavevector, high-frequency spin wave excitations that are inaccessible +with free-space light. The antenna facilitates sub-diffraction confinement of +electromagnetic field, which enhances the local field intensity and generates +momentum components significantly larger than those of free-space light. Our +approach provides access to high frequency spin waves important for fast +nanomagnetic devices, and can be generalized to other types of excitations and +light scattering techniques.",2004.05314v1 +2020-12-01,Design of an optomagnonic crystal: towards optimal magnon-photon mode matching at the microscale,"We put forward the concept of an optomagnonic crystal: a periodically +patterned structure at the microscale based on a magnetic dielectric, which can +co-localize magnon and photon modes. The co-localization in small volumes can +result in large values of the photon-magnon coupling at the single quanta +level, which opens perspectives for quantum information processing and quantum +conversion schemes with these systems. We study theoretically a simple geometry +consisting of a one-dimensional array of holes with an abrupt defect, +considering the ferrimagnet Yttrium Iron Garnet (YIG) as the basis material. We +show that both magnon and photon modes can be localized at the defect, and use +symmetry arguments to select an optimal pair of modes in order to maximize the +coupling. We show that an optomagnonic coupling in the kHz range is achievable +in this geometry, and discuss possible optimization routes in order to improve +both coupling strengths and optical losses.",2012.00760v2 +2020-12-04,Nutation in antiferromagnetic resonance,"The effect of inertial spin dynamics is compared between ferromagnetic, +antiferromagnetic and ferrimagnetic systems. The linear response to an +oscillating external magnetic field is calculated within the framework of the +inertial Landau--Lifshitz--Gilbert equation using analytical theory and +computer simulations. Precession and nutation resonance peaks are identified, +and it is demonstrated that the precession frequencies are reduced by the spin +inertia, while the lifetime of the excitations is enhanced. The interplay +between precession and nutation is found to be the most prominent in +antiferromagnets, where the timescale of the exchange-driven sublattice +dynamics is comparable to inertial relaxation times. Consequently, +antiferromagnetic resonance techniques should be better suited for the search +for intrinsical inertial spin dynamics on ultrafast timescales than +ferromagnetic resonance.",2012.02790v3 +2020-12-08,Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound,"The structural, electronic and magnetic properties of Fe7S8 material have +been studied within the framework of the ab-initio calculations, the mean field +approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two +forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2 +are the most probable configurations. A mixed Ising model with ferromagnetic +spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and +with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has +been used to study the magnetic properties of this compound. We demonstrated +that the magnetic phase transition can be either of the first or of the second +order, depending on the value of the exchange interaction and crystal field. +The presence of vacancies in every second iron layer leads to incomplete +cancellation of magnetic moments, hence to the emergence of the ferrimagnetism. +Anomalies in the magnetization behavior have been found and compared with the +experimental results.",2012.04306v1 +2020-12-21,Inverse Faraday Effect in an Optomagnonic Waveguide,"Single-mode high-index-contrast waveguides have been ubiquitously exploited +in optical, microwave, and phononic structures for achieving enhanced +wave-matter interactions. Although micro-scale optomechanical and +electro-optical devices have been widely studied, optomagnonic devices remain a +grand challenge at the microscale. Here, we introduce a planar optomagnonic +waveguide platform based on a ferrimagnetic insulator that simultaneously +supports single transverse mode of spin waves (magnons) and highly confined +optical modes. The co-localization of spin and light waves gives rise to +enhanced inverse Faraday effect, and as a result, magnons are excited by an +effective magnetic field generated by interacting optical photons. Moreover, +the strongly enhanced optomagnonic interaction allows us to observe such effect +using low-power (milliwatt level) light signals in the continuous-wave form, as +opposed to high-intensity (megawatt peak power) light pulses that are typically +required in magnetic bulk materials or thin films. The optically-driven magnons +are detected electrically with preserved phase coherence, showing the +feasibility for launching spin waves with low-power continuous optical fields.",2012.11119v2 +2020-12-29,Strongly modulated ultrafast demagnetization and magnetization precession dynamics in ferrimagnetic Gdx(CoFe)1-x alloys via 3d-4f intersublattice exchange coupling,"Manipulation of the intersublattice interaction strengh (JRE-TM) in rare +earth (RE)-transition metal (TM) alloys is a key issue to understand how +efficiently the laser-induced angular momentum transfers from 3d to 4f spins +and to have a better control of the ultrafast spin dynamics. In this work, the +relationships between laser-induced demagnetization process and the +intersublattice 3d-4f interaction for the GdCoFe alloys were systematically +studied. The ultrafast two-stage demagnetization process could change into a +one-stage mode as the angular momentum transferring channel between 3d and 4f +spins is switched off, which could be modulated by JRE-TM. Furthermore, both +the effective g-factor and damping constant deduced by the subsequently +laser-induced magnetization precession process diverge at the angular momentum +compensation point based on the ferromagnetic resonance method with the LLG +equations. The results provide an alternative way to efficiently manipulate the +ultrafast demagnetization time for practical applications.",2012.14620v1 +2021-01-04,"Electronic, magnetic and optical properties of penta-BN$_2$ nanoribbons: a first principles study","The search for new materials is a very intense task in many technological +areas. In 2015, a new variant of graphene was proposed, the pentagraphene, +which was followed by the propose of a pentagonal boron nitride structure +called penta-BN$_2$. Based on these structures, we investigated the electronic, +magnetic, and optical properties of penta-BN$_2$ nanoribbons (p-BNNRs) +considering four different kinds of edges, carefully closing the valence shells +with H atoms to prevent dangling bonds. To achieve this goal, we used +first-principles calculations in a density functional theory framework. Our +findings showed that the p-BNNRs have a rich magneto-electronic behavior, +varying from semiconductor to half-metal. We obtained that they are +ferrimagnetic, having an intrinsic magnetism, which allow potential +applications in spintronic or spinwaves. From an optical absorption point of +view, they mainly absorb at ultraviolet region of the spectrum, especially at +UV-B region, which could indicate a potential application as a UV filter.",2101.00879v1 +2021-01-07,Quantum annealing simulation of out-of-equilibrium magnetization in a spin-chain compound,"Geometrically frustrated spin-chain compounds such as Ca3Co2O6 exhibit +extremely slow relaxation under a changing magnetic field. Consequently, both +low-temperature laboratory experiments and Monte Carlo simulations have shown +peculiar out-of-equilibrium magnetization curves, which arise from trapping in +metastable configurations. In this work we simulate this phenomenon in a +superconducting quantum annealing processor, allowing us to probe the impact of +quantum fluctuations on both equilibrium and dynamics of the system. Increasing +the quantum fluctuations with a transverse field reduces the impact of +metastable traps in out-of-equilibrium samples, and aids the development of +three-sublattice ferrimagnetic (up-up-down) long-range order. At equilibrium we +identify a finite-temperature shoulder in the 1/3-to-saturated phase +transition, promoted by quantum fluctuations but with entropic origin. This +work demonstrates the viability of dynamical as well as equilibrium studies of +frustrated magnetism using large-scale programmable quantum systems, and is +therefore an important step toward programmable simulation of dynamics in +materials using quantum hardware.",2101.02769v1 +2021-01-07,Squeezing Microwaves by Magnetostriction,"Squeezed light finds many important applications in quantum information +science and quantum metrology, and has been produced in a variety of physical +systems involving optical nonlinear processes. Here, we show how a nonlinear +magnetostrictive interaction in a ferrimagnet in cavity magnomechanics can be +used to reduce quantum noise of the electromagnetic field. We show optimal +parameter regimes where a substantial and stationary squeezing of the microwave +output field can be achieved. The scheme can be realized within the reach of +current technology in cavity electromagnonics and magnomechanics. Our work +provides a new and practicable approach for producing squeezed vacuum states of +electromagnetic fields, and may find promising applications in quantum +information processing and quantum metrology.",2101.02796v3 +2021-01-16,Universal Critical Exponents of the Magnetic Domain Wall Depinning Transition,"Magnetic field driven domain wall dynamics in a ferrimagnetic GdFeCo thin +film with perpendicular magnetic anisotropy is studied using low temperature +magneto-optical Kerr microscopy. Measurements performed in a practically +athermal condition allow for the direct experimental determination of the +velocity ($ \beta = 0.30 \pm 0.03 $) and correlation length ($ \nu = 1.3 \pm +0.3 $) exponents of the depinning transition. The whole family of exponents +characterizing the transition is deduced, providing evidence that the depinning +of magnetic domain walls is better described by the quenched Edwards-Wilkinson +universality class.",2101.06555v3 +2012-05-08,Theory of High T$_c$ Ferrimagnetism in a Multi-orbital Mott Insulator,"We propose a model for the multi-orbital material Sr$_2$CrOsO$_6$ (SCOO), an +insulator with remarkable magnetic properties and the highest $T_c \simeq 725$ +K among {\em all} perovskites with a net moment. We derive a new criterion for +the Mott transition $(\widetilde{U}_{1} \widetilde{U}_{2})^{1/2}>2.5W$ using +slave rotor mean field theory, where $W$ is the bandwidth and +$\widetilde{U}_{1(2)}$ are the effective Coulomb interactions on Cr(Os) +including Hund's coupling. We show that SCOO is a Mott insulator, where the +large Cr $\widetilde{U}_{1}$ compensates for the small Os $\widetilde{U}_{2}$. +The spin sector is described by a frustrated antiferromagnetic Heisenberg model +that naturally explains the net moment arising from canting and also the +observed non-monotonic magnetization $M(T)$. We predict characteristic magnetic +structure factor peaks that can be probed by neutron experiments.",1205.1811v2 +2012-05-22,Partial disorder in an Ising-spin Kondo lattice model on a triangular lattice,"Phase diagram of an Ising-spin Kondo lattice model on a triangular lattice +near 1/3-filling is investigated by Monte Carlo simulation. We identify a +partially disordered phase with coexistence of magnetic order and paramagnetic +moments, which was unstable in two-dimensional Ising models with localized +spins only. The partial disorder emerges in the competing regime between a +twosublattice stripe phase and three-sublattice ferrimagnetic phase, at finite +temperatures above an electronic phase separation. The peculiar magnetic +structure accompanies a charge order and develops a gap in the electronic +structure. The results manifest a crucial role of the nonperturbative interplay +between spin and charge degrees of freedom in stabilizing the partial disorder.",1205.4826v1 +2012-05-31,Magnetic Nanoparticles in the Interstellar Medium: Emission Spectrum and Polarization,"The presence of ferromagnetic or ferrimagnetic nanoparticles in the +interstellar medium would give rise to magnetic dipole radiation at microwave +and submm frequencies. Such grains may account for the strong mm-wavelength +emission observed from a number of low-metallicity galaxies, including the +Small Magellanic Cloud. We show how to calculate the absorption and scattering +cross sections for such grains, with particular attention to metallic Fe, +magnetite Fe3O4, and maghemite gamma-Fe2O3, all potentially present in the +interstellar medium. The rate of Davis-Greenstein alignment by magnetic +dissipation is also estimated. We determine the temperature of free-flying +magnetic grains heated by starlight and we calculate the polarization of the +magnetic dipole emission from both free-fliers and inclusions. For inclusions, +the magnetic dipole emission is expected to be polarized orthogonally relative +to the normal electric dipole radiation. Finally, we present self-consistent +dielectric functions for metallic Fe, magnetite Fe3O4, and maghemite +gamma-Fe2O3, enabling calculation of absorption and scattering cross sections +from microwave to X-ray wavelengths.",1205.7021v2 +2017-04-29,Theory of magnetism in La$_2$NiMnO$_6$,"The magnetism of ordered and disordered La$_2$NiMnO$_6$ is explained using a +model involving double exchange and superexchange. The concept of majority spin +hybridization in the large coupling limit is used to explain the ferromagnetism +of La$_2$NiMnO$_6$ as compared to the ferrimagnetism of Sr$_{2}$FeMoO$_{6}$. +The ferromagnetic insulating ground state in the ordered phase is explained. +The essential role played by the Ni-Mn superexchange between the Ni $e_{g}$ +electron spins and the Mn $t_{2g}$ core electron spins in realizing this ground +state, is outlined. In presence of antisite disorder, the model system is found +to exhibit a tendency of becoming a spin-glass at low temperatures, while it +continues to retain a ferromagnetic transition at higher temperatures, similar +to recent experimental observations [D. Choudhury .et.al., Phys. Rev. Lett. +108, 127201 (2012)]. This reentrant spin-glass or reentrant ferromagnetic +behaviour is explained in terms of the competition of the ferromagnetic double +exchange between the Ni $e_{g}$ and the Mn $e_{g}$ electrons, and the +ferromagnetic Ni-Mn superexchange, with the antiferromagnetic antisite Mn-Mn +superexchange.",1705.00177v2 +2017-05-08,"Re-entrant spin-glass freezing and magneto-dielectric behavior of Li3NiRuO6, a layered rock-salt related oxide","We report the results of neutron diffraction, ac and dc magnetization, +heat-capacity, complex permittivity, and pyrocurrent measurements on an oxide, +Li3NiRuO5, hitherto not paid much attention in the literature, except for a +previous report on its promising electrochemical performance. We emphasize on +the following findings: (i) Observation of re-entrant spin-glass behavior; that +is, this oxide undergoes ferrilmagnetic ordering below 8- K, entering +spin-glass regime around 12 K. (ii) There is no prominent feature in the +complex dielectric permittivity (in particular, at the magnetic transitions) in +the absence of external magnetic field, indicative of the absence of +ferroelectricity. However, there is a distinct evidence for magneto-dielectric +(MDE) coupling. The sign of MDE coupling also changes as the sample is cooled +from ferrimagnetic state to spin-glass regime. (iii) There are pyroelectric +anomalies in the vicinity of 30-70 K, presumably from thermally stimulated +depolarization current.",1705.02868v1 +2017-05-18,The Final Chapter In The Saga Of YIG,"The magnetic insulator Yttrium Iron Garnet can be grown with exceptional +quality, has a ferrimagnetic transition temperature of nearly 600 K, and is +used in microwave and spintronic devices that can operate at room temperature. +The most accurate prior measurements of the magnon spectrum date back nearly 40 +years, but cover only 3 of the lowest energy modes out of 20 distinct magnon +branches. Here we have used time-of-flight inelastic neutron scattering to +measure the full magnon spectrum throughout the Brillouin zone. We find that +the existing model of the excitation spectrum, well known from an earlier work +titled ""The Saga of YIG"", fails to describe the optical magnon modes. Using a +very general spin Hamiltonian, we show that the magnetic interactions are both +longer-ranged and more complex than was previously understood. The results +provide the basis for accurate microscopic models of the finite temperature +magnetic properties of Yttrium Iron Garnet, necessary for next-generation +electronic devices.",1705.06594v1 +2017-05-25,Monte Carlo study of an anisotropic Ising multilayer with antiferromagnetic interlayer couplings,"We present a Monte Carlo study of the magnetic properties of an Ising +multilayer ferrimagnet. The system consists of two kinds of non-equivalent +planes, one of which is site-diluted. All intralayer couplings are +ferromagnetic. The different kinds of planes are stacked alternately and the +interlayer couplings are antiferromagnetic. We perform the simulations using +the Wolff algorithm and employ multiple histogram reweighting and finite-size +scaling methods to analyze the data with special emphasis on the study of +compensation phenomena. Compensation and critical temperatures of the system +are obtained as functions of the Hamiltonian parameters and we present a +detailed discussion about the contribution of each parameter to the presence or +absence of the compensation effect. A comparison is presented between our +results and those reported in the literature for the same model using the pair +approximation. We also compare our results with those obtained through both the +pair approximation and Monte Carlo simulations for the bilayer system.",1705.10192v2 +2017-05-30,Focused issue on antiferromagnetic spintronics: An overview (Part of a collection of reviews on antiferromagnetic spintronics),"This focused issue attempts to provide a comprehensive introduction into the +field of antiferromagnetic spintronics. Apart from the brief overview below, it +features five review articles. The intention is to cover in a coherent and +complementary way key physical aspects of the antiferromagnetic spintronics +research. These range from microelectronic memory devices and optical +manipulation and detection of antiferromagnetic spins, to the fundamentals of +antiferromagnetic dynamics in uniform or spin-textured systems, and to the +interplay of antiferromagnetic spintronics with topological phenomena. The +antiferromagnetic ordering can take a number of forms including fully +compensated collinear, non-collinear, and non-coplanar magnetic lattices, +compensated and uncompensated ferrimagnets, or metamagnetic materials hosting +an antiferromagnetic to ferromagnetic phase transition. Apart from the variety +of distinct magnetic crystal structures, the focused issue also encompasses +spintronic phenomena and devices studied in antiferromagnet/ferromagnet +heterostructures and in synthetic antiferromagnets.",1705.10489v1 +2017-09-12,Direct observation of magnon-phonon coupling in yttrium iron garnet,"The magnetic insulator yttrium iron garnet (YIG) with a ferrimagnetic +transition temperature of $\sim$560 K has been widely used in microwave and +spintronic devices. Anomalous features in the spin Seeback effect (SSE) +voltages have been observed in Pt/YIG and attributed to the magnon-phonon +coupling. Here we use inelastic neutron scattering to map out low-energy spin +waves and acoustic phonons of YIG at 100 K as a function of increasing magnetic +field. By comparing the zero and 9.1 T data, we find that instead of splitting +and opening up gaps at the spin wave and acoustic phonon dispersion +intersecting points, magnon-phonon coupling in YIG enhances the hybridized +scattering intensity. These results are different from expectations of +conventional spin-lattice coupling, calling for new paradigms to understand the +scattering process of magnon-phonon interactions and the resulting +magnon-polarons.",1709.03940v1 +2017-09-21,Current-induced magnetization switching using electrically-insulating spin-torque generator,"Current-induced magnetization switching through spin-orbit torques (SOTs) is +the fundamental building block of spin-orbitronics. The SOTs generally arise +from the spin-orbit coupling of heavy metals. However, even in a +heterostructure where a metallic magnet is sandwiched by two different +insulators, a nonzero current-induced SOT is expected because of the broken +inversion symmetry; an electrical insulator can be a spin-torque generator. +Here, we demonstrate current-induced magnetization switching using an +insulator. We show that oxygen incorporation into the most widely used +spintronic material, Pt, turns the heavy metal into an electrically-insulating +generator of the SOTs, enabling the electrical switching of perpendicular +magnetization in a ferrimagnet sandwiched by electrically-insulating oxides. We +further found that the SOTs generated from the Pt oxide can be controlled +electrically through voltage-driven oxygen migration. These findings open a +route towards energy-efficient, voltage-programmable spin-orbit devices based +on solid-state switching of heavy metal oxidation.",1709.07127v1 +2017-09-26,Magnetic-field-induced suppression of spin Peltier effect in Pt/${\rm Y_{3}Fe_{5}O_{12}}$ system at room temperature,"We report the observation of magnetic-field-induced suppression of the spin +Peltier effect (SPE) in a junction of a paramagnetic metal Pt and a +ferrimagnetic insulator ${\rm Y_{3}Fe_{5}O_{12}}$ (YIG) at room temperature. +For driving the SPE, spin currents are generated via the spin Hall effect from +applied charge currents in the Pt layer, and injected into the adjacent thick +YIG film. The resultant temperature modulation is detected by a commonly-used +thermocouple attached to the Pt/YIG junction. The output of the thermocouple +shows sign reversal when the magnetization is reversed and linearly increases +with the applied current, demonstrating the detection of the SPE signal. We +found that the SPE signal decreases with the magnetic field. The observed +suppression rate was found to be comparable to that of the spin Seebeck effect +(SSE), suggesting the dominant and similar contribution of the low-energy +magnons in the SPE as in the SSE.",1709.08997v1 +2018-03-07,Ultra-Fast Ferrimagnetic All Spin Logic Device,"All spin logic device (ASLD) blazes an alternative path for realizing +ultra-low power computing in the Post-Moore era. However, initial device +structure relying on ferromagnetic input/output and spin transfer torque (STT) +driven magnetization switching degrades its performance and even hinders its +realization. In this paper, we propose an ASLD based on rare-earth +(RE)-transition-metal (TM) ferromagnetic alloy that can achieve an ultra-high +frequency up to terahertz. The spin orbit torque (SOT) induced fast precession +near the spin angular momentum compensated point is investigated through the +macrospin model. Combining the non-local spin current diffusing from the input +to the output, a deterministic picosecond switching can be realized without any +external magnetic field. Our results show that ASLD has the potential to exceed +the performance of mainstream computing.",1803.02552v1 +2018-03-09,Strong anomalous Nernst effect in collinear magnetic Weyl semimetals without net magnetic moments,"We predict a large anomalous Nernst effect in the inverse Heusler compensated +ferrimagnets Ti$_2$Mn$X$ ($X$=Al,Ga,In) with vanishing net magnetic moments. +Though the net magnetic moment is zero, the Weyl points in these systems lead +to a large anomalous Nernst conductivity (ANC) due to the lack of a magnetic +sublattice that inverses the sign of the Berry curvature. In comparison to the +noncollinear antiferromagnets Mn$_3$Sn and Mn$_3$Ge, the high ANC stems almost +entirely from the Weyl points in this class of compounds, and thus, it is +topologically protected. This work shows for the first time a large ANC with +zero net magnetic moments in collinear systems, which is helpful for +comprehensive understanding of the thermoelectric effect in zero-moment +magnetic materials and its further applications.",1803.03439v3 +2018-03-13,Spin wave localization and guiding by magnon band structure engineering in yttrium iron garnet,"In spintronics the propagation of spin-wave excitations in magnetically +ordered materials can also be used to transport and process information. One of +the most popular materials in this regard is the ferrimagnetic insulator +yttrium-iron-garnet due its exceptionally small spin-wave damping parameter. +While the small relaxation rate allows for large propagation length of magnetic +excitations, it also leads to non-locality of the magnetic properties. By +imaging spin waves their band structure is mapped. In doing so wave vector +selection is shown to suppress dispersion effects to a large extent allowing +for local measurements of spin relaxation. Moreover we demonstrate even higher +control of magnon propagation by employing the wave vector selectivity near an +avoided crossing of different spin-wave modes where the group velocity +approaches zero. Here local engineering of the dispersion allows constructing +magnonic waveguides and at the same time reveals the local relaxation +properties.",1803.04943v3 +2018-06-01,Dirac-Surface-State Modulated Spin Dynamics in a Ferrimagnetic Insulator at Room Temperature,"This work demonstrates dramatically modified spin dynamics of magnetic +insulator (MI) by the spin-momentum locked Dirac surface states of the adjacent +topological insulator (TI) which can be harnessed for spintronic applications. +As the Bi-concentration x is systematically tuned in 5 nm thick (BixSb1-x)2Te3 +TI film, the weight of the surface relative to bulk states peaks at x = 0.32 +when the chemical potential approaches the Dirac point. At this concentration, +the Gilbert damping constant of the precessing magnetization in 10 nm thick +Y3Fe5O12 MI film in the MI/TI heterostructures is enhanced by an order of +magnitude, the largest among all concentrations. In addition, the MI acquires +additional strong magnetic anisotropy that favors the in-plane orientation with +similar Bi-concentration dependence. These extraordinary effects of the Dirac +surface states distinguish TI from other materials such as heavy metals in +modulating spin dynamics of the neighboring magnetic layer.",1806.00151v1 +2018-06-07,Terahertz Emission from Compensated Magnetic Heterostructures,"Terahertz emission spectroscopy (TES) has recently played an important role +in unveiling the spin dynamics at a terahertz (THz) frequency range. So far, +ferromagnetic (FM)/nonmagnetic (NM) heterostructures have been intensively +studied as THz sources. Compensated magnets such as a ferrimagnet (FIM) and +antiferromagnet (AFM) are other types of magnetic materials with interesting +spin dynamics. In this work, we study TES from compensated magnetic +heterostructures including CoGd FIM alloy or IrMn AFM layers. Systematic +measurements on composition and temperature dependences of THz emission from +CoGd/Pt bilayer structures are conducted. It is found that the emitted THz +field is determined by the net spin polarization of the laser induced spin +current rather than the net magnetization. The temperature robustness of the +FIM based THz emitter is also demonstrated. On the other hand, an AFM plays a +different role in THz emission. The IrMn/Pt bilayer shows negligible THz +signals, whereas Co/IrMn induces sizable THz outputs, indicating that IrMn is +not a good spin current generator, but a good detector. Our results not only +suggest that a compensated magnet can be utilized for robust THz emission, but +also provide a new approach to study the magnetization dynamics especially near +the magnetization compensation point.",1806.02517v1 +2018-07-18,Magnon-photon-phonon entanglement in cavity magnomechanics,"We show how to generate tripartite entanglement in a cavity magnomechanical +system which consists of magnons, cavity microwave photons, and phonons. The +magnons are embodied by a collective motion of a large number of spins in a +macroscopic ferrimagnet, and are driven directly by an electromagnetic field. +The cavity photons and magnons are coupled via magnetic dipole interaction, and +the magnons and phonons are coupled via magnetostrictive (radiation +pressure-like) interaction. We show optimal parameter regimes for achieving the +tripartite entanglement where magnons, cavity photons, and phonons are +entangled with each other, and we further prove that the steady state of the +system is a genuinely tripartite entangled state. The entanglement is robust +against temperature. Our results indicate that cavity magnomechanical systems +could provide a promising platform for the study of macroscopic quantum +phenomena.",1807.07158v3 +2018-07-23,Bias dependent spin injection into graphene on YIG through bilayer hBN tunnel barriers,"We study the spin injection efficiency into single and bilayer graphene on +the ferrimagnetic insulator Yttrium-Iron-Garnet (YIG) through an exfoliated +tunnel barrier of bilayer hexagonal boron nitride (hBN). The contacts of two +samples yield a resistance-area product between 5 and 30 k$\Omega\mu$m$^2$. +Depending on an applied DC bias current, the magnitude of the non-local spin +signal can be increased or suppressed below the noise level. The spin injection +efficiency reaches values from -60% to +25%. The results are confirmed with +both spin valve and spin precession measurements. The proximity induced +exchange field is found in sample A to be (85 $\pm$ 30) mT and in sample B +close to the detection limit. Our results show that the exceptional spin +injection properties of bilayer hBN tunnel barriers reported by Gurram et al. +are not limited to fully encapsulated graphene systems but are also valid in +graphene/YIG devices. This further emphasizes the versatility of bilayer hBN as +an efficient and reliable tunnel barrier for graphene spintronics.",1807.08481v1 +2018-07-25,Role of interfaces in the biased composition of TbFe(Co) thin films,"Ferrimagnetic TbFe or TbFeCo amorphous alloy thin films have been grown by +co-evaporation in ultra-high vacuum. They exhibit an out-of-plane magnetic +anisotropy up to their Curie temperature with a nucleation and propagation +reversal mechanism suitable for current induced domain wall motion. Rutherford +back scattering experiments confirmed a fine control of the Tb depth-integrated +composition within the evaporation process. However, a large set of +experimental techniques were used to evidence an interface related contribution +in such thin films as compared to much thicker samples. In particular, scanning +transmission electron microscopy experiments evidence a depth dependent +composition and perturbed top and bottom interfaces with preferential oxidation +and diffusion of terbium. Despite of that, amorphous and homogeneous alloy film +remains in a bulk-like part. The composition of that bulk-like part of the +magnetic layer, labeled as effective composition, is biased when compared with +the depth-integrated composition. The magnetic properties of the film are +mostly dictated by this effective composition, which we show changes with +different top and bottom interfaces.",1807.09570v1 +2018-07-27,Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers,"We report broadband spectroscopy and numerical analysis by which we explore +propagating spin waves in a magnetic bilayer consisting of a 23 nm thick +permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer, +we observe a characteristic mode that exhibits a considerably larger group +velocity at small in-plane magnetic field than both the magnetostatic and +perpendicular standing spin waves. Using the finite element method, we confirm +the observations by simulating the mode profiles and dispersion relations. They +illustrate the hybridization of spin wave modes due to exchange coupling at the +interface. The high-speed propagating mode found in the bilayer can be utilized +to configure multi-frequency spin wave channels enhancing the performance of +spin wave based logic devices.",1807.10508v2 +2018-07-30,Investigating the magnetic ground state of the skyrmion host material Cu$_{2}$OSeO$_{3}$ using long-wavelength neutron diffraction,"We present long-wavelength neutron diffraction data measured on both single +crystal and polycrystalline samples of the skyrmion host material +Cu$_{2}$OSeO$_{3}$. We observe magnetic satellites around the $(0\bar{1}1)$ +diffraction peak not accessible to other techniques, and distinguish helical +from conical spin textures in reciprocal space. We confirm successive +transitions from helical to conical to field polarised ordered spin textures as +the external magnetic field is increased. The formation of a skyrmion lattice +with propagation vectors perpendicular to the field direction is observed in a +region of the field-temperature phase diagram that is consistent with previous +reports. Our measurements show that not only the field-polarised phase but also +the helical ground state are made up of ferrimagnetic clusters instead of +individual spins. These clusters are distorted Cu tetrahedra, where the spin on +one Cu ion is anti-aligned with the spin on the three other Cu ions.",1807.11333v1 +2018-08-03,"Structural, Ferroelectric, Magnetic and Magnetoelectric Response in Multiferroic (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 Particulate Composites","Multiferroic particulate composites have been fabricated by taking the +morphotropic phase boundary composition of ferroelectric phase +Bi(Ni1/2Ti1/2)O3-PbTiO3 and magnetic phase (Ni,Zn)Fe2O4. The ferroelectric +phase has coexisting monoclinic and tetragonal perovskite structures with space +group Pm and P4mm, respectively whereas the magnetic phase has spinel cubic +structure with space group Fd3m. Rietveld structural analysis for the each +components of composite reveals that the tetragonality (c/a) of the +ferroelectric phase continuously increases with increasing the concentration of +magnetic phase suggesting partial ionic diffusion between ferroelectric and +magnetic phases, after composite formation. Composition dependent M\""ossbauer +spectra of (1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/x(Ni,Zn)Fe2O4 reveals the +superparamagnetic like behavior for the ferroelectric rich composition with +x=0.2. The magnetic ordering increases for the composition with x=0.4 and 0.6 +which completely transform into ferrimagnetic for the composition with x=0.9 +for the magnetic phase rich compositions. Unlike the ferroelectric or magnetic +components which do not exhibit the magnetoelectric response separately, large +value of magnetoelectric coefficient (30 mV/Oe-cm) in +(1-x)Bi(Ni1/2Ti1/2)O3-PbTiO3/xNi0.6Zn0.4Fe2O4 composite makes it promise for +multifunctional applications.",1808.01148v1 +2018-08-13,Gilbert damping phenomenology for two-sublattice magnets,"We present a systematic phenomenological description of Gilbert damping in +two-sublattice magnets. Our theory covers the full range of materials from +ferro- via ferri- to antiferromagnets. Following a Rayleigh dissipation +functional approach within a Lagrangian classical field formulation, the theory +captures intra- as well as cross-sublattice terms in the Gilbert damping, +parameterized by a 2$\times$2 matrix. When spin-pumping into an adjacent +conductor causes dissipation, we obtain the corresponding Gilbert damping +matrix in terms of the interfacial spin-mixing conductances. Our model +reproduces the experimentally observed enhancement of the ferromagnetic +resonance linewidth in a ferrimagnet close to its compensation temperature +without requiring an increased Gilbert parameter. It also predicts new +contributions to damping in an antiferromagnet and suggests the resonance +linewidths as a direct probe of the sublattice asymmetry, which may stem from +boundary or bulk.",1808.04385v2 +2018-08-15,Ground state with nonzero spontaneous magnetization of the two-dimensional spin-1/2 Heisenberg antiferromagnet with frustration,"The S = 1/2 Heisenberg antiferromagnet on the two-dimensional pyramid lattice +is studied by the numerical-diagonalization method. This lattice is obtained by +the combination of the Lieb lattice and the square lattice. It is known that +when interaction on the square lattice is increased from the ferrimagnetic +limit of strong interaction on the Lieb lattice, this system shows gradual +decrease and disappearance of spontaneous magnetization in the ground state. +The present study treats the region near the case of the square-lattice +antiferromagnet accompanied by isolated spins by numerical-diagonalization +calculations of finite-size clusters with the maximum size of 39 sites. Our +numerical results suggest the existence of a new phase with small but nonzero +spontaneous magnetization between two zero-spontaneous-magnetization phases.",1808.04997v1 +2018-08-20,On the order of the phase transition in the spin-1 Baxter-Wu model,"In this work we investigate the order of the phase transition of the spin-1 +Baxter-Wu model. We used extensive entropic simulations to describe the +behavior of quantities which reveal the order of the phase transition. We +applyied finite-sizing scaling laws for continuous and discontinuous phase +transitions. Our results show that this system exhibits an indeterminacy +regarding the order of the phase transition, i.e., the results are conclusive +for both transitions, whether continuous or discontinuous. In such a scenario +we carried out a study of the configurations in the region of the phase +transition, which confirmed that the model seems to undergo a tetracritical +transition, with the coexistence of a ferromagnetic and three ferrimagnetic +configurations, suggesting that it may be a multicritical point belonging to a +critical line of an external or a crystalline fields, where the continuous and +the discontinuous phase transitions may coexist reflecting different features +of the system",1808.06701v1 +2018-08-23,First harmonic measurements of the spin Seebeck effect,"We present measurements of the spin Seebeck effect (SSE) by a technique that +combines alternating currents (AC) and direct currents (DC). The method is +applied to a ferrimagnetic insulator/heavy metal bilayer, +Y$_3$Fe$_5$O$_{12}$(YIG)/Pt. Typically, SSE measurements use an AC current to +produce an alternating temperature gradient and measure the voltage generated +by the inverse spin-Hall effect in the heavy metal at twice the AC frequency. +Here we show that when Joule heating is associated with AC and DC bias +currents, the SSE response occurs at the frequency of the AC current drive and +can be larger than the second harmonic SSE response. We compare the first and +second harmonic responses and show that they are consistent with the SSE. The +field dependence of the voltage response is used to characterize the +damping-like and field-like torques. This method can be used to explore +nonlinear thermoelectric effects and spin dynamics induced by temperature +gradients.",1808.07813v1 +2018-08-29,Critical behavior and magnetocaloric effect in Mn$_3$Si$_2$Te$_6$,"The critical properties and magnetocaloric effect of semiconducting +ferrimagnet Mn$_3$Si$_2$Te$_6$ single crystals have been investigated by