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2005-05-11 | Above-room-temperature ferromagnetism in half-metallic Heusler compounds NiCrP, NiCrSe, NiCrTe and NiVAs: A first-principles study | We study the interatomic exchange interactions and Curie temperatures in
half-metallic semi Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study
is performed within the framework of density functional theory. The calculation
of exchange parameters is based on the frozen-magnon approach. It is shown that
the exchange interactions in NiCrZ vary strongly depending on the Z
constituent. The Curie temperature, Tc, is calculated within the mean field and
random phase approximations. The difference between two estimations is related
to the properties of the exchange interactions. The predicted Curie
temperatures of all four systems are considerably higher than room temperature.
The relation between the half-metallicity and the value of the Curie
temperature is discussed. The combination of a high spin-polarization of charge
carriers and a high Curie temperature makes these Heusler alloys interesting
candidates for spintronics applications. | 0505299v1 |
2006-11-17 | Electronic structure of half-metallic magnets | We have analyzed the electronic structure of half-metallic magnets based on
first principles electronic structure calculations of a series of semi-Heusler
alloys. The characteristic feature of the electronic structure of semi-Heusler
systems is a d-d gap in the density of states lying at/close to the Fermi level
depending on the number of valence electrons. We have employed various
indicators of chemical bonding to understand the origin of the gap in these
systems, which is crucial for their half-metallic property. The density of
states of other half-metallic magnets also supports a gap and it is a generic
feature of these systems. We have discussed in some details the origin of
magnetism, in particular, how the presence of the gap is crucial to stabilize
half-metallic ferro and ferri magnetism in these systems. Finally, we have
studied the role of magnetic impurities in semiconducting semi-Heusler systems.
We show with the aid of model supercell calculations that these systems are not
only ferromagnetic but also half-metallic with possibly high Curie temperature. | 0611476v1 |
2013-04-12 | Crossover of magnetoresistance in the zerogap half-metallic Heusler alloy Fe2CoSi | This work reports on the band structure and magneto-transport investigations
of the inverse Heusler compound Fe2CoSi. The first-principles calculations
reveal that Fe2CoSi has a very peculiar band structure with a conducting
property in the majority spin channel and a nearly zero bandgap in the minority
spin channel. The synthesized Fe2CoSi sample shows a high-ordered inverse
Heusler structure with a magnetic moment of 4.88 {\mu}B at 5 K and a high Curie
temperature of 1038 K. With increasing temperature, a crossover from positive
to negative magnetoresistance (MR) is observed. Complemented with the Hall
effect measurements, we suggest the intriguing crossover of MR can be ascribed
to the dominant spin carriers changing from the gapless minority spin channel
to the majority spin channel at Fermi level. | 1304.3517v1 |
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 |
2013-09-24 | Electronic structure and magnetism of new scandium-based full Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn) | First principles FPLAPWcalculations were performed in the framework of
Density Functional Theory (DFT), to study the electronic structures and
magnetic properties for the new full-Heusler compounds: Sc2CoZ (Z=Si, Ge, Sn).
The investigated materials are stable against decomposition, in ferromagnetic
configuration and crystallize in the inverse Heusler structures. The
half-metallic properties as function of the variation of unit cell volumes are
analysed regarding the fourth main group constituent elements. The electronic
structure calculations for Sc2CoSi and Sc2CoSn show half-metallic characters,
with indirect band gaps of 0.544 eV and 0.408 eV at optimized lattice
parameters of 6.28 A and 6.62 A, respectively. For Sc2CoGe compound, the Fermi
energy is not pinned inside the energy band gap from minority density of
states, neither for unit cell contraction or for enlargement. The calculated
total magnetic moments are 1muB/f.u., for all compounds, in agreement with
Slater-Pauling rule. | 1309.6256v3 |
2018-10-11 | Unconventional transport behavior in the Quaternary Heusler compounds CoFeTiSn and CoFeVGa | We report here the electrical transport and magnetic properties of the newly
synthesized quaternary Heusler compound CoFeTiSn and CoFeVGa. We observe a
striking change in the electronic transport properties of CoFeTiSn as the
system undergoes the paramagnetic to ferromagnetic transition. While the sample
shows an activated semiconducting behaviour in the paramagnetic phase, it turns
abruptly to a metallic phase with the onset of ferromagnetic transition. We
have compared the system with other Hesuler compounds showing similar anomaly
in transport, and it appears that CoFeTiSn has much similarities with the
Fe$_2$VAl compound having pseudogap in the paramagnetic phase. In sharp