bulk +magnetization and heat capacity around $T_c$. Critical exponents $\beta = +0.41\pm0.01$ with a critical temperature $T_c = 74.18\pm0.08$ K and $\gamma = +1.21\pm0.02$ with $T_c = 74.35\pm0.05$ K are deduced by the Kouvel-Fisher plot, +whereas $\delta = 4.29\pm0.05(3.40\pm0.02)$ is obtained by a critical isotherm +analysis at $T = 74(75)$ K. The magnetic exchange distance is found to decay as +$J(r)\approx r^{-4.79}$, which lies between the mean-field and 3D Heisenberg +models. Moreover, the magnetic entropy change $-\Delta S_M$ features a maximum +at $T_c$, i.e., $-\Delta S_M^{max} \sim$ 2.53(1.67) J kg$^{-1}$ K$^{-1}$ with +in-plane(out-of-plane) field change of 5 T, confirming large magnetic +anisotropy. The heat capacity measurement further gives $-\Delta S_M^{max}$ +$\sim$ 2.94 J kg$^{-1}$ K$^{-1}$ and the corresponding adiabatic temperature +change $\Delta T_{ad}$ $\sim$ 1.14 K with out-of-plane field change of 9 T.",1808.09949v1 +2018-12-05,Spin-imbalance-induced transverse magnetization in the Hofstadter-Hubbard model,"The fermionic, time-reversal invariant Hofstadter-Hubbard model with a +population difference between the two spin states is investigated. In the +strongly interacting regime, where the system can be described by an effective +spin model, we find an exotic spin structure by means of classical Monte-Carlo +calculations. Remarkably, this spin structure exhibits a transverse net +magnetization perpendicular to the magnetization induced by the population +imbalance. It is thus inherently different from canted antiferromagnetism. We +further investigate effects of quantum fluctuations within the dynamical +mean-field approximation and obtain a rich phase diagram including +ferromagnetic, anti-ferromagnetic, ferrimagnetic, and transverse magnetization +phases.",1812.02001v2 +2018-12-24,Interfacial Spin Seebeck effect in noncollinear magnetic systems,"The interplay between spin and heat currents at magnetic +insulator|nonmagnetic metal interfaces has been a subject of much scrutiny +because of both fundamental physics and the promise for technological +applications. While ferrimagnetic and, more recently, antiferromagnetic systems +have been extensively investigated, a theory generalizing the heat-to-spin +interconversion in noncollinear magnets is still lacking. Here, we establish a +general framework for thermally-driven spin transport at the interface between +a noncollinear magnet and a normal metal. Modeling the interfacial coupling +between localized and itinerant magnetic moments via an exchange Hamiltonian, +we derive an expression for the spin current, driven by a temperature +difference, for an arbitrary noncollinear magnetic order. Our theory reproduces +previously obtained results for ferromagnetic and antiferromagnet systems.",1812.09890v2 +2019-01-15,"Group theoretical analysis of structural instability, vacancy ordering and magnetic transitions in the system troilite (FeS) - pyrrhotite (Fe$_{1-x}$S)","A group-theoretical framework to describe vacancy ordering and magnetism in +the Fe$_{1-x}$S system is developed. This framework is used to determine the +sequence of crystal structures consistent with the observed magnetic structures +of troilite (FeS), and to determine the crystallographic nature of the +low-temperature Besnus transition in Fe$_{0.875}$S. We conclude that the Besnus +transition is a magnetically driven transition characterised by the rotation of +the moments out of the ac-plane, accompanied by small atomic displacements that +lower the symmetry to triclinic at low temperatures. Based on our phase +diagram, we predict related magnetically driven phase transitions at low +temperatures in all the commensurate superstructures of pyrrhotite. The exact +nature of the transition is determined by the symmetry of the vacancy ordered +state Based on this we predict spin-flop transitions in 3C and 5C pyrrhotite +and a transition akin to the Besnus transition in 6C pyrrhotite. Furthermore, +we clarify that 3C and 4C pyrrhotite carry a ferrimagnetic moment whereas 5C +and 6C are antiferromagnetic.",1901.04756v1 +2019-01-15,"SiC-YiG X band quantum sensor for sensitive surface paramagnetic resonance applied to chemistry, biology, physics","Here I present the SiC-YiG Quantum Sensor, allowing electron paramagnetic +resonance (EPR) studies of monolayer or few nanometers thick chemical, +biological or physical samples located on the sensor surface. It contains two +parts, a 4H-SiC substrate with many paramagnetic silicon vacancies (V2) located +below its surface, and YIG ferrimagnetic nanostripes. Spins sensing properties +are based on optically detected double electron-electron spin resonance under +the strong magnetic field gradient of nanostripes. Here I describe fabrication, +magnetic, optical and spins sensing properties of this sensor. I show that the +target spins sensitivity is at least five orders of magnitude larger than the +one of standard X band EPR spectrometer, for which it constitutes, combined +with a fiber bundle, a powerful upgrade for sensitive surface EPR. This sensor +can determine the target spins planes EPR spectrum, their positions with a +nanoscale precision of +/- 1 nm, and their 2D concentration down to +1/(20nm.20nm).",1901.05073v1 +2019-01-18,Magnonic Weyl states in Cu2OSeO3,"The multiferroic ferrimagnet Cu$_2$OSeO$_3$ with a chiral crystal structure +attracted a lot of recent attention due to the emergence of magnetic skyrmion +order in this material. Here, the topological properties of its magnon +excitations are systematically investigated by linear spin-wave theory and +inelastic neutron scattering. When considering Heisenberg exchange interactions +only, two degenerate Weyl magnon nodes with topological charges $\pm$2 are +observed at high-symmetry points. Each Weyl point splits into two as the +symmetry of the system is further reduced by including into consideration the +nearest-neighbor Dzyaloshinsky-Moriya interaction, crucial for obtaining an +accurate fit to the experimental spin-wave spectrum. The predicted topological +properties are verified by surface state and Chern number analysis. +Additionally, we predict that a measurable thermal Hall conductivity can be +associated with the emergence of the Weyl points, the position of which can be +tuned by changing the crystal symmetry of the material.",1901.06192v1 +2019-01-21,The magnetic structure and spin-flop transition in the A-site columnar-ordered quadruple perovskite $\mathrm{TmMn_3O_6}$,"We present the magnetic structure of $\mathrm{TmMn_3O_6}$, solved via neutron +powder diffraction - the first such study of any $R\mathrm{Mn_3O_6}$ A-site +columnar-ordered quadruple perovskite to be reported. We demonstrate that long +range magnetic order develops below 74 K, and at 28 K a spin-flop transition +occurs driven by $f$-$d$ exchange and rare earth single ion anisotropy. In both +magnetic phases the magnetic structure may be described as a collinear +ferrimagnet, contrary to conventional theories of magnetic order in the +manganite perovskites. Instead, we show that these magnetic structures can be +understood to arise due to ferro-orbital order, the A, A$'$ and A$''$ site +point symmetry, $mm2$, and the dominance of A-B exchange over both A-A and B-B +exchange, which together are unique to the $R\mathrm{Mn_3O_6}$ perovskites.",1901.06874v1 +2019-01-25,Focused ion beam modification of non-local magnon-based transport in yttrium iron garnet/platinum heterostructures,"We study the impact of Ga ion exposure on the local and non-local +magnetotransport response in heterostructures of the ferrimagnetic insulator +yttrium iron garnet and platinum. In particular, we cut the yttrium iron garnet +layer in between two electrically separated wires of platinum using a Ga ion +beam, and study the ensuing changes in the magnetoresistive response. We find +that the non-local magnetoresistance signal vanishes when the yttrium iron +garnet film between the Pt wires is fully cut, although the local spin Hall +magnetoresistance signal remains finite. This observation corroborates the +notion that pure spin currents carried by magnons are crucial for the non-local +magnetotransport effects observed in magnetic insulator/metal nanostructures.",1901.08894v1 +2019-01-27,Computational search for ultrasmall and fast skyrmions in the Inverse Heusler family,"Skyrmions are magnetic excitations that are potentially ultrasmall and +topologically protected, making them interesting for high-density +all-electronic ultrafast storage applications. While recent experiments have +confirmed the existence of various types of skyrmions, their typical sizes are +much larger than traditional domain walls, except at very low temperature. In +this work, we explore the optimal material parameters for hosting ultra-small, +fast, and room temperature stable skyrmions. As concrete examples, we explore +potential candidates from the inverse Heusler family. Using first-principles +calculations of structural and magnetic properties, we identify several +promising ferrimagnetic inverse Heusler half-metal/near half-metals and analyze +their phase space for size and metastability.",1901.09446v1 +2019-02-08,Magnetic Multipoles in a Ruthenate Ca3Ru2O7,"Compulsory Dirac multipoles in the bilayer perovskite Ca3Ru2O7 are absent in +published analyses of experimental data. In a first step at correcting +knowledge of the magnetic structure, we have analysed existing Bragg +diffraction patterns gathered on samples held well below the N\'eel temperature +at which A-type antiferromagnetic order of axial dipoles spontaneously +develops. Patterns were gathered with neutrons, and linearly polarized x-rays +tuned in energy to a ruthenium atomic resonance. Neutron diffraction data +contains solid evidence of Dirac dipoles (anapoles or toroidal moments). No +such conclusion is reached with existing x-ray diffraction data, which instead +is ambiguous on the question. To address this shortcoming by future +experiments, we calculated additional diffraction patterns. Chiral order of +Dirac multipoles is allowed by magnetic space-group PCna21, and it can be +exposed in Bragg diffraction using circularly polarized x-rays. Likewise, a +similar experiment can expose a chiral order of axial dipoles. A magnetic field +applied parallel to the b-axis creates a ferrimagnetic structure in which bulk +magnetization arises from field-induced nonequivalent Ru sites (magnetic +space-group Pm'c'21).",1902.02978v1 +2019-03-06,Microwave magnon damping in YIG films at millikelvin temperatures,"Magnon systems used in quantum devices require low damping if coherence is to +be maintained. The ferrimagnetic electrical insulator yttrium iron garnet (YIG) +has low magnon damping at room temperature and is a strong candidate to host +microwave magnon excitations in future quantum devices. Monocrystalline YIG +films are typically grown on gadolinium gallium garnet (GGG) substrates. In +this work, comparative experiments made on YIG waveguides with and without GGG +substrates indicate that the material plays a significant role in increasing +the damping at low temperatures. Measurements reveal that damping due to +temperature-peak processes is dominant above 1 K. Damping behaviour that we +show can be attributed to coupling to two-level fluctuators (TLFs) is observed +below 1 K. Upon saturating the TLFs in the substrate-free YIG at 20 mK, +linewidths of 1.4 MHz are achievable: lower than those measured at room +temperature.",1903.02527v3 +2019-04-09,Angular momentum compensation manipulation to room temperature of the ferrimagnet Ho$_{3-x}$Dy$_x$Fe$_5$O$_{12}$ detected by the Barnett effect,"We demonstrate that the angular momentum compensation temperature $T_A$, at +which the net angular momentum in the sample disappears, can be controlled in +Ho$_3$Fe$_5$O$_{12}$ by partially substituting Dy for Ho. The $T_A$ can be +detected using the Barnett effect, by which mechanical rotation magnetizes an +object due to spin-rotation coupling. We found that $T_A$ increases with the Dy +content and clarified that the $T_A$ of Ho$_{1.5}$Dy$_{1.5}$Fe$_5$O$_{12}$ +coincides with room temperature. The Barnett effect enables us to explore +materials applicable to magnetic devices utilizing the angular momentum +compensation only by rotating the powder sample at room temperature.",1904.04567v1 +2019-04-10,Magnetization-polarization cross-control near room temperature in hexaferrite single crystals,"Mutual control of the electricity and magnetism in terms of magnetic (H) and +electric (E) fields, the magnetoelectric (ME) effect, offers versatile low +power-consumption alternatives to current data storage, logic gate, and +spintronic devices. Despite its importance, E-field control over magnetization +(M) with significant magnitude was observed only at low temperatures. Here we +have successfully stabilized a simultaneously ferrimagnetic and ferroelectric +phase in a Y-type hexaferrite single crystal up to T=450K and demonstrated the +reversal of large non-volatile M by E field close to room temperature. +Manipulation of the magnetic domains by E field is directly visualized at room +temperature by using magnetic force microscopy. The present achievement +provides an important step towards the application of bulk ME multiferroics.",1904.05017v1 +2019-08-13,Converting Faraday rotation into magnetization in europium chalcogenides,"We present a simple semiclassical model to sustain that in europium +chalcogenides (EuX), Faraday rotation (FR) in the transparency gap is +proportional to the magnetization of the sample, irrespective of the material's +magnetic phase, temperature, or applied magnetic field. The model is validated +by FR and magnetization measurements in EuSe in the temperature interval +1.7-300K, covering all EuSe magnetic phases (paramagnetic, antiferromagnetic +type I or type II, ferrimagnetic and ferromagnetic). Furthermore, by combining +the semiclassical model with the explicit electronic energy structure of EuX, +the proportionality coefficient between magnetization and FR is shown to be +dependent only on the wavelength and the band gap. Due to its simplicity, the +model has didactic value, moreover, it provides a working tool for converting +FR into magnetization in EuX. Possible extension of the model to other +intrinsic magnetic semiconductors is discussed.",1908.04444v1 +2019-08-28,Critical size limits for collinear and spin spiral magnetism in CoCr$_2$O$_4$,"The multiferroic behavior of CoCr$_2$O$_4$ results from the appearance of +conical spin-spiral magnetic ordering, which induces electric polarization. The +magnetic ground state has a complex size dependent behavior, which collapses +when reaching a critical particle size. Here, the magnetic phase stability of +CoCr$_2$O$_4$ in the size range of 3.6 - 14.0 nm is presented in detail using +the combination of neutron diffraction with XYZ polarization analysis and +macroscopic magnetization measurements. We establish critical coherent domain +sizes for the formation of the spin spiral and ferrimagnetic structure and +reveal the evolution of the incommensurate spin spiral vector with particle +size. We further confirm the presence of ferroelectric polarization in the spin +spiral phase for nanocrystalline CoCr$_2$O$_4$.",1908.10582v1 +2019-11-08,The delta-chain with ferro- and antiferromagnetic interactions in applied magnetic field,"We study the thermodynamics of the delta-chain with competing ferro- and +antiferromagnetic interactions in an external magnetic field which generalizes +the field-free case studied previously. This model plays an important role for +the recently synthesized compound Fe$_{10}$Gd$_{10}$ which is nearly quantum +critical. The classical version of the model is solved exactly and explicit +analytical results for the low-temperature thermodynamics are obtained. The +spin-$s$ quantum model is studied using exact diagonalization and +finite-temperature Lanzos techniques. Particular attention is focused on the +magnetization and the susceptibility. The magnetization of the classical model +in the ferromagnetic part of the phase diagram defines the universal scaling +function which is valid for the quantum model. The dependence of the +susceptibility on the spin quantum number $s$ at the critical point between the +ferro- and ferrimagnetic phases is studied and the relation to +Fe$_{10}$Gd$_{10}$ is discussed.",1911.03081v1 +2019-11-13,Perpendicular Magnetic Anisotropy in Conducting NiCo2O4 Films from Spin-Lattice Coupling,"High perpendicular magnetic anisotropy (PMA), a property needed for nanoscale +spintronic applications, is rare in oxide conductors. We report the observation +of a PMA up to 0.23 MJ/m3 in modestly strained epitaxial NiCo2O4 (NCO) films +which are room-temperature ferrimagnetic conductors. Spin-lattice coupling +manifested as magnetoelastic effect was found as the origin of the PMA. The +in-plane xx-yy states of Co on tetrahedral sites play crucial role in the +magnetic anisotropy and spin-lattice coupling with an energy scale of 1 +meV/f.u. The elucidation of the microscopic origin paves a way for engineering +oxide conductors for PMA using metal/oxygen hybridizations.",1911.05322v1 +2019-11-18,Particle size controlled magnetic loss in magnetite nanoparticles in RF-microwave region,"Frequency dependant complex magnetic permeability is used to understand +RF-microwave behaviour of magnetic nanoparticles in the frequency range 250 MHz +to 3 GHz. The stable dispersions of Fe3O4 nanoparticles with mean size varying +between 11 to 16 nm are prepared for this purpose. The effect of mean particle +size and external static magnetic field over microwave absorption properties of +magnetic fluid is studied. It is observed that frequency of ferrimagnetic +resonance, frequency of maximum absorption, loss tangent and reflection loss +(RL) can be controlled by modifying mean particle size and strength of applied +external static magnetic field. This kind of study can be useful for +radio-microwave devices like tunable attenuator, EM sheilder, and other +applications like Hyperthermia.",1911.07467v1 +2019-11-27,Observation of the Magnon Polarization,"We measure the mode-resolved direction of the precessional motion of the +magnetic order, i.e., magnon polarization, via the chiral term of inelastic +polarized neutron scattering spectra. The magnon polarisation is important in +spintronics, affecting thermodynamic properties such as the magnitude and sign +of the spin Seebeck effect. The observation of both signs of magnon +polarization in Y3Fe5O12 also gives direct proof of its ferrimagnetic nature. +The experiments agree very well with atomistic simulations of the scattering +cross section.",1911.11968v1 +2019-11-30,"A magnetocaloric study on the series of 3d-metal chromites ACr$_{2}$O$_{4}$ where A = Mn, Fe, Co, Ni, Cu and Zn","The 3d-metal chromites ACr$_2$O$_4$ where A is a magnetic ion, show the +paramagnetic to ferrimagnetic phase transition at T$_C$ while for non-magnetic +A-site ion, ACr$_2$O$_4$ show paramagnetic to antiferromagnetic phase +transition at T$_N$. In this report, we present the detailed study of magnetic +and the magnetocaloric effect (MCE) of the 3d-metal chromites ACr$_{2}$O$_{4}$ +(where A = Mn, Fe, Co, Ni, Cu, and Zn) near T$_C$ and T$_N$. We find the +magnitude of MCE (-$\Delta$S$_M$) decreases on decreasing the magnetic moment +of A-site ion with an exception for CuCr$_{2}$O$_{4} $. Additionally, to know +more about the order and nature of phase transition, we have made a scaling +analysis of (-$\Delta$S$_{M}$) for all the chromites across the phase +transition temperatures T$_C$ and T$_N$.",1912.00116v1 +2019-12-14,"Electron doping and correlation effects on crystal, electronic and magnetic structures of A$_2$NRuO$_6$ (A2 = Ba$_2$, BaLa; N = V, Cr, Fe)","Density functional methods have been used to study the crystal, electronic +and magnetic structures of new ordered double perovskites A2NRuO6 (A2 = Ba2, +BaLa; N = V, Cr, Fe). In the doped compounds, the A-site was replaced by 1:1 of +Ba and La cations, BaLaNRuO6. All compounds of A2NRuO6 crystallize in cubic +symmetry with space group Fm-3m and tilt system a0a0a0. The electronic and +magnetic calculations were performed by the full-potential linear muffin-tin +orbital method using both the generalized gradient approximation and GGA plus +on-site electron correlation effect GGA+U. In GGA, Ba2NRuO6 shows +half-metallic, semiconducting and metallic behavior for N = V, Cr, Fe, +respectively, completely change to half-metallic when A2 = BaLa. While, GGA+U +method yields clearly half-metallic in all compounds, except for Ba2FeRuO6, +shows an insulating behavior. Also, the results of magnetic structures +calculations reveal that the A2NRuO6 compounds have ferrimagnetic nature if N = +V and Cr, switch to ferromagnetic when N = Fe. The V3+, Cr3+, Fe3+ and Ru5+ +ions are in high spin magnetic moments states due to the antiferromagnetic +coupling.",1912.06843v1 +2019-12-23,Peculiarities of electronic transport and magnetic state in half-metallic ferromagnetic and spin gapless semiconducting Heusler alloys,"A brief survey of experimental and theoretical studies of half-metallic +ferromagnets (HMFs) and spin gapless semiconductors is given, the possible +candidates being the X$_2$YZ (X = Mn, Fe, Co; Y = Ti, V, Cr, Mn, Fe, Co, Ni; Z += Al, Si, Ga, Ge, In, Sn, Sb) Heusler alloys. The data on the electrical +resistivity, normal and anomalous Hall Effect, and magnetic properties are +presented. It is shown that the Co$_2$FeZ alloys demonstrate properties of +conventional ferromagnets, the HMF properties being also manifested at the +variation of the Z-component. The Fe$_2$YAl and Mn$_2$YAl alloys show at the +variation of the Y-component both metallic and semiconducting electronic +characteristics, the magnetic properties, changing from the ferromagnetic to +compensated ferrimagnetic state. The HMF and spin gapless semiconductor states +are supposed to exist in these Heusler alloys systems.",1912.10771v1 +2020-03-09,Ab initio description of the Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ electronic structure,"Bi-based cuprate superconductors are important materials for both fundamental +research and applications. As in other cuprates, the superconducting phase in +the Bi compounds lies close to an antiferromagnetic phase. Our density +functional theory calculations based on the +strongly-constrained-and-appropriately-normed (SCAN) exchange correlation +functional in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ reveal the persistence of +magnetic moments on the copper ions for oxygen concentrations ranging from the +pristine phase to the optimally hole-doped compound. We also find the existence +of ferrimagnetic solutions in the heavily doped compounds, which are expected +to suppress superconductivity.",2003.04034v3 +2020-03-11,Excitation and relaxation dynamics of spin-waves triggered by ultrafast photo-induced demagnetization in a ferrimagnetic insulator,"Excitation and propagation dynamics of spin waves in an iron-based garnet +film under out-of-plane magnetic field were investigated by time-resolved +magneto-optical imaging. The experimental results and the following data +analysis by phase-resolved spin-wave tomography reveal the excitation of spin +waves triggered by photo-induced demagnetization (PID) along the sample depth +direction. Moreover, the fast relaxation of PID accompanied by the spin +transfer due to spin-wave emission was observed. Possible scenarios of PID in +the garnet film are discussed. Finally, we develop a model for the spin-wave +excitation triggered by PID and explain the magnetic-field dependence in the +amplitude of the observed spin waves.",2003.05159v1 +2020-03-18,Pressure-induced inverse order-disorder transition in double perovskites,"Given the consensus that pressure improves cation order in most of known +materials, a discovery of pressure-induced disorder could require +reconsideration of order-disorder transition in solid state physics/chemistry +and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 synthesized at ambient +pressure show B-site order, while the polymorphs synthesized at 6 and 15 GPa +are partially-ordered and disordered respectively. With the decrease of +ordering degrees, the lattices are shrunken and the crystal structures alter +from monoclinic to orthorhombic symmetry. Correspondingly, long-range +ferrimagnetic order in the B-site ordered phases are gradually overwhelmed by +B-site disorder. Theoretical calculations suggest that unusual unit cell +compressions under external pressures unexpectedly stabilize the disordered +phases of Y2CoIrO6 and Y2CoRuO6.",2003.08025v3 +2020-03-20,A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations,"In the present work, the aspects of magnetic and structural properties of +Ni-Mn-Ga alloys are described in the framework of fist-principles approach and +mapped into ternary composition diagrams. The stable atomic arrangement and +magnetic alignment for compositions with cubic austenite and tetragonal +martensite structures across phase diagrams are predicted. It is shown that Ni- +and Ga-rich compositions possess the regular Heusler structure in contrast to +Mn-rich compositions with inverse Heusler structure as favorable one. +Compositions with unstable austenite structure are concentrated in the left and +right sides of diagram whereas compositions with unstable martensite structure +are located in the low-middle part of diagram. The magnetic phase diagrams +showing regions with the ferromagnetic order and the complex ferrimagnetic +order for austenitic and martensitic compositions are obtained. The results of +calculations are in a good agreement with available experimental data.",2003.09128v1 +2020-03-30,Spontaneous Rotation of Ferrimagnetism Driven by Antiferromagnetic Spin Canting,"Spin-reorientation phase transitions that involve the rotation of a +crystal$'$s magnetization have been well characterized in distorted-perovskite +oxides such as the orthoferrites. In these systems spin reorientation occurs +due to competing rare-earth and transition metal anisotropies coupled via +$f$-$d$ exchange. Here, we demonstrate an alternative paradigm for spin +reorientation in distorted perovskites. We show that the +$R_2\mathrm{CuMnMn_4O_{12}}$ (R = Y or Dy) triple A-site columnar-ordered +quadruple perovskites have three ordered magnetic phases and up to two +spin-reorientation phase transitions. Unlike the spin-reorientation phenomena +in other distorted perovskites, these transitions are independent of rare-earth +magnetism, but are instead driven by an instability towards antiferromagnetic +spin canting likely originating in frustrated Heisenberg exchange interactions, +and the competition between Dzyaloshinskii-Moriya and single-ion anisotropies.",2003.13774v1 +2020-05-07,Detecting quadrupole: a hidden source of magnetic anisotropy for Manganese alloys,"Mn-based alloys exhibit unique properties in the spintronics materials +possessing perpendicular magnetic anisotropy (PMA) beyond the Fe and Co-based +alloys. It is desired to figure out the quantum physics of PMA inherent to +Mn-based alloys, which have never been reported. Here, the origin of PMA in +ferrimagnetic Mn$_{3-{\delta}}$Ga ordered alloys is investigated to resolve +antiparallel-coupled Mn sites using x-ray magnetic circular and linear +dichroism (XMCD/XMLD) and a first-principles calculation. We found that the +contribution of orbital magnetic moments in PMA is small from XMCD and that the +finite quadrupole-like orbital distortion through spin-flipped electron hopping +is dominant from XMLD and theoretical calculations. These findings suggest that +the spin-flipped orbital quadrupole formations originate from the PMA in +Mn$_{3-{\delta}}$Ga and bring the paradigm shift in the researches of PMA +materials using x-ray magnetic spectroscopies.",2005.03249v1 +2020-05-07,Structural and magnetic behavior of Cr$_2$Co$_{(1-x)}$Cr$_x$Al inverse Heusler alloys,"We report the structural and magnetic behavior of single phase inverse +Heusler alloys Cr$_2$Co$_{(1-x)}$Cr$_x$Al ($x = $ 0, 0.2, 0.4) using x-ray +diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic +susceptibility measurements. Interestingly, the Rietveld refinement of XRD data +with the space group I$\bar{4}m2$ reveal a tetragonal distortion with c/a ratio +around 1.38 in these inverse Heusler structures. The bulk compositions have +been confirmed by energy dispersive x-ray spectroscopy measurements. The active +Raman mode F$_{2g}$ is observed at 320~cm$^{-1}$, which confirms the X-type +Heusler structure as the A2 and B2 type structures are known to be not Raman +active. The area of F$_{2g}$ mode decreases with Cr concentration, which +indicate the origin of this mode due to Co vibrations. The isothermal +magnetization data confirm the magnetic moment close to zero ($\le$0.02 +$\mu_B/f.u.$) at $\approx$70~kOe and negligible coercive field suggest the +fully compensated ferrimagnetic nature of these samples. The susceptibility +behavior indicates irreversibility between zero-field and field-cooled curves +and complex magnetic interactions at low temperatures.",2005.03528v1 +2020-05-13,Interplay between magnetism and charge instabilities in layered NbSe$_{2}$,"Using ab initio methods based on density functional theory, the electronic +and magnetic structure of layered hexagonal NbSe$_{2}$ is studied. In the case +of single-layer NbSe$_{2}$ it is found that, for all the functionals +considered, the magnetic solution is lower in energy than the non-magnetic +solution. The magnetic ground-state is ferrimagnetic with a magnetic moment of +1.09 $\mu_{B}$ at the Nb atoms and a magnetic moment of 0.05 $\mu_{B}$, in the +opposite direction, at the Se atoms. Our calculations show that single-layer +NbSe$_{2}$ does not display a charge density wave instability unless a graphene +layer is considered as a substrate. Then, two kinds of 3$\times$3 charge +density waves are found, which are observed in our STM experiments. This +suggest that the driving force of charge instabilities in NbSe$_{2}$ differ in +bulk and in the single-layer limit. Our work sets magnetism into play in this +highly-correlated 2D material, which is crucial to understand the formation +mechanisms of 2D superconductivity and charge density wave order.",2005.06210v1 +2020-05-16,All-optical switching of magnetic domains in Co/Gd heterostructures with Dzyaloshinskii-Moriya Interaction,"Given the development of hybrid spintronic-photonic devices and chiral +magnetic structures, a combined interest in all-optical switching (AOS) of +magnetization and current-induced domain wall motion in synthetic ferrimagnetic +structures with strong Dzyaloshinskii-Moriya Interaction (DMI) is emerging. In +this study, we report a study on single-pulse all-optical toggle switching and +asymmetric bubble expansion in specially engineered Co/Gd-based multilayer +structures. In the absence of any external magnetic fields, we look into the +AOS properties and the potential role of the DMI on the AOS process as well as +the stability of optically written micro-magnetic domains. Particularly, +interesting dynamics are observed in moon-shaped structures written by two +successive laser pulses. The stability of domains resulting from an interplay +of the dipolar interaction and domain-wall energy are compared to simple +analytical models and micromagnetic simulations.",2005.07969v2 +2020-05-19,Dissipation-based Quantum Sensing of Magnons with a Superconducting Qubit,"Hybrid quantum devices expand the tools and techniques available for quantum +sensing in various fields. Here, we experimentally demonstrate quantum sensing +of the steady-state magnon population in a magnetostatic mode of a +ferrimagnetic crystal. Dispersively coupling the magnetostatic mode to a +superconducting qubit allows the detection of magnons using Ramsey +interferometry with a sensitivity on the order of $10^{-3}$ +$\text{magnons}/\sqrt{\text{Hz}}$. The protocol is based on dissipation as +dephasing via fluctuations in the magnetostatic mode reduces the qubit +coherence proportionally to the number of magnons.",2005.09250v1 +2020-06-26,Interfacing topological insulators and ferrimagnets: Bi$_2$Te$_3$ and Fe$_3$O$_4$ heterostructures grown by molecular beam epitaxy,"Relying on the magnetism induced by the proximity effect in heterostructures +of topological insulators and magnetic insulators is one of the promising +routes to achieve the quantum anomalous Hall effect. Here we investigate +heterostructures of Bi$_2$Te$_3$ and Fe$_3$O$_4$. By growing two different +types of heterostructures by molecular beam epitaxy, Fe$_3$O$_4$ on +Bi$_2$Te$_3$ and Bi$_2$Te$_3$ on Fe$_3$O$_4$, we explore differences in +chemical stability, crystalline quality, electronic structure, and transport +properties. We find the heterostructure Bi$_2$Te$_3$ on Fe$_3$O$_4$ to be a +more viable approach, with transport signatures in agreement with a gap opening +in the topological surface states.",2006.14914v1 +2020-08-06,Boris Computational Spintronics -- High Performance Multi-Mesh Magnetic and Spin Transport Modelling Software,"This work discusses the design and testing of a new computational spintronics +research software. Boris is a comprehensive multi-physics open-source software, +combining micromagnetics modelling capabilities with drift-diffusion spin +transport modelling and heat flow solver in multi-material structures. A +multi-mesh paradigm is employed, allowing modelling of complex multi-layered +structures with independent discretization and arbitrary relative positioning +between different computational meshes. Implemented micromagnetics models +include not only ferromagnetic materials modelling, but also two-sublattice +models, allowing simulations of antiferromagnetic and ferrimagnetic materials, +fully integrated in the multi-mesh and multi-material design approach. High +computational performance is an important design consideration in Boris, and +all computational routines can be executed on GPUs, in addition to CPUs. In +particular a modified 3D convolution algorithm is used to compute the +demagnetizing field on the GPU, termed pipelined convolution, and benchmark +comparisons with existing GPU-accelerated software Mumax3 have shown +performance improvements up to twice faster.",2008.02478v1 +2020-08-07,Cavity magnon polariton based precision magnetometry,"A photon-magnon hybrid system can be realised by coupling the electron spin +resonance of a magnetic material to a microwave cavity mode. The quasiparticles +associated with the system dynamics are the cavity magnon polaritons, which +arise from the mixing of strongly coupled magnons and photons. We illustrate +how these particles can be used to probe the magnetisation of a sample with a +remarkable sensitivity, devising suitable spin-magnetometers which ultimately +can be used to directly assess oscillating magnetic fields. Specifically, the +capability of cavity magnon polaritons of converting magnetic excitations to +electromagnetic ones, allows for translating to magnetism the quantum-limited +sensitivity reached by state-of-the-art electronics. Here we employ hybrid +systems composed of microwave cavities and ferrimagnetic spheres, to +experimentally implement two types of novel spin-magnetometers.",2008.03062v2 +2020-08-12,Determination of Niobium Cavity Magnetic Field Screening via a Dispersively Hybridized Magnonic Sensor,"A method for determining the internal DC magnetic field inside a +superconducting cavity is presented. The method relies on the relationship +between magnetic field and frequency of the Kittel mode of a ferrimagnetic +sphere, hybridised in the dispersive regime of the superconducting cavity. +Results were used to experimentally determine the level of screening a +superconducting Nb cavity provides as it changes from perfect diamagnetism to +no screening. Two cavity geometries were tested, a cylinder and single post +re-entrant cavity. Both demonstrated a consistent value of field that enters +the cavity, expected to be the superheating critical field. Hysteresis in the +screened field during ramp up and ramp down of the external magnetic field due +to trapped vortices was also observed. Some abnormal behaviour was observed in +the cylindrical cavity in the form of plateaus in the internal field above the +first critical field, and we discuss the potential origin of this behaviour. +The measurement approach would be a useful diagnostic for axion dark matter +searches, which plan on using superconducting materials but need to know +precisely the internal magnetic field.",2008.05073v2 +2020-08-15,Magnon laser based on Brillouin light scattering,"An analogous laser action of magnons would be a subject of interest and is +crucial for the study of nonlinear magnons spintronics. Here, we demonstrate +the magnon laser behavior based on Brillouin light scattering in a +ferrimagnetic insulator sphere which supports optical whispering gallery modes +and magnon resonances. We show that the excited magnon plays what has +traditionally been the role of the Stokes wave and is coherently amplified +during the Brillouin scattering process, making magnon laser possible. +Furthermore, the stimulating excited magnon number increasing exponentially +with the input light power can be manipulated by adjusting the external +magnetic field. In addition to providing insight into magneto-optical +interaction, the study of magnon laser action will help to develop novel +technologies for handling spin-wave excitations and could affect scientific +fields beyond magnonics. Potential applications range from preparing coherent +magnon sources to operating onchip functional magnetic devices.",2008.06628v2 +2020-08-30,Element-specific field-induced spin reorientation and an unusual tetracritical point in MnCr2S4,"The ferrimagnetic spinel MnCr2S4 shows a variety of magnetic-field-induced +phase transitions owing to bond frustration and strong spin-lattice coupling. +However, the site-resolved magnetic properties at the respective field-induced +phases in high magnetic fields remain elusive. Our soft x-ray magnetic circular +dichroism studies up to 40 T directly evidence element-selective +magnetic-moment reorientations in the field-induced phases. The complex +magnetic structures are further supported by entropy changes extracted from +magnetocaloric-effect measurements. Moreover, thermodynamic experiments reveal +an unusual tetracritical point in the H-T phase diagram of MnCr2S4 due to +strong spin-lattice coupling.",2008.13285v3 +2020-08-31,Modulation of spin conversion in a 1.5 nm-thick Pd film by ionic gating,"Gate-induced modulation of the spin-orbit interaction (SOI) in a 1.5 nm-thick +Pd thin film grown on a ferrimagnetic insulator was investigated. Efficient +charge accumulation by ionic gating enables a substantial upshift in the Fermi +level of the Pd film, which was corroborated by suppression of the resistivity +in the Pd. Electromotive forces arising from the inverse spin Hall effect in Pd +under spin pumping were substantially modulated by the gating, in consequence +of the modulation of the spin Hall conductivity of Pd as in an ultrathin Pt +film. The same experiment using a thin Cu film, for which the band structure is +largely different from Pd and Pt and its SOI is quite small, provides further +results supporting our claim. The results obtained help in developing a +holistic understanding of the gate-tunable SOI in solids and confirm a previous +explanation of the significant modulation of the spin Hall conductivity in an +ultrathin Pt film by gating.",2008.13438v1 +2020-09-11,Electron-Phonon Interactions in Flat Band Systems,"Existing Quantum Monte Carlo studies have investigated the properties of +fermions on a Lieb (CuO$_2$) lattice interacting with an on-site, or +near-neighbor electron-electron coupling. Attention has focused on the +interplay of such interactions with the macroscopic degeneracy of local zero +energy modes, from which Bloch states can be formed to produce a flat band in +which energy is independent of momentum. The resulting high density of states, +in combination with the Stoner criterion, suggests that there should be +pronounced instabilities to ordered phases. Indeed, a theorem by Lieb +rigorously establishes the existence of ferrimagnetic order. Here we study the +charge density wave phases induced by electron-phonon coupling on the Lieb +lattice, as opposed to previous work on electron-electron interactions. Our key +result is the demonstration of charge density wave (CDW) phases at one-third +and two-thirds fillings, characterized by long-range density density +correlations between doubly occupied sites on the minority or majority +sublattice, and an accompanying gap. We also compute the transition temperature +to the ordered phase as a function of the electron-phonon coupling.",2009.05595v3 +2020-09-24,Pressure-Temperature Phase Diagram of $α$-Mn,"Electrical resistivity and ac-susceptibility measurements under high pressure +were carried out in high-quality single crystals of $\alpha$-Mn. The +pressure-temperature phase diagram consists of an antiferromagnetic ordered +phase (0<$P$<1.4 GPa, $T 1500 ppm) can be achieved in an insulating transition metal +oxide CaBaCo4O7 where the ferrimagnetic ordering at TC ~ 62 K is associated +with a huge change in the lattice. Moreover, because this material is +pyroelectric with a non-switchable electric polarization (P), the giant +magnetostriction results in a record-breaking magnetoelectric effect - a +gigantic change of electric polarization (deltaP ~ 1.6 {\mu}C/cm2) in response +to the applied magnetic field up to 60 T. Geometric frustration as well as the +orbital instability of Co2+/Co3+ ions is believed to play a crucial role in the +giant magnetostriction. Our study provides new insights on how to achieve both +giant magnetostriction and pronounced magnetoelectric effect in insulating +transition metal oxides.",2109.11149v1 +2021-09-23,Percolation on Lieb lattices,"We study site- and bond-percolation on a class of lattices referred to as +Lieb lattices. In two dimensions the Lieb lattice (LL) is also known as the +decorated square lattice, or as the CuO$_2$ lattice; in three dimensions it can +be generalized to a layered Lieb lattice (LLL) or to a perovskite lattice (PL). +Emergent electronic phenomena, such as topological states and ferrimagnetism, +have been predicted to occur in these systems, which may be realized in optical +lattices as well as in solid state. Since the study of the interplay between +quantum fluctuations and disorder in these systems requires the availability of +accurate estimates of geometrical critical parameters, such as percolation +thresholds and correlation length exponents, here we use Monte Carlo +simulations to obtain these data for Lieb lattices when a site (or bond) is +present with probability $p$. We have found that the thresholds satisfy a +mean-field (Bethe lattice) trend, namely that the critical concentration, +$p_c$, increases as the average coordination number decreases; our estimates +for the correlation length exponent are in line with the expectation that there +is no change in the universality class.",2109.11384v1 +2021-10-07,Ultrafast element- and depth-resolved magnetization dynamics probed by transverse magneto-optical Kerr effect spectroscopy in the soft x-ray range,"We report on time- and angle-resolved transverse magneto-optical Kerr effect +spectroscopy in the soft x-ray range that, by analysis via +polarization-dependent magnetic scattering simulations, allows us to determine +the spatio-temporal and element-specific evolution of femtosecond laser-induced +spin dynamics in nanostructured magnetic materials. In a ferrimagnetic GdFe +thin film system, we correlate a reshaping spectrum of the magneto-optical Kerr +signal to depth-dependent magnetization dynamics and disentangle contributions +due to non-equilibrium electron transport and nanoscale heat diffusion on their +intrinsic time scales. Our work provides a quantitative insight into +light-driven spin dynamics occurring at buried interfaces of complex magnetic +heterostructures, which can be tailored and functionalized for future +opto-spintronic devices.",2110.03599v2 +2021-11-12,Classical analog of qubit logic based on a magnon Bose-Einstein condensate,"We present a classical version of several quantum bit (qubit) functionalities +using a two-component magnon Bose-Einstein condensate formed at opposite +wavevectors in a room-temperature yttrium-iron-garnet ferrimagnetic film. The +macroscopic wavefunctions of these two condensates serve as orthonormal basis +states that form a system being a classical counterpart of a single qubit. +Solving the Gross-Pitaevskii equation and employing micromagnetic numerical +simulations, we first show how to initialize the system in one of the basis +states: the application of wavevector-selective parallel parametric pumping +allows us to form only a single condensate in one of the two lowest energy +states of the magnon gas. Next, by translating the concept of Rabi-oscillations +into the wavevector domain, we demonstrate how to manipulate the magnon-BEC +system along the polar axis in the Bloch sphere representation. We also discuss +the manipulation regarding the azimuthal angle.",2111.06798v2 +2021-11-14,Single-sideband microwave-to-optical conversion in high-Q ferrimagnetic microspheres,"Coherent conversion of microwave and optical photons can significantly expand +the ability to control the information processing and communication systems. +Here, we experimentally demonstrate the microwave-to-optical frequency +conversion in a magneto-optical whispering gallery mode microcavity. By +applying a magnetic field parallel to the microsphere equator, the intra-cavity +optical field will be modulated when the magnon is excited by the microwave +drive, leading to microwave-to-optical conversion via the magnetic Stokes and +anti-Stokes scattering processes. The observed single sideband conversion +phenomenon indicates a non-trivial optical photon-magnon interaction mechanism, +which is derived from the magnon induced both the frequency shift and modulated +coupling rate of optical modes. In addition, we demonstrate the single-sideband +frequency conversion with an ultrawide tuning range up to 2.5GHz, showing its +great potential in microwave-to-optical conversion.",2111.07325v1 +2021-11-16,Optical sensing of magnons via the magnetoelastic displacement,"We show how to measure a steady-state magnon population in a magnetostatic +mode of a ferromagnet or ferrimagnet, such as yttrium iron garnet. We adopt an +optomechanical approach and utilize the magnetoelasticity of the ferromagnet. +The magnetostrictive force dispersively couples magnons to the deformation +displacement of the ferromagnet, which is proportional to the magnon +population. By further coupling the mechanical displacement to an optical +cavity that is resonantly driven by a weak laser, the magnetostrictively +induced displacement can be sensed by measuring the phase quadrature of the +optical field. The phase shows an excellent linear dependence on the magnon +population for a not very large population, and can thus be used as a +`magnometer' to measure the magnon population. We further study the effect of +thermal noises, and find a high signal-to-noise ratio even at room temperature. +At cryogenic temperatures, the resolution of magnon excitation numbers is +essentially limited by the vacuum fluctuations of the phase, which can be +significantly improved by using a squeezed light.",2111.08376v2 +2021-11-30,First and second order magnetic anisotropy and damping of europium iron garnet under high strain,"Understanding and tailoring static and dynamic properties of magnetic +insulator thin films is important for spintronic device applications. Here, we +grow atomically flat epitaxial europium iron garnet (EuIG) thin films by pulsed +laser deposition on (111)-oriented garnet substrates with a range of lattice +parameters. By controlling the lattice mismatch between EuIG and the +substrates, we tune the strain in EuIG films from compressive to tensile +regime, which is characterized by X-ray diffraction. Using ferromagnetic +resonance, we find that in addition to the first-order perpendicular magnetic +anisotropy which depends linearly on the strain, there is a significant +second-order one that has a quadratic strain dependence. Inhomogeneous +linewidth of the ferromagnetic resonance increases notably with increasing +strain, while the Gilbert damping parameter remains nearly constant (~ +2x10^-2). These results provide valuable insight into the spin dynamics in +ferrimagnetic insulators and useful guidance for material synthesis and +engineering of next-generation spintronics applications.",2111.15142v1 +2021-12-02,"Phases of rotating baryonic matter: non-Abelian chiral soliton lattices, antiferro-isospin chains, and ferri/ferromagnetic magnetization","A chiral soliton lattice (CSL), proposed as the ground state of rotating +baryonic matter at a finite density, is shown to be unstable in a large +parameter region for two flavors owing to pion condensations, leading to two +types of non-Abelian (NA) CSL phases (dimer and deconfining phases). We +determine the phase diagram where the dimer phase meets the other phases and +QCD vacuum at three tricritical points. The critical angular velocity for +NA-CSLs is lower than the $\eta$-CSL. Each NA soliton carries an isospin, and +an antiferro-isospin chain is formed leading to gapless isospinons. The +anomalous coupling to the magnetic field provides the NA-CSL ($\eta$-CSL) with +a ferrimagnetic (ferromagnetic) magnetization.",2112.01381v1 +2021-12-27,Observation of magnon cross-Kerr effect in cavity magnonics,"When there is a certain amount of field inhomogeneity, the biased +ferrimagnetic crystal will exhibit the higher-order magnetostatic (HMS) mode in +addition to the uniform-precession Kittel mode. In cavity magnonics, we show +both experimentally and theoretically the cross-Kerr-type interaction between +the Kittel mode and HMS mode. When the Kittel mode is driven to generate a +certain number of excitations, the HMS mode displays a corresponding frequency +shift and vice versa. The cross-Kerr effect is caused by an exchange +interaction between these two spin-wave modes. Utilizing the cross-Kerr effect, +we realize and integrate a multi-mode cavity magnonic system with only one +yttrium iron garnet (YIG) sphere. Our results will bring new methods to +magnetization dynamics studies and pave a way for novel cavity magnonic devices +by including the magnetostatic mode-mode interaction as an operational degree +of freedom.",2112.13807v1 +2021-12-27,An Effective Field Theory of Magneto-Elasticity,"We utilize the coset construction to derive the effective field theory of +magnon-phonon interactions in (anti)-ferromagnetic and ferrimagnetic insulating +materials. The action is used to calculate the equations of motion which +generalize the Landau-Lifshitz and stress equations to allow for +magneto-acoustic couplings to all orders in the fields at lowest order in the +derivative expansion. We also include the symmetry breaking effects due to +Zeeman, and Dzyaloshinsky-Moriya interactions. This effective theory is a +toolbox for the study of magneto-elastic phenomena from first principles. As an +example we use this theory to calculate the leading order contribution to the +magnon decay width due to its the decay into phonons.",2112.13873v3 +2022-01-10,A theory for anisotropic magnetoresistance in materials with two vector order parameters,"Anisotropic magnetoresistance (AMR) and related planar Hall resistance (PHR) +are ubiquitous phenomena of magnetic materials. Although the universal angular +dependences of AMR and PHR in magnetic polycrystalline materials with one order +parameter are well known, no similar universal relation for other class of +magnetic materials are known to date. Here I present a general theory of +galvanomagnetic effects in magnetic materials with two vector order parameters, +such as magnetic single crystals with a dominated crystalline axis or +polycrystalline non-collinear ferrimagnetic materials. It is shown that AMR and +PHR have a universal angular dependence. In general, both longitudinal and +transverse resistivity are non-reciprocal in the absence of inversion symmetry: +Resistivity takes different value when the current is reversed. Different from +simple magnetic polycrystalline materials where AMR and PHR have the same +magnitude, and $\pi/4$ out of phase, the magnitude of AMR and PHR of materials +with two vector order parameters are not the same in general, and the phase +difference is not $\pi/4$. Instead of $\pi$ periodicity of the usual AMR and +PHR, the periodicities of materials with two order parameters are $2\pi$.",2201.03316v1 +2022-01-31,Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment,"In this paper, we present the structural, electronic, magnetic and transport +properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and +(200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure. +Magnetization measurements indicate a high Curie temperature and a negligibly +small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are +indicative of fully compensated ferrimagnetism in the alloy. +Temperature-dependent resistivity indicates metallic nature. Ab-initio +calculation of fully ordered NbVTiAl structure confirms a nearly half metallic +behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment +of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One +of the main objective of the present paper is to resolve and explain the +long-standing discrepancy between theoretical prediction and experimental +observation of magnetization for V-based quaternary Heusler alloys, in general. +To gain an in-depth understanding, we modelled various disordered states and +its subsequent effect on the magnetic and electronic properties. The +discrepancy is attributed to the A2 disorder present in the system, as +confirmed by our XRD data. The presence of disorder also causes the emergence +of finite states at the Fermi level, which impacts the spin polarization of the +system.",2201.13037v1 +2022-02-15,Optically-induced magnetization switching in NiCo2O4 thin films using ultrafast lasers,"Recently, all-optical magnetization control has been garnering considerable +attention in realizing next-generation ultrafast magnetic information devices. +Here, employing a magneto-optical Kerr effect (MOKE) microscope, we observed +the laser-induced magnetization switching of ferrimagnetic oxide NiCo2O4 (NCO) +epitaxial thin films with perpendicular magnetic anisotropy, where the sample +was pumped at 1030-nm laser pulses, and magnetic domain images were acquired +via the MOKE microscope with a white light emitting diode. Laser pulses +irradiated an NCO thin film at various temperatures from 300 K to 400 K while +altering the parameters of pulse interval, fluence, and the number of pulses +with the absence of the external magnetic field. We observed accumulative +all-optical switching at 380 K and above. Our observation of oxide NCO thin +films facilitates the realization of chemically stable magnetization switching +using ultrafast lasers, and without applying a magnetic field.",2202.07257v1 +2022-02-22,Magnetic properties of equiatomic CrMnFeCoNi,"Magnetic, specific heat, and structural properties of the equiatomic Cantor +alloy system are reported for temperatures between 5 kelvin and 300 kelvin, and +up to fields of 70 kilo-oersted. Magnetization measurements performed on +as-cast, annealed, and cold-worked samples reveal a strong processing history +dependence and that high-temperature annealing after cold-working does not +restore the alloy to a pristine state. Measurements on known precipitates show +that the two transitions, detected at 43 kelvin and 85 kelvin, are intrinsic to +the Cantor alloy and not the result of an impurity phase. Experimental and ab +initio density functional theory (DFT) computational results suggest that these +transitions are a weak ferrimagnetic transition and a spin-glass-like +transition, respectively, and magnetic and specific heat measurements provide +evidence of significant Stoner enhancement and electron-electron interactions +within the material.",2202.11073v1 +2022-03-08,Enhancement of thermal spin pumping by orbital angular momentum of rare earth iron garnet,"In a bilayer of ferromagnetic and non-magnetic metal, spin pumping can be +generated by a thermal gradient. The spin current generation depends on the +spin mixing conductance of the interface and the magnetic properties of the +ferromagnetic layer. Due to its low intrinsic damping, rare earth iron garnet +is often used for the ferromagnetic layer in the spin Seebeck experiment. +However, it is actually a ferrimagnetic with antiferromagnetically coupled +magnetic lattices and the contribution of rare earth magnetic lattice of rare +earth iron garnet on thermal spin pumping is not well understand. Here we focus +on the effect of magnetic properties of lanthanide and show that the orbital +angular momentum of rare earth iron garnet enhances thermal spin current +generation of lanthanide substituted yttrium iron garnet.",2203.03915v2 +2022-03-18,Plasmonic dichroism and all-optical magnetization switching in nanophotonic structures with GdFeCo,"We report on a phenomenon of plasmonic dichroism observed in magnetic +materials with the transverse magnetization under the excitation of the surface +plasmon polariton waves. The effect originates from the interplay of the two +magnetization-dependent contributions to the material absorption, both of which +are enhanced under plasmon excitation. Similar to the recently discovered +effect of a all-optical helicity-dependent magnetization switching, this effect +provides a possibility to perform a deterministic magnetization switching to +the desired state. We show by electromagnetic modeling that laser pulses +exciting counter-propagating plasmons can be used to write +M or -M state in a +deterministic way independent on the initial magnetization state. The presented +approach applies to various ferrimagnetic materials exhibiting the phenomenon +of all-optical switching of thermal nature and broadens the horizons of their +applications in data storage devices.",2203.09956v1 +2022-03-22,A strategic high throughput search for identifying stable Li based half Heusler alloys for spintronics applications,"In this work, high throughput DFT calculations are performed on the alkali +metal-based half Heusler alloys; LiY$_p$Y$^\prime_{1-p}$S (Y, Y$^\prime$ = V, +Cr, Mn, Fe, Co, Ni and $\mathit{p}$ = 0, 0.25, 0.5, 0.75, 1). Starting with 243 +structural replica, systematic filters are designed to select the energetically +and vibrationally favorable compositions by considering the contributions +stemming from the magnetic alignments of the ions. Thereby, 26 dynamically +stable magnetic compositions are identified, of which 10 are found to be +ferromagnetic (FM), 4 antiferromagnetic (AFM) and 12 ferrimagnetic (FiM). 4 FM +and 8 FiM ones are found to show 100 $\%$ spin polarization. Further, +tetragonal distortion is found to be present in 4 FM, 3 FiM and 4 AFM +compositions, which indicates the possibility of easy-axis magnetocrystalline +anisotropy. The ferromagnetic LiFe$_{0.5}$Mn$_{0.5}$S and antiferromagnetic +LiFeS are found to have the most prominent easy-axis magnetocrystalline +anisotropy.",2203.11794v1 +2022-03-30,Ferromagnetism and doublon localization in a Wannier-Hubbard chain,"We derive a ""Wannier-Hubbard"" model consisting of an array of overlapping +atomic orbitals interacting via a local Coulomb interaction. Transforming to an +orthogonal Wannier basis set, the resulting Hamiltonian displays long range +hopping and interactions, with new terms such as correlated hopping and +ferromagnetic direct exchange, among others. We numerically study the +one-dimensional version of the model at half-filling using the density matrix +renormalization group (DMRG) method, unveiling a rich phase diagram as a +function of the interaction $U$ and the overlap $s$ with metallic, and +ferromagnetic phases, separated by a ferrimagnetic region. Our results indicate +a path toward understanding new emergent phases under pressure and beyond +standard model Hamiltonians.",2203.16483v2 +2022-04-01,Effect of interfacial spin mixing conductance on gyromagnetic ratio of Gd substituted Y$_{3}$Fe$_{5}$O$_{12}$,"Due to its low intrinsic damping, Y$_3$Fe$_5$O$_{12}$ and its substituted +variations are often used for ferromagnetic layer at spin pumping experiment. +Spin pumping is an interfacial spin current generation in the interface of +ferromagnet and non-magnetic metal, governed by spin mixing conductance +parameter $G^{\uparrow\downarrow}$. $G^{\uparrow\downarrow}$ has been shown to +enhance the damping of the ferromagnetic layer. The theory suggested that the +effect of $G^{\uparrow\downarrow}$ on gyromagnetic ratio only come from its +negligible imaginary part. In this article, we show that the different damping +of ferrimagnetic lattices induced by $G^{\uparrow\downarrow}$ can affect the +gyromagnetic ratio of Gd-substituted Y$_3$Fe$_5$O$_{12}$.",2204.00310v1 +2022-04-07,Topological multiferroic order in twisted transition metal dichalcogenide bilayers,"Layered van der Waals materials have risen as powerful platforms to +artificially engineer correlated states of matter. Here we show the emergence +of a multiferroic order in a twisted dichalcogenide bilayer superlattice at +quarter-filling. We show that the competition between Coulomb interactions +leads to the simultaneous emergence of ferrimagnetic and ferroelectric orders. +We derive the magnetoelectric coupling for this system, which leads to a direct +strong coupling between the charge and spin orders. We show that, due to +intrinsic spin-orbit coupling effects, the electronic structure shows a +non-zero Chern number, thus displaying a topological multiferroic order. We +show that this topological state gives rise to interface modes at the different +magnetic and ferroelectric domains of the multiferroic. We demonstrate that +these topological modes can be tuned with external electric fields as well as +triggered by supermoire effects generated by a substrate. Our results put +forward twisted van der Waals materials as a potential platform to explore +multiferroic symmetry breaking orders and, ultimately, controllable topological +excitations in magnetoelectric domains.",2204.03360v2 +2022-04-14,Tuning the coexistence regime of incomplete and tubular skyrmions in ferro/ferri/ferromagnetic trilayers,"The development of skyrmionic devices requires a suitable tuning of material +parameters in order to stabilize skyrmions and control their density. It has +been demonstrated recently that different skyrmion types can be simultaneously +stabilized at room temperature in heterostructures involving ferromagnets, +ferrimagnets and heavy metals, offering a new platform of coding binary +information in the type of skyrmion instead of the presence/absence of +skyrmions. Here, we tune the energy landscape of the two skyrmion types in such +heterostructures by engineering the geometrical and material parameters of the +individual layers. We find that a fine adjustment of the ferromagnetic layer +thickness and thus its magnetic anisotropy, allows the trilayer system to +support either one of the skyrmion types or the coexistence of both and with +varying densities.",2204.06808v2 +2022-05-06,Vacuum material properties and Cherenkov radiation in Logarithmic Electrodynamics,"We study some observational signatures of nonlinearities of the +electromagnetic field. First to all we show the vital role played by +nonlinearities in triggering a material behavior of the vacuum with +$(\varepsilon > 0, \mu <0)$, which corresponds to a ferrimagnetic material. +Secondly, the permittivity and susceptibility induced by nonlinearities are +considered in order to obtain the refractive index via the dispersion relation +for logarithmic electrodynamics. Finally, we consider the electromagnetic +radiation produced by a moving charged particle interacting with a medium +characterized by nonlinearities of the electromagnetic field. To this end we +consider logarithmic electrodynamics. The result shows that the radiation is +driven by the medium through which the particle travels like the one that +happens in the Cherenkov effect.",2205.03252v1 +2022-05-10,"Structural, electronic and magnetic properties of La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$ double perovskite","In this work, we report the synthesis and investigation of structural, +electronic, and magnetic properties of +La$_{1.5}$Ca$_{0.5}$(Co$_{0.5}$Fe$_{0.5}$)IrO$_6$. Our polycrystalline sample +forms as a single-phase double perovskite in monoclinic $P2_{1}/n$ space group. +Co and Ir are most likely in bivalent and tetravalent oxidation states, +respectively, while Mossbauer spectroscopy indicates that Fe is in a trivalent +state. The ac and dc magnetization data suggest a ferrimagnetic behavior +resulting from the presence of two antiferromagnetic sublattices at Co/Fe and +Ir sites. The large coercive field H_C $\simeq$ 32 kOe observed at 10 K, +comparable to that of other double perovskites of interest for hard magnets, is +discussed in terms of the structural distortion and the spin and orbital +magnetic moments of the transition metal ions.",2205.04778v1 +2022-05-13,Fast scanning nitrogen-vacancy magnetometry by spectrum demodulation,"We demonstrate a spectrum demodulation technique for greatly speeding up the +data acquisition rate in scanning nitrogen-vacancy center magnetometry. Our +method relies on a periodic excitation of the electron spin resonance by fast, +wide-band frequency sweeps combined with a phase-locked detection of the +photo-luminescence signal. The method can be extended by a frequency feedback +to realize real-time tracking of the spin resonance. Fast scanning magnetometry +is especially useful for samples where the signal dynamic range is large, of +order millitesla, like for ferro- or ferrimagnets. We demonstrate our method by +mapping stray fields above the model antiferromagnet $\alpha$-Fe$_2$O$_3$ +(hematite) at pixel rates of up to 100\,Hz and an image resolution exceeding +one megapixel.",2205.06579v1 +2022-06-08,Metal-insulator transition in the disordered Hubbard model of the Lieb lattice,"Using the determinant quantum Monte Carlo method, we investigate the +metal-insulator transition in the interacting disordered Hubbard model of a +Lieb lattice, in which the system characterizes the flat band centered at the +Fermi level. By choosing suitable electron densities, we ensure the weak +interaction sign problem to improve the reliability of our results. It is found +that disorder and on-site Coulomb repulsive interaction produce interesting +effects that induce the metal-insulator transition which is impossible in the +half-filled case. The density of states at the Fermi energy is still finite in +the thermodynamic limit, suggesting that the system is an Anderson insulator +rather than a Mott insulator. Moreover, this doping system is paramagnetic, +unlike the half-filled system, which is ferrimagnetic.",2206.03890v1 +2022-06-12,Stationary optomagnonic entanglement and magnon-to-optics quantum state transfer via opto-magnomechanics,"We show how to prepare a steady-state entangled state between magnons and +optical photons in an opto-magnomechanical configuration, where a mechanical +vibration mode couples to a magnon mode in a ferrimagnet by the dispersive +magnetostrictive interaction, and to an optical cavity by the radiation +pressure. We find that, by appropriately driving the magnon mode and the cavity +to simultaneously activate the magnomechanical Stokes and the optomechanical +anti-Stokes scattering, a stationary optomagnonic entangled state can be +created. We further show that, by activating the magnomechanical state-swap +interaction and subsequently sending a weak red-detuned optical pulse to drive +the cavity, the magnonic state can be read out in the cavity output field of +the pulse via the mechanical transduction. The demonstrated entanglement and +state-readout protocols in such a novel opto-magnomechanical configuration +allow us to optically control, prepare, and read out quantum states of +collective spin excitations in solids, and provide promising opportunities for +the study of quantum magnonics, macroscopic quantum states, and magnonic +quantum information processing.",2206.05688v3 +2022-06-29,Mechanical Bistability in Kerr-modified Cavity Magnomechanics,"Bistable mechanical vibration is observed in a cavity magnomechanical system, +which consists of a microwave cavity mode, a magnon mode, and a mechanical +vibration mode of a ferrimagnetic yttrium-iron-garnet (YIG) sphere. The +bistability manifests itself in both the mechanical frequency and linewidth +under a strong microwave drive field, which simultaneously activates three +different kinds of nonlinearities, namely, magnetostriction, magnon self-Kerr, +and magnon-phonon cross-Kerr nonlinearities. The magnon-phonon cross-Kerr +nonlinearity is first predicted and measured in magnomechanics. The system +enters a regime where Kerr-type nonlinearities strongly modify the conventional +cavity magnomechanics that possesses only a radiation-pressure-like +magnomechanical coupling. Three different kinds of nonlinearities are +identified and distinguished in the experiment. Our work demonstrates a new +mechanism for achieving mechanical bistability by combining magnetostriction +and Kerr-type nonlinearities, and indicates that such Kerr-modified cavity +magnomechanics provides a unique platform for studying many distinct +nonlinearities in a single experiment.",2206.14588v2 +2022-07-06,Topological magnons on the triangular kagome lattice,"We present the topology of magnons on the triangular kagome lattice (TKL) by +calculating its Berry curvature, Chern number and edge states. In addition to +the ferromagnetic state, the TKL hosts ferrimagnetic ground state as its two +sublattices can couple with each other either ferromagnetically or +antiferromagnetically. Using Holstein-Primakoff (HP) boson theory and Green's +function approach, we find that the TKL has a rich topological band structure +with added high Chern numbers compared with the kagome and honeycomb lattices. +The magnon edge current allows a convenient calculation of thermal Hall +coefficients and the orbital angular momentum gives correlation to the +Einstein-de Haas effect. We apply the calculations to the TKL and derive the +topological gyromagnetic ratio showing a nonzero Einstein-de Haas effect in the +zero temperature limit. Our results render the TKL as a potential platform for +quantum magnonics applications including high-precision mechanical sensors and +information transmission.",2207.02886v2 +2022-08-05,Interfacial phase frustration stabilizes unconventional skyrmion crystals,"Chiral magnetic phases with an unconventional topological twist in the +magnetization are of huge interest due to their potential in spintronics +applications. Here, we present a general method to induce such exotic magnetic +phases using interfacial phase frustration within artificially grown +superlattices. To demonstrate our method, we consider a multilayer with two +different chiral magnetic phases as the competing orders at the top and bottom +and show, using Monte Carlo calculations, that the interfacial phase +frustration is realized at the central layer. In particular, we obtain three +unconventional phases: a checkerboard skyrmion crystal, an incommensurate +skyrmion stripe, and a ferrimagnetic skyrmion crystal. In these +frustration-induced phases, the spin chirality driven topological Hall +conductivity can be largely enhanced. This method provides a playground to +realize unconventional magnetic phases in any family of materials that can be +grown in superlattices.",2208.03255v1 +2022-08-23,Microwave-optics Entanglement via Cavity Optomagnomechanics,"Microwave-optics entanglement is a vital component for building hybrid +quantum networks. Here, a new mechanism for preparing stationary entanglement +between microwave and optical cavity fields in a cavity optomagnomechanical +system is proposed. It consists of a magnon mode in a ferrimagnetic crystal +that couples directly to a microwave cavity mode via the magnetic dipole +interaction, and indirectly to an optical cavity through the deformation +displacement of the crystal. The mechanical displacement is induced by the +magnetostrictive force and coupled to the optical cavity via radiation +pressure. Both the opto- and magnomechanical couplings are dispersive. +Magnon-phonon entanglement is created via magnomechanical parametric +down-conversion, which is further distributed to optical and microwave photons +via simultaneous optomechanical beamsplitter interaction and electromagnonic +state-swap interaction, yielding stationary microwave-optics entanglement. The +microwave-optics entanglement is robust against thermal noise, which will find +broad potential applications in quantum networks and quantum information +processing with hybrid quantum systems.",2208.10703v2 +2022-08-23,Reversal of nanomagnets by propagating magnons in ferrimagnetic yttrium iron garnet enabling nonvolatile magnon memory,"Despite the unprecedented downscaling of CMOS integrated circuits, +memory-intensive machine learning and artificial intelligence applications are +limited by data conversion between memory and processor. There is a challenging +quest for novel approaches to overcome this so-called von Neumann bottleneck. +Magnons are the quanta of spin waves and transport angular momenta through +magnets. They enable power-efficient computation without charge flow and would +solve the conversion problem if spin wave amplitudes could be stored directly +in a magnetic memory cell. Here, we report the reversal of ferromagnetic +nanostripes by spin waves which propagate through an underlying spin-wave bus +made from yttrium iron garnet. Thereby, the charge-free angular momentum flow +is stored after transmission over a macroscopic distance. We show that spin +waves can reverse large arrays of ferromagnetic stripes at a strikingly small +power level of nW. Combined with the already existing wave logic, our discovery +is path-breaking for the new era of magnonics-based in-memory computation and +beyond von Neumann computer architectures.",2208.10923v1 +2022-08-31,Unusual kinetic properties of usual Heusler alloys,"The review considers various groups of Heusler compounds, which can have the +properties of a semiconductor, a half-metallic ferromagnet, a spin gapless +semiconductor, a topological semimetal, and a noncollinear antiferromagnet. In +these Heusler compounds, ""conventional"" from the point of view of the crystal +structure, unusual kinetic and magnetic properties can be observed, which are +caused by the features of their electronic structure (e.g., presence of an +energy gap for one spin projection) and magnetic state (e.g., strong +ferromagnetism, compensated ferrimagnetism, etc.). Their magnetic and kinetic +characteristics are very sensitive to external influences. Depending on the +alloy composition and external parameters, transitions between the considered +states can be realized. All this opens up further prospects for controlling the +electronic and magnetic characteristics of such compounds and their practical +application.",2208.14868v1 +2022-09-06,Spin-phonon interaction and short range order in $\mathrm{Mn_3Si_{2}Te_6}$,"The vibrational properties of ferrimagnetic $\mathrm{Mn_3Si_{2}Te_6}$ single +crystals are investigated using Raman spectroscopy and density functional +theory calculations. Eighteen Raman-active modes are identified, fourteen of +which are assigned according to with the trigonal symmetry. Four additional +peaks, obeying the $A_{1g}$ selection rules, are attributed to the overtones. +The unconventional temperature evolution of the $A_{1g}^5$ mode self-energy +suggests a competition between different short-range magnetic correlations that +significantly impact the spin-phonon interaction in $\mathrm{Mn_3Si_{2}Te_6}$. +The research provides a comprehensive insight to the lattice properties, +studies their temperature dependence and shows the arguments for existence of +competing short-range magnetic phases in $\mathrm{Mn_3Si_{2}Te_6}$.",2209.02664v1 +2022-10-03,Chirality-induced one-way quantum steering between two waveguide-mediated ferrimagnetic microspheres,"One-way quantum steering is of importance for quantum technologies, such as +secure quantum teleportation. In this paper, we study the generation of one-way +quantum steering between two distant yttrium iron garnet (YIG) microspheres in +chiral waveguide electromagonics. We consider that the magnon mode with the +Kerr nonlinearity in each YIG sphere is chirally coupled to left- and +right-propagating guided photons in the waveguide. We find that quantum +steering between the magnon modes is absent with non-chirality but is present +merely in the form of one way (i.e., one-way steering) when the chirality +occurs. The maximal achievable steering is obviously improved as the chirality +degree increases. We further find that when the waveguide's outputs are +subjected to continuous homodyne detection, the steering can be considerably +enhanced and asymmetric steering with strong entanglement can also be achieved +by tuning the chirality. Our study shows that chirality can be explored to +effectively realize one-way quantum steering. Compared to other studies on +achieving asymmetric steering via controlling intrinsic dissipation, e.g. +cavity loss rates, our scheme merely depends on the chirality enabled via +positioning the micromagnets in the waveguide and is continuously adjustable +and experimentally more feasible.",2210.00710v1 +2022-10-10,Three-state Potts nematic order in stacked frustrated spin models with SO(3) symmetry,"We propose stacked two-dimensional lattice designs of frustrated and SO(3) +symmetric spin models consisting of antiferromagnetic (AFM) triangular and +ferromagnetic (FM) sixfold symmetric sublattices that realize emergent Z3 Potts +nematic order. Considering bilinear-biquadratic spin interactions, our models +describe an SO(3)-symmetric triangular lattice AFM subject to a fluctuating +magnetization arising from the FM coupled sublattice. We focus on the classical +AFM-FM windmill model and map out the zero- and finite-temperature phase +diagram using Monte Carlo simulations and analytical calculations. We discover +a state with composite Potts nematic order above the ferrimagnetic +three-sublattice up-up-down ground state and relate it to Potts phases in +SO(3)-broken Heisenberg and Ising AFMs in external magnetic fields. Finally, we +show that the biquadratic exchange in our model is automatically induced by +thermal and quantum fluctuations in the purely bilinear Heisenberg model, +easing the requirements for realizing these lattice designs experimentally.",2210.04900v2 +2022-11-02,Pump--probe x-ray microscopy of photo-induced magnetization dynamics at MHz repetition