contrast, CoFeVGa shows a predominantly semiconducting behaviour down to 90 K,
below which it shows a window of metallic region. Both the compositions show
negative Seebeck coefficient varying linearly with temperature. The value of
the Seebeck coefficient of CoFeTiSn is comparable to that of many Heusler
alloys identified as potential thermoelectric materials. | 1810.04865v1 |
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 |
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 |
2001-03-23 | Premartensitic Transition in Ni2+xMn1-xGa Heusler Alloys | The temperature dependencies of the resistivity and magnetization of a series
of Ni2+XMn1-XGa (X = 0 - 0.09) alloys were investigated. Along with the
anomalies associated with ferromagnetic and martensitic transitions,
well-defined anomalies were observed at the temperature of premartensitic
transformation. The premartensitic phase existing in a temperature range 200 -
260 K in the stoichiometric Ni2MnGa is suppressed by the martensitic phase with
increasing Ni content and vanishes in Ni2.09Mn0.91Ga composition. | 0103483v1 |
2002-02-27 | Electronic Structure and Charge Dynamics of Huesler Alloy Fe2TiSn Probed by Infrared and Optical Spectroscopy | We report on the electrodynamics of a Heusler alloy Fe2TiSn probed over four
decades in energy: from the far infrared to the ultraviolet. Our results do not
support the suggestion of Kondo-lattice behavior inferred from specific heat
measurements. Instead, we find a conventional Drude-like response of free
carriers, with two additional absorption bands centered at around 0.1 and 0.87
eV. The latter feature can be interpreted as excitations across a pseudogap, in
accord with band structure calculations. | 0202512v2 |
2004-07-07 | A critical discussion of calculated modulated structures, Fermi surface nesting and phonon softening in magnetic shape memory alloys Ni$_2$Mn(Ga, Ge, Al) and Co$_2$Mn(Ga, Ge) | A series of first principles calculations have been carried out in order to
discuss electronic structure, phonon dynamics, structural instabilities and the
nature of martensitic transformations of the Heusler alloys Ni$_2$Mn(Ga, Ge,
Al) and Co$_2$Mn(Ga, Ge). The calculations show that besides electronic
pecularities like Fermi--surface nesting, hybridizing optical and acoustic
phonon modes are important for the stabilization of the modulated martensitic
structures. | 0407157v1 |
2007-11-19 | Room Temperature Magnetocaloric Effect in Ni-Mn-In | We have studied the effect of magnetic field on a non-stoichiometric Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ that undergoes a martensitic as well as a
magnetic transition near room temperature. Temperature dependent magnetization
measurements demonstrate the influence of magnetic field on the structural
phase transition temperature. From the study of magnetization as a function of
applied field, we show the occurrence of inverse-magnetocaloric effect
associated with this magneto-structural transition. The magnetic entropy change
attains a value as high as 25 J/kg-K (at 5 T field) at room temperature as the
alloy transforms from the austenitic to martensitic phase with a concomitant
magnetic ordering. | 0711.2896v1 |
2017-07-26 | Magnetism from intermetallics and perovskite oxides | This work has been presented by RJCV to obtain his PhD degree at Fluminense
Federal University, in March of 2017. We focused on the synthesis of compounds
and then on their magneto-strucutral characterization; mainly due to the
interplay of these physical properties. We have prepared intermetallic alloys
(including Heusler alloys) and perovskite oxides (manganites and cobaltites);
in bulk and nanoparticles. A thorough analysis of the influence of the
morphology and crystal structure on the magnetic properties of these compounds
is addressed. | 1707.09868v2 |
2016-12-22 | Ab initio Study of Effect of Co Substitution on the Magnetic Properties of Ni and Pt-based Heusler Alloys | Using density functional theory based calculations, we have carried out
in-depth studies of effect of Co substitution on the magnetic properties of Ni
and Pt-based shape memory alloys. We show the systematic variation of the total
magnetic moment, as a function of Co doping. A detailed analysis of evolution
of Heisenberg exchange coupling parameters as a function of Co doping has been
presented here. The strength of RKKY type of exchange interaction is found to
decay with the increase of Co doping. | 1612.07518v1 |
2007-07-05 | Engineering the electronic, magnetic and gap-related properties of the quinternary half-metallic Heusler alloys | We review the electronic and magnetic properties of the quinternary full
Heusler alloys of the type Co$_2$[Cr$_{1-x}$Mn$_x$][Al$_{1-y}$Si$_y$] employing
three different approaches : (i) the coherent potential approximation (CPA),
(ii) the virtual crystal approximation (VCA), and (iii) supercell calculations
(SC). All three methods give similar results and the local environment
manifested itself only for small details of the density of states. All alloys
under study are shown to be half-metals and their total spin moments follow the
so-called Slater-Pauling behavior of the ideal half-metallic systems. We
especially concentrate on the properties related to the minority-spin band-gap.