rates,"We present time-resolved scanning x-ray microscopy measurements with +picosecond photo-excitation via a tailored infrared pump laser at a scanning +transmission x-ray microscope. Specifically, we image the laser-induced +demagnetization and remagnetization of thin ferrimagnetic GdFe films proceeding +on a few nanoseconds time scale. Controlling the heat load on the sample via +additional reflector and heat-sink layers allows us to conduct destruction-free +measurements at a repetition rate of \SI{50}{\mega\hertz}. Near-field +enhancement of the photo-excitation and controlled annealing effects lead to +laterally heterogeneous magnetization dynamics which we trace with +\SI{30}{\nano\meter} spatial resolution. Our work opens new opportunities to +study photo-induced dynamics on the nanometer scale, with access to picosecond +to nanosecond timescales, which is of technological relevance, especially in +the field of magnetism.",2211.01230v2 +2022-12-01,Nonreciprocal Phonon Propagation in a Metallic Chiral Magnet,"The phonon magnetochiral effect (MChE) is the nonreciprocal acoustic and +thermal transports of phonons caused by the simultaneous breaking of the mirror +and time-reversal symmetries. So far, the phonon MChE has been observed only in +a ferrimagnetic insulator Cu2OSeO3, where the nonreciprocal response disappears +above the Curie temperature of 58 K. Here, we study the nonreciprocal acoustic +properties of a room-temperature ferromagnet Co9Zn9Mn2 for unveiling the phonon +MChE close to the room temperature. Surprisingly, the nonreciprocity in this +metallic compound is enhanced at higher temperatures and observed up to 250 K. +This clear contrast between insulating Cu2OSeO3 and metallic Co9Zn9Mn2 suggests +that metallic magnets have a mechanism to enhance the nonreciprocity at higher +temperatures. From the ultrasound and microwave-spectroscopy experiments, we +conclude that the magnitude of the phonon MChE of Co9Zn9Mn2 mostly depends on +the magnon bandwidth, which increases at low temperatures and hinders the +magnon-phonon hybridization. Our results suggest that the phonon nonreciprocity +could be further enhanced by engineering the magnon band of materials.",2212.00225v2 +2022-12-14,Ordered creation and motion of skyrmions with surface acoustic wave,"Magnetic skyrmions with a well-defined spin texture have shown unprecedented +potential for various spintronic applications owning to their topologically +non-trivial and quasiparticle properties. To put skyrmions into practical +technology, efficient manipulation, especially the inhibition of skyrmion Hall +effect (SkHE) has been intensively pursued. In spite of the recent progress +made on reducing SkHE in several substituted systems, such as ferrimagnets and +synthetic antiferromagnets, the organized creation and current driven motion of +skyrmions with negligible SkHE in ferromagnets remain challenging. Here, by +embeding the [Co/Pd] multilayer into a surface acoustic wave (SAW) delay line, +we experimentally realized the ordered generation of magnetic skyrmions. The +resultant current-induced skyrmions movement with negligible SkHE was observed, +which can be attributed to the energy redistribution of the system during the +excitation of SAW. Our findings open up an unprecedentedly new perspective for +manipulating topological solitons, and would advance the development of +skyrmionics and spin acousto-electronics.",2212.06997v1 +2022-12-15,Electric field tuning of magnetic states in single magnetic molecules,"Single magnetic molecules may be the smallest functional magnets. An +electric-field controllable spin state of magnetic molecules is of fundamental +importance for applications while its realization remains challenging. To date +the observed spin-electric interaction based on spin-orbit coupling or spin +dipole coupling is useful to tune fine spin structures but too weak to flip the +spin state. In this work, we propose a new mechanism to realize enhanced +spin-electric coupling and flip the spin states by tuning the spin +superexchange between local spins. Using first-principles calculations and +Heisenberg Hamiltonian, we demonstrate this effect in a family of magnetic +molecules, transition metallic Porphyrins. We show that their d-{\pi} and +{\pi}-{\pi} spin superexchange couplings are determined by the relative +energies of d and {\pi} electronic states, which are sensitive to the applied +electric field. Therefore, applying electric field can tune a wide range of +magnetic ground states, including ferromagnetic, ferrimagnetic, and +antiferromagnetic configurations. This spin-electric coupling may provide a new +approach for designing and controlling molecular spintronics.",2212.08010v1 +2023-02-07,Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications,"We report the structural, magnetic, and interfacial spin transport properties +of epitaxial terbium iron garnet (TbIG) ultrathin films deposited by magnetron +sputtering. High crystallinity was achieved by growing the films on gadolinium +gallium garnet (GGG) substrates either at high temperature, or at room +temperature followed by thermal annealing, above 750 {\deg}C in both cases. The +films display large perpendicular magnetic anisotropy (PMA) induced by +compressive strain, and tunable structural and magnetic properties through +growth conditions or the substrate lattice parameter choice. The ferrimagnetic +compensation temperature (TM) of selected TbIG films was measured through +temperature-dependent anomalous Hall effect (AHE) in Pt/TbIG heterostructures. +In the studied films, TM was found to be between 190-225 K, i.e., approximately +25-60 K lower than the bulk value, which is attributed to the combined action +of Tb deficiency and oxygen vacancies in the garnet lattice evidenced by x-ray +photoelectron spectroscopy measurements. Sputtered TbIG ultrathin films with +large PMA and highly tunable properties reported here can provide a suitable +material platform for a wide range of spintronic experiments and device +applications.",2302.03758v1 +2023-02-09,Single-shot laser-induced switching of an exchange biased antiferromagnet,"Ultrafast manipulation of magnetic order has challenged our understanding the +fundamental and dynamic properties of magnetic materials. So far single shot +magnetic switching has been limited to ferrimagnetic alloys and multilayers. In +ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, exchange bias (He) arises +from the interfacial exchange coupling between the two layers and reflects the +microscopic orientation of the antiferromagnet. Here we demonstrate the +possibility of single shot switching of the antiferromagnet (change of the sign +and amplitude of He) with a single femtosecond laser pulse in IrMn/CoGd +bilayers. We demonstrate the switching for a wide range of fluences for +different layer thicknesses and compositions. Atomistic simulations predict +ultrafast switching and recovery of the AFM magnetization on a timescale of 2 +ps. These results provide the fastest and the most energy-efficient method to +set the exchange bias and pave the way to potential applications for ultrafast +spintronic devices.",2302.04510v1 +2023-02-06,Chiral and flat-band magnetic cluster excitations in a ferromagnetic kagome metal,"TbMn6Sn6 is a metallic ferrimagnet that displays signatures of band topology +arising from a combination of uniaxial ferromagnetism and spin-orbit coupling +within its Mn kagome layers. Whereas the low energy magnetic excitations can be +described as collective spin waves using a local moment Heisenberg model, +sharply defined optical and flat-band collective magnon modes are not observed. +In their place, we find overdamped chiral and flat-band spin correlations that +are localized to hexagonal plaquettes within the kagome layer.",2302.04846v1 +2023-02-17,Control of the magnon-polariton hybridization with a microwave pump,"Pump-induced magnon modes (PIMs) are recently discovered elementary +excitations in ferrimagnets that offer significant tunability to spin dynamics. +Here, we investigate the coupling between a PIM and cavity magnon polaritons +(CMPs) by driving a cavity magnonic system away from equilibrium with a +microwave pump. In our experiment, the Walker mode simultaneously couples with +the PIM and cavity photons and thus combines two strongly coherent coupling +processes in a single cavity structure. Such a PIM-CMP hybridization system +acquires complementary properties from both the PIM and CMPs, allowing it to be +freely manipulated by the magnetic field, the pump power and the pump +frequency. These coherent manipulations exhibit unique behaviors beyond the +intrinsic properties limited by the material nature and electromagnetic +boundary conditions, thereby creating opportunities for extending the control +of hybrid devices.",2302.08665v2 +2023-02-26,Highly Tunable Intrinsic Exchange Bias from Interfacial Reconstruction in Epitaxial NixCoyFe3-x-yO4(111)/α-Al2O3(0001) Thin Films,"Intrinsic exchange bias up to 12.6 kOe is observed in +NixCoyFe3-x-yO4(111)/{\alpha}-Al2O3(0001) (0<=x+y<=3) epitaxial thin films +where 0.15<=y<=2. An interfacial layer of rock-salt structure emerges between +NixCoyFe3-x-yO4 thin films and {\alpha}-Al2O3 substrates and is proposed as the +antiferromagnetic layer unidirectionally coupled with ferrimagnetic +NixCoyFe3-x-yO4. In NiCo2O4(111)/{\alpha}-Al2O3(0001) films, results of +reflection high energy electron diffraction, X-ray photoelectron spectroscopy, +X-ray reflectometry, and polarized neutron reflectometry support that the +interfacial layer is antiferromagnetic NixCo1-xO (0.32<=x<=0.49) of rock-salt +structure; the interfacial layer and exchange bias can be controlled by growth +oxygen pressure revealing the key role of oxygen in the mechanism of the +interfacial reconstruction. This work establishes a family of intrinsic +exchange bias materials with great tunability by stoichiometry and growth +parameters and emphasizes the strategy of interface engineering in controlling +material functionalities.",2302.13227v3 +2023-03-01,Thermodynamic determination of the equilibrium first-order phase-transition line hidden by hysteresis in a phase diagram,"Phase diagrams form the basis for the study of material science, and the +profiles of phase-transition lines separating different thermodynamic phases +include comprehensive information about thermodynamic quantities, such as +latent heat. However, in some materials exhibiting field-induced first-order +transitions (FOTs), the equilibrium phase-transition line is hidden by the +hysteresis region associated with the FOT; thus, it cannot be directly +determined from measurements of resistivity, magnetization, etc. Here, we +demonstrate a thermodynamics-based method for determining the hidden +equilibrium FOT line. This method is verified for the FOT between +antiferromagnetic and ferrimagnetic states in magneto-electric compounds +(Fe$_{0.95}$Zn$_{0.05}$)$_{2}$Mo$_{3}$O$_{8}$. The equilibrium FOT line +determined based on the Clausius-Clapeyron equation exhibits a reasonable +profile in terms of the third law of thermodynamics, and it shows marked +differences from the midpoints of the hysteresis region. Our findings highlight +that care should be taken for referring to the hysteresis midpoint line when +discussing field-induced latent heat or magnetocaloric effects.",2303.00327v1 +2023-03-27,Temperature dependent study of the spin dynamics of coupled Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$/Pt trilayers,"In this study, we investigate the dynamic response of a Y$_3$Fe$_5$O$_{12}$ +(YIG)/ Gd$_3$Fe$_5$O$_{12}$ (GdIG)/ Pt trilayer system by measurements of the +ferromagnetic resonance (FMR) and the pumped spin current detected by the +inverse spin Hall effect. This trilayer system offers the unique opportunity to +investigate the spin dynamics of the ferrimagnetic GdIG, close to its +compensation temperature. We show that our trilayer acts as a highly tunable +spin current source. Our experimental results are supported by micro-magnetic +simulations. As the detected spin current in the top Pt layer is distinctly +dominated by the GdIG layer, this gives the unique opportunity to investigate +the excitation and dynamic properties of GdIG while comparing it to the +broadband FMR absorption spectrum of the heterostructure.",2303.15085v1 +2023-04-04,Full quantum theory for magnon transport in two-sublattice magnetic insulators and magnon junctions,"Magnon, as elementary excitation in magnetic systems, can carry and transfer +angular momentum. Due to the absence of Joule heat during magnon transport, +researches on magnon transport have gained considerable interests over the past +decade. Recently, a full quantum theory has been employed to investigate magnon +transport in ferromagnetic insulators (FMIs). However, the most commonly used +magnetic insulating material in experiments, yttrium iron garnet (YIG), is a +ferrimagnetic insulator (FIMI). Therefore, a full quantum theory for magnon +transport in FIMI needs to be established. Here, we propose a Green's function +formalism to compute the magnon bulk and interface current in both FIMIs and +antiferromagnetic insulators (AFMIs). We investigate the spatial distribution +and temperature dependence of magnon current in FIMIs and AFMIs generated by +temperature or spin chemical potential step. In AFMIs, magnon currents +generated by temperature step in the two sublattices cancel each other out. +Subsequently, we numerically simulate the magnon junction effect using the +Green's function formalism, and result shows near 100\% magnon junction ratio. +This study demonstrates the potential for investigating magnon transport in +specific magnonic devices using a full quantum theory.",2304.01930v1 +2023-04-21,Magnetic Structures and Spin-wave Excitations in Rare-Earth Iron Garnets near the Compensation Temperature,"We introduce a simple model for the ferrimagnetic non-collinear ``magnetic +umbrella"" states of rare-earth iron garnets (REIG), common when the rare-earth +moments have non-zero orbital angular momentum. The spin-wave excitations are +calculated within linear spin wave theory and temperature effects via +mean-field theory. This could be used to determine the magnetic polarization of +each mode and thereby the spin currents generated by thermal excitations +including the effects of mixed chirality. The spectra reproduce essential +features seen in more complete models, with hybridization between the rare +earth crystal field excitations and the propagating mode on the iron moments. +By the symmetry of the model, only one rare earth mode hybridizes, inducing a +gap at zero wave number and level repulsion at finite frequency. At the +compensation point, the hybridization gap closes and finally, as we approach +the N\'eel temperature, the hybridization gap appears to reopen. The chirality +of the lowest mode changes its sign around the frequency at which the level +repulsion occurs. This is important to estimate the spin current generation in +REIGs.",2304.10695v1 +2023-04-26,Rapid-prototyping of microscopic thermal landscapes in Brillouin light scattering spectroscopy,"Since temperature and its spatial and temporal variations affect a wide range +of physical properties of material systems, they can be used to create +reconfigurable spatial structures of various types in physical and biological +objects. This paper presents an experimental optical setup for creating tunable +two-dimensional temperature patterns on a micrometer scale. As an example of +its practical application, we have produced temperature-induced magnetization +landscapes in ferrimagnetic yttrium iron garnet films and investigated them +using micro-focused Brillouin light scattering spectroscopy. It is shown that, +due to the temperature dependence of the magnon spectrum, temperature changes +can be visualized even for microscale thermal patterns.",2304.13658v2 +2023-05-15,Magnetic order and electronic transport properties in the Mn$_3$Al compound: the role of the structural state,"Electronic transport and magnetic properties of bulk and rapid melt quenched +samples of the Mn$_3$Al Heusler alloy were studied. A correlation between the +magnetic and structural states was established. For a cast sample, there is no +ferromagnetic moment, and the behavior of the magnetic susceptibility (break at +low temperatures and the Curie-Weiss law with high values of the paramagnetic +Curie temperature) indicates a frustrated antiferromagnetic state. At the same +time, for a rapid melt quenched sample, a ferrimagnetic state is observed with +a moment close to compensation. The results of measurements of the electrical +resistivity and the Hall effect evidence as well in favor of the implementation +of these magnetic states.",2305.08646v1 +2023-05-24,Dirac half-semimetallicity and antiferromagnetism in graphene nanoribbon/hexagonal boron nitride heterojunctions,"Half-metals have been envisioned as active components in spintronic devices +by virtue of their completely spin-polarized electrical currents. Actual +materials hosting half-metallic phases, however, remain scarce. Here, we +predict that recently fabricated heterojunctions of zigzag nanoribbons embedded +in two-dimensional hexagonal boron nitride are half-semimetallic, featuring +fully spin-polarized Dirac points at the Fermi level. The half-semimetallicity +originates from the transfer of charges from hexagonal boron nitride to the +embedded graphene nanoribbon. These charges give rise to opposite energy shifts +of the states residing at the two edges while preserving their intrinsic +antiferromagnetic exchange coupling. Upon doping, an +antiferromagnetic-to-ferrimagnetic phase transition occurs in these +heterojunctions, with the sign of the excess charge controlling the spatial +localization of the net magnetic moments. Our findings demonstrate that such +heterojunctions realize tunable one-dimensional conducting channels of +spin-polarized Dirac fermions that are seamlessly integrated into a +two-dimensional insulator, thus holding promise for the development of +carbon-based spintronics.",2305.15214v1 +2023-05-29,Magnetic properties of delta- and kagome-like chains with competing interactions,"We study the delta-chain with spin-$1$ on basal sites and spin-$\frac{1}{2}$ +on apical sites. The Heisenberg interaction between neighbor basal spins is +antiferromagnetic (AF) and the interaction between basal and apical spins is +ferromagnetic (F). We show that the magnetization curve of this model is the +same as that of the spin-$\frac{1}{2}$ kagome-like chain with competing +Heisenberg interactions. The ground state phase diagram of the latter as a +function of the ratio between the AF and F interaction, $\alpha $, consists of +the ferromagnetic, ferrimagnetic and singlet phases. We study the magnetic +properties in each ground state phase and analyze the magnetization curves. We +show that there are magnetization plateaus and jumps in definite regions of +value $\alpha$. We compare the magnetic properties of considered models with +those of the spin-$\frac{1}{2}$ delta chain.",2305.18124v1 +2023-06-01,Inelastic neutron scattering investigation of the crystal field excitations of NdCo$_5$,"We present an inelastic neutron scattering study of the crystal electric +field levels in the intermetallic ferrimagnets RECo$_{5}$ (RE = Nd and Y). In +NdCo$_{5}$, measurements at $5~$K reveal two levels at approximately 28.9 and +52.9 meV. Crystal field calculations including the exchange field +$B_{\textrm{exc}}$ from the Co sites account for both of these, as well as the +spectrum at temperatures above the spin-reorientation transition at $\sim +280$~K. In particular, it is found that both a large hexagonal crystal field +parameter $A_{6}^6\langle r^6 \rangle$ and $B_{\textrm{exc}}$ are required to +reproduce the data, with the latter having a much larger value than that +deduced from previous computational and experimental studies. Our study sheds +light on the delicate interplay of terms in the rare-earth Hamiltonian of +RECo$_5$ systems, and is therefore expected to stimulate further experimental +and computational work on the broader family of rare-earth permanent magnets.",2306.00821v1 +2023-06-05,Spin Hall magnetoresistance in Pt/Y$_{3}$Fe$_{5}$O$_{12}$ bilayers grown on Si and Gd$_{3}$Ga$_{5}$O$_{12}$ substrates,"We study spin Hall magnetoresistance (SMR) in Pt/ferrimagnetic insulator +Y$_{3}$Fe$_{5}$O$_{12}$ (YIG) bilayers by focusing on crystallinity, +magnetization, and interface roughness by controlling post-annealing +temperatures. The SMR in the Pt/YIG grown on Si substrate is comparable to that +grown on widely used Gd$_{3}$Ga$_{5}$O$_{12}$ substrate, indicating that the +large SMR can be achieved irrespective to the crystallinity. We deduced the +spin mixing conductance from the Pt thickness dependence of the SMR to find the +high interface quality of the optimized Pt/YIG grown on Si in terms of spin +current. We also clarified that the SMR correlates well with the magnetization, +the interface roughness, and carrier density. These findings highlight that +optimizing YIG properties is a key to control of magnetization by spin current, +leading to the development of low power consumption spintronic device based on +the magnetic insulator.",2306.02575v1 +2023-06-12,Insight into the structural and magnetotransport properties of epitaxial heterostructures $α$-Fe$_2$O$_3$-Pt(111): Role of the reversed layer sequence,"We report on the chemical structure and spin Hall magnetoresistance (SMR) in +epitaxial $\alpha$-Fe$_2$O$_3$(hematite)(0001)/Pt(111) bilayers with hematite +thicknesses of 6 nm and 15 nm grown by molecular beam epitaxy on a MgO(111) +substrate. Unlike previous studies that involved Pt overlayers on hematite, the +present hematite films were grown on a stable Pt buffer layer and displayed +structural changes as a function of thickness. These structural differences +(the presence of a ferrimagnetic phase in the thinner film) significantly +affected the magnetotransport properties of the bilayers. We observed a sign +change of the SMR from positive to negative when the thickness of hematite +increased from 6 nm to 15 nm. For $\alpha$-Fe$_2$O$_3$(15 nm)/Pt, we +demonstrated room-temperature switching of the N\'eel order with rectangular, +nondecaying switching characteristics. Such structures open the way to +extending magnetotransport studies to more complex systems with double +asymmetric metal/hematite/Pt interfaces.",2306.07149v1 +2023-06-25,Electric-power efficiency of anomalous Hall current,"The electric-power dissipation of the anomalous-Hall current injected into a +lateral load circuit is studied. The anomalous-Hall current is generated by a +$\mathrm{Co_{75}Gd_{25}}$ ferrimagnetic Hall bar and injected into lateral +contacts lithographied at the two edges. The current, the voltage and the power +injected in the lateral circuit are studied as a function of the magnetization +state, the load resistance $R_l$, and the temperature. The power efficiency +shows a sharp maximum as a function $R_l$, which corresponds to the condition +of the resistance matching of the two sub-circuits. The maximum power +efficiency is of the order of the square of anomalous-Hall angle. The +observations are in agreement with recent predictions based on a +non-equilibrium variational approach.",2306.14226v2 +2023-06-26,Origin of magnetic ordering in half-Heusler RuMnGa,"The half-Heusler alloy RuMnGa having valence electron count (VEC) 18 has +recently been theoretically proposed to exhibit compensated ferrimagnetic +(CFiM) character instead of the expected nonmagnetic ground state. On the other +hand, a preliminary experimental study proposed ferromagnetic (FM) ordering. As +no half-Heusler system with VEC 18 is known to exhibit magnetic ordering, we +have investigated the details of crystal structure and magnetic properties of +RuMnGa using a combination of experimental tools, viz., x-ray and neutron +diffraction techniques, dc and ac susceptibility, isothermal magnetisation, +heat capacity, resistivity and neutron depolarisation measurements. Rietveld +refinements of x-ray and neutron diffraction data suggest single phase nature +of the compound with elemental composition RuMn$_{0.86}$Ga$_{1.14}$. We have +shown that the system exhibits FM-type ordering owing to the inherent presence +of this minor off-stoichiometry, showing very low magnetic moment. The system +also exhibits reentrant canonical spin-glass behaviour, which is rarely +observed in half-Heusler alloys. The temperature coefficient of resistivity +changes its sign from negative to positive and further to negative as the +temperature decreases.",2306.14836v1 +2023-06-29,Broken-symmetry magnetic phases in two-dimensional triangulene crystals,"We provide a comprehensive theory of magnetic phases in two-dimensional +triangulene crystals, using both Hubbard model and density functional theory +(DFT) calculations. We consider centrosymmetric and non-centrosymmetric +triangulene crystals. In all cases, DFT and mean-field Hubbard model predict +the emergence of broken-symmetry antiferromagnetic (ferrimagnetic) phases for +the centrosymmetric (non-centrosymmetric) crystals. This includes the special +case of the [4,4]triangulene crystal, whose non-interacting energy bands +feature a gap with flat valence and conduction bands. We show how the lack of +contrast between the local density of states of these bands, recently measured +via scanning tunneling spectroscopy, is a natural consequence of a +broken-symmetry N\'eel state that blocks intermolecular hybridization. Using +random phase approximation, we also compute the spin wave spectrum of these +crystals, including the recently synthesized [4,4]triangulene crystal. The +results are in excellent agreement with the predictions of a Heisenberg spin +model derived from multi-configuration calculations for the unit cell. We +conclude that experimental results are compatible with an antiferromagnetically +ordered phase where each triangulene retains the spin predicted for the +isolated species.",2306.17153v1 +2023-07-13,Magnon-magnon coupling in synthetic ferrimagnets,"Magnetic multilayers with interlayer exchange coupling have been widely +studied for both static and dynamic regimes. Their dynamical responses depend +on the exchange coupling strength and magnetic properties of individual layers. +Magnetic resonance spectra in such systems are conveniently discussed in terms +of coupling of acoustic and optical modes. At a certain value of applied +magnetic field, the two modes come close to being degenerate and the spectral +gap indicates the strength of mode hybridisation. In this work, we +theoretically and experimentally study the mode hybridisation of +interlayer-exchange-coupled moments with dissimilar magnetisation and thickness +of two ferromagnetic layers. In agreement with symmetry analysis for +eigenmodes, our low-symmetry multilayers exhibit sizable spectral gaps for all +experimental conditions. The spectra agree well with the predictions from the +Landau-Lifshitz-Gilbert equation at the macrospin limit whose parameters are +independently fixed by static measurements.",2307.06888v2 +2023-07-14,Signature of geometry modulation on interface magnetism emerged in isomeric IrO2-CoFe2O4 heterostructures,"The interface composed of magnets and strong spin-orbit coupling (SOC) +materials forms an important platform for spintronic devices and intriguing +magnetic phenomena, such as the chiral spin textures and magnetic proximity +effect (MPE). The interface exchange interaction and Dzyaloshinskii-Moriya +interaction (DMI) have been discussed in a wide range of heterostructures, +while the crystal stacking geometry modulation on these interface interactions +has rarely been considered. Here, we show a pronounced geometry modulation on +the interface magnetism through comparing a rutile and an anatase IrO2 capping +on a ferrimagnetic CoFe2O4. The rutile heterostructure with a high-symmetry +interface shows a conventional anomalous Hall effect (AHE) profile due to the +MPE. In contrast, the anatase one with a low-symmetry interface exhibits a +topological-like AHE even at zero-field, suggesting the emergence of +non-coplanar magnetic order at the interface. Our results suggest that the +influence of DMI at the interface can be more accentuated by forming a +low-symmetry interface and raises a new means of designing interface magnetism +via the geometry modulation.",2307.07169v2 +2023-07-21,Magnetism and topological property in icosahedral quasicrystal,"Quasicrystal (QC) has no periodicity but has a unique rotational symmetry +forbidden in periodic crystals. Lack of microscopic theory of the crystalline +electric field (CEF) in the QC and approximant crystal (AC) has prevented us +from understanding the electric property, especially the magnetism. By +developing the general formulation of the CEF in the rare-earth based QC and +AC, we have analyzed the CEF in the QC Au-SM-Tb and AC (SM=Si, Ge, and Ga). The +magnetic anisotropy arising from the CEF plays an important role in realizing +unique magnetic states on the icosahedron (IC). By constructing the minimal +model with the magnetic anisotropy, we have analyzed the ground-state +properties of the IC, 1/1 AC, and QC. The hedgehog state is characterized by +the topological charge of one and the whirling-moment state is characterized by +the topological charge of three. The uniform arrangement of the ferrimagnetic +state is stabilized in the QC with the ferromagnetic (FM) interaction, which is +a candidate for the magnetic structure recently observed FM long-range order in +the QC Au-Ga-Tb. The uniform arrangement of the hedgehog state is stabilized in +the QC with the antiferromagnetic interaction, which suggests the possibility +of the topological magnetic long-range order.",2307.11898v1 +2023-08-07,Frustration relief and reorientation transition in the kagome-like dolerophanite Cu$_2$OSO$_4$,"We present a theoretical study of dolerophanite Cu$_2$OSO$_4$, a layered +kagome-like spin-$\frac{1}{2}$ magnetic insulator that can be described either +as a system of chains coupled through dimers or as a kagome lattice where every +third spin is replaced by a ferromagnetic spin dimer. Building on insights from +ab initio calculations, classical numerical minimizations, and semiclassical +expansions, we arrive at a minimal microscopic description that accounts for +the experimental data reported so far, including the nature of the magnetic +order, the reported spin length, and the observed anisotropy. The latter arises +by a peculiar competition between the antisymmetric (Dzyaloshinskii-Moriya) and +the symmetric part of the exchange anisotropy, which gives rise to a two-step +re-orientation process involving two successive continuous phase transitions. +Our work uncovers mechanisms stabilizing canted ferrimagnetic order in kagome +systems, and highlights strong magnetic anisotropy in the presence if +dissimilar magnetic orbitals on crystallographically nonequivalent Cu sites. We +also show how these anisotropy terms affect the spin-wave spectrum and how they +can be tracked experimentally.",2308.03599v2 +2023-08-16,Growth of millimeter-sized high-quality CuFeSe$_2$ single crystals by the molten salt method and study of their semiconducting behavior,"An eutectic AlCl$_3$/KCl molten salt method in a horizontal configuration was +employed to grow millimeter-sized and composition homogeneous CuFeSe$_2$ single +crystals due to the continuous growth process in a temperature gradient induced +solution convection. The typical as-grown CuFeSe$_2$ single crystals in cubic +forms are nearly 1.6$\times$1.2$\times$1.0 mm3 in size. The chemical +composition and homogeneity of the crystals was examined by both inductively +coupled plasma atomic emission spectroscopy and energy dispersive spectrometer +with Cu:Fe:Se = 0.96:1.00:1.99 consistent with the stoichiometric composition +of CuFeSe$_2$. The magnetic measurements suggest a ferrimagnetic or weak +ferromagnetic transition below T$_C$ = 146 K and the resistivity reveals a +semiconducting behavior and an abrupt increase below T$_C$.",2308.08223v1 +2023-08-17,Magnetic Order in A Quenched-High-Temperature-Phase of Cu-Doped MnBi,"Permanent magnets are of great importance due to their vast applications. +MnBi has been proposed to be a potential permanent magnet that can be widely +used while past efforts have been focused on optimizing the ferromagnetic +low-temperature phase of MnBi. Herein, we report a series of new materials, +CuxMn1-xBi, crystallizing in a quenched high-temperature-phase (QHTP) +MnBi-related structure. We synthesized single crystals of CuxMn1-xBi and found +that they crystallize in an unreported trigonal structure (P -31c). Magnetic +properties measurements imply high-temperature antiferromagnetic (AFM) ordering +and low-temperature ferromagnetic or ferrimagnetic (FM/FiM) ordering. By +analyzing the doping effect on crystal structure and magnetic properties, we +established a magnetic phase diagram for Cu-doped MnBi and attributed the AFM +and FM/FiM to two different atomic sites of Mn.",2308.08952v2 +2023-08-17,Characterization of the Magnetocaloric Effect in RMn6Sn6 including High Entropy Alloys,"We present a comprehensive study of the magnetocaloric effect (MCE) in a +family of kagome magnets with formula RMn6Sn6 (R=Tb, Ho, Er, and Lu). These +materials have a small rare-earth content and tunable magnetic ordering, hence +they provide a venue to study the fundamentals of the MCE. We examine the +effect of different types of order (ferrimagnetic and antiferromagnetic) and +the presence of a metamagnetic transition on the MCE. We extend the study to +high-entropy rare-earth alloys of the family. Our results suggest several +guidelines for enhancing the MCE in tunable magnetic materials with a small +rare-earth content.",2308.09161v2 +2023-09-19,Chiral Skyrmions Interacting with Chiral Flowers,"The chiral nature of active matter plays an important role in the dynamics of +active matter interacting with chiral structures. Skyrmions are chiral objects, +and their interactions with chiral nanostructures can lead to intriguing +phenomena. Here, we explore the random-walk dynamics of a thermally activated +chiral skyrmion interacting with a chiral flower-like obstacle in a +ferromagnetic layer, which could create topology-dependent outcomes. It is a +spontaneous mesoscopic order-from-disorder phenomenon driven by the thermal +fluctuations and topological nature of skyrmions that exists only in +ferromagnetic and ferrimagnetic systems. The interactions between the skyrmions +and chiral flowers at finite temperatures can be utilized to control the +skyrmion position and distribution without applying any external driving force +or temperature gradient. The phenomenon that thermally activated skyrmions are +dynamically coupled to chiral flowers may provide a new way to design +topological sorting devices.",2309.10338v2 +2023-09-22,Laser-induced real-space topology control of spin wave resonances,"Femtosecond laser excitation of materials that exhibit magnetic spin textures +promises advanced magnetic control via the generation of ultrafast and +non-equilibrium spin dynamics. We explore such possibilities in ferrimagnetic +[Fe(0.35 nm)/Gd(0.40 nm)]$_{160}$ multilayers, which host a rich diversity of +magnetic textures from stripe domains at low magnetic fields, a dense +bubble/skyrmion lattice at intermediate fields, and a single domain state for +high magnetic fields. Using femtosecond magneto-optics, we observe distinct +coherent spin wave dynamics in response to a weak laser excitation allowing us +to unambiguously identify the different magnetic spin textures. Moreover, +employing strong laser excitation we show that we achieve versatile control of +the coherent spin dynamics via non-equilibrium and ultrafast transformation of +magnetic spin textures by both creating and annihilating bubbles/skyrmions. We +corroborate our findings by micromagnetic simulations and by Lorentz +transmission electron microscopy before and after laser exposure.",2309.12956v1 +2023-10-11,The Fractal-Lattice Hubbard Model,"Here, we investigate the fractal-lattice Hubbard model using various +numerical methods: exact diagonalization, the self-consistent diagonalization +of a (mean-field) Hartree-Fock Hamiltonian and state-of-the-art Auxiliary-Field +Quantum Monte Carlo. We focus on the Sierpinski triangle with Hausdorff +dimension $1.58$ and consider several generations. In the tight-binding limit, +we find compact localised states, which are also explained in terms of symmetry +and linked to the formation of a ferrimagnetic phase at weak interaction. +Simulations at half-filling revealed the persistence of this type of magnetic +order for every value of interaction strength and a Mott transition for U/t +$\sim$ 4.5. In addition, we found a remarkable dependence on the Hausdorff +dimension regarding $i)$ the number of compact localised states in different +generations, $ii)$ the scaling of the total many-body ground-state energy in +the tight-binding limit, and $iii)$ the density of the states at the corners of +the lattice for specific values of electronic filling. Moreover, in the +presence of an intrinsic spin-orbit coupling, the zero-energy compact localized +states become entangled and give rise to inner and outer corner modes.",2310.07813v1 +2023-10-24,Characterisation of ferroelectric domains in magnetite (Fe3O4),"Magnetite has long been investigated across many disciplines due to the +interplay between its ferroic order parameters, namely its ferrimagnetism, +ferroelasticity and ferroelectricty. Despite this, the experimental difficulty +in measuring low temperature real space images of the ferroelectric domains has +meant that the local behaviour of ferroelectric domains emergent below the 38 K +phase transition have yet to be realised. This work presents real space images +of the ferroelectric domains, and uses piezo force microscopy to, as a function +of temperature, probe the onset of piezoelectricty and ferroelectricity across +the 38 K transition",2310.15891v1 +2023-10-30,Plasma treatment as an unconventional molecular magnet engineering method,"Molecular magnetism aims to design materials with unique properties at the +molecular level, focusing on the systematic synthesis of new chemical +compounds. In this paper, we propose an alternative route to engineer molecular +magnetic materials through plasma irradiation. Our research indicates that the +long-range magnetic order temperature in the three-dimensional +$\mathrm{\{[Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8]\cdot 4H_2O\}_n}$ molecular +ferrimagnet increases by 20 K after plasma treatment. The core structure of the +compound does not reveal significant changes after plasma processing, as +confirmed by the X-ray powder diffraction analysis. The observed results are +attributed to the release of crystallized water molecules. The described +procedure can serve as a viable approach to altering the magnetic properties of +the molecular systems.",2310.19467v1 +2023-11-01,Giant anomalous Hall effect in epitaxial Mn$_{3.2}$Ge films with a cubic kagome structure,"We report on the first example of epitaxial Mn$_{3 + \delta}$Ge thin films +with a cubic $L1_2$ structure. The films are found to exhibit frustrated +ferromagnetism with an average magnetization corresponding to +0.98$~\pm~$0.06$~\mu_B$/Mn, far larger than the parasitic ferromagnetism in +hexagonal Mn$_3$Ge and the partially compensated ferrimagnetism in tetragonal +Mn$_3$Ge. The Hall conductivity is the largest reported for the kagome magnets +with a low temperature value of $\sigma_{xy} = 1587~$S/cm. Density functional +calculations predict that a chiral antiferromagnetic structure is lower in +energy than a ferromagnetic configuration in an ordered stoichiometric crystal. +However, chemical disorder driven by the excess Mn in our films explains why a +frustrated 120$^\circ$ spin structure is not observed. Comparisons between the +magnetization and the Hall resistivity indicate that a non-coplanar spin +structure contributes the Hall signal. Anisotropic magnetoresistance and planar +Hall effect with hysteresis up to 14 T provides further insights into this +material.",2311.00683v1 +2023-12-09,Magnetic properties of ferro-antiferromagnetic spin triangle chain,"We study the frustrated spin-$\frac{1}{2}$ model consisting of a linear chain +of triangles with ferro (F)- and antiferromagnetic (AF) interactions connected +by ferromagnetic interactions (triangles chain). The ground state phase diagram +as a function of the frustration parameter (a ratio of F and AF interactions) +and the interaction between triangles consists of the ferromagnetic, two +ferrimagnetic and the singlet phases. We study the magnetic properties in these +phases and analyze the magnetization curves. We show that there are the +magnetization plateau in the singlet phase and the magnetization jumps in some +region of this phase. We study the low-thermodynamics and its relation to the +specific structure of the excitation spectrum of the triangle chain.",2312.05544v1 +2023-12-19,Macroscopic entanglement between ferrimagnetic magnons and atoms via crossed optical cavity,"We consider a two-dimensional opto-magnomechanical (OMM) system including two +optical cavity modes, a magnon mode, a phonon mode, and a collection of +two-level atoms. In this study, we demonstrate the methodology for generating +stationary entanglement between two-level atoms and magnons, which are +implemented using two optical cavities inside the setup. Additionally, we +investigate the efficiency of transforming entanglement from atom-phonon +entanglement to atom-magnon entanglement. The magnons are stimulated by both a +bias magnetic field and a microwave magnetic field, and they interact with +phonons through the mechanism of magnetostrictive interaction. This interaction +generates magnomechanical displacement, which couples to an optical cavity via +radiation pressure. We demonstrate that by carefully selecting the frequency +detuning of an optical cavity, it is possible to achieve an increase in +bipartite entanglements. Furthermore, this improvement is found to be resistant +to changes in temperature. The entanglement between atoms and magnons plays a +crucial role in the construction of hybrid quantum networks. Our modeling +approach exhibits potential applications in the field of magneto-optical trap +systems as well.",2312.11864v1 +2023-12-20,Spin wave confinement in hybrid superconductor-ferrimagnet nanostructure,"Eddy currents in a superconductor shield the magnetic field in its interior +and are responsible for the formation of a magnetic stray field outside of the +superconducting structure. The stray field can be controlled by the external +magnetic field and affect the magnetization dynamics in the magnetic system +placed in its range. In the case of a hybrid system consisting of a +superconducting strip placed over a magnetic layer, we predict theoretically +the confinement of spin waves in the well of the static stray field. The number +of bound states and their frequencies can be controlled by an external magnetic +field. We have presented the results of semi-analytical calculations +complemented by numerical modeling.",2312.13029v1 +2023-12-29,Spin-orbit torques and magnetization switching in Gd/Fe multilayers generated by current injection in NiCu alloys,"Light transition metals have recently emerged as a sustainable material class +for efficient spin-charge interconversion. We report measurements of +current-induced spin-orbit torques generated by Ni$_{1-x}$Cu$_{x}$ alloys in +perpendicularly magnetized ferrimagnetic Gd/Fe multilayers. We show that the +spin-orbit torque efficiency of Ni$_{1-x}$Cu$_{x}$ increases with the Ni/Cu +atomic ratio, reaching values comparable to those of Pt for Ni$_{55}$Cu$_{45}$. +Furthermore, we demonstrate magnetization switching of a 20-nm-thick Gd/Fe +multilayer with a threshold current that decreases with increasing Ni +concentration, similar to the spin-orbit torque efficiency. Our findings show +that Ni$_{1-x}$Cu$_{x}$$-$based magnetic heterostructures allow for efficient +control of the magnetization by electric currents.",2312.17652v1 +2024-01-06,Cavity magnonics with domain walls in insulating ferromagnetic wires,"Magnetic domain walls (DWs) are topological defects that exhibit robust +low-energy modes that can be harnessed for classical and neuromorphic +computing. However, the quantum nature of these modes has been elusive thus +far. Using the language of cavity optomechanics, we show how to exploit a +geometric Berry-phase interaction between the localized DWs and the extended +magnons in short ferromagnetic insulating wires to efficiently cool the DW to +its quantum ground state or to prepare nonclassical states exhibiting a +negative Wigner function that can be extracted from the power spectrum of the +emitted magnons. Moreover, we demonstrate that magnons can mediate long-range +entangling interactions between qubits stored in distant DWs, which could +facilitate the implementation of a universal set of quantum gates. Our proposal +relies only on the intrinsic degrees of freedom of the ferromagnet, and can be +naturally extended to explore the quantum dynamics of DWs in ferrimagnets and +antiferromagnets, as well as quantum vortices or skyrmions confined in +insulating magnetic nanodisks.",2401.03164v1 +2024-01-10,Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque,"We investigated the magnetization reversal of a perpendicularly magnetized +nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOT). +Our findings demonstrate that both the field-like (FL) and damping-like (DL) +components of SOT in CCP can efficiently induce ultrafast magnetization +reversal without any symmetry-breaking means. For a wide frequency range of the +CCP, the minimal current density obtained is significantly smaller compared to +the current density of conventional SOT-reversal. This ultrafast reversal is +due to the CCP triggering enhanced energy absorption (emission) of the +magnetization from (to) the FL- and DL-components of SOT before (after) +crossing over the energy barrier. We also verified the robustness of the +CCP-driven magnetization reversal at room temperature. Moreover, this strategy +can be extended to switch the magnetic states of perpendicular synthetic +antiferromagnetic (SAF) and ferrimagnetic (SFi) nanodevices. Therefore, these +studies enrich the basic understanding of field-free SOT-reversal and provide a +novel way to realize ultrafast SOT-MRAM devices with various free layer +designs: ferromagnetic, SAF, and SFi.",2401.04882v2 +2024-01-15,Calculating Magnetic Properties of Two-Dimensional Materials for Memory Applications,"Calculating magnetic properties of two-dimensional materials is crucial for +implementing memory devices (like USB drive, RAM, hard disk drive of computers) +having reduced size. Two dimensional materials can be implemented as a thin +film which can reduce the size of memory devices. These materials as well as +devices made with magnetic two-dimensional materials are of current research +interest in industry and academia. From the materials project database, crystal +structure file of 30 two dimensional materials have been downloaded to +calculate their magnetic properties. BURAI Quantum espresso software has been +used to extract magnetic properties of 30 two dimensional (2D) materials. These +30 materials have magnetic Fe, Ni, Co, Mn, and Cr atoms in their molecular +structure. Magnetic materials play a key and vital role in today's modern-day +technology. There are five different types of magnetic materials. The +classification magnetic materials are diamagnetism, paramagnetic, +ferromagnetism, ferrimagnetism, and anti-ferromagnetism. Total energy of +different magnetic configurations has been calculated to find the most stable +magnetic configurations of these materials.",2401.07980v1 +2024-01-22,Generating magnon Bell states via parity measurement,"We propose a scheme to entangle two magnon modes based on parity measurement. +In particular, we consider a system that two yttrium-iron-garnet spheres are +coupled to a $V$-type superconducting qutrit through the indirect interactions +mediated by cavity modes. An effective parity-measurement operator that can +project the two macroscopic spin systems to the desired subspace emerges when +the ancillary qutrit is projected to the ground state. Consequently, +conventional and multi-excitation magnon Bell states can be generated from any +separable states with a nonvanishing population in the desired subspace. The +target state can be distilled with a near-to-unit fidelity only by several +rounds of measurements and can be stabilized in the presence of decoherence. In +addition, a single-shot version of our scheme is obtained by shaping the +detuning in the time domain. Our scheme that does not rely on any nonlinear +effect brings insight to the entangled-state generation in massive +ferrimagnetic materials via quantum measurement.",2401.11684v1 +2024-01-29,Competing magnetic states on the surface of multilayer ABC-stacked graphene,"We study interaction-mediated magnetism on the surface of ABC-multilayer +graphene driven by its zero-energy topological flat bands. Using the +random-phase approximation we treat onsite Hubbard repulsion and find multiple +competing magnetic states, due to both intra- and inter-valley scattering, with +the latter causing an enlarged magnetic unit cell. At half-filling and when the +Hubbard repulsion is weak, we observe two different ferromagnetic orders. Once +the Hubbard repulsion becomes more realistic, new ferrimagnetic orders arise +with distinct incommensurate intra- or inter-valley scattering vectors +depending on interaction strength and doping, leading to a multitude of +competing magnetic states.",2401.16345v1 +2024-01-20,Maximizing bipolar sensitivity for anomalous Nernst thermopiles in heat flux sensing in amorphous GdCo alloys,"A Heat Flux Sensor (HFS) facilitates the visualization of heat flow, unlike a +temperature sensor, and is anticipated to be a key technology in managing waste +heat. Commercialized HFS devices, which are based on the Seebeck effect, are +notably expensive due to fabrication challenges and the need for sensitive +calibration. Recently, an HFS utilizing the Anomalous Nernst Effect (ANE) has +been proposed as a solution to these issues, garnering significant interest in +enhancing the transverse Seebeck coefficient. However, ideal materials for HFS +not only require a large transverse Seebeck coefficient but also meet several +criteria including low thermal conductivity and a bipolar nature of the +transverse Seebeck coefficient. In this study, we have investigated ANE in +amorphous ferrimagnetic GdCo alloys, revealing their numerous advantages as HFS +materials. These include unparalleled sensitivity comparable to Co2MnGa, the +ability to exhibit both positive and negative ANE, versatility for deposition +on various substrates, and a small longitudinal Seebeck coefficient. These +qualities position GdCo films as promising candidates for the advancement of +ANE-based HFS technology.",2402.04259v1 +2024-02-08,Modulation of magnetization in BiFeO$_3$ using circularly polarized light,"BiFeO$_3$ is a multiferroic material featuring ferroelectricity and +noncollinear antiferromagnetism, the latter manifested as a cycloid of spin +density. Definitive and efficient control of the characteristic spin texture of +BiFeO$_3$ is attractive for emerging quantum devices. In this regard, +crystal-field $d\rightarrow d$ excitations localized on Fe atomic sites in +BiFeO$_3$ provide an avenue for manipulation of the spin texture as they induce +a complex interplay among the spin, charge, and lattice degrees of freedom. In +this work, the ab initio GW-BSE method is used to characterize these +excitations within an excitonic picture. We find that the $d-d$ transitions +appear as strongly bound, chiral, spin-flip excitons deep within the electronic +band gap as a result of the intricate competition between the lattice +potential, the antiferromagnetic ordering, the spin-orbit coupling, and the +electron-hole interaction. Most crucially, these excitons are composed of +electron-hole pairs with opposite spins that constitute almost all of their +$\pm \hbar$ total angular momentum. These excitons of specific angular momentum +can be selectively excited using circularly polarized light, consequently +modulating the local magnetic moment giving rise to transient ferrimagnetism.",2402.05430v2 +2024-02-15,Explaining all-optical switching in ferrimagnets with heavy rare-earth elements by varying the spin-flip scattering probability of Gd in Co$_x$Gd$_{100-x}$ alloys and Co/Gd bilayers,"Using the microscopic three temperature model, we simulate single-pulse +all-optical switching (AOS) in alloys and bilayers consisting of Co and Gd. In +particular, we investigate its dependence on the spin-flip probability of Gd +$a_\mathrm{sf,Gd}$, a material parameter describing the strength of spin-phonon +coupling. We do so to elucidate the mechanisms behind all-optical switching in +systems where Co is coupled to heavy rare-earth elements with higher damping +such as Tb. In alloys, our observations are twofold. First, an increase of +$a_\mathrm{sf,Gd}$ leads to a broadening of the range of compositions for which +AOS is observed. Second, the ideal Co content is decreased as +$a_\mathrm{sf,Gd}$ is varied. For bilayers, our analysis indicates that +switching is most efficient when $a_\mathrm{sf,Gd}$ takes on small values. +Conversely, increasing the value of $a_\mathrm{sf,Gd}$ leads to a general +suppression of AOS. Comparing alloys to bilayers, we find that AOS in alloys +exhibits greater resilience to variations in $a_\mathrm{sf,Gd}$ than it does in +bilayers.",2402.09878v1 +2024-02-20,Magnetic transitions of biphenylene network layers induced by external perturbations,"We present a comprehensive investigation of the magnetic ordering in +biphenylene network (BPN) layers, employing density functional theory (DFT) +calculations under external perturbations, including uniaxial strains and hole +doping. We compute fully relaxed structures, energy bands, and magnetic states +by performing DFT calculations augmented with extended Hubbard interactions, +encompassing both on-site and inter-site interactions, to accurately capture +electron correlations. We emphasize the importance of the extended Hubbard +forces by contrasting BPN layers with and without the forces. Our results +reveal that in their fully relaxed structures, both BPN monolayer and bilayer +are non-magnetic. We exploit external perturbations to induce magnetic +ordering. The application of uniaxial strains induces magnetic phase +transitions, leading to ferrimagnetic and antiferromagnetic states in BPN +monolayer and bilayer, respectively. Additionally, we investigate hole doping +as an alternative mechanism for inducing magnetic transitions. Our findings +shed light on the tunability of magnetic properties in BPN layers through +external perturbations, demonstrating the promise of low-dimensional materials +in future spintronics and nanoelectronic applications.",2402.13129v1 +2024-02-27,"Novel Ternary AgIICoIIIF5 Fluoride: Synthesis, Structure and Magnetic Characteristics","We present a new compound in the silver cobalt fluoride system, featuring +paramagnetic silver (d9) and high-spin cobalt (d6), synthesized by solid state +method in an autoclave under F2 overpressure. Based on powder X ray +diffraction, we determined that AgIICoIIIF5 crystallizes in a monoclinic system +with space group C2/c. The calculated fundamental band gap falls in the visible +range of the electromagnetic spectrum, and the compound has the character of +charge-transfer insulator. AgCoF5 is a ferrimagnet with one predominant +superexchange magnetic interaction constant between mixed spin cations (Ag ... +Co) of minus 62 meV (SCAN result). Magnetometric measurements conducted on a +powdered sample allowed the identification of a transition at 128 K, which +could indicate magnetic ordering.",2402.17399v1 +2024-02-28,Plasma-induced magnetic phase in 3D $\mathrm{Mn^{II}-Nb^{IV}}$ octacyanidometalate with magnetic sponge behavior,"A new magnetic phase with $T_C = 72 \ \mathrm K$ was obtained by exposing the +three-dimensional $\mathrm{\{ [Mn^{II}(H_2O)_2]_2[Nb^{IV}(CN)_8] \cdot 4H_2O \} +_n}$ coordination ferrimagnet ($T_C = 49 \ \mathrm K$) to air, oxygen, +nitrogen, and argon-based plasma. The X-ray powder diffraction pattern revealed +that the unit cell shrank after plasma treatment, leading to a 20% enhancement +of the superexchange couplings, as estimated from the mean-field approximation +(MFA) model. Although no stable dehydrated form was found in the +thermogravimetric analysis, the observed changes are attributed to the removal +of crystallization water molecules. The plasma-induced magnetic phase could not +be obtained by exposing the studied material to 0% relative humidity during +dynamic vapor sorption. Instead, the material underwent a major structural +reorganization after dehydration, necessitating an extended MFA model to +reproduce the magnetic susceptibility. These findings demonstrate that +plasma-induced changes can create unique magnetic phases in molecule-based +systems that are otherwise unobtainable.",2402.18195v1 +2024-02-29,Nano-Electromagnetic Super-dephasing in Collective Atom-Atom Interactions,"Pure dephasing and spontaneous emission are two non-unitary processes of +atoms or spins interacting with fluctuating electromagnetic (EM) modes. +Collective spontaneous emission (e.g., superradiance) originates from +interactions with EM modes in resonance with atoms and has received +considerable attention. Meanwhile, the analogous collective dephasing phenomena +remain poorly understood. Here, we introduce the nano-EM super-dephasing +phenomenon arising in the photonic environment near lossy material interfaces. +We show that this effect is enhanced by over 10 orders of magnitude compared to +free space or photonic cavities due to the presence of long-range correlations +in low-frequency evanescent EM fluctuations. We unravel the universality of +nano-EM super-dephasing behaviors near ferrimagnets, metals, and +superconductors and their dependence on low-frequency material properties. We +demonstrate that the scaling of nano-EM super-dephasing is independent of EM +modes' wavelengths and differs from the conventional $N^2$ scaling of +superradiance by analyzing the decoherence of entangled states, including GHZ +states. Finally, we show how to experimentally isolate and control +super-dephasing to open interesting frontiers for scalable quantum systems.",2402.18816v1 +2024-03-12,Magnetic Phase Diagram and Skyrmions of the Hubbard Model on the Beta-Mn Type Lattice,"Magnetic phase diagram for the Hubbard model on the Beta-Mn type lattice has +been calculated as a function of the Coulomb interaction energy parameter U and +the electron number per atom n by using the generalized Hartree-Fock +approximation combined with the recursion method for electronic-structure +calculations. The ferromagnetic state, the ferrimagnetic state, and the +helimagnetic state as well as the 3Q multiple spin density waves (3QMSDW) +states have been obtained on the U-n plane. Their detailed structures are +examined with use of the Fourier analysis. It is shown that the calculated +phase diagram and the Dzyaloshinskii-Moriya interaction elucidate the magnetic +interactions for the itinerant-electron skyrmions in transition metal alloys +and compounds on the Beta-Mn type lattice.",2403.07443v1 +2024-03-25,Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2,"The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent +interest for efficient spin-wave excitation due to its low Gilbert damping +ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we +report a clean spin pumping signal detected on V(TCNE)x/metal bilayer +structures, free from spin rectification or thermal artifacts. On-chip coupling +of microwave power is achieved via a coplanar waveguide to measure the in-plane +angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance +conditions with respect to a constant external magnetic field. A signature of +pure spin current from V(TCNE)x is observed in both platinum and permalloy +metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics +studies in molecule/solid-state heterostructures.",2403.16429v2 +2024-04-02,Understanding spin currents from magnon dispersion and polarization: Spin-Seebeck effect and neutron scattering study on Tb3Fe5O12,"Magnon spin currents in the ferrimagnetic garnet Tb3Fe5O12 with 4f electrons +were examined through the spin-Seebeck effect and neutron scattering +measurements. The compound shows a magnetic compensation, where the +spin-Seebeck signal reverses above and below Tcomp = 249.5(4) K. Unpolarized +neutron scattering unveils two major magnon branches with finite energy gaps, +which are well-explained in the framework of spin-wave theory. Their +temperature dependencies and the direction of the precession motion of magnetic +moments, i.e. magnon polarization, defined using polarized neutrons, explain +the reversal at Tcomp and decay of the spin-Seebeck signals at low +temperatures. We illustrate an example that momentum- and energy-resolved +microscopic information is a prerequisite to understanding the magnon spin +current.",2404.01603v1 +2024-04-02,Field-induced spin polarization in lightly Cr-substituted layered antiferromagnet NiPS3,"Tuning magnetic properties in layered magnets is an important route to +realize novel phenomenon related to two-dimensional (2D) magnetism. Recently, +tuning antiferromagnetic (AFM) properties through substitution and +intercalation techniques have been widely studied in MPX3 compounds. +Interesting phenomena, such as diverse AFM structures and even the signatures +of ferrimagnetism, have been reported. However, long-range ferromagnetic (FM) +ordering has remained elusive. In this work, we explored the magnetic +properties of the previously unreported Cr-substituted NiPS3. We found that Cr +substitution is extremely efficient in controlling spin orientation in NiPS3. +Our study reveals a field-induced spin polarization in lightly (9%) +Cr-substituted NiPS3, which is likely attributed to the attenuation of AFM +interactions and magnetic anisotropy due to Cr doping. Our work provides a +possible strategy to achieve FM phase in AFM MPX3, which could be useful for +investigating 2D magnetism as well as potential device applications.",2404.02091v1 +2021-03-30,"Enormous Berry-Curvature-Driven Anomalous Hall Effect in Topological Insulator (Bi,Sb)2Te3 on Ferrimagnetic Europium Iron Garnet beyond 400 K","To realize the quantum anomalous Hall effect (QAHE) at elevated temperatures, +the approach of magnetic proximity effect (MPE) was adopted to break the +time-reversal symmetry in the topological insulator (Bi0.3Sb0.7)2Te3 (BST) +based heterostructures with a ferrimagnetic insulator europium iron garnet +(EuIG) of perpendicular magnetic anisotropy. Here we demonstrate phenomenally +large anomalous Hall resistance (RAHE) exceeding 8 {\Omega} (\r{ho}AHE of 3.2 +{\mu}{\Omega}*cm) at 300 K and sustaining to 400 K in 35 BST/EuIG samples, +surpassing the past record of 0.28 {\Omega} (\r{ho}AHE of 0.14 +{\mu}{\Omega}*cm) at 300 K. The remarkably large RAHE as attributed to an +atomically abrupt, Fe-rich interface between BST and EuIG. Importantly, the +gate dependence of the AHE loops shows no sign change with varying chemical +potential. This observation is supported by our first-principles calculations +via applying a gradient Zeeman field plus a contact potential on BST. Our +calculations further demonstrate that the AHE in this heterostructure is +attributed to the intrinsic Berry curvature. Furthermore, for gate-biased 4 nm +BST on EuIG, a pronounced topological Hall effect (THE) coexisting with AHE is +observed at the negative top-gate voltage up to 15 K. Interface tuning with +theoretical calculations has opened up new opportunities to realize +topologically distinct phenomena in tailored magnetic TI-based +heterostructures.",2103.16487v4 +1995-12-26,The Hubbard Model: Introduction and Selected Rigorous Results,"The Hubbard model is a ""highly oversimplified model"" for electrons in a solid +which interact with each other through extremely short ranged repulsive +(Coulomb) interaction. The Hamiltonian of the Hubbard model consists of two +pieces; H_hop which describes quantum mechanical hopping of electrons, and Hint +which describes nonlinear repulsive interaction. Either H_hop or H_int alone is +easy to analyze, and does not favor any specific order. But their sum +H=H_hop+H_int is believed to exhibit various nontrivial phenomena including +metal-insulator transition, antiferromagnetism, ferrimagnetism, ferromagnetism, +Tomonaga-Luttinger liquid, and superconductivity. It is believed that we can +find various interesting ""universality classes"" of strongly interacting +electron systems by studying the idealized Hubbard model. + In the present article we review some mathematically rigorous results on the +Hubbard model which shed light on ""physics"" of this fascinating model. We +mainly concentrate on magnetic properties of the model at its ground states. We +discuss Lieb-Mattis theorem on the absence of ferromagnetism in one dimension, +Koma-Tasaki bounds on decay of correlations at finite temperatures in +two-dimensions, Yamanaka-Oshikawa-Affleck theorem on low-lying excitations in +one-dimension, Lieb's important theorem for half-filled model on a bipartite +lattice, Kubo-Kishi bounds on the charge and superconducting susceptibilities +of half-filled models at finite temperatures, and three rigorous examples of +saturated ferromagnetism due to Nagaoka, Mielke, and Tasaki. We have tried to +make the article accessible to nonexperts by describing basic definitions and +elementary materials in detail.",9512169v4 +1996-10-08,Low-Lying Excited States and Low-Temperature Properties of an Alternating Spin-1 / Spin-1/2 Chain : A DMRG study,"We report spin wave and DMRG studies of the ground and low-lying excited +states of uniform and dimerized alternating spin chains. The DMRG procedure is +also employed to obtain low-temperature thermodynamic properties of the system. +The ground state of a 2N spin system with spin-1 and spin-1/2 alternating from +site to site and interacting via an antiferromagnetic exchange is found to be +ferrimagnetic with total spin $s_G=N/2$ from both DMRG and spin wave analysis. +Both the studies also show that there is a gapless excitation to a state with +spin $s_G-1$ and a gapped excitation to a state with spin $s_G+1$. +Surprisingly, the correlation length in the ground state is found to be very +small from both the studies for this gapless system. For this very reason, we +show that the ground state can be described by a variational ``ansatz'' of the +product type. DMRG analysis shows that the chain is susceptible to a +conditional spin-Peierls' instability. The DMRG studies of magnetization, +magnetic susceptibility ($\chi$) and specific heat show strong magnetic-field +dependence. The product $\chi T$ shows a minimum as a function of +temperature($T$) at low-magnetic fields and the minimum vanishes at +high-magnetic fields. This low-field behaviour is in agreement with earlier +experimental observations. The specific heat shows a maximum as a function of +temperature and the height of the maximum increases sharply at high magnetic +fields. It is hoped that these studies will motivate experimental studies at +high-magnetic fields.",9610080v1 +1997-04-07,A DMRG Study of Low-Energy Excitations and Low-Temperature Properties of Alternating Spin Systems,"We use the density matrix renormalization group (DMRG) method to study the +ground and low-lying excited states of three kinds of uniform and dimerized +alternating spin chains. The DMRG procedure is also employed to obtain +low-temperature thermodynamic properties of these systems. We consider a 2N +site system with spins $s_1$ and $s_2$ alternating from site to site and +interacting via a Heisenberg antiferromagnetic exchange. The three systems +studied correspond to $(s_1 ,s_2 )$ being equal to $(1,1/2),(3/2,1/2)$ and +$(3/2,1)$; all of them have very similar properties. The ground state is found +to be ferrimagnetic with total spin $s_G =N(s_1 - s_2)$. We find that there is +a gapless excitation to a state with spin $s_G -1$, and a gapped excitation to +a state with spin $s_G +1$. Surprisingly, the correlation length in the ground +state is found to be very small for this gapless system. The DMRG analysis +shows that the chain is susceptible to a conditional spin-Peierls instability. +Furthermore, our studies of the magnetization, magnetic susceptibility $\chi$ +and specific heat show strong magnetic-field dependences. The product $\chi T$ +shows a minimum as a function of temperature T at low magnetic fields; the +minimum vanishes at high magnetic fields. This low-field behavior is in +agreement with earlier experimental observations. The specific heat shows a +maximum as a function of temperature, and the height of the maximum increases +sharply at high magnetic fields. Although all the three systems show +qualitatively similar behavior, there are some notable quantitative differences +between the systems in which the site spin difference, $|s_1 - s_2|$, is large +and small respectively.",9704057v1 +1997-11-13,The singlet-triplet magnetism and induced spin fluctuations in the high-$T_c$ copper oxides,"High-$T_c$ cuprates like $La_{2-x}Sr_{x}CuO_{4}$ and $YBa_{2-x}Cu_{3}O_{6+x}$ +are considered as a system of the electron and hole polar pseudo-Jahn-Teller +$CuO_{4}$ centers $[{CuO}_{4}^{7-}]_{JT}$ and $[CuO_{4}^{5-}]_{JT}$, +respectively, or a system of the local bosons moving in a lattice of the hole +centers. Ground manifold of the polar centers includes three terms $^{1}A_{1g}$ +(Zhang-Rice singlet), $^{1}E_{u}$, $^{3}E_{u}$ with different spin +multiplicity, orbital degeneracy and parity that provides an unconventional +multi-mode behaviour of the cuprates. The spin subsystem of the copper oxides +within the polar Jahn-Teller $CuO_{4}$ centers model is a two-component spin +liquid and corresponds to a singlet-triplet magnet with possible noncollinear +spin configurations. In the framework of a modified mean field approximation +some kinds of spin ordering are discussed including as a trivial singlet or +triplet states as a pure quantum singlet-triplet mixed state. A local boson +movement is accompanied by a modulation of the spin density on the site +resulting in the so called induced spin fluctuations. Some unconventional +features of the induced spin fluctuations are considered including an +appearance of the induced longitudinal ferrimagnetism with an appropriate +contribution to the spin susceptibility, a possibility to observe and examine +the charge fluctuations with the help of the traditional magnetic methods such +as the magnetic inelastic neutron scattering and the spin lattice relaxation +experiments. The suggested model, in comparison with the nearly +antiferromagnetic Fermi-liquid model, represents new approach to the +description of the spin system of the high-$T_c$ cuprates.",9711116v1 +1998-06-21,Diagonal Ladders: A New Class of Models for Strongly Coupled Electron Systems,"We introduce a class of models defined on ladders with a diagonal structure +generated by $n_p$ plaquettes. The case $n_p=1$ corresponds to the necklace +ladder and has remarkable properties which are studied using DMRG and recurrent +variational ansatzes. The AF Heisenberg model on this ladder is equivalent to +the alternating spin-1/spin-1/2 AFH chain which is known to have a +ferrimagnetic ground state (GS). For doping 1/3 the GS is a fully doped (1,1) +stripe with the holes located mostly along the principal diagonal while the +minor diagonals are occupied by spin singlets. This state can be seen as a Mott +insulator of localized Cooper pairs on the plaquettes. A physical picture of +our results is provided by a $t_p-J_p$ model of plaquettes coupled diagonally +with a hopping parameter $t_d$. In the limit $t_d \to \infty$ we recover the +original $t-J$ model on the necklace ladder while for weak hopping parameter +the model is easily solvable. The GS in the strong hopping regime is +essentially an ""on link"" Gutzwiller projection of the weak hopping GS. We +generalize the $t_p-J_p-t_d$ model to diagonal ladders with $n_p >1$ and the 2D +square lattice. We use in our construction concepts familiar in Statistical +Mechanics as medial graphs and Bratelli diagrams.",9806251v1 +1999-07-28,Ground state of an $S=1/2$ distorted diamond chain - model of $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8 C_4 SO_2$,"We study the ground state of the model Hamiltonian of the trimerized $S=1/2$ +quantum Heisenberg chain $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8 C_4 SO_2$ in which +the non-magnetic ground state is observed recently. This model consists of +stacked trimers and has three kinds of coupling constants between spins; the +intra-trimer coupling constant $J_1$ and the inter-trimer coupling constants +$J_2$ and $J_3$. All of these constants are assumed to be antiferromagnetic. By +use of the analytical method and physical considerations, we show that there +are three phases on the $\tilde J_2 - \tilde J_3$ plane ($\tilde J_2 \equiv +J_2/J_1$, $\tilde J_3 \equiv J_3/J_1$), the dimer phase, the spin fluid phase +and the ferrimagnetic phase. The dimer phase is caused by the frustration +effect. In the dimer phase, there exists the excitation gap between the +two-fold degenerate ground state and the first excited state, which explains +the non-magnetic ground state observed in $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8 +C_4 SO_2$. We also obtain the phase diagram on the $ \tilde J_2 - \tilde J_3$ +plane from the numerical diagonalization data for finite systems by use of the +Lanczos algorithm.",9907440v3 +1999-12-30,Ground State Properties of an S=1/2 Distorted Diamond Chain,"We investigate the ground state properties of an S=1/2 distorted diamond +chain described by the Hamiltonian ${\cal +H}=J_1\sum_\ell\bigl\{\bigl(\vecS_{3\ell-1}\cdot\vecS_{3\ell} ++\vecS_{3\ell}\cdot\vecS_{3\ell+1}\bigr)+J_2\vecS_{3\ell-2}\cdot\vecS_{3\ell-1} ++J_3\bigl(\vecS_{3\ell-2}\cdot\vecS_{3\ell}+\vecS_{3\ell}\cdot\vecS_{3\ +ell+2}\bigr)-H S_{\ell}^z\bigr\}$ ($J_1,~J_2,~J_3\geq0$), which models well a +trimerized S=1/2 spin chain system +Cu$_3$Cl$_6$(H$_2$O)$_2$$\cdot$2H$_8$C$_4$SO$_2$. Using an exact +diagonalization method by means of the Lancz\""os technique, we determine the +ground state phase diagram in the H=0 case, composed of the dimerized, spin +fluid, and ferrimagnetic phases. Performing a degenerate perturbation +calculation, we analyze the phase boundary line between the latter two phases +in the $J_2,~J_3\llJ_1$ limit, the result of which is in good agreement with +the numerical result. We calculate, by the use of the density matrix +renormalization group method, the ground state magnetization curve for the case +(a) where $J_1=1.0$, $J_2=0.8$, and $J_3=0.5$, and the case (b) where +$J_1=1.0$, $J_2=0.8$, and $J_3=0.3$. We find that in the case (b) the +2/3-plateau appears in addition to the 1/3-plateau which also appears in the +case (a). The translational symmetry of the Hamiltonian $\cal H$ is +spontaneously broken in the 2/3-plateau state as well as in the dimerized +state.",9912482v1 +2001-01-23,Finite-Size and surface effects in maghemite nanoparticles: Monte Carlo simulations,"Finite-size and surface effects in fine particle systems are investigated by +Monte Carlo simulation of a model of a $\gamma$-Fe$_2$O$_3$ (maghemite) single +particle. Periodic boundary conditions have been used to simulate the bulk +properties and the results compared with those for a spherical shaped particle +with free boundaries to evidence the role played by the surface on the +anomalous magnetic properties displayed by these systems at low temperatures. +Several outcomes of the model are in qualitative agreement with the +experimental findings. A reduction of the magnetic ordering temperature, +spontaneous magnetization, and coercive field is observed as the particle size +is decreased. Moreover, the hysteresis loops become elongated with high values +of the differential susceptibility, resembling those from frustrated or +disordered systems. These facts are consequence of the formation of a surface +layer with higher degree of magnetic disorder than the core, which, for small +sizes, dominates the magnetization processes of the particle. However, in +contradiction with the assumptions of some authors, our model does not predict +the freezing of the surface layer into a spin-glass-like state. The results +indicate that magnetic disorder at the surface simply facilitates the thermal +demagnetization of the particle at zero field, while the magnetization is +increased at moderate fields, since surface disorder diminishes ferrimagnetic +correlations within the particle. The change in shape of the hysteresis loops +with the particle size demonstrates that the reversal mode is strongly +influenced by the reduced atomic coordination and disorder at the surface.",0101348v1 +2001-11-28,On the origin of neutron magnetic scattering in anti-site disordered Sr2FeMoO6 double perovskites,"Anti-site disordering in Sr2FeMoO6 double perovskites (containing Mo atoms at +Fe positions, and viceversa) has recently been shown to have a dramatic +influence in their magnetic and magnetotransport properties. In the present +study, two polycrystalline Sr2FeMoO6 samples showing different degrees of +anti-site disorder (a nominally 'ordered' sample with 70% of cationic ordering +and a nominally 'disordered' sample with 18% of cationic ordering) have been +examined by magnetic measurements and neutron powder diffraction (NPD) +techniques in the 15-500K temperature range. Our main finding is that the +'disordered' sample exhibits a strong magnetic scattering (noticeable even at +500K), comparable to that displayed by the 'ordered' one below TC= 415 K. For +the 'disordered' sample, the magnetic scattering exhibited on low angle Bragg +positions, is not to be ascribed to a (non-existent) ferrimagnetic ordering: +our results suggest that it originates upon naturally-occurring groups of Fe +cations in which strong antiferromagnetic (AFM) Fe-O-Fe superexchange +interactions are promoted, similar to those existing in the LaFeO3 perovskite. +These Fe groups are not magnetically isolated, but coupled by virtue of Fe-O-Mo +AFM interactions, which maintain the long-range coherence of this AFM +structure. Susceptibility measurements confirm the presence of AFM interactions +below 770 K.",0111524v1 +2002-05-09,Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6,"Magnetic dc susceptibility ($\chi$) and electron spin resonance (ESR) +measurements in the paramagnetic regime, are presented. We found a Curie-Weiss +(CW) behavior for $\chi$(T) with a ferromagnetic $\Theta = 446(5)$ K and +$\mu_{eff} = 4.72(9) \mu_{B}/f.u.