We present the possibility to engineer the properties of these alloys by
changing the relative concentrations of the low-valent transition metal and
$sp$ atoms in a continuous way. Our results show that for realistic
applications, ideal are the compounds rich in Si and Cr since they combine
large energy gaps (around 0.6 eV), robust half-metallicity with respect to
defects (the Fermi level is located near the middle of the gap) and high values
of the majority-spin density of states around the Fermi level which are needed
for large values of the perfectly spin-polarized current in spintronic devices
like spin-valves or magnetic tunnel junctions. | 0707.0728v1 |
2015-01-22 | High spin polarization and large spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy | In this paper, we investigate CoFeCrAl alloy by means of various experimental
techniques and ab-initio calculations to look for half-metallic nature. The
alloy is found to exist in the cubic Heusler structure, with presence of B2
ordering. Saturation magnetization (MS) value of about 2 Bohr magneton/f.u. is
observed at 8 K under ambient pressure, which is in good agreement with the
Slater-Pauling rule. MS values are found to be independent of pressure, which
is a prerequisite for half-metals. The ab-initio electronic structure
calculations predict half-metallic nature for the alloy with a spin slitting
energy of 0.31 eV. Importantly, this system shows a high current spin
polarization value of 0.67 [with error of 0.02], as deduced from the point
contact Andreev reflection (PCAR) measurements. Linear dependence of electrical
resistivity with temperature indicates the possibility of reasonably high spin
polarization at elevated temperatures (~150 K) as well. All these suggest that
CoFeCrAl is a promising material for the spintronic devices. | 1501.05599v1 |
2017-12-05 | Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys | Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler
alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn,
Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of
up to 100 kOe. It was found that varying Y in affects strongly the electric
resistivity and its temperature dependence $\rho(T)$, while this effect is not
observed upon changing Z. When Y is varied, extrema (maximum or minimum) are
observed in $\rho(T)$ near the Curie temperature $T_C$. At $T < T_C$, the
$\rho(T)$ behavior can be ascribed to a change in electronic energy spectrum
near the Fermi level. The coefficients of the normal and anomalous Hall effect
were determined. It was shown that the latter coefficient, $R_S$, is related to
the residual resistivity $\rho_0$ by a power law $R_S \sim \rho_0^k/M_S$ with
$M_S$ the spontaneous magnetization. The exponent $k$ was found to be 1.8 for
Co$_2$FeZ alloys, which is typical for asymmetric scattering mechanisms, and
2.9 for Co$_2$YAl alloys, which indicates an additional contribution to the
anomalous Hall effect. The temperature dependence of resistivity at low
temperatures is analyzed and discussed in the framework of the two-magnon
scattering theory. | 1712.01584v1 |
2021-07-24 | Unravelling the phonon scattering mechanism in Half-Heusler alloys ZrCo1-xIrxSb (x = 0, 0.1, and 0.25) | Insight about the scattering mechanisms responsible for reduction in the
lattice thermal conductivity (\k{appa}L) in Half-Heusler alloys (HHA) is
imperative. In this context, we have thoroughly investigated the temperature
response of thermal conductivity of ZrCo1-xIrxSb (x = 0, 0.1 and 0.25). For
ZrCoSb, \k{appa}L is found to be ~15.13 W/m-K at 300 K, which is drastically
reduced to ~4.37 W/m-K in ZrCo0.9Ir0.1Sb. This observed reduction is ascribed
to softening of acoustic phonon modes and point defect scattering, on
substitution of heavier mass. However, no further reduction in \k{appa}L is
observed in ZrCo0.75Ir0.25Sb, because of identical scattering parameter. This
has been elucidated based on the Klemens Callaway model. Also, in the parent
alloy, phonon-phonon scattering mechanism plays a significant role in heat
conduction process, whereas in Ir substituted alloys, point defect scattering