$, this being lower than that expected for +either $Fe^{3+}(5.9\mu_{B})$ or $Fe^{2+}(4.9\mu_{B})$ ions. The ESR g-factor $g += 2.01(2)$, is associated with $Fe^{3+}$. We obtained an excellent description +of the experiments in terms of two interacting sublattices: the localized +$Fe^{3+}$ ($3d^{5}$) cores and the delocalized electrons. The coupled equations +were solved in a mean-field approximation, assuming for the itinerant electrons +a bare susceptibility independent on $T$. We obtained $\chi_{e}^{0} = 3.7$ +$10^{-4}$ emu/mol. We show that the reduction of $\mu_{eff}$ for $Fe^{3+}$ +arises from the strong antiferromagnetic (AFM) interaction between the two +sublattices. At variance with classical ferrimagnets, we found that $\Theta$ is +ferromagnetic. Within the same model, we show that the ESR spectrum can be +described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the +absence of a $g$-shift. Surprisingly, as observed in CMR manganites, no +narrowing effects of the ESR linewidth is detected in spite of the presence of +the strong magnetic coupling. These results provide evidence that the magnetic +order in $Sr_{2}FeMoO_{6}$ does not originates in superexchange interactions, +but from a novel mechanism recently proposed for double perovskites.",0205187v1 +2002-07-03,Magnetic enhancement of Co$_{0.2}$Zn$_{0.8}$Fe$_2$O$_4$ spinel oxide by mechanical milling,"We report the magnetic properties of mechanically milled +Co$_{0.2}$Zn$_{0.8}$Fe$_2$O$_4$ spinel oxide. After 24 hours milling of the +bulk sample, the XRD spectra show nanostructure with average particle size +$\approx$ 20 nm. The as milled sample shows an enhancement in magnetization and +ordering temperature compared to the bulk sample. If the as milled sample is +annealed at different temperatures for the same duration, recrystallization +process occurs and approaches to the bulk structure on increasing the annealing +temperatures. The magnetization of the annealed samples first increases and +then decreases. At higher annealing temperature ($\sim$ 1000$^{0}$C) the system +shows two coexisting magnetic phases {\it i.e.}, spin glass state and +ferrimagnetic state, similar to the as prepared bulk sample. The room +temperature M\""{o}ssbauer spectra of the as milled sample, annealed at +300$^{0}$C for different durations (upto 575 hours), suggest that the observed +change in magnetic behaviour is strongly related with cations redistribution +between tetrahedral (A) and octahedral (O) sites in the spinel structure. Apart +from the cation redistribution, we suggest that the enhancement of +magnetization and ordering temperature is related with the reduction of B site +spin canting and increase of strain induced anisotropic energy during +mechanical milling.",0207095v1 +2002-11-12,High temperature susceptibility in electron doped Ca1-xYxMnO3: Double Exchange vs Superexchange,"We present a study of the magnetic properties of the electron doped +manganites Ca1-xYxMnO3 (for 0<=x<=0.25) in the paramagnetic regime. For the +less doped samples (x<=0.1) the magnetic susceptibility, c(T), follows a +Curie-Weiss (CW) law only for T > 450 K and, below this temperature, c^-1(T) +shows a ferrimagnetic-like curvature. We approached the discussion of these +results in terms of a simple mean-field model where double exchange, +approximated by a ferromagnetic Heisenberg-like interaction between Mn3+ and +Mn4+ ions, competes with classical superexchange. For higher levels of doping +(x>=0.15), the CW behaviour is observed down to the magnetic ordering +temperature (Tmo) and a better description of c(T) was obtained by assuming +full delocalization of the eg electrons. In order to explore the degree of +delocalization as a function of T and x, we analyzed the problem through +Montecarlo simulations. Within this picture we found that at high T the +electrons doped are completely delocalized but, when Tmo is approached, they +form magnetic polarons of large spin that cause the observed curvature in +c^-1(T) for x<=0.1.",0211242v1 +2004-11-29,Strong correlation effects of the Re 5$d$ electrons on the metal-insulator transition in Ca$_2$FeReO$_6$,"We have investigated the electronic structure of polycrystalline +Ca$_2$FeReO$_6$ using photoemission spectroscopy and band-structure +calculations within the local-density approximation+$U$ (LDA+$U$) scheme. In +valence-band photoemission spectra, a double-peak structure which is +characteristic of the metallic double perovskite series has been observed near +the Fermi level ($E_{\rm F}$), although it is less distinct compared to the +Sr$_2$FeMoO$_6$ case. The leading near-$E_{\rm F}$ structure has a very weak +spectral weight at $E_{\rm F}$ above the metal-insulator transition (MIT) +temperature $T_{\rm MI}$ of $\sim$140 K, and it loses the $E_{\rm F}$ weight +below $T_{\rm MI}$, forming a small energy gap. + To reproduce this small energy gap in the calculation, we require a very +large effective $U$ ($U_{\rm eff}$) for Re (4 eV) in addition to a relatively +large $U_{\rm eff}$ for Fe (4 eV). Although the most of the experimental +features can be interpreted with the help of the band theory, the overall +agreement between the theory and the experiment was not satisfactory. We +demonstrate that the effective transfer integral between Fe and Re is actually +smaller than that between Fe and Mo in Ca$_2$FeMoO$_6$, which can explain both +MIT and very high ferrimagnetic transition temperature.",0411714v1 +2005-07-05,Valence instability of cerium under pressure in the Kondo-like perovskite La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$,"Effect of hydrostatic pressure and magnetic field on electrical resistance of +the Kondo-like perovskite manganese oxide, +La$_{0.1}$Ce$_{0.4}$Sr$_{0.5}$MnO$_3$ with a ferrimagnetic ground state, have +been investigated up to 2.1 GPa and 9 T. In this compound, the Mn-moments +undergo double exchange mediated ferromagnetic ordering at $T_{\rm C}$ $\sim$ +280 K and there is a resistance maximum, $T_{\rm max}$ at about 130 K which is +correlated with an antiferromagnetic ordering of {\it cerium} with respect to +the Mn-sublattice moments. Under pressure, the $T_{\rm max}$ shifts to lower +temperature at a rate of d$T_{max}$/d$P$ = -162 K/GPa and disappears at a +critical pressure $P_{\rm c}$ $\sim$ 0.9 GPa. Further, the coefficient, $m$ of +$-logT$ term due to Kondo scattering decreases linearly with increase of +pressure showing an inflection point in the vicinity of $P_{\rm c}$. These +results suggest that {\it cerium} undergoes a transition from Ce$^{3+}$ state +to Ce$^{4+}$/Ce$^{3+}$ mixed valence state under pressure. In contrast to +pressure effect, the applied magnetic field shifts $T_{\rm max}$ to higher +temperature presumably due to enhanced ferromagnetic Mn moments.",0507094v1 +2005-08-29,"Magnetic Properties of J-J-J' Quantum Heisenberg Chains with Spin S=1/2, 1, 3/2 and 2 in a Magnetic Field","By means of the density matrix renormalization group (DMRG) method, the +magnetic properties of the J-J-J$^{\prime}$ quantum Heisenberg chains with spin +$S=1/2$, 1, 3/2 and 2 in the ground states are investigated in the presence of +a magnetic field. Two different cases are considered: (a) when $J$ is +antiferromagnetic and $J^{\prime}$ is ferromagnetic (i.e. the AF-AF-F chain), +the system is a ferrimagnet. The plateaus of the magnetization are observed. It +is found that the width of the plateaus decreases with increasing the +ferromagnetic coupling, and disappears when $% J^{\prime}/J$ passes over a +critical value. The saturated field is observed to be independent of the +ferromagnetic coupling; (b) when $J$ is ferromagnetic and $J^{\prime}$ is +antiferromagnetic (i.e. the F-F-AF chain), the system becomes an +antiferromagnet. The plateaus of the magnetization are also seen. The width of +the plateaus decreases with decreasing the antiferromagnetic coupling, and +disappears when $J^{\prime}/J $ passes over a critical value. Though the ground +state properties are quite different, the magnetization plateaus in both cases +tend to disappear when the ferromagnetic coupling becomes more dominant. +Besides, no fundamental difference between the systems with spin half-integer +and integer has been found.",0508685v1 +2006-05-19,Spin-flop transition in antiferromagnetic multilayers,"A comprehensive theoretical investigation on the field-driven reorientation +transitions in uniaxial multilayers with antiferromagnetic coupling is +presented. It is based on a complete survey of the one-dimensional solutions +for the basic phenomenological (micromagnetic) model that describes the +magnetic properties of finite stacks made from ferromagnetic layers coupled +antiferromagnetically through spacer layers. The general structure of the phase +diagrams is analysed. At a high ratio of uniaxial anisotropy to +antiferromagnetic interlayer exchange, only a succession of collinear magnetic +states is possible. With increasing field first-order (metamagnetic) +transitions occur from the antiferromagnetic ground-state to a set of +degenerate ferrimagnetic states and to the saturated ferromagnetic state. At +low anisotropies, a first-order transition from the antiferromagnetic +ground-state to an inhomogeneous spin-flop state occurs. Between these two +regions, transitional magnetic phases occupy the range of intermediate +anisotropies. Detailed and quantitative phase diagrams are given for the basic +model of antiferromagnetic multilayer systems with N = 2 to 16 layers. The +connection of the phase diagrams with the spin-reorientation transitions in +bulk antiferromagnets is discussed. The limits of low anisotropy and large +numbers of layers are analysed by two different representations of the magnetic +energy, namely, in terms of finite chains of staggered vectors and in a general +continuum form. It is shown that the phenomena widely described as ``surface +spin-flop'' are driven only by the cut exchange interactions and the +non-compensated magnetic moment at the surface layers of a stacked +antiferromagnetic system.",0605493v1 +2006-06-02,The Coupled Cluster Method Applied to the {\it XXZ} Model on the Square Lattice,"A review of the coupled cluster method (CCM) applied to lattice quantum spin +systems is presented here. The CCM formalism is explained and an application to +the spin-half {\it XXZ} model on the square lattice is presented. Low orders of +approximation are carried out analytically and a high-order CCM formulation is +presented. Results for the SUB2 approximation are carried out numerically for +SUB2-$m$ and analytically for SUB2. It is found that SUB2-$m$ results converge +rapidly to the full SUB2 solution, including new results for the SUB2-$m$ +limiting points compared to the SUB2 critical point. Results for the +ground-state energy and the sublattice magnetisation are presented. A study of +the excitation spectrum of this model at the SUB2 critical point is given. +Indeed, the shape of the excitation spectrum at the SUB2 critical point is +identical to that predicted by spin-wave theory for the isotropic model, albeit +with a multiplicative factor of 1.1672. This result compares very well to +results of cumulant series expansions and Monte Carlo simulation that again +predict a similar shape for the excitation spectrum, but with multiplicative +factors of 1.18 and 1.21$\pm$0.03, respectively. Results for the isotropic +Heisenberg model on the square lattice for the spin-one antiferromagnet and the +spin-one/spin-half ferrimagnet are also given.",0606060v1 +2006-07-12,Title Cluster-Variational Treatment of Disordered Mixed Spin Ising Model,"A disordered alloy Ap B1-p where both A and B represent the magnetic atoms +with respective spin SA =1/2 and SB =1 and whose magnetic interaction can be +described through Ising Hamiltonian is treated using the cluster-variational +method. In this method it is assumed that the system is built out of building +block which is embedded in an effective field. Taking building block as 4-atom +cluster the approximate free energy of the alloy is then obtained by treating +the interactions between spins within the cluster of all possible +configurations in exact manner and the rest of the interaction by an effective +variational field . The magnetization M and transition temperature Tc are then +calculated for different concentration and exchange parameters (JAA, JBB and +JAB). The magnetization M exhibits different kinds of ferrimagnetic behaviour +depending on concentration and relative strength of intra- and inter- +sub-network exchange interactions. For antiferromagnetic JAB, the sub-network +magnetization saturates and aligned antiferromagnetically at low temperature. +The existence of compensation temperature Tcm, where total magnetization +reverses its direction, depends sensitively on relative values of JAA/ JAB and +JBB/ JAB and p. For B (A)-rich alloy with small JAB, the direction of net +magnetization remains same upto Tc and a maximum of M appears at intermediate T +< Tc when JBB>> JAA (JBB<< JAA).When magnitude of JAB > JAA, JBB, Tc exhibits a +maximum with p. The transition temperature is much less than the mean-field +value for all cases. The magnetic susceptibility for diverges and is +Curie-Wiess like at T >>Tc. The meta-magnetic behaviour at high magnetic field +has been found. Some of these results are in tune with experimental observation +in amorphous rare-earth-transition metal alloys.",0607299v1 +2006-10-18,Magnetic Properties and Metastable States in Spin-Crossover Transition of Co-Fe Prussian Blue Analogues,"The combination of spin transitions and magnetic ordering provides an +interesting structure of phase transitions in Prussian blue analogues (PBAs). +To understand the structure of stable and metastable states of Co-Fe PBA, it is +necessary to clarify free energy as a function of magnetization and the +fraction of the high-temperature component. Including the magnetic interaction +between high-temperature states, we study the magnetic phase transition of +Co-Fe PBA in addition to spin transitions. Here, we take into account the +degeneracy changes due to charge transfer between Co and Fe atoms accompanying +the spin transition. In this study, the charge transfer between Co and Fe atoms +is explicitly taken into account and also the ferrimagnetic structure of Co-Fe +PBAs is expressed in the proper way. First, we found systematic changes in the +structures of stable and metastable states as functions of system parameters +using mean field theory. In particular, the existence of a metastable +magnetic-ordered high-temperature state is confirmed at temperatures lower than +that of the hysteresis region of spin transitions. Second, we found that the +magnetic interaction causes complex ordering processes of a spin transition and +a magnetic phase transition. The effect of a magnetic field on the phase +structure is also investigated and we found metamagnetic magnetization +processes. Finally, the dynamical properties of this metastable state are +studied by Monte Carlo method.",0610500v2 +2006-12-06,Epitaxial Bi2FeCrO6 Multiferroic Thin Films,"We present here experimental results obtained on Bi2FeCrO6 (BFCO) epitaxial +films deposited by laser ablation directly on SrTiO3 substrates. It has been +theoretically predicted, by Baettig and Spaldin, using first-principles density +functional theory that BFCO is ferrimagnetic (with a magnetic moment of 2 Bohr +magneton per formula unit) and ferroelectric (with a polarization of ~80 +microC/cm2 at 0K). The crystal structure has been investigated using X-ray +diffraction which shows that the films are epitaxial with a high crystallinity +and have a degree of orientation depending of the deposition conditions and +that is determined by the substrate crystal structure. Chemical analysis +carried out by X-ray Microanalysis and X-ray Photoelectron Spectroscopy (XPS) +indicates the correct cationic stoichiometry in the BFCO layer, namely +(Bi:Fe:Cr = 2:1:1). XPS depth profiling revealed that the oxidation state of Fe +and Cr ions in the film remains 3+ throughout the film thickness and that both +Fe and Cr ions are homogeneously distributed throughout the depth. +Cross-section high-resolution transmission electron microscopy images together +with selected area electron diffraction confirm the crystalline quality of the +epitaxial BFCO films with no identifiable foreign phase or inclusion. The +multiferroic character of BFCO is proven by ferroelectric and magnetic +measurements showing that the films exhibit ferroelectric and magnetic +hysteresis at room temperature. In addition, local piezoelectric measurements +carried out using piezoresponse force microscopy (PFM) show the presence of +ferroelectric domains and their switching at the sub-micron scale.",0612168v1 +2007-07-13,Effect of antiferromagnetic exchange interactions on the Glauber dynamics of one-dimensional Ising models,"We study the effect of antiferromagnetic interactions on the single spin-flip +Glauber dynamics of two different one-dimensional (1D) Ising models with spin +$\pm 1$. The first model is an Ising chain with antiferromagnetic exchange +interaction limited to nearest neighbors and subject to an oscillating magnetic +field. The system of master equations describing the time evolution of +sublattice magnetizations can easily be solved within a linear field +approximation and a long time limit. Resonant behavior of the magnetization as +a function of temperature (stochastic resonance) is found, at low frequency, +only when spins on opposite sublattices are uncompensated owing to different +gyromagnetic factors (i.e., in the presence of a ferrimagnetic short range +order). The second model is the axial next-nearest neighbor Ising (ANNNI) +chain, where an antiferromagnetic exchange between next-nearest neighbors (nnn) +is assumed to compete with a nearest-neighbor (nn) exchange interaction of +either sign. The long time response of the model to a weak, oscillating +magnetic field is investigated in the framework of a decoupling approximation +for three-spin correlation functions, which is required to close the system of +master equations. The calculation, within such an approximate theoretical +scheme, of the dynamic critical exponent z, defined as ${1/\tau} \approx ({1/ +{\xi}})^z$ (where \tau is the longest relaxation time and \xi is the +correlation length of the chain), suggests that the T=0 single spin-flip +Glauber dynamics of the ANNNI chain is in a different universality class than +that of the unfrustrated Ising chain.",0707.1953v1 +2007-11-04,Torque magnetometry study of metamagnetic transitions in single-crystal HoNi2B2C at T\approx 1.9 K,"Metamagnetic transitions in single-crystal rare-earth nickel borocarbide +HoNi$_2$B$_2$C have been studied at T\approx 1.9 K with a Quantum Design torque +magnetometer. This compound is highly anisotropic with a variety of +metamagnetic states at low temperature which includes antiferromagnetic, +ferrimagnetic, non-collinear and ferromagnetic-like (saturated paramagnet) +states. The critical fields of the transitions depend crucially on the angle +$\theta$ between applied field and the easy axis [110]. Measurements of torque +along the c-axis have been made while changing the angular direction of the +magnetic field (parallel to basal tetragonal $ab$-planes) and with changing +field at fixed angle over a wide angular range. Two new phase boundaries in the +region of the non-collinear phase have been observed, and the direction of the +magnetization in this phase has been precisely determined. At low field the +antiferromagnetic phase is observed to be multidomain. In the angular range +very close to the hard axis [100] ($-6^{\circ} \lesssim\phi \lesssim +6^{\circ}$, where $\phi$ is the angle between field and the hard axis) the +magnetic behavior is found to be ``frustrated'' with a mixture of phases with +different directions of the magnetization.",0711.0533v1 +2007-12-28,"Half Semimetallic Antiferromagnetism in the Sr$_2$CrTO$_6$ System, T=Os, Ru","Double perovskite Sr$_2$CrOsO$_6$ is (or is very close to) a realization of a +spin-asymmetric semimetallic compensated ferrimagnet, according to first +principles calculations. This type of near-half metallic antiferromagnet is an +unusual occurrence, and more so in this compound because the zero gap is +accidental rather than being symmetry determined. The large spin-orbit coupling +(SOC) of osmium upsets the spin balance (no net spin moment without SOC): it +reduces the Os spin moment by 0.27 $\mu_B$ and induces an Os orbital moment of +0.17 $\mu_B$ in the opposite direction. The effects combine (with small oxygen +contributions) to give a net total moment of 0.54 $\mu_B$ per cell in \scoo, +reflecting a large impact of SOC in this compound. This value is in moderately +good agreement with the measured saturation moment of 0.75 $\mu_B$. The value +of the net moment on the Os ion obtained from neutron diffraction (0.73 $\mu_B$ +at low temperature) differs from the calculated value (1.14 $\mu_B$). Rather +surprisingly, in isovalent Sr$_2$CrRuO$_6$ the smaller SOC-induced spin changes +and orbital moments (mostly on Ru) almost exactly cancel. This makes +Sr$_2$CrRuO$_6$ a ""half (semi)metallic antiferromagnet"" (practically vanishing +net total moment) even when SOC is included, with the metallic channel being a +small-band-overlap semimetal. Fixed spin moment (FSM) calculations are +presented for each compound, illustrating how they provide different +information than in the case of a nonmagnetic material. These FSM results +indicate that the Cr moment is an order of magnitude stiffer against +longitudinal fluctuations than is the Os moment.",0712.4308v1 +2008-03-06,Dimers on the Triangular Kagome Lattice,"We derive exact results for close-packed dimers on the triangular kagome +lattice (TKL), formed by inserting triangles into the triangles of the kagome +lattice. Because the TKL is a non-bipartite lattice, dimer-dimer correlations +are short-ranged, so that the ground state at the Rokhsar-Kivelson (RK) point +of the corresponding quantum dimer model on the same lattice is a short-ranged +spin liquid. Using the Pfaffian method, we derive an exact form for the free +energy, and we find that the entropy is 1/3 ln2 per site, regardless of the +weights of the bonds. The occupation probability of every bond is 1/4 in the +case of equal weights on every bond. Similar to the case of lattices formed by +corner-sharing triangles (such as the kagome and squagome lattices), we find +that the dimer-dimer correlation function is identically zero beyond a certain +(short) distance. We find in addition that monomers are deconfined on the TKL, +indicating that there is a short-ranged spin liquid phase at the RK point. We +also find exact results for the ground state energy of the classical Heisenberg +model. The ground state can be ferromagnetic, ferrimagnetic, locally coplanar, +or locally canted, depending on the couplings. From the dimer model and the +classical spin model, we derive upper bounds on the ground state energy of the +quantum Heisenberg model on the TKL.",0803.0742v2 +2008-11-28,Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6,"It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting +plateaus in the magnetization as a function of the magnetic field at low +temperatures. The origin of them is still controversial. In this paper we study +the thermal behavior of this compound with a single-flip Monte Carlo simulation +on a triangular lattice and demonstrate the decisive influence of metastable +states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We +consider the [Co2O6]n chains as giant magnetic moments described by large Ising +spins on planar clusters with open boundary conditions. With this simple +frozen-moment model we obtain stepped magnetization curves which agree quite +well with the experimental results for different sweeping rates. We describe +particularly the out-of-equilibrium states that split the low-temperature 1/3 +plateau into three steps. They relax thermally to the 1/3 plateau, which has +long-range order at the equilibrium. Such states are further analyzed with +snapshots unveiling a domain-wall structure that is responsible for the +observed behavior of the 1/3 plateau. A comparison is also given of the exact +results in small triangular clusters with our Monte Carlo results, providing +further support for our thermal description of this compound.",0811.4772v1 +2008-12-04,Sign reversal in the exchange bias and the collapse of hysteresis width across the magnetic compensation temperature in a single crystal of Nd0.75Ho0.25Al2,"In the admixed Nd0.75Ho0.25Al2 system, magnetic moments of Nd and Ho +occupying the same crystallographic site are antiferromagnetically coupled and +the chosen stoichiometry displays a magnetic compensation behavior (Tcomp of +about 24 K) in all orientations. In the vicinity of Tcomp, the conduction +electron polarization (CEP) assumes the role of a soft ferromagnet exchange +coupled to a pseudo-antiferromagnet comprising Nd/Ho moments, resulting in an +asymmetry in the hysteretic (M-H) loop, i.e., the notion of an exchange bias +field (Hexch). Across Tcomp, the CEP contribution reverses sign, and in +consonance, the asymmetry in the M-H loop also undergoes a phase reversal. +Interestingly, the width of the M-H loop shows a divergence, followed by a +collapse on approaching Tcomp from either end. The observed behavior confirms a +long standing prediction based on a phenomenological model for ferrimagnetic +systems. The field induced changes across Tcomp leave an imprint of a +quasi-phase transition in the heat capacity data. Magneto-resistance (\Delta R +/ R vs T) has an oscillatory response, in which the changes across Tc and Tcomp +can be recognized.",0812.0931v1 +2009-01-30,Ferromagnetism in Co7(TeO3)4Br6: A byproduct of complex antiferromagnetic order and single-ion anisotropy,"Pronounced anisotropy of magnetic properties and complex magnetic order of a +new oxi-halide compound Co7(TeO3)4Br6 has been investigated by powder and +single crystal neutron diffraction, magnetization and ac susceptibility +techniques. Anisotropy of susceptibility extends far into the paramagnetic +temperature range. A principal source of anisotropy are anisotropic properties +of the involved octahedrally coordinated single Co(2+) ions, as confirmed by +angular-overlap-model calculations presented in this work. Incommensurate +antiferromagnetic order sets in at TN=34 K. Propagation vector is strongly +temperature dependent reaching k1=(0.9458(6), 0, 0.6026(5)) at 30 K. A +transition to a ferrimagnetic structure with k2=0 takes place at TC=27 K. +Magnetically ordered phase is characterized by very unusual anisotropy as well: +while M-H scans along b-axis reveals spectacularly rectangular but otherwise +standard ferromagnetic hysteresis loops, M-H studies along other two principal +axes are perfectly reversible, revealing very sharp spin flop (or spin flip) +transitions, like in a standard antiferromagnet (or metamagnet). Altogether, +the observed magnetic phenomenology is interpreted as an evidence of competing +magnetic interactions permeating the system, first of all of the single ion +anisotropy energy and the exchange interactions. Different coordinations of the +Co(2+)-ions involved in the low-symmetry C2/c structure of Co7(TeO3)4Br6 render +the exchange-interaction network very complex by itself. Temperature dependent +changes in the magnetic structure, together with an abrupt emergence of a +ferromagnetic component, are ascribed to continual spin reorientations +described by a multi-component, but yet unknown, spin Hamiltonian.",0901.4878v1 +2010-01-20,Theory of Room Temperature Ferromagnet V(TCNE)_x (1.5 < x < 2): Role of Hidden Flat Bands,"Theoretical studies on the possible origin of room temperature ferromagnetism +(ferromagnetic once crystallized) in the molecular transition metal complex, +V(TCNE)_x (1.50; (B) J1>0, J2<0; and (C) J1<0, J2>0, where J1 and J2 +are the exchange couplings between spins in the chain and along the rung, +respectively. The low-lying and magnetic properties are explored jointly by the +real-space renormalization group, spin wave, and density-matrix renormalization +group methods, while the transfer-matrix renormalization group method is +invoked to study the thermodynamics. It is found that the magnon spectra +consist of a gapless and two gapped branches. Two branches in case (C) have +intersections. The coupling dependence of low-energy gaps are analyzed. In a +magnetic field, an m=3/2 (m is the magnetization per unit cell) plateau is +observed for case (A), while two plateaux at m=1/2 and 3/2 are observed for +cases (B) and (C). Between the two plateaux in cases (B) and (C), the +sublattice magnetizations for the spins coupled by ferromagnetic interactions +have novel decreasing regions with increasing the magnetic field. At finite +temperature, the zero-field susceptibility temperature product chi*T and +specific heat exhibit distinct exotic features with varying the couplings and +temperature for different cases. chi*T is found to converge as T approaches +zero, which is different from the divergent behavior in the spin-(1/2,1) +mixed-spin chain without pendants. The observed thermodynamic behaviors are +also discussed with the help of their low-lying excitations.",1006.0794v1 +2010-09-28,Absence of Ferromagnetism in Mn-doped Tetragonal Zirconia,"In a recent letter, it has been predicted within first principle studies that +Mn-doped ZrO2 compounds could be good candidate for spintronics application +because expected to exhibit ferromagnetism far beyond room temperature. Our +purpose is to address this issue experimentally for Mn-doped tetragonal +zirconia. We have prepared polycrystalline samples of Y0.15(Zr0.85-yMny)O2 +(y=0, 0.05, 0.10, 0.15 & 0.20) by using standard solid state method at +equilibrium. The obtained samples were carefully characterized by using x-ray +diffraction, scanning electron microscopy, elemental color mapping, X-ray +photoemission spectroscopy and magnetization measurements. From the detailed +structural analyses, we have observed that the 5% Mn doped compound +crystallized into two symmetries (dominating tetragonal & monoclinic), whereas +higher Mn doped compounds are found to be in the tetragonal symmetry only. The +spectral splitting of the Mn 3s core-level x-ray photoelectron spectra confirms +that Mn ions are in the Mn3+ oxidation state and indicate a local magnetic +moment of about 4.5 {\mu}B/Mn. Magnetic measurements showed that compounds up +to 10% of Mn doping are paramagnetic with antiferromagnetic interactions. +However, higher Mn doped compound exhibits local ferrimagnetic ordering. Thus, +no ferromagnetism has been observed for all Mn-doped tetragonal ZrO2 samples.",1009.5583v2 +2011-05-03,Simulation of Quantum Magnetism in Mixed Spin Systems with Impurity Doped Ion Crystal,"We propose the realization of linear crystals of cold ions which contain +different atomic species for investigating quantum phase transitions and +frustration effects in spin system beyond the commonly discussed case of +$s=1/2$. Mutual spin-spin interactions between ions can be tailored via the +Zeeman effect by applying oscillating magnetic fields with strong gradients. +Further, collective vibrational modes in the mixed ion crystal can be used to +enhance and to vary the strength of spin-spin interactions and even to switch +those forces from a ferro- to an antiferromagnetic character. We consider the +behavior of the effective spin-spin couplings in an ion crystal of spin-1/2 +ions doped with high magnetic moment ions with spin S=3. We analyze the ground +state phase diagram and find regions with different spin orders including +ferrimagnetic states. In the most simple non-trivial example we deal with a +linear $\{$Ca$^+$, Mn$^+$, Ca$^+\}$ crystal with spins of $\{1/2,3,1/2}$. To +show the feasibility with current state-of-the-art experiments, we discuss how +quantum phases might be detected using a collective Stern-Gerlach effect of the +ion crystal and high resolution spectroscopy. Here, the state-dependent +laser-induced fluorescence of the indicator spin-1/2 ion, of species +$^{40}$Ca$^+$, reveals also the spin state of the simulator spin-3 ions, +$^{50}$Mn$^+$ as this does not possess suitable levels for optical excitation +and detection.",1105.0598v1 +2011-12-18,Ground state factorization of heterogeneous spin models in magnetic fields,"The exact factorized ground state of a heterogeneous (ferrimagnetic) spin +model which is composed of two spins ($\rho, \sigma$) has been presented in +detail. The Hamiltonian is not necessarily translational invariant and the +exchange couplings can be competing antiferromagnetic and ferromagnetic +arbitrarily between different sub-lattices to build many practical models such +as dimerized and tetramerized materials and ladder compounds. The condition to +get a factorized ground state is investigated for non-frustrated spin models in +the presence of a uniform and a staggered magnetic field. According to the +lattice model structure we have categorized the spin models in two different +classes and obtained their factorization conditions. The first class contains +models in which their lattice structures do not provide a single uniform +magnetic field to suppress the quantum correlations. Some of these models may +have a factorized ground state in the presence of a uniform and a staggered +magnetic field. However, in the second class there are several spin models in +which their ground state could be factorized whether a staggered field is +applied to the system or not. For the latter case, in the absence of a +staggered field the factorizing uniform field is unique. However, the degrees +of freedom for obtaining the factorization conditions are increased by adding a +staggered magnetic field.",1112.4127v1 +2012-10-19,"Ferromagnetic structures in Mn2CoGa and Mn2CoAl doped by Co, Cu, V, and Ti","The structure and magnetic properties in doped Heusler alloys of Mn2CoGa and +Mn2CoAl have been investigated by experiments and calculations. The main group +elements of Ga and Al are substituted by the magnetic or non-magnetic +transition metals, Co, Cu, V, and Ti in the alloy systems. Three kinds of local +ferromagnetic structures, Co-Mn-Co, Mn-Co-Mn and Mn-Co-V, have been found. They +embed in the native ferrimagnetic matrix and increase the magnetization with +different increments. The Co-Mn-Co ferromagnetic structure shows the largest +increment of 6.18{\mu}B /atom. In addition, interesting results for +non-magnetic Cu increasing the magnetization and the V atom having a large +ferromagnetic moment of about 1.0{\mu}B have been obtained. The exchange +interaction energy can be increased by the newly added Co and depleted by +supporting a ferromagnetic coupling in other substitution cases, and showing +the variation of the TC. Our calculation of electronic structure verifies the +strong d-d hybridization when the three ferromagnetic structures are achieved. +It has also been found that the covalent effect from the Ga and Al determines +the generation of the local ferromagnetic structure and the tolerance for +dopant content.",1210.5357v1 +2012-10-20,Tunable spin reorientation transition and magnetocaloric effect in Sm0.7-xLaxSr0.3MnO3 series,"We report electrical resistivity, magnetic and magnetocaloric properties in +Sm0.7-xLaxSr0.3MnO3 series for x= 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, and +0.7. All the compounds show second order paramagnetic to ferromagnetic +transition at T = Tc which is tunable anywhere between 83 K and 373 K with a +proper choice of the doping level (x). The insulating ferromagnet x= 0 +transforms to ferromagnetic metal below Tc for x= 0.1 and the insulator-metal +transition temperature shifts up with increasing x. The magnetization (M) +exhibits an interesting behavior as a function of temperature and doping level. +The field-cooled M(T) of all but x= 0.7 compound show a cusp at a temperature +T* much below Tc. While the Tc increases monotonically with increasing x, T* +increases gradually, attains a maximum value (T*= 137 K) for x= 0.6 and +decreases rapidly thereafter. It is suggested that the decrease of M(T) below +T* is due to ferrimagnetic interaction between Sm(4f) and Mn(3d) sublattices +that promotes spin-reorientation transition of the Mn-sublattice. The observed +anomalous feature in M(T) does not have impact on the dc resistivity. Magnetic +entropy change (delta Sm) was estimated from magnetization isotherms. The sign +of delta Sm is found to change from negative above T* to positive below T* +indicating the coexistence of normal and inverse magnetocaloric effects. delta +Sm is nearly composition independent (-delta Sm is about 1.5 J/Kg K for delta H += 1 Tesla) and refrigeration capacity lies between 50 and 80 J/kg K for x = +0.1-0.6. The tunability of Curie temperature with a nearly constant delta Sm +value along with high refrigeration capacity makes this series of compounds +interesting for magnetic refrigeration over a wide temperature range.",1210.5595v1 +2012-10-22,"Structure, magnetism and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys","The structure, magnetism, magnetic compensation behavior, exchange +interaction and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 +(x=0-25) alloys have been systematically investigated by both experiments and +first-principles calculations. We found that all the samples exhibited body +centered cubic structures with a high degree of atomic ordering. With +increasing Ga content, the composition dependence of lattice parameters shows a +kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be +attributed to the enhanced covalent effect between the Ga and the transition +metals. Furthermore, a complicated magnetic competition has been revealed in +Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically +decrease and results in a magnetic moment compensation behavior. In +Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional +ferrimagnetic configuration was established in the native ferromagnetic matrix, +which causes the molecular moment monotonously decreases and the exchange +interaction enhances gradually. The electronic structure calculations indicate +that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the +itinerant and localized magnetism. Our study will be helpful to understand the +nature of magnetic ordering as well as to tune magnetic compensation and +electronic properties of Heusler alloys.",1210.5810v1 +2012-10-22,Electronic structure and magnetic and optical properties of double perovskite Bi2FeCrO6 from first-principles investigation,"Double perovskite Bi$_2$FeCrO$_6$, related with BiFeO$_3$, is very +interesting because strong ferroelectricity and high magnetic Curie temperature +beyond room temperature are observed in it. However, existing +density-functional-theory (DFT) studies, using pseudo-potentials, produce +metallic ground state under the local density approximation (LDA) and need +LDA+U method to yield needed nonmetallic ground state, resulting in low +magnetic Curie temperature (below 130 K). Here, we optimize its crystal +structure and then investigate its electronic structure and magnetic and +optical properties by combining the full-potential augmented plane wave method +with Monte Carlo simulation. Our optimized structure is a robust ferrimagnetic +semiconductor. This nonmetallic phase is formed due to crystal field splitting +and spin exchange splitting, in contrast to Mott-Hubbard states in previous DFT +studies. Spin exchange constants and optical properties are calculated. Our ab +initio magnetic Curie temperature is 450 K, much higher than previous DFT-based +value and consistent with experimental results. Our study and analysis reveals +that the main magnetic mechanism is an antiferromagnetic superexchange between +Fe and Cr over the intermediate O atom. These results are useful to +understanding such perovskite materials and exploring their potential +applications.",1210.5981v2 +2012-10-24,Theory of Half-Metallic Double Perovskites I: Double Exchange Mechanism,"The double perovskite material \SFMO has the rare and desirable combination +of a half-metallic ground state with 100% spin polarization and ferrimagnetic +\Tc$\simeq 420$K, well above room temperature. In this two-part paper, we +present a comprehensive theoretical study of the magnetic and electronic +properties of half metallic double perovskites. In this paper we present exact +diagonalization calculations of the ""fast"" Mo electronic degrees coupled to +""slow"" Fe core spin fluctuations treated by classical Monte Carlo techniques. +From the temperature dependence of the spin-resolved density of states, we show +that the electronic polarization at the chemical potential is proportional to +magnetization as a function of temperature. We also consider the effects of +disorder and show that excess Fe leaves the ground state half-metallic while +anti-site disorder greatly reduces the polarization. In a companion paper +titled ""Theory of Half-Metallic Double Perovskites II: Effective Spin +Hamiltonian and Disorder Effects"", we derive an effective classical spin +Hamiltonian that provides a new framework for understanding the magnetic +properties of half-metallic double perovskites including the effects of +disorder. Our results on the dependence of the spin polarization on temperature +and disorder has important implications for spintronics.",1210.6687v2 +2012-10-29,Continuous magnetic phase transition in half-frustrated Ca2Os2O7,"We present the specific heat, magnetization, optical spectroscopy +measurements and the firstprinciple calculations on the Weberite structure +Ca2Os2O7 single crystal/polycrystalline sample. The Ca2Os2O7 shows a +Curie-Weiss nature at high temperature and goes into a ferrimagnetic insulating +state at 327 K on cooling. A \lambda-like peak is observed at 327 K in the +specific heat implying a second-order phase transition. The vanishing +electronic specific heat at low temperature suggests a full energy gap. At high +temperature above the transition, small amount of itinerant carriers with short +life time \tau are observed, which is gapped at 20 K with a direct gap of 0:24 +eV . Our first principle calculations indicate that the anti-ferromagnetic +(AFM) correlation with intermediate Coulomb repulsion U could effectively split +Os(4b) t2g bands and push them away from Fermi level(EF). On the other hand, a +non-collinear magnetic interaction is needed to push the Os(4c) bands away from +EF, which could be induced by Os(4c)-Os(4c) frustration. Therefore, AFM +correlation, Coulomb repulsion U and non-collinear interaction all play +important roles for the insulating ground state in Ca2Os2O7.",1210.7571v1 +2013-02-25,Monte Carlo investigation of a spherical ferrimagnetic core-shell nanoparticle under a time dependent magnetic field,"Monte Carlo simulation based on Metropolis algorithm has been used with a +great success to analyze the dynamic phase transition properties of a single +spherical core-shell nanoparticle system with a spin-3/2 core surrounded by a +spin-1 shell layer with antiferromagnetic interface coupling under the +influence of a time dependent oscillating magnetic filed. It has been found +that the dynamic phase boundaries strongly depend on the Hamiltonian parameters +such as for the high amplitude and period values of the external field, the +phase transition temperature sharply changes whereas it tends to slowly alter +as the reduced magnitude of interlayer parameter $\mathrm{J_{int}/J_{sh}}$ +increases. Moreover, it is observed that the magnetization curves of the +particle have been found to obey P-type, N-type and Q-type classification +schemes under certain conditions. Much effort has also been paid to the +influence of the particle size on the thermal and magnetic properties of the +particle. Finally, a comparison of our observations with those of recently +published study including dynamic treatments of a nanocubic core-shell system +is represented and the findings indicate that there exists a qualitatively good +agreement with some relatively distinct differences.",1302.6227v2 +2013-04-10,Magnetization and spin dynamics of the spin S=1/2 hourglass nanomagnet Cu5(OH)2(NIPA)4*10H2O,"We report a combined experimental and theoretical study of the spin S=1/2 +nanomagnet Cu5(OH)2(NIPA)4*10H2O (Cu5-NIPA). Using thermodynamic, electron spin +resonance and 1H nuclear magnetic resonance measurements on one hand, and ab +initio density-functional band-structure calculations, exact diagonalizations +and a strong coupling theory on the other, we derive a microscopic magnetic +model of Cu5-NIPA and characterize the spin dynamics of this system. The +elementary five-fold Cu2+ unit features an hourglass structure of two +corner-sharing scalene triangles related by inversion symmetry. Our microscopic +Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange +couplings in each triangle, stabilizing a single spin S=1/2 doublet ground +state (GS), with an exactly vanishing zero-field splitting (by Kramer's +theorem), and a very large excitation gap of \Delta~68 K. Thus, Cu5-NIPA is a +good candidate for achieving long electronic spin relaxation (T1) and coherence +(T2) times at low temperatures, in analogy to other nanomagnets with low-spin +GS's. Of particular interest is the strongly inhomogeneous distribution of the +GS magnetic moment over the five Cu2+ spins. This is a purely +quantum-mechanical effect since, despite the non-frustrated nature of the +magnetic couplings, the GS is far from the classical collinear ferrimagnetic +configuration. Finally, Cu5-NIPA is a rare example of a S=1/2 nanomagnet +showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at +intermediate temperatures.",1304.2826v1 +2013-04-18,"Magnetostructural transition, metamagnetism, and magnetic phase coexistence in Co10Ge3O16","Co10Ge3O16 crystallizes in an intergrowth structure featuring alternating +layers of spinel and rock salt. Variable-temperature powder synchrotron X-ray +and neutron diffraction, magnetometry, and heat capacity experiments reveal a +magnetostructural transition at T_N = 203 K. This rhombohedral-to-monoclinic +transition involves a slight elongation of the CoO6 octahedra along the apical +axis. Below T_N, the application of a large magnetic field causes a +reorientation of the Co^2+ Ising spins. This metamagnetic transition is +first-order as evidenced by a latent heat observed in temperature-dependent +measurements. This transition is initially seen at T = 180 K as a broad upturn +in the M-H near H_C = 3.9 T. The upturn sharpens into a kink at T = 120 K and a +""butterfly"" shape emerges, with the transition causing hysteresis at high +fields while linear and reversible behavior persists at low fields. H_C +decreases as temperature is lowered and the loops at positive and negative +fields merge beneath T = 20 K. The antiferromagnetism is described by k_M = (00 +1/2) and below T = 20 K a small uncompensated component with k_M = (000) +spontaneously emerges. Despite the Curie-Weiss analysis and ionic radius +indicating the Co2+ is in its high-spin state, the low-temperature M-H trends +toward saturation at M_S = 1.0 uB/Co. We conclude that the field-induced state +is a ferrimagnet, rather than a S = 1/2 ferromagnet. The unusual H-T phase +diagram is discussed with reference to other metamagnets and Co(II) systems.",1304.5000v3 +2013-05-14,Long-range FMR driven spin pumping through a nonmagnetic insulator,"Ferromagnetic resonance (FMR) driven spin pumping is an emerging technique +for injection of a pure spin current from a ferromagnet (FM) into a +non-magnetic (NM) material without an accompanying charge current. It is widely +believed that this pumping proceeds exclusively via a short-range exchange +interaction at the FM/NM interface. Here we report robust, long-range spin +pumping from the ferrimagnetic double perovskite Sr2FeMoO6 (SFMO) into Pt +across an insulating barrier up to 200 nm thick, and systematically rule out +all known spurious effects. This result demonstrates dynamic spin injection +over a distance far beyond the coupling range of the exchange interaction, +exposing the need to consider other coupling mechanisms. The characteristic +length scale for magnetic textures in Sr2FeMoO6 is approximately 150 nm, +resulting from structural antiphase boundaries, thus raising the possibility +that magnetic dipole coupling underlies the observed long range spin transfer. +This discovery reveals a route to dynamic angular momentum transfer between a +FM and a NM in the absence of mediation by itinerant electrons and promises new +spin-functional devices employing long-range spin pumping.",1305.3016v2 +2013-07-18,"Comment on ""Pt magnetic polarization on Y3Fe5O12 and magnetotransport characteristics""","In a recent Letter [Y.M. Lu et al., Phys. Rev. Lett. 110, 147207 (2013)], Lu +et al. reported on ""ferromagneticlike transport properties"" of thin films of +Pt, deposited ex situ via sputtering on the ferrimagnetic insulator Y3Fe5O12. +The authors found a magnetoresistance in Pt displaying a hysteresis +corresponding to the coercive field of Y3Fe5O12, consistent with the findings +of other groups. While the latter interpreted their data in terms of the +recently proposed spin-Hall magnetoresistance, Lu et al. attributed their +observation to a magnetic proximity effect. To support this interpretation, +they measured the X-ray magnetic circular dichroism (XMCD) at the Pt L2,3 edges +from a Pt/Y3Fe5O12 sample with a Pt thickness of 1.5 nm and derived an average +induced magnetic moment of 0.054 Bohr magnetons per Pt atom. This is +contradictory to the results of our previous comprehensive XMCD study of three +different Pt/Y3Fe5O12 samples with Pt thicknesses of 3, 7, and 10 nm from which +we identified an upper limit of (0.003 +/- 0.001) Bohr magnetons per Pt +[Gepr\""ags et al., Appl. Phys. Lett. 101, 262407 (2012), arXiv:1211.0916].",1307.4869v1 +2013-10-23,Magnetic properties and electronic structure of Mn-Ni-Ga magnetic shape memory alloys,"Influence of disorder, antisite defects, martensite transition and +compositional variation on the magnetic properties and electronic structure of +Mn$_2$NiGa and Mn$_{1+x}$Ni$_{2-x}$Ga magnetic shape memory alloys have been +studied by using full potential spin-polarized scalar relativistic +Korringa-Kohn-Rostocker (FP-SPRKKR) method. Mn$_2$NiGa is ferrimagnetic and its +total spin moment increases when disorder in the occupancy of Mn$_{\rm Ni}$ (Mn +atom in Ni position) is considered. The moment further increases when Mn-Ga +antisite defect[1] is included in the calculation. A reasonable estimate of +$T_C$ for Mn$_2$NiGa is obtained from the exchange parameters for the +disordered structure. Disorder influences the electronic structure of +Mn$_2$NiGa through overall broadening of the density of states and a decrease +in the exchange splitting. Inclusion of antisite defects marginally broaden the +minority spin partial DOS (PDOS), while the majority spin PDOS is hardly +affected. For Mn$_{1+x}$Ni$_{2-x}$Ga where 1$\geq$$x$$\geq$0, as $x$ decreases, +Mn$_{\rm Mn}$ moment increases while Mn$_{\rm Ni}$ moment decreases in both +austenite and martensite phases. For $x$$\geq$ 0.25, the total moment of the +martensite phase is smaller compared to the austenite phase, which indicates +possible occurrence of inverse magnetocaloric effect. We find that the +redistribution of Ni 3$d$- Mn$_{\rm Ni}$ 3$d$ minority spin electron states +close to the Fermi level is primarily responsible for the stability of the +martensite phase in Mn-Ni-Ga.",1310.6130v2 +2013-11-06,Phase diagram and exotic spin-spin correlations of anisotropic Ising model on the Sierpiński gasket,"The anisotropic antiferromagnetic Ising model on the fractal Sierpi\'{n}ski +gasket is intensively studied, and a number of exotic properties are disclosed. +The ground state phase diagram in the plane of magnetic field-interaction of +the system is obtained. The thermodynamic properties of the three plateau +phases are probed by exploring the temperature-dependence of magnetization, +specific heat, susceptibility and spin-spin correlations. No phase transitions +are observed in this model. In the absence of a magnetic field, the unusual +temperature dependence of the spin correlation length is obtained with $0 +\leq$J$_b/$J$_a<1$, and an interesting crossover behavior between different +phases at J$_b/$J$_a=1$ is unveiled, whose dynamics can be described by the +J$_b/$J$_a$-dependence of the specific heat, susceptibility and spin +correlation functions. The exotic spin-spin correlation patterns that share the +same special rotational symmetry as that of the Sierpi\'{n}ski gasket are +obtained in both the $1/3$ plateau disordered phase and the $5/9$ plateau +partially ordered ferrimagnetic phase. Moreover, a quantum scheme is formulated +to study the thermodynamics of the fractal Sierpi\'{n}ski gasket with +Heisenberg interactions. We find that the unusual temperature dependence of the +correlation length remains intact in a small quantum fluctuation.",1311.1502v2 +2013-11-18,Assembly-mediated Interplay of Dipolar Interactions and Surface Spin Disorder in Colloidal Maghemite Nanoclusters,"Controlled assembly of single-crystal, colloidal maghemite nanoparticles is +facilitated via a high-temperature polyol-based pathway. Structural +characterization shows that size-tunable nanoclusters of 50 and 86 nm diameters +(D), with high dispersibility in aqueous media, are composed of $\sim$ 13 nm +(d) crystallographically oriented nanoparticles. The interaction effects are +examined against the increasing volume fraction, $\phi$, of the inorganic +magnetic phase that goes from individual colloidal nanoparticles ($\phi$= 0.47) +to clusters ($\phi$= 0.72). The frozen-liquid dispersions of the latter exhibit +weak ferrimagnetic behavior at 300 K. Comparative Mossbauer spectroscopic +studies imply that intra-cluster interactions come into play. A new insight +emerges from the clusters temperature-dependent ac susceptibility that displays +two maxima in $\chi$''(T), with strong frequency dispersion. Scaling-law +analysis, together with the observed memory effects suggest that a superspin +glass state settles-in at T$_{B}$ $\sim$ 160-200 K, while at +lower-temperatures, surface spin-glass freezing is established at T$_{f}$ +$\sim$40- 70 K. In such nanoparticle-assembled systems, with increased $\phi$, +Monte Carlo simulations corroborate the role of the inter-particle dipolar +interactions and that of the constituent nanoparticles surface spin disorder in +the emerging spin-glass dynamics.",1311.4302v2 +2014-04-29,Magnetic nano-fluctuations in a frustrated magnet,"Frustrated systems exhibit remarkable properties due to the high degeneracy +of their ground states. Stabilised by competing interactions, a rich diversity +of typically nanometre-sized phase structures appear in polymer and colloidal +systems, while the surface of ice pre-melts due to geometrically frustrated +interactions. Atomic spin systems where magnetic interactions are frustrated by +lattice geometry provide a fruitful source of emergent phenomena, such as +fractionalised excitations analogous to magnetic monopoles. The degeneracy +inherent in frustrated systems may prevail all the way down to absolute zero +temperature, or it may be lifted by small perturbations or entropic effects. In +the geometrically frustrated Ising--like magnet Ca3Co2O6, we follow the +temporal and spatial evolution of nanoscale magnetic fluctuations firmly +embedded inside the spin--density--wave magnetic structure. These fluctuations +are a signature of a competing ferrimagnetic phase with an incommensurability +that is different from, but determined by the host. As the temperature is +lowered, the fluctuations slow down into a super-paramagnetic regime of stable +spatiotemporal nano-structures.",1404.7398v1 +2014-09-01,Magnetic structures in the rich magnetic phase diagram of Ho$_2$RhIn$_8$,"The magnetic phase diagram of the tetragonal Ho$_2$RhIn$_8$ compound has +similar features to many related systems, revealing a zero magnetic field AF1 +and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase +were not reported yet for any of the related compounds. In addition, only the +Ho$_2$RhIn$_8$ phase diagram contains a small region of the incommensurate +zero-field AF3 phase. We have performed a number of neutron diffraction +experiments on single crystals of Ho$_2$RhIn$_8$ using several diffractometers +including experiments in both horizontal and vertical magnetic fields up to 4 +T. We present details of the magnetic structures in all magnetic phases of the +rich phase diagram of Ho$_2$RhIn$_8$. The Ho magnetic moments point along the +tetragonal $c$ axis in every phase. The ground-state AF1 phase is characterized +by propagation vector $\textbf{k}$ = (1/2, 0, 0). The more complex +ferrimagnetic AF2 phase is described by four propagation vectors +$\textbf{k}_{0}$ = (0, 0, 0), $\textbf{k}_{1}$ = (1/2, 0, 0), $\textbf{k}_{2}$ += (0, 1/2, 1/2), $\textbf{k}_{3}$ = (1/2, 1/2, 1/2). The magnetic structure in +the AF3 phase is incommensurate with $\textbf{k}_{AF3}$ = (0.5, $\delta$, 0). +Our results are consistent with theoretical calculations based on crystal field +theory.",1409.0433v2 +2014-09-03,Nanoscale confinement of all-optical switching in TbFeCo using plasmonic antennas,"All-optical switching (AOS) of magnetic domains by femtosecond laser pulses +was first observed in the transition metal-rare earth (TM-RE) alloy GdFeCo1-5; +this phenomenon demonstrated the potential for optical control of magnetism for +the development of ever faster future magnetic recording technologies. The +technological potential of AOS has recently increased due to the discovery of +the same effect in other materials, including RE-free magnetic multilayers6,7. +However, to be technologically meaningful, AOS must compete with the bit +densities of conventional storage devices, restricting optically-switched +magnetic areas to sizes well below the diffraction limit. Here, we demonstrate +reproducible and robust all-optical switching of magnetic domains of 53 nm size +in a ferrimagnetic TbFeCo alloy using gold plasmonic antenna structures. The +confined nanoscale magnetic reversal is imaged around and beneath plasmonic +antennas using x-ray resonant holographic imaging. Our results demonstrate the +potential of future AOS-based magnetic recording technologies.",1409.1280v1 +2014-12-11,Spontaneous formation of kagome network and Dirac half-semimetal on a triangular lattice,"In spin-charge coupled systems, geometrical frustration of underlying lattice +structures can give rise to nontrivial magnetic orders and electronic states. +Here we explore such a possibility in the Kondo lattice model with classical +localized spins on a triangular lattice by using a variational calculation and +simulated annealing. We find that the system exhibits a four-sublattice +collinear ferrimagnetic phase at 5/8 filling for a large Hund's-rule coupling. +In this state, the system spontaneously differentiates into the up-spin kagome +network and the isolated down-spin sites, which we call the kagome network +formation. In the kagome network state, the system becomes Dirac +half-semimetallic: The electronic structure shows a massless Dirac node at the +Fermi level, and the Dirac electrons are almost fully spin polarized due to the +large Hund's-rule coupling. We also study the effect of off-site Coulomb +repulsion in the kagome network phase where the system is effectively regarded +as a 1/3-filling spinless fermion system on the kagome lattice. We find that, +at the level of the mean-field approximation, a $\sqrt{3} \times \sqrt{3}$-type +charge order occurs in the kagome network state, implying the possibility of +fractional charge excitations in this triangular lattice system. Moreover, we +demonstrate that the kagome network formation with fully-polarized Dirac +electrons are controllable by an external magnetic field.",1412.3643v2 +2015-01-27,"Magnon spectra and strong spin-lattice coupling in magnetically frustrated MnB2O4 (B = Mn,V): Inelastic light scattering studies","The ferrimagnetic spinels MnB2O4 (B = Mn,V) exhibit a similar series of +closely spaced magnetic and structural phase transitions at low temperatures, +reflecting both magnetic frustration and a strong coupling between the spin and +lattice degrees of freedom. Careful studies of excitations in MnB2O4 (B = +Mn,V), and the evolution of these excitations with temperature, are important +for obtaining a microscopic description of the role that magnetic excitations +and spin-lattice coupling play in the low temperature phase transitions of +these materials. We report an inelastic light (Raman) scattering study of the +temperature and magnetic field dependences of one- and two-magnon excitations +in MnV2O4 and Mn3O4. We observe a pair of q=0 one-magnon modes at 74 cm^{-1} +and 81 cm^{-1} in MnV2O4, which is in contrast with the single 80 cm^{-1} q=0 +magnon that has been reported for MnV2O4 based on previous neutron scattering +measurements and spin wave calculations. Additionally, we find that the +two-magnon energy of MnV2O4 decreases (""softens"") with decreasing temperature +below T_{N}, which we attribute to strong coupling between magnetic and +vibrational excitations near the zone boundary.",1501.06897v1 +2015-02-18,"Magnetocrystalline anisotropic effect in GdCo$_{1-x}$Fe$_x$AsO ($x = 0, 0.05$)","From a systematic study of the electrical resistivity $\rho(T,H)$, magnetic +susceptibility $\chi(T,H)$, isothermal magnetization $M(H)$ and the specific +heat $C(T,H)$, a temperature-magnetic field ($T$-$H$) phase diagram has been +established for GdCo$_{1-x}$Fe$_x$AsO ($x = 0$ and $0.05$) polycrystalline +compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic +(FM) transition of Co $3d$ electrons ($T_\textup{C}^\textup{Co}$) and +antiferromagnetic (AFM) transition of Gd $4f$ electrons +($T_\textup{N}^\textup{Gd}$). For the Fe-doped sample ($x=0.05$), an extra +magnetic reorientation transition takes place below $T_\textup{N}^\textup{Gd}$, +which is likely associated with Co moments. The two magnetic species of Gd and +Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM) +behavior in the magnetic susceptibility. Upon decreasing the temperature ($T < +T_\textup{C}^\textup{Co}$), the magnetocrystalline anisotropy breaks up the FM +order of Co by aligning the moments with the local easy axes of the various +grains, leading to a spin reorientation transition at +$T_\textup{R}^\textup{Co}$. By applying a magnetic field, +$T_\textup{R}^\textup{Co}$ monotonically decreases to lower temperatures, while +the $T_\textup{N}^\textup{Gd}$ is relatively robust against the external field. +On the other hand, the applied magnetic field pulls the magnetization of grains +from the local easy direction to the field direction via a first-order +reorientation transition, with the transition field ($H_\textup{M}$) increasing +upon cooling the temperature.",1502.05139v1 +2015-03-09,High pressure floating zone growth and structural properties of ferrimagnetic quantum paraelectric BaFe$_{12}$O$_{19}$,"High quality single crystals of BaFe$_{12}$O$_{19}$ were grown using the +floating zone technique in flowing oxygen pressurized to 100 atm. Single +crystal neutron diffraction was used to determine the nuclear and magnetic +structure of BaFe$_{12}$O$_{19}$ at 4 K and 295 K. At both temperatures, there +exist local electric dipoles formed by the off-mirror-plane displacements of +magnetic Fe$^{3+}$ ions at the bipyramidal sites. The displacement at 4 K is +about half of that at room temperature. The temperature dependence of the +specific heat shows no anomaly associated with long range polar ordering in the +temperature range from 1.90-300 K. The inverse dielectric permittivity, +$1/\varepsilon$, along the c-axis shows a $T^2$ temperature dependence between +10 K and 20 K, with a significantly reduced temperature dependence displayed +below 10 K. Moreover, as the sample is cooled below 1.4 K there is an anomalous +sharp upturn in $1/\varepsilon$. These features resemble those of classic +quantum paraelectrics such as SrTiO$_3$. The presence of the upturn in +$1/\varepsilon$ indicates that BaFe$_{12}$O$_{19}$ is a critical quantum +paraelectric system with Fe$^{3+}$ ions involved in both magnetic and electric +dipole formation.",1503.02568v1 +2015-07-27,Ultrafast laser-induced changes of the magnetic anisotropy in a low-symmetry iron garnet film,"We explore a thermal mechanism of changing the anisotropy by femtosecond +laser pulses in dielectric ferrimagnetic garnets by taking a low symmetry +(YBiPrLu)3(FeGa)5O12 film grown on the (210)-oriented Gd3Ga5O12 substrate as a +model media. We demonstrate by means of spectral magneto-optical pump-probe +technique and phenomenological analysis, that the magnetization precession in +such a film is triggered by laser-induced changes of the growth-induced +magnetic anisotropy along with the well-known ultrafast inverse Faraday effect. +The change of magnetic anisotropy is mediated by the lattice heating induced by +laser pulses of arbitrary polarization on a picosecond time scale. We show that +the orientation of the external magnetic field with respect to the +magnetization easy plane noticeably affects the precession excited via the +anisotropy change. Importantly, the relative contributions from the ultrafast +inverse Faraday effect and the change of different growth-induced anisotropy +parameters can be controlled by varying the applied magnetic field strength and +direction. As a result, the amplitude and the initial phase of the excited +magnetization precession can be gradually tuned.",1507.07437v2 +2015-10-05,Absence of magnetic proximity effects in magnetoresistive Pt/CoFe2O4 hybrid interfaces,"Ultra-thin Pt films grown on insulating ferrimagnetic CoFe2O4 (111) epitaxial +films display a magnetoresistance upon rotating the magnetization of the +magnetic layer. We report here X-ray magnetic circular dichroism (XMCD) +recorded at Pt-L2,3 and Pt-M3 edges. The results indicate that the Pt magnetic +moment, if any, is below the detection limit (< 0.001 {\mu}$_B$/Pt), thus +strongly favoring the view that the presence of CoFe2O4 does not induce the +formation of magnetic moments in Pt. Therefore, the observed magnetoresistance +cannot be attributed to some sort of proximity-induced magnetic moments at Pt +ions and subsequent magnetic-field dependent scattering. It thus follows that +either bulk (spin Hall and Inverse spin Hall Effects) or interface (Rashba) +spin-orbit related effects dominate the observed magnetoresistance. +Furthermore, comparison of bulk magnetization and XMCD data at (Fe,Co)-L2,3 +edges suggests the presence of some spin disorder in the CoFe2O4 layer which +may be relevant for the observed anomalous non-saturating field-dependence of +spin Hall magnetoresistance.",1510.01080v4 +2015-10-06,Spin Hall magnetoresistance as a probe for surface magnetization in Pt/CoFe$_2$O$_4$ bilayers,"We study the spin Hall magnetoresistance (SMR) in Pt grown $\textit{in situ}$ +on CoFe$_2$O$_4$ (CFO) ferrimagnetic insulating (FMI) films. A careful analysis +of the angle-dependent and field-dependent longitudinal magnetoresistance +indicates that the SMR contains a contribution that does not follow the bulk +magnetization of CFO but it is a fingerprint of the complex magnetism at the +surface of the CFO layer, thus signaling SMR as a tool for mapping surface +magnetization. A systematic study of the SMR for different temperatures and CFO +thicknesses gives us information impossible to obtain with any standard +magnetometry technique. On one hand, surface magnetization behaves +independently of the CFO thickness and does not saturate up to high fields, +evidencing that the surface has its own anisotropy. On the other hand, +characteristic zero-field magnetization steps are not present at the surface +while they are relevant in the bulk, strongly suggesting that antiphase +boundaries are the responsible of such intriguing features. In addition, a +contribution from ordinary magnetoresistance of Pt is identified, which is only +distinguishable due to the low resistivity of the $\textit{in-situ}$ grown Pt.",1510.01449v2 +2015-10-07,Metallic nanolines ruled by grain boundaries in graphene: an ab initio study,"We have performed an ab initio investigation of the energetic stability, and +the electronic properties of transition metals (TMs = Mn, Fe, Co, and Ru) +adsorbed on graphene upon the presence of grain boundaries (GBs). Our results +reveal an energetic preference for the TMs lying along the GB sites (TM/GB). +Such an energetic preference has been strengthened by increasing the +concentration of the TM adatoms; giving rise to TM nanolines on graphene ruled +by GBs. Further diffusion barrier calculations for Fe adatoms support the +formation of those TM nanolines. We find that the energy barriers parallel to +the GBs are sligthly lower in comparision with those obtained for the defect +free graphene; whereas, perpendicularly to the GBs the Fe adatoms face higher +energy barriers. Fe and Co (Mn) nanolines are ferromagnetic (ferrimagnetic), in +contrast the magnetic state of Ru nanolines is sensitive to the Ru/GB +adsorption geometry. The electronic properties of those TM nanolines were +characterized through extensive electronic band structure calculations. The +formation of metallic nanolines is mediated by a strong hybridization between +the TM and the graphene ($\pi$) orbitals along the GB sites. Due to the net +magnetization of the TM nanolines, our band structure results indicate an +anisotropic (spin-polarized) electronic current for some TM/GB systems.",1510.02066v1 +2016-02-26,Multiferroic clusters: a new perspective for relaxor-type room-temperature multiferroics,"Multiferroics are promising for sensor and memory applications, but despite +all efforts invested in their research no single-phase material displaying both +ferroelectricity and large magnetization at room-temperature has hitherto been +reported. This situation has substantially been improved in the novel relaxor +ferroelectric single-phase , where polar nanoregions (PNR) transform into +static-PNR (SPNR) as evidenced by piezoresponse force microscopy (PFM) and +simultaneously enable congruent multiferroic clusters (MFC) to emerge from +inherent ferrimagnetic Bi(Fe,Co)O3 regions as verified by magnetic force +microscopy (MFM) and secondary ion mass spectrometry (SIMS). On these MFC, +exceptionally large direct and converse magnetoelectric coupling coefficients, +at room-temperature, were measured by PFM and MFM respectively. We expect the +non-ergodic relaxor properties which are governed by the Bi0.5K0.5TiO3 +component to play a vital role in the strong ME coupling, by providing an +electrically and mechanically flexible environment to MFC. This new class of +non-ergodic relaxor multiferroics bears great potential for applications. +Especially the prospect of a ME nanodot storage device seems appealing.",1602.08348v1 +2016-03-02,Effects of magnetic field and twin domains on magnetostructural phase mixture in Mn3O4: Raman scattering studies of untwinned crystals,"The ferrimagnetic spinel Mn3O4 exhibits large and anisotropic changes in +electronic and structural properties in response to an applied magnetic field. +These changes are thought to result from the field-dependent tuning---via +strong spin-lattice coupling---between two nearly degenerate magnetostructural +phases. Recent variable-magnetic-field studies of Mn3O4 have been performed on +melt-grown crystals, which can exhibit twin domains due to a Jahn-Teller +structural transition below the melting temperature. Because of the near +degeneracy of the magnetostructural phases, however, strain associated with the +twin domains likely affects the magnetic responses of Mn3O4. In this report, we +present a variable-magnetic-field Raman scattering study of untwinned Mn3O4 +crystals grown out of a flux below the Jahn-Teller structural transition. We +measure distinct q = 0 magnetic and vibrational excitation spectra for each +isolated magnetostructural phase of untwinned Mn3O4 crystals and determine the +symmetries of the observed excitations. We determine how the magnetostructural +phase mixture changes in response to magnetic fields applied in the magnetic +easy plane. Lastly, by comparing results on flux- and melt-grown Mn3O4 +crystals, we show that the intrinsic mixture of the two magnetostructural +phases is indeed strongly influenced by the presence of twin domains.",1603.00843v1 +2016-04-26,First principles studies of the Gilbert damping and exchange interactions for half-metallic Heuslers alloys,"Heusler alloys have been intensively studied due to the wide variety of +properties that they exhibit. One of these properties is of particular interest +for technological applications, i.e. the fact that some Heusler alloys are +half-metallic. In the following, a systematic study of the magnetic properties +of three different Heusler families $\textrm{Co}_2\textrm{Mn}\textrm{Z}$, +$\text{Co}_2\text{Fe}\text{Z}$ and $\textrm{Mn}_2\textrm{V}\textrm{Z}$ with +$\text{Z}=\left(\text{Al, Si, Ga, Ge}\right)$ is performed. A key aspect is the +determination of the Gilbert damping from first principles calculations, with +special focus on the role played by different approximations, the effect that +substitutional disorder and temperature effects. Heisenberg exchange +interactions and critical temperature for the alloys are also calculated as +well as magnon dispersion relations for representative systems, the +ferromagnetic $\textrm{Co}_2\textrm{Fe}\textrm{Si}$ and the ferrimagnetic +$\textrm{Mn}_2\textrm{V}\textrm{Al}$. Correlations effects beyond standard +density-functional theory are treated using both the local spin density +approximation including the Hubbard $U$ and the local spin density +approximation plus dynamical mean field theory approximation, which allows to +determine if dynamical self-energy corrections can remedy some of the +inconsistencies which were previously reported for these alloys.",1604.07552v1 +2016-04-29,Spin Seebeck effect through antiferromagnetic NiO,"We report temperature-dependent spin-Seebeck measurements on Pt/YIG bilayers +and Pt/NiO/YIG trilayers, where YIG (Yttrium iron garnet, Y$_3$Fe$_5$O$_{12}$) +is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. +The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG +bilayers, the temperature gradient applied to the YIG stimulates dynamic spin +injection into the Pt, which generates an inverse spin Hall voltage in the Pt. +The presence of a NiO layer dampens the spin injection exponentially with a +decay length of $2 \pm 0.6$ nm at 180 K. The decay length increases with +temperature and shows a maximum of $5.5 \pm 0.8$ nm at 360 K. The temperature +dependence of the amplitude of the spin-Seebeck signal without NiO shows a +broad maximum of $6.5 \pm 0.5$ $\mu$V/K at 20 K. In the presence of NiO, the +maximum shifts sharply to higher temperatures, likely correlated to the +increase in decay length. This implies that NiO is most transparent to magnon +propagation near the paramagnet-antiferromagnet transition. We do not see the +enhancement in spin current driven into Pt reported in other papers when 1-2 nm +NiO layers are sandwiched between Pt and YIG.",1604.08659v2 +2016-06-21,"Theoretical and Experimental Investigation on Structural, Electronic and Magnetic Properties of layered Mn5O8","We have investigated the crystal, electronic, and magnetic structure of Mn5O8 +by means of state of-the-art density functional theory calculations and neutron +powder diffraction (NPD) measurements. This compound stabilizes in the +monoclinic structure with space group C2/m where the Mn ions are in the +distorted octahedral and trigonal prismatic coordination with oxygen atoms. The +calculated structural parameters based on total energy calculations are found +to be in excellent agreement with low temperature NPD measurements when we +accounted correct magnetic structure and Coulomb correlation effect into the +computation. Bond strength analysis based on crystal orbital Hamiltonian +population between constituents indicating strong anisotropy in the bonding +behavior which results in layered nature of its crystal structure. Using fully +relativistic generalized-gradient approximation with Hubbard U (GGA+U) we found +that the magnetic ordering in Mn5O8 is A-type antiferromagnetic and the +direction of easy axis is [1 0 0] in agreement with susceptibility and NPD +measurements. However, the calculation without the inclusion of HubbardU leads +to ferrimagnetic half metal as ground state contradictory to experimental +findings, indicating the presence of strong Coulomb correlation effect in this +material. The GGA calculations without Coulomb correction effect itself is +sufficient to reproduce our experimentally observed magnetic moments in various +Mn sites.",1606.06603v1 +2016-07-15,Picosecond all-optical switching of magnetic tunnel junctions,"Control of magnetism without using magnetic fields enables large-scale +integration of spintronic devices for memory, computation and communication in +the beyond-CMOS era. Mechanisms including spin torque transfer, spin Hall +effect, and electric field or strain assisted switching have been implemented +to switch magnetization in various spintronic devices. Their operation speed, +however, is fundamentally limited by the spin precession time to be longer than +10-100 picoseconds. Overcoming such a speed constraint is critical for the +prospective development of spintronics. Here we report the demonstration of +picosecond all-optical switching of a magnetic tunnel junction (MTJ)- the +building block of spintronic logic and memory -only using single telecom-band, +infrared laser pulses. This first optically switchable MTJ uses ferrimagnetic +GdFeCo as the free layer, and its switching is directly readout by measuring +its tunneling magnetoresistance with a DR/R ratio of 0.6%. An instrument +limited switching repetition rate at MHz has been demonstrated, but the +fundamental limit should be higher than tens of GHz. This result represents an +important step toward integrated opto-spintronic devices that combines +spintronics and photonics technologies to enable ultrafast conversion between +fundamental information carriers of electron spins and photons.",1607.04615v1 +2016-10-08,Enhancement of Impedance by Chromium Substitution and Correlation with DC Resistivity in Cobalt Ferrite,"Chromium substituted cobalt ferrite with grain size less than the single +domain (approx. 70 nm) has been prepared by the sol-gel method. XRD analysis +reveals that the samples crystallize to cubic symmetry with spacegroup number +227. Two transition temperatures (TD (approx. 450 K) and TM (approx. 