(below 500 K) and phonon-phonon scattering (above 750 K) are the dominant
scattering mechanisms. The minimum \k{appa}L is found to be ~1.73 W/m-K (at 950
K) in ZrCo0.9Ir0.1Sb, which is the lowest reported value till now, for n-type
Zr based HHA. Our studies indicate that partial substitution of heavier mass
element Ir at Co-site effectively reduces the \k{appa}L of n-type ZrCoSb,
without modifying the nature of charge carriers. | 2107.11567v1 |
2019-04-24 | Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl | We present a detailed study of structural, magnetic and thermodynamic
properties of a series of Heusler alloys Fe2-xMnxCrAl (x=0, 0.25, 0.5, 0.75 and
1). Structural investigation of this series is carried out using high
resolution synchrotron X-ray diffraction. Results suggest that with increasing
Mn concentration, the L21 structure of Fe2CrAl is destabilized. The DC
magnetization results show a decrement in paramagnetic (PM) to ferromagnetic
(FM) phase transition temperature (TC) with increasing Mn concentration. From
the systematic analysis of magnetic memory effect, heat capacity, time
dependent magnetization, and DC field dependent AC susceptibility studies it is
observed that, Fe2CrAl exhibits cluster glass(CG)-like transition approximately
at 3.9 K (Tf2). The alloys, Fe1.75Mn0.25CrAl and Fe1.5Mn0.5CrAl exhibit double
CG-like transitions near Tf1~22 K, Tf2~4.2 K and Tf1~30.4 K, Tf2~9.5 K
respectively, however, in Fe1.25Mn0.75CrAl, a single CG-like transition is
noted at Tf2~11.5 K below TC. Interestingly, FeMnCrAl shows the absence of long
ranged magnetic ordering and this alloy undergoes three CG-like transitions at
~ 22 K (Tf*), 16.6 K (Tf1) and 11 K (Tf2). At high temperatures, a detailed
analysis of temperature response of inverse DC susceptibility clearly reveals
the observation of Griffiths phase (GP) above 300 K (T*) in Fe2CrAl and this
phase persists with Mn concentration with a decrement in T*. | 1904.10648v2 |
2018-08-07 | Theoretical Investigation on the Effect of multinary Isoelectronic Substitution on TiCoSb based half-Heusler alloys | To understand the effect of isoelectronic substitution on thermoelectric
properties of TiCoSb based half - Heusler (HH) alloys, we have systematically
studied the transport properties with substitution of Zr at Ti and Bi at Sb
sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and
parent TiCoSb are investigated using the full potential linearized augmented
plane wave method and the thermoelectric transport properties are calculated on
the basis of semiclassical Boltzmann transport theory. The band analysis of the
calculated band structures reveal that TixZr1-xCoSbxBi1-x has semiconducting
behavior with indirect band gap at x = 0.25, 0.5 concentration and direct band
gap behavior at x = 0.75 concentration. The TixZr1-xCoSbxBi1-x (x = 0.25, 0.5,
0.75) compounds show smaller band gap values as compared to the pure TiCoSb.
The d electrons of Ti/Zr and Co dominate the electronic transport properties of
TixZr1-xCoSbxBi1-x system. All these systems follow the empirical rule of 18
valence-electron content to bring semiconductivity in HH alloys. The
isoelectronic substitution in TiCoSb can tune the band structure by shifting
the Fermi level. This provides us lot of possibilities to get the desired band
gap values for designing thermoelectrics with high efficiency. In this study we
have showed that the isoelectronic substitution at both Ti and Sb site of
TiCoSb has very small effect for increasing the ZT values and one should go for
isoelectronic substitution at any one sites of TiCoSb HH alloys alone to
improve ZT. | 1808.02514v1 |
2018-04-15 | $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ Heusler Alloys : A promising material for spintronics application | In this article, we investigated the effect of Cr substitution in place of Fe
on the structural, magnetic and transport properties of $\mathrm{Co_2FeSi}$
alloy. A comprehensive structural analysis is done using X-ray diffraction
(XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy.
Quaternary Heusler compounds $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ with Cr content (x =
0.1, 0.3, 0.5) were found to crystallize in cubic structure. The synchrotron
based EXAFS studies reveal that the anti-site disorder increases with the
increase in Cr concentration. The saturation magnetization values in all the
alloys are found to be less than those expected from the Slater-Pauling rule,
which may be due to the some inherent disorder. A detailed resistivity analysis
in the temperature range of 5-300 K is done, taking into account different
scattering mechanisms. The residual resistivity ratio is found to decrease with
increasing Cr concentration. A disorder induced resistivity minimum due to weak
localization effect is seen for x = 0.5. The resistivity measurements also
indicate that the half-metallic character survives upto 100 K for x = 0.1,
whereas the alloys with x= 0.3 and 0.5 show signature of half- metallic nature
even at higher temperatures. First principles calculation done with a more
robust exchange correlation functional (namely HSE-06) confirms the half
metallicity in the entire concentration range. Theoretically simulated band gap
and magnetic moments compliment the experimental findings and are compared
wherever possible. All these properties make $\mathrm{Co_2Fe_{1-x}Cr_xSi}$ a
promising material for spintronics application. | 1804.05321v1 |
2019-08-21 | Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi | We report a combined theoretical and experimental investigation of
half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi.
Room temperature XRD analysis reveals that the alloy crystallizes in L21
disorder instead of pristine Y-type structure due to 50% swap disorder between
the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal
a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity
measurement reveals the presence of localization effect below 35 K while above
100 K, a linear dependence is observed. Resistivity behavior indicates the
absence of single magnon scattering, which indirectly supports the
half-metallic nature. The majority spin band near the Fermi level clearly
indicates the overlap of flat eg bands with sharply varying conduction bands
that are responsible for the localization. In-depth analysis of the projected
atomic d-orbital character of band structure reveals unusual bonding, giving
rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder
calculations indicate the robustness of half-metallic nature, even when the
structure changes from Y-type to L21-type, with no major change in the net
magnetization of the system. Thus, robust half-metallic nature, stable
structure, and high Curie temperature make this alloy quite a promising
candidate to be used as a source of highly spin-polarized currents in
spintronic applications. | 1908.07804v1 |
2021-07-31 | Optical phonon modes assisted thermal conductivity in p-type ZrIrSb Half-Heusler alloy: A combined experimental and computational study | Half Heusler (HH) alloys with 18 valence electron count have attracted
significant interest in the area of research related to thermoelectrics.
Understanding the novel transport properties exhibited by these systems with
semiconducting ground state is an important focus area in this field. Large
thermal conductivity shown by most of the HH alloy possesses a major hurdle in
improving the figure of merit (ZT). Additionally, understanding the mechanism
of thermal conduction in heavy constituents HH alloys is an interesting aspect.
Here, we have investigated the high temperature thermoelectric properties of
ZrIrSb through experimental studies, phonon dispersion and electronic band
structure calculations. ZrIrSb is found to exhibit substantially lower
magnitude of resistivity and Seebeck coefficient near room temperature, owing
to existence of anti-site disorder between Ir/Sb and vacant sites.
Interestingly, in ZrIrSb, lattice thermal conductivity is governed by coupling
between the acoustic and low frequency optical phonon modes, which originates
due to heavier Ir/Sb atoms. This coupling leads to an enhancement in the
Umklapp processes due to the optical phonon excitations near zone boundary,
resulting in a lower magnitude of \k{appa}L. Our studies point to the fact that
the simultaneous existence of two heavy mass elements within a simple unit cell
can substantially decrease the lattice degrees of freedom. | 2108.00210v1 |
2023-04-11 | Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts | Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as
magnetocaloric effect during the magneto-structural phase transition, making
this material interesting for solid-state cooling application. Material
processing by additive manufacturing can overcome difficulties related to
machinability of the alloys, caused by their intrinsic brittleness. Since the
magnetic properties and transition temperature are highly sensitive to the
chemical composition, it is essential to understand and monitoring these
properties over the entire processing chain. In the present work the
microstructural and magnetic properties from gas-atomized powder to
post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was
used for processing, promoting the evolution of a polycrystalline
microstructure being characterized by elongated grains along the building
direction. A complete and sharp martensitic transformation can be achieved
after applying a subsequent heat treatment at 1173 K for 24 h. The
Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing
lead to an increase of the transition temperature of 45 K and a decrease of
magnetization, clearly pointing at the necessity of controlling the
composition, oxygen partial pressure and magnetic properties over the entire
processing chain. | 2304.05383v1 |
2023-09-20 | Effects of disorder on the magnetic properties of the Heusler alloy V$_{2}$FeAl | Magnetic properties of multicomponent alloys depend sensitively on the degree
of atomic order on the different crystallographic sites. In this work we
demonstrate the magnetic contrast between bulk and thin-film samples of the
Heusler alloy V$_{2}$FeAl. Arc-melted bulk ingots show practically no site
preference of the elements (A2 structure), whereas magnetron-sputtered
thin-film samples display a higher degree of atomic ordering with a tendency
towards XA-type order. Electronic structure calculations favour ferrimagnetic
XA-type ordering, and the effect of different pairwise atomic disorder on the
element specific and net magnetic moments are evaluated to reproduce
experimental observations. XA-type thin-films with iron moment of 1.24
$\mu_{\mathrm{B}}$ determined by X-ray magnetic circular dichroism are in
agreement with calculation, but the measured net moment of 1.0
$\mu_{\mathrm{B}}$ per formula unit and average vanadium moment are smaller
than expected from calculations. The measured Curie temperature is
approximately 500 K. Films with a higher degree of disorder have a
T$_{\mathrm{C}}$ close to 300 K with a net moment of 0.1 $\mu_{\mathrm{B}}$ at
low temperature. The large calculated vanadium moments are destroyed by partial
disorder on $4d$ vanadium sites. By contrast, the arc-melted and annealed bulk
alloy with a fully-disordered A2 structure shows no spontaneous magnetization;
it is a Pauli paramagnet with dimensionless susceptibility
$\chi_{\mathrm{v}}=-2.95\times10^{-4}$. | 2309.11480v1 |
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 |
2013-07-08 | Significant ZT Enhancement in p-type Ti(Co,Fe)Sb-InSb Nanocomposites via a Synergistic High Mobility Electron Injection Energy filtering and Boundary Scattering Approach | It has been demonstrated that InSb nanoinclusions, which are formed in situ,
can simultaneously improve all three individual thermoelectric properties of
the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater.
58, 4795 (2010)]. In the work presented herein, we have adopted the same
approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of
resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient
measurements indicate that the combined high mobility electron injection, low
energy electron filtering, and boundary scattering, again, lead to a
simultaneous improvement of all three individual thermoelectric properties:
enhanced Seebeck coefficient and electrical conductivity as well as reduced
lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900
K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent
improvement over the nanoinclusion-free sample. This represents a rare case
that the same nanostructuring approach successfully works for both p-type and
n-type thermoelectric materials of the same class, hence pointing to a
promising materials design route for higher performance half-Heusler materials
in the future and hopefully will realize similar improvement in TE devices
based on such half Heusler alloys. | 1307.2160v1 |
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 |
2015-12-15 | Half-metallic, Co-based quaternary Heuslers for spintronics: defect- and pressure-induced transitions and properties | Heusler compounds offer potential as spintronic devices due to their
spin-polarization and half-metallicity properties, where electron spin-majority
(minority) manifold exhibits states (band gap) at the electronic chemical
potential, yielding full spin-polarization in a single manifold. Yet, Heuslers
often exhibit intrinsic disorder that degrades its half-metallicity and
spin-polarization. Using density-functional theory, we analyze the electronic
and magnetic properties of equiatomic Heusler ($L$2$_{1}$) CoMnCrAl and
CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder
(thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl
undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained
for a limited range. Antisite disorder between Co-Al pairs in CoMnCrAl and
Co-Ge pairs in CoFeCrGe is energetically the most favored, and retain
half-metallic character in Co-excess samples. However, Co-deficient samples
undergo a transition from half-metallic to metallic, with a discontinuity in
the saturation magnetization. For binary swaps, configurations that compete
with the ground state are identified and show no loss of half-metallicity;
however, the minority-spin bandgap and magnetic moments vary depending on the
atoms swapped. For single binary swaps, there is a significant energy cost in
CoMnCrAl but with no loss of half metallicity. Although a few configurations in
CoFeCrGe energetically compete with the ground statei, however the
minority-spin bandgap and magnetic moments vary depending on the atoms swapped.
These informations should help in controlling these potential spintronic
materials. | 1512.04805v2 |
2018-03-05 | Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds | Newly emerged materials from the family of Heuslers and complex oxides
exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much
higher than even room temperature. In this work, using the semiclassical
top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that
utilizes such ferromagnetic semiconductors as channel materials, in addition to
ferromagnetic source/drain contacts. Such a device could retain the spin
polarization of injected electrons in the channel, the loss of which limits the
operation of traditional spin transistors with non-ferromagnetic channels. We
examine the operation of four material systems that are currently considered
some of the most prominent known ferromagnetic semiconductors, three
Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family
(NiFe2O4). We describe their bandstructures by using data from DFT
calculations. We investigate under which conditions high spin polarization and
significant ION/IOFF ratio, two essential requirements for the spin-MOSFET
operation, are both achieved. We show that these particular Heusler channels,
in their bulk form, do not have adequate bandgap to provide high ION/IOFF
ratios, and have small magnetoconductance compared to state-of-the-art devices.
However, with confinement into ultra-narrow sizes down to a few nanometers, and
by engineering their spin dependent contact resistances, they could prove
promising channel materials for the realization of spin-MOSFET transistor
devices that offer combined logic and memory functionalities. Although the main
compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4
alone, we expect that the insight we provide is relevant to other classes of
such materials as well. | 1803.01789v1 |
2021-02-22 | Structural, magnetic, and magnetocaloric properties of Fe2CoAl Heusler nanoalloy | Spherical nanoparticles (NPs) of size 14 nm, made of intermetallic Fe2CoAl
(FCA) Heusler alloy, are synthesized via the co-precipitation and thermal
deoxidization method. X-ray diffraction (XRD) and selected area electron
diffraction (SAED) patterns confirm that the present nanoalloy is crystallized
in A2-disordered cubic Heusler structure. Magnetic field (H) and temperature
(T) dependent magnetization (M) results reveal that the NPs are soft
ferromagnetic (FM) with high saturation magnetization (Ms) and Curie
temperature (Tc). Fe2CoAl nanoalloy does not follow the Slater Pauling (SP)
rule, possibly because of the disorder present in the system. We also
investigate its magnetic phase transition (MPT) and magnetocaloric (MC)
properties. The peak value of the magnetic entropy change vs T curve at a
magnetic field change of 20 kOe corresponds to about 2.65 J/kg-K, and the
observed value of refrigeration capacity (RCP) is as large as 44 J/kg,
suggesting a large heat conversion in magnetic refrigeration cycle. The Arrott
plot and the nature of the universal curve accomplish that the FM to
paramagnetic (PM) phase transition in Fe2CoAl nanoalloy is of second-order. The
present study suggests that the Fe2CoAl nanoscale system is proficient, useful
and a good candidate for the spintronics application and opens up a window for
further research on full-Heusler based magnetic refrigerants. | 2102.11195v2 |
1999-11-25 | Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation | The results of fluorescence measurements of magnetic circular dichroism (MCD)
in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and
Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the
Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold
excitation in materials with the half-metallic character of the electronic
structure. A theoretical model for the description of resonance scattering of
polarized x-rays is suggested. | 9911415v1 |
2002-03-04 | X-ray spectra of 3d metals of Heusler alloys and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$ compounds | The Mn x-ray emission spectra and x-ray photoemission spectra of Mn-based
Heusler alloys Co$_2$MnAl, Co$_2$MnSb and La$_{1-x}$Sm$_x$Mn$_2$Si$_2$
compounds (x=0, 0.8) have been measured and discussed in connection with a
value local magnetic moment at Mn site. The spectra peculiarities reflect also
the localization degree of 3d valence electrons of 3d metals in considered
compounds. | 0203069v3 |
2002-03-26 | Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys | We study the origin of the gap and the role of chemical composition in the
half-ferromagnetic Heusler alloys using the full-potential screened KKR method.
In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap.
Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are
semiconductors, but when Z_t > 18 antibonding states are also populated, thus
the paramagnetic phase becomes unstable and the half-ferromagnetic one is
stabilized. The minority occupied bands accommodate a total of nine electrons
and the total magnetic moment per unit cell in mu_B is just the difference
between Z_t and $2 \times 9$. While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the $sp$ atom
results in a practically rigid shift of the bands and the loss of
half-metallicity. Finally we show that expanding or contracting the lattice
parameter by 2% preserves the minority-spin gap. | 0203534v3 |
2004-04-07 | First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb) | The interatomic exchange interactions and Curie temperatures in Ni-based full
Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework
of the density-functional theory. The calculation of the exchange parameters is
based on the frozen-magnon approach. Despite closeness of the experimental
Curie temperatures for all four systems their magnetism appeared to differ
strongly. This difference involves both the Mn-Mn and Mn-Ni exchange
interactions. The Curie temperatures, Tc, are calculated within the mean-field
approximation by solving a matrix equation for a multi-sublattice system. Good
agreement with experiment for all four systems is obtained. The role of
different exchange interactions in the formation of Tc of the systems is
discussed. | 0404162v1 |
2004-10-28 | Spin injection from the Heusler alloy Co_2MnGe into Al_0.1Ga_0.9As/GaAs heterostructures | Electrical spin injection from the Heusler alloy Co_2MnGe into a p-i-n
Al_0.1Ga_0.9As/GaAs light emitting diode is demonstrated. A maximum
steady-state spin polarization of approximately 13% at 2 K is measured in two
types of heterostructures. The injected spin polarization at 2 K is calculated
to be 27% based on a calibration of the spin detector using Hanle effect
measurements. Although the dependence on electrical bias conditions is
qualitatively similar to Fe-based spin injection devices of the same design,
the spin polarization injected from Co_2MnGe decays more rapidly with
increasing temperature. | 0410751v1 |
2005-04-26 | Pressure dependence of the Curie temperature in Ni2MnSn Heusler alloy: A first-principles study | The pressure dependence of electronic structure, exchange interactions and
Curie temperature in ferromagnetic Heusler alloy Ni2MnSn has been studied
theoretically within the framework of the density-functional theory. The
calculation of the exchange parameters is based on the frozen--magnon approach.
The Curie temperature, Tc, is calculated within the mean-field approximation by
solving the matrix equation for a multi-sublattice system. In agrement with
experiment the Curie temperature increased from 362K at ambient pressure to 396
at 12 GPa. Extending the variation of the lattice parameter beyond the range
studied experimentally we obtained non-monotonous pressure dependence of the
Curie temperature and metamagnetic transition. We relate the theoretical
dependence of Tc on the lattice constant to the corresponding dependence
predicted by the empirical interaction curve. The Mn-Ni atomic interchange
observed experimentally is simulated to study its influence on the Curie
temperature. | 0504644v1 |
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 |
2005-06-06 | Unusual transport properties of ferromagnetic Heusler alloy Co$_2$TiSn | We report results of magnetization, zero field resistivity and
magnetoresistance measurements in ferromagnetic Heusler alloy Co$_2$TiSn. There
is a striking change in the character of electron transport as the system
undergoes the paramagnetic to ferromagnetic transition. In the paramagnetic
state the nature of the electron transport is like that of a semiconductor and
this changes abruptly to metallic behaviour at the onset of ferromagnetic
ordering. Application of external magnetic field tends to suppress this
semiconducting like transport leading to a negative magnetoresistance which
reaches a peak in the vicinity of Curie temperature. Comparison is made with
the similar unusual behaviour observed in other systems including UNiSn and
manganites. | 0506126v1 |
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 |
2006-05-31 | Spin- and time-resolved photoemission studies of thin Co2FeSi Heusler alloy films | We have studied the possibly half metallic Co2FeSi full Heusler alloy by
means of spin- and time-resolved photoemission spectroscopy. For excitation,
the second and fourth harmonic of femtosecond Ti:sapphire lasers were used,
with photon energies of 3.1 eV and 5.9 eV, respectively. We compare the
dependence of the measured surface spin polarization on the particular
photoemission mechanism, i.e. 1-photon-photoemission (1PPE) or 2-photon
photoemission (2PPE). The observed differences in the spin polarization can be
explained by a spin-dependent lifetime effect occurring in the 2-photon
absorption process. The difference in escape depth of the two methods in this
context suggests that the observed reduction of spin polarization (compared to
the bulk) cannot be attributed just to the outermost surface layer but takes
place at least 4-6 nm away from the surface. | 0606006v1 |
2006-08-31 | Magnetic phase diagram of the semi-Heusler alloys from first-principles | The magnetic phase diagram of the Mn-based semi-Heusler alloys is determined
at T=0 using first-principles calculations in conjunction with the
frozen-magnon approximation. We show that the magnetism in these systems
strongly depends on the number of conduction electrons, their spin polarization
and the position of the unoccupied Mn 3d states with respect to Fermi energy.
Various magnetic phases are obtained depending on these characteristics. The
conditions leading to diverse magnetic behavior