600 K) +have been observed from the impedance verses temperature measurement. TD +increases with the increase in frequency due to dipole response to the +frequency. TM is comparable with the para-ferrimagnetic transition temperature +of cobalt ferrite, which is independent of frequency. This result is well +supported by the temperature dependent DC conductivity measurement. The +modified Debye relaxation could be explained the impedance spectra of +CoFe2-xCrxO4. The grain and grain boundary effect on impedance spectroscopy has +been observed from Cole-Cole analysis. The ac conductivity follows Arrhenius +behavior at different frequencies. All the samples exhibit the negative +temperature coefficient of resistance behavior which reveals the semiconducting +behavior of the material. The Mott VRH model could explain the DC electrical +conductivity. Both ac impedance and DC resistivity are well co-related each +other to explain the electron transport properties in Cr substituted cobalt +ferrite. The electrical transport properties could be explained by the electron +hopping between different metal ions via oxygen in the material.",1610.02489v1 +2016-10-26,Doping of Ga in antiferromagnetic semiconductor alpha-Cr2O3oxide and its effects on modified magnetic and electronic properties,"The samples of Ga doped Cr2O3 oxide have been prepared using chemical +co-precipitation route. X-ray diffraction pattern and Raman spectra have +confirmed rhombohedral crystal structure with space group R3-C. Magnetic +measurement has indicated the dilution of antiferromagnetic (AFM) spin order in +Ga doped alpha-Cr2O3 system oxide, where the AFM transition temperature of bulk +alpha-Cr2O3 oxide at about 320 K has been suppressed and ferrimagnetic behavior +is observed from the analysis of the temperature dependence of magnetization +data below 350 K. Apart from Ga doping effect, the spin freezing (50 K-70 K) +and superparamagnetic behavior of the surface spins at lower temperatures, +typically below 50 K, have been exhibited due to nano-sized grains of the +samples. All the samples showed non-linear current-voltage (I-V) +characteristics. However, I-V characteristics of the Ga doped samples are +remarkably different from alpha-Cr2O3 sample. The I-V curves of Ga doped +samples have exhibited many unique electronic properties, e.g., bi-stable (low +resistance- LR and high resistance-HR) electronic states and negative +differential resistance (NDR). Optical absorption spectra revealed three +electronic transitions in the samples associated with band gap energy at about +2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively.",1610.08426v1 +2017-02-14,Magnetism of monomer MnO and heterodimer FePt@MnO nanoparticles,"We report about the magnetic properties of antiferromagnetic (AF) MnO +nanoparticles (NPs) with different sizes (6-19nm). Using a combination of +polarized neutron scattering and magnetometry we were able to resolve +previously observed peculiarities. Magnetometry, on the one hand, reveals a +peak in the zero field cooled (ZFC) magnetization curves at low temperatures +(~25K) but no feature around the N\'eel temperature at 118K. On the other hand, +polarized neutron scattering shows the expected behavior of the AF order +parameter vanishing around 118K. Moreover, hysteresis curves measured at +various temperatures reveal an exchange bias effect indicating a coupling of an +AF core to a ferromagnetic (FM)-like shell. ZFC data measured at various fields +exclude a purely superparamagnetic (SPM) scenario. We conclude that the +magnetic behavior of MnO particles can be explained by a superposition of +SPM-like thermal fluctuations of the AF-N\'eel vector inside the AF core and a +strong magnetic coupling to a ferrimagnetic Mn$_2$O$_3$ or Mn$_3$O$_4$ shell. +In addition, we have studied heterodimer ('Janus') particles, where a FM FePt +particle is attached to the AF MnO particle. Via the exchange bias effect, the +magnetic moment of the FePt subunit is stabilized by the MnO.",1702.04312v1 +2017-02-17,Origin of magnetic frustration in Bi$_3$Mn$_4$O$_{12}$(NO$_3$),"Bi$_3$Mn$_4$O$_{12}$(NO$_3$) (BMNO) is a honeycomb bilayers anti-ferromagnet, +not showing any ordering down to very low temperatures despite having a +relatively large Curie-Weiss temperature. Using ab initio density functional +theory, we extract an effective spin Hamiltonian for this compound. The +proposed spin Hamiltonian consists of anti-ferrimagnetic Heisenberg terms with +coupling constants ranging up to third intra-layer and fourth inter-layer +neighbors. Performing Monte Carlo simulation, we obtain the temperature +dependence of magnetic susceptibility and so the Curie-Weiss temperature and +find the coupling constants which best matches with the experimental value. We +discover that depending on the strength of the interlayer exchange couplings, +two collinear spin configurations compete with each other in this system. Both +states have in plane N{\'e}el character, however, at small interlayer coupling +spin directions in the two layers are antiparallel (N$_1$ state) and +discontinuously transform to parallel (N$_2$ state) by enlarging the interlayer +couplings at a first order transition point. Classical Monte Carlo simulation +and density matrix renormalization group calculations confirm that exchange +couplings obtained for BMNO are in such a way that put this material {at the +phase boundary of a first order phase transition}, where the trading between +these two collinear spin states prevents it from setting in a magnetically +ordered state.",1702.05255v2 +2017-03-02,Diversity of quantum ground states and quantum phase transitions of a spin-1/2 Heisenberg octahedral chain,"The spin-1/2 Heisenberg octahedral chain with regularly alternating monomeric +and square-plaquette sites is investigated using various analytical and +numerical methods: variational technique, localized-magnon approach, exact +diagonalization (ED) and density-matrix renormalization group (DMRG) method. +The model belongs to the class of flat-band systems and it has a rich +ground-state phase diagram including phases with spontaneously broken +translational symmetry. Moreover, it exhibits an anomalous low-temperature +thermodynamics close to continuous or discontinuous field-driven quantum phase +transitions between three quantum ferrimagnetic phases, tetramer-hexamer phase, +monomer-tetramer phase, localized-magnon phase and two different spin-liquid +phases. If the intra-plaquette coupling is at least twice as strong as the +monomer-plaquette coupling, the variational method furnishes a rigorous proof +of the monomer-tetramer ground state in a low-field region and the +localized-magnon approach provides an exact evidence of a single magnon trapped +at each square plaquette in a high-field region. In the rest of parameter space +we have numerically studied the ground-state phase diagram and magnetization +process using DMRG and ED methods. It is shown that the zero-temperature +magnetization curve may involve up to four intermediate plateaus at zero, +one-fifth, two-fifth and three-fifth of the saturation magnetization, while the +specific heat exhibits a striking low-temperature peak in a vicinity of +discontinuous quantum phase transitions.",1703.00715v2 +2017-03-31,Giant Ferrimagnetism and Polarization in a Mixed Metal Perovskite Metal-Organic Framework,"Perovskite metal-organic frameworks (MOFs) have recently emerged as potential +candidates for multiferroicity. However, the compounds synthesized so far +possess only weak ferromagnetism and low polarization. Additionally, the very +low magnetic transition temperatures ($T_c$) also pose a challenge to the +application of the materials. We have computationally designed a mixed metal +perovskite MOF -[C(NH2)3][(Cu0.5Mn0.5)(HCOO)3]- that is predicted to have +magnetization two orders of magnitude larger than its parent +([C(NH2)3][Cu(HCOO)3]), a significantly larger polarization (9.9 {\mu}C/cm2), +and an enhanced $T_c$ of up to 56 K, unprecedented in perovskite MOFs. A +detailed study of the magnetic interactions revealed a novel mechanism leading +to the large moments as well as the increase in the $T_c$. Mixing a +non-Jahn-Teller ion (Mn$^{2+}$) into a Jahn-Teller host (Cu$^{2+}$) leads to +competing lattice distortions which are possibly responsible for the enhanced +polarization. The MOF is thermodynamically stable as evidenced by the computed +enthalpy of formation, and can likely be synthesized. Our work represents a +first step towards rational design of multiferroic perovskite MOFs through the +largely unexlpored mixed metal approach.",1703.10853v3 +2017-08-13,Quantum percolation phase transition and magneto-electric dipole glass in hexagonal ferrites,"Hexagonal ferrites do not only have enormous commercial impact ({\pounds}2 +billion/year in sales) due to applications that include ultra-high density +memories, credit card stripes, magnetic bar codes, small motors and low-loss +microwave devices, they also have fascinating magnetic and ferroelectric +quantum properties at low temperatures. Here we report the results of tuning +the magnetic ordering temperature in PbFe$_{12-x}$Ga$_x$O$_{19}$ to zero by +chemical substitution $x$. The phase transition boundary is found to vary as +$T_N \sim (1-x/x_c)^{2/3}$ with $x_c$ very close to the calculated spin +percolation threshold which we determine by Monte Carlo simulations, indicating +that the zero-temperature phase transition is geometrically driven. We find +that this produces a form of compositionally-tuned, insulating, ferrimagnetic +quantum criticality. Close to the zero temperature phase transition we observe +the emergence of an electric-dipole glass induced by magneto-electric coupling. +The strong frequency behaviour of the glass freezing temperature $T_m$ has a +Vogel-Fulcher dependence with $T_m$ finite, or suppressed below zero in the +zero frequency limit, depending on composition $x$. These quantum-mechanical +properties, along with the multiplicity of low-lying modes near to the +zero-temperature phase transition, are likely to greatly extend applications of +hexaferrites into the realm of quantum and cryogenic technologies.",1708.03945v1 +2018-02-13,Quadratic magnetooptic spectroscopy setup based on photoelastic light modulation,"In most of the cases the magnetooptic Kerr effect (MOKE) techniques rely +solely on the effects linear in magnetization ($\bm{M}$). Nevertheless, a +higher-order term being proportional to $\bm{M}$$^2$ and called quadratic MOKE +(QMOKE) can additionally contribute to experimental data. Handling and +understanding the underlying origin of QMOKE could be the key to utilize this +effect for investigation of antiferromagnetic materials in the future due to +their vanishing first order MOKE contribution. Also, better understanding of +QMOKE and hence better understanding of magnetooptic (MO) effects in general is +very valuable, as the MO effect is very much employed in research of ferro- and +ferrimagnetic materials. Therefore, we present our QMOKE and longitudinal MOKE +spectroscopy setup with a spectral range of 0.8--5.5\,eV. The setup is based on +light modulation through a photoelastic modulator and detection of +second-harmonic intensity by a lock-in amplifier. To measure the Kerr +ellipticity an achromatic compensator is used within the setup, whereas without +it Kerr rotation is measured. The separation of QMOKE spectra directly from the +measured data is based on measurements with multiple magnetization directions. +So far the QMOKE separation algorithm is developed and tested for but not +limited to cubic (001) oriented samples. The QMOKE spectra yielded by our setup +arise from two quadratic MO parameters $G_s$ and $2G_{44}$, being elements of +quadratic MO tensor $\bm{G}$, which describe perturbation of the permittivity +tensor in the second order in $\bm{M}$.",1802.04717v1 +2018-02-20,Magnon-photon coupling in a non-collinear magnetic insulator Cu$_2$OSeO$_3$,"Anticrossing behavior between magnons in a non-collinear chiral magnet +Cu$_2$OSeO$_3$ and a two-mode X-band microwave resonator was studied in the +temperature range 5-100K. In the field-induced ferrimagnetic phase, we observed +a strong coupling regime between magnons and two microwave cavity modes with a +cooperativity reaching 3600. In the conical phase, cavity modes are +dispersively coupled to a fundamental helimagnon mode, and we demonstrate that +the magnetic phase diagram of Cu$_2$OSeO$_3$ can be reconstructed from the +measurements of the cavity resonance frequency. In the helical phase, a +hybridized state of a higher-order helimagnon mode and a cavity mode - a +helimagnon polariton - was found. Our results reveal a new class of magnetic +systems where strong coupling of microwave photons to non-trivial spin textures +can be observed.",1802.07113v3 +2018-02-20,Ultrafast magnetization dynamics in pure and doped Heusler and inverse Heusler alloys,"By using a multiscale approach based on first-principles density functional +theory combined with atomistic spin dynamics, we investigate the electronic +structure and magnetization dynamics of an inverse Heusler and a Heusler +compound and their alloys, i. e. Mn$_{2-x}Z_x$CoAl and Mn$_{2-x}Z_x$VAl, where +$Z$ = Mo, W, Os and Ru, respectively. A signature of the ferrimagnetic ordering +of Mn$_{2}$CoAl and Mn$_{2}$VAl Heusler alloys is reflected in the calculated +Heisenberg exchange constants. They decay very rapidly with the interatomic +distance and have short range, which is a consequence of the existence of the +finite gap in the minority spin band. The calculated Gilbert damping parameter +of both Mn$_2$CoAl and Mn$_2$VAl is high compared to other half-metals, but +interestingly in the particular case of the inverse Mn$_{2}$CoAl alloys and due +to the spin-gapless semiconducting property, the damping parameters decrease +with the doping concentration in clear contradiction to the general trend. +Atomistic spin dynamics simulations predict ultrafast magnetisation switching +in Mn$_{2}$CoAl and Mn$_{2}$VAl under the influence of an external magnetic +field, starting from a threshold field of $2\text{T}$. Our overall finding +extends with Heusler and inverse Heusler alloys, the class of materials that +exhibits laser induced magnetic switching.",1802.07195v1 +2018-04-04,Heterobimetallic Dy-Cu coordination compound as a classical-quantum ferrimagnetic chain of regularly alternating Ising and Heisenberg spins,"A classical-quantum chain composed of regularly alternating Ising and +Heisenberg spins is rigorously solved by considering two distinct local +anisotropy axes of the Ising spins. The ground-state phase diagram and +magnetization curves are examined depending on a spatial orientation of the +applied magnetic field. The phase diagram totally consists of four distinct +phases and a few macroscopically degenerate points, where an outstanding +coexistence of perfect order and complete disorder occurs within the so-called +'half-fire, half-ice' state. The zero-temperature magnetization curves +generally exhibit a smooth dependence on a magnetic field owing to a canting +angle between two coplanar anisotropy axes of the Ising spins, which enforces a +misalignment of the magnetization vector from a direction of the applied +magnetic field. It is evidenced that the investigated spin-chain model +reproduces magnetic features of the heterobimetallic coordination compound +Dy(NO)$_{3}$(DMSO)$_{2}$Cu(opba)(DMSO)$_{2}$ (DMSO=dimethylsulfoxide, +opba=orthophenylenebisoxamato). The high-field magnetization data reported for +the powder sample of this polymeric coordination compound generally display a +substantial smoothing on account of a powder averaging.",1804.01551v2 +2018-04-06,Effect of Substrate Temperature on Structural and Magnetic Properties of c-axis Ori-ented Spinel Ferrite Ni0.65Zn0.35Fe2O4 (NZFO) Thin Films,"Varying the substrate temperature changes structural and magnetic properties +of spinel ferrite NZFO thin films. XRD of films grown at different temperature +display only 004 reflections, without any secondary peaks, showing growth +orientation along the c axis. We find an increase in crystalline quality of +these thin films with the rise of substrate temperature. The surface topography +of the thin films grown on various growth temperatures conditions reveal that +these films are smooth with low roughness, however the thin films grown at 800 +C exhibit lowest average and rms roughness among all thin films. We find iron +and nickel to be more oxidized i,e greater Fe and Ni content in films grown and +annealed at 700 C and 800 C, compared to those grown at lower temperatures. The +magnetic moment is observed to increase with an increase of substrate +temperature and all thin films possess high saturation magnetization and low +coercive field at room temperature. Films grown at 800 C exhibit a +ferrimagnetic paramagnetic phase transition well above room temperature. The +observed large magnetizations with soft magnetic behavior in NZFO thin films +above room temperature suggest potential application in memory, spintronics, +and multifunctional devices.",1804.02458v2 +2018-11-10,Magnetic Order and Lattice Instabilities in Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$ Heusler based Magnetic Shape-Memory Alloys,"The magnetic correlations in the austenite phase and the consequent +martensitic transition in inverse magnetocaloric alloys, +Ni$_{2}$Mn$_{1+x}$Sn$_{1-x}$, have been a matter of debate for decades. We +conclusively establish using {\it ab initio} phonon calculations that the spin +alignment of excess Mn at the Sn site (Mn$_{Sn}$) with the existing Mn in the +unit cell in the high temperature cubic phase of Ni-Mn-Sn alloy is +ferromagnetic (FM), and not ferrimagnetic (FI), resolving a long lasting +controversy. Using first principles density functional perturbation theory +(DFPT), we observe an instability of the TA$_{2}$ mode along the $\Gamma$-M +direction in the FM phase, very similar to that observed in the prototypical +ferromagnetic shape memory alloy (FSMA) Ni$_{2}$MnGa. This specific instability +is not observed in the FI phase. Further finite temperature first principles +lattice dynamics calculations reveal that at 300 K the FM phase becomes +mechanically stable, while the FI phase continue to remain unstable providing +credence to the fact that the high-temperature phase has FM order. These +results will be primordial to understand the magneto-structural properties of +this class of compounds.",1811.04221v1 +2018-11-19,A magnetocaloric study of the magnetostructural transitions in NiCr$_2$O$_4$,"The spinel NiCr$_2$O$_4$ is known to show a ferrimagnetic transition at $T_c += 70$~K, and magneto-structural transitions at $T_s = 30$~K and $T_o = 20$~K\@. +We present a detailed magnetic and magnetocaloric effect (MCE $= -\Delta +S_{M}(T)$) study across these transitions. The $-\Delta S_{M}(T)$ shows a +positive anomaly at $T_c$, $T_s$, and $T_o$. In addition to these anomalies, we +report a new unreported feature at $T \approx 8.5$~K where $-\Delta S_{M}(T)$ +shows a negative anomaly or the inverse MCE. An Arrot plot of the isothermal +magnetization data reveals important information about the nature of the +possible phases revealed in $-\Delta S_{M}(T)$. We have also made a scaling +analysis of the $-\Delta S_{M}(T)$ data around these transitions. This analysis +suggests that the transition at $T_c$ is a second-order Mean field like +transition, the transition at $T_s$ is not second order and is non-mean field +like, while the new transition at $T = 8.5$~K is non-mean field like but is +second order in nature. Our study demonstrates that magnetocaloric effect is +sensitive to magneto-structural changes in materials and can be used for the +identification of new phases and transitions.",1811.07836v1 +2019-05-09,Spin-Hall Topological Hall Effect in Highly Tunable Pt/Ferrimagnetic-Insulator Bilayers,"Electrical detection of topological magnetic textures such as skyrmions is +currently limited to conducting materials. While magnetic insulators offer key +advantages for skyrmion technologies with high speed and low loss, they have +not yet been explored electrically. Here, we report a prominent topological +Hall effect in Pt/Tm$_3$Fe$_5$O$_{12}$ bilayers, where the pristine +Tm$_3$Fe$_5$O$_{12}$ epitaxial films down to 1.25 unit cell thickness allow for +tuning of topological Hall stability over a broad range from 200 to 465 K +through atomic-scale thickness control. Although Tm$_3$Fe$_5$O$_{12}$ is +insulating, we demonstrate the detection of topological magnetic textures +through a novel phenomenon: 'spin-Hall topological Hall effect' (SH-THE), where +the interfacial spin-orbit torques allow spin-Hall-effect generated spins in Pt +to experience the unique topology of the underlying skyrmions in +Tm$_3$Fe$_5$O$_{12}$. This novel electrical detection phenomenon paves a new +path for utilizing a large family of magnetic insulators in future skyrmion +technologies.",1905.03650v1 +2019-05-10,Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy,"The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for +spin-gapless semiconductors (SGSs). However, to date, there have been no +experimental attempts at fabricating a junction device. This paper reports a +fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with +CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction +measurements show that the (001) CoFeCrAl electrode films with atomically flat +surfaces have a $B2$-ordered phase. The saturation magnetization is 380 +emu/cm$^3$, almost the same as the value given by the Slater--Pauling--like +rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87% +and 165%, respectively. Cross-sectional electron diffraction analysis shows +that the MTJs have MgO interfaces with fewer dislocations. The temperature- and +bias-voltage-dependence of the transport measurements indicates magnon-induced +inelastic electron tunneling overlapping with the coherent electron tunneling. +X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic +arrangement of the Co and Fe magnetic moments of $B2$-ordered CoFeCrAl, in +contrast to the ferrimagnetic arrangement predicted for the $Y$-ordered state +possessing SGS characteristics. Ab-initio calculations taking account of the +Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect +of the Cr-Fe swap disorder on the ability for electronic states to allow +coherent electron tunneling is discussed.",1905.04070v1 +2020-07-08,"Probing low temperature non-equilibrium magnetic state in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments","The low temperature lattice structure and magnetic properties of +Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite have been investigated using experimental +results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac +susceptibility, neutron diffraction and neutron depolarization techniques. The +samples have been prepared by chemical co-precipitation of the Fe and Co +nitrates solution in high alkaline medium and subsequent thermal annealing of +the precipitates in the temperature range of 200- 900 $^\circ$C. Rietveld +refinement of the SXRD patterns at room temperature indicated two-phased cubic +spinel structure for the samples annealed at temperatures 200-600 $^\circ$C. +The samples annealed at temperatures 700 $^\circ$C and 900 $^\circ$C (CF90) +have been best fitted with single phased lattice structure. Refinement of the +neutron diffraction patterns in the temperature range of 5-300 K confirmed +antiferromagnetic (AFM) Co$_3$O$_4$ and ferrimagnetic (FIM) +Co$_{2.75}$Fe$_{0.25}$O$_4$ phases for the sample annealed at 600 $^\circ$C and +single FIM phase of Co$_{2.75}$Fe$_{0.25}$O$_4$ for the CF90 sample. Magnetic +measurements have shown a non-equilibrium magnetic structure, consisting of the +high temperature FIM phase and low temperature AFM phase. The magnetic phases +are sensitive to magnetic fields, where high temperature phase is suppressed at +higher magnetic fields by enhancing the low temperature AFM phase, irrespective +of annealing temperature of the samples.",2007.03906v1 +2020-07-24,"Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices","Iridium is a very promising material for spintronic applications due to its +interesting magnetic properties such as large RKKY exchange coupling as well as +its large spin-orbit coupling value. Ir is for instance used as a spacer layer +for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, +only a few studies of the spintronic parameters of this material have been +reported. In this paper, we present inverse spin Hall effect - spin pumping +ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the +values of the effective spin Hall angle, the spin diffusion length within +iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to +have reliable results, we performed the same experiments on CoFeB/Pt bilayers, +which behavior is well known due to numerous reported studies. Our experimental +results show that the spin diffusion length within iridium is 1.3 nm for +resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow +\downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle +of iridium has the same sign than the one of platinum and is evaluated at 26% +of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt +and 2% for Ir. These relevant parameters shall be useful to consider Ir in new +concepts and devices combining spin-orbit torque and spin-transfer torque.",2007.12413v1 +2020-07-25,Direct Visualization of Irreducible Ferrielectricity in Crystals,"In solids, charge polarity can one-to-one correspond to spin polarity +phenomenologically, e.g. ferroelectricity/ferromagnetism, +antiferroelectricity/antiferromagnetism, and even +dipole-vortex/magnetic-vortex, but ferrielectricity/ferrimagnetism kept telling +a disparate story in microscopic level. Since the definition of a charge dipole +involves more than one ion, there may be multiple choices for a dipole unit, +which makes most ferrielectric orders equivalent to ferroelectric ones, i.e. +this ferrielectricity is not necessary to be a real independent branch of +polarity. In this work, by using the spherical aberration-corrected scanning +transmission electron microscope, we visualize a nontrivial ferrielectric +structural evolution in BaFe2Se3, in which the development of two polar +sub-lattices is out-of-sync, for which we term it as irreducible +ferrielectricity. Such irreducible ferrielectricity leads to a non-monotonic +behavior for the temperature-dependent polarization, and even a compensation +point in the ordered state. Our finding unambiguously distinguishes +ferrielectrics from ferroelectrics in solids.",2007.12828v1 +2020-07-30,Coexistence of distinct skyrmion phases observed in hybrid ferromagnetic/ferrimagnetic multilayers,"Materials hosting magnetic skyrmions at room temperature could enable new +computing architectures as well as compact and energetically efficient magnetic +storage such as racetrack memories. In a racetrack device, information is coded +by the presence/absence of magnetic skyrmions forming a chain that is moved +through the device. The skyrmion Hall effect that would eventually lead to an +annihilation of the skyrmions at the edges of the racetrack can be suppressed +for example by anti-ferromagnetically-coupled skyrmions. However, avoiding +modifications of the inter-skyrmion distances in the racetrack remains +challenging. As a solution to this issue, a chain of bits could also be encoded +by two different solitons such as a skyrmion and a chiral bobber. The major +limitation of this approach is that it has solely been realized in B20-type +single crystalline material systems that support skyrmions only at low +temperatures, thus hindering the efficacy for future applications. Here we +demonstrate that a hybrid ferro/ferri/ferromagnetic multilayer system can host +two distinct skyrmion phases at room temperature. By matching quantitative +magnetic force microscopy data with micromagnetic simulations, we reveal that +the two phases represent tubular skyrmions and partial skyrmions (similar to +skyrmion bobbers). Furthermore, the tubular skyrmion can be converted into a +partial skyrmion. Such multilayer systems may thus serve as a platform for +designing skyrmion memory applications using distinct types of skyrmions and +potentially for storing information using the vertical dimension in a thin film +device.",2007.15427v1 +2013-08-17,Thickness and power dependence of the spin-pumping effect in Y3Fe5O12/Pt heterostructures measured by the inverse spin Hall effect,"The dependence of the spin-pumping effect on the yttrium iron garnet +(Y3Fe5O12, YIG) thickness detected by the inverse spin Hall effect (ISHE) has +been investigated quantitatively. Due to the spin-pumping effect driven by the +magnetization precession in the ferrimagnetic insulator YIG film a +spin-polarized electron current is injected into the Pt layer. This spin +current is transformed into electrical charge current by means of the ISHE. An +increase of the ISHE-voltage with increasing film thickness is observed and +compared to the theoretically expected behavior. The effective damping +parameter of the YIG/Pt samples is found to be enhanced with decreasing YIG +film thickness. The investigated samples exhibit a spin mixing conductance of +g=(7.43 \pm 0.36) \times 10^{18} m^{-2} and a spin Hall angle of theta_{ISHE} = +0.009 \pm 0.0008. Furthermore, the influence of nonlinear effects on the +generated voltage and on the Gilbert damping parameter at high excitation +powers are revealed. It is shown that for small YIG film thicknesses a +broadening of the linewidth due to nonlinear effects at high excitation powers +is suppressed because of a lack of nonlinear multi-magnon scattering channels. +We have found that the variation of the spin-pumping efficiency for thick YIG +samples exhibiting pronounced nonlinear effects is much smaller than the +nonlinear enhancement of the damping.",1308.3787v1 +2013-08-25,Enhanced ferromagnetic moment in Co-doped BiFeO3 thin films studied by soft X-ray circular dichroism,"BiFeO$_3$ (BFO) shows both ferroelectricity and magnetic ordering at room +temperature but its ferromagnetic component, which is due to spin canting, is +negligible. Substitution of transition-metal atoms such as Co for Fe is known +to enhance the ferromagnetic component in BFO. In order to reveal the origin of +such magnetization enhancement, we performed soft x-ray absorption spectroscopy +(XAS) and soft x-ray magnetic circular dichroism (XMCD) studies of +BiFe$_{1-x}$Co$_x$O$_3$ ({\it x} = 0 to 0.30) (BFCO) thin films grown on +LaAlO$_3$(001) substrates. The XAS results indicated that the Fe and Co ions +are in the Fe$^{3+}$ and Co$^{3+}$ states. The XMCD results showed that the Fe +ions show ferromagnetism while the Co ions are antiferromagnetic at room +temperature. The XAS and XMCD measurements also revealed that part of the +Fe$^{3+}$ ions are tetrahedrally co-ordinated by oxygen ions but that the XMCD +signals of the octahedrally coordinated Fe$^{3+}$ ions increase with Co +content. The results suggest that an impurity phase such as the ferrimagnetic +$\gamma$-Fe$_2$O$_3$ which exists at low Co concentration decreases with +increasing Co concentration and that the ferromagnetic component of the +Fe$^{3+}$ ion in the octrahedral crystal fields increases with Co +concentration, probably reflecting the increased canting of the Fe$^{3+}$ ions.",1308.5672v1 +2014-03-12,The quantum origins of skyrmions and half-skyrmions in Cu2OSeO3,"The Skyrme-particle, the $skyrmion$, was introduced over half a century ago +and used to construct field theories for dense nuclear matter. But with +skyrmions being mathematical objects - special types of topological solitons - +they can emerge in much broader contexts. Recently skyrmions were observed in +helimagnets, forming nanoscale spin-textures that hold promise as information +carriers. Extending over length-scales much larger than the inter-atomic +spacing, these skyrmions behave as large, classical objects, yet deep inside +they are of quantum origin. Penetrating into their microscopic roots requires a +multi-scale approach, spanning the full quantum to classical domain. By +exploiting a natural separation of exchange energy scales, we achieve this for +the first time in the skyrmionic Mott insulator Cu$_2$OSeO$_3$. Atomistic ab +initio calculations reveal that its magnetic building blocks are strongly +fluctuating Cu$_4$ tetrahedra. These spawn a continuum theory with a skyrmionic +texture that agrees well with reported experiments. It also brings to light a +decay of skyrmions into half-skyrmions in a specific temperature and magnetic +field range. The theoretical multiscale approach explains the strong +renormalization of the local moments and predicts further fingerprints of the +quantum origin of magnetic skyrmions that can be observed in Cu$_2$OSeO$_3$, +like weakly dispersive high-energy excitations associated with the Cu$_4$ +tetrahedra, a weak antiferromagnetic modulation of the primary ferrimagnetic +order, and a fractionalized skyrmion phase.",1403.2921v1 +2016-11-28,Synthesis of low-moment CrVTiAl: a potential room temperature spin filter,"The efficient production of spin-polarized currents at room temperature is +fundamental to the advancement of spintronics. Spin-filter materials --- +semiconductors with unequal band gaps for each spin channel --- can generate +spin-polarized current without the need for spin-polarized contacts. In +addition, a spin-filter material with zero magnetic moment would have the +advantage of not producing strong fringing fields that would interfere with +neighboring electronic components and limit the volume density of devices. The +quaternary Heusler compound CrVTiAl has been predicted to be a zero-moment +spin-filter material with a Curie temperature in excess of 1000 K. In this +work, CrVTiAl has been synthesized with a lattice constant of $a = 6.15 \AA$. +Magnetization measurements reveal an exceptionally low moment of $\mu = 2.3 +\times 10^{-3} \mu_B/f.u.$ at a field of $\mu_0 H = 2 T$, that is independent +of temperature between T = 10 K and 400 K, consistent with the predicted +zero-moment ferrimagnetism. Transport measurements reveal a combination of +metallic and semiconducting components to the resistivity. Combining a +zero-moment spin-filter material with nonmagnetic electrodes would lead to an +essentially nonmagnetic spin injector. These results suggest that CrVTiAl is a +promising candidate for further research in the field of spintronics.",1611.09307v3 +2017-04-20,Orbital and spin ordering physics of the Mn$_3$O$_4$ spinel,"Motivated by recent experiments, we present a comprehensive theoretical study +of the geometrically frustrated strongly correlated magnetic insulator +Mn$_3$O$_4$ spinel oxide based on a microscopic Hamiltonian involving lattice, +spin and orbital degrees of freedom. Possessing the physics of degenerate e$_g$ +orbitals, this system shows a strong Jahn-Teller effect at high temperatures. +Further, careful attention is paid to the special nature of the superexchange +physics arising from the 90$^o$ Mn-O-Mn bonding angle. The Jahn-Teller and +superexchange-based orbital-spin Hamiltonians are then analysed in order to +track the dynamics of orbital and spin ordering. We find that a +high-temperature structural transition results in orbital ordering whose nature +is mixed with respect to the two originally degenerate $e_{g}$ orbitals. This +ordering of orbitals is shown to relieve the intrinsic geometric frustration of +the spins on the spinel lattice, leading to ferrimagnetic Yafet-Kittel ordering +at low-temperatures. Finally, we develop a model for a magnetoelastic coupling +in Mn$_3$O$_4$, enabling a systematic understanding of the experimentally +observed complexity in the low-temperature structural and magnetic +phenomenology of this spinel. Our analysis predicts that a quantum +fluctuation-driven orbital-spin liquid phase may be stabilised at low +temperatures upon the application of pressure.",1704.06026v1 +2018-05-03,Spin Canting and Orbital Order in Spinel Vanadate Thin Films,"We report on the epitaxial film growth and characterization of CoV$_2$O$_4$, +a near-itinerant spinel vanadate, grown on (001) SrTiO$_3$. The symmetry +lowering of the unit cell from cubic in the bulk to orthorhombic in the films +results in dramatic differences in the magnetic anisotropy compared to bulk, as +determined from structural and magnetic characterization. Bulk cubic +CoV$_2$O$_4$ has been found to defy predictions by showing orbital degeneracy +seemingly lasting to very low temperatures, with only small anomalies in +magnetization and neutron experiments signaling a possible spin/orbital glass +transition at T = 90 K. In epitaxial thin films presented in this paper, +structurally tuning the CoV$_2$O$_4$ away from cubic symmetry leads to a +completely different low temperature non-collinear ground state. Via +magnetization and neutron scattering measurements we show that the 90 K +transition is associated with a major spin reorientation away from the +ferrimagnetic easy axis [001] to the [110] direction. Furthermore, the V-spins +cant away from this direction with extracted perpendicular moments providing +evidence of a larger canting angle compared to bulk. This result indicates that +compressive strain pushes the system deeper into the insulating state, i.e., +away from the localized - itinerant crossover regime.",1805.01520v1 +2018-05-24,Antiferromagnetically assisted electron-phonon coupling and spin-lattice interaction in Fe-based superconductors,"We present a theoretical ab-initio approach that allows us to explicitly +calculate the superconducting transition temperatures (Tc) of the iron-based +superconductors of LaFeAsO1-xFx, SmFeAsO1-xFx, NdFeAsO1-xFx, Ba1-xKxFe2As2, +FeSe and LiFeAs that fit perfectly with the experiments. We consider recent +evidence that electron-phonon coupling may have been underestimated previously, +and a prediction that antiferromagnetism can greatly enhance electron-phonon +coupling through localized iron d orbitals. We then include the contribution of +these localized orbitals in a McMillan formalism. In addition, we take into +account the spin-lattice interaction between the spin-polarized electrons at +the Fermi surface and the iron orbitals in combination with a modified exchange +Hamiltonian involving a ferrimagnetic coupling between Fe and As. With this +approach we can accurately calculate the Tc of FeSe (11 family), LiFeAs (111 +family), LaFeAsO0.9F0.1 (1111 family) and BaFe2As2 (122 family) as a function +of pressure. In addition, we also obtain the correct doping dependence of Tc of +LaFeAsO0.9F0.1 (1111 family) and BaFe2As2 (122 family).",1805.09754v5 +2013-09-09,FeCr$_2$S$_4$ in magnetic fields: possible evidence for a multiferroic ground state,"We report on neutron diffraction, thermal expansion, magnetostriction, +dielectric, and specific heat measurements on polycrystalline FeCr2S4 in +external magnetic fields. The ferrimagnetic ordering temperatures +$T_{\mathrm{C}}\approx 170$ K and the transition at $T_{\mathrm{OO}}\approx 10$ +K, which has been associated with orbital ordering, are only weakly shifted in +magnetic fields up to 9 T. The cubic lattice parameter is found to decrease +when entering the state below $T_{\mathrm{OO}}$. The magnetic moments of the +Cr- and Fe-ions are reduced from the spin-only values throughout the +magnetically ordered regime, but approach the spin-only values for fields +$>$5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments +indicate a contraction of the sample below about 60 K. Below $T_{\mathrm{OO}}$ +this contraction is followed by a moderate expansion of the sample for fields +larger than $\sim$4.5 T. The transition at $T_{\mathrm{OO}}$ is accompanied by +an anomaly in the dielectric constant. The dielectric constant depends on both +the strength and orientation of the external magnetic field with respect to the +applied electric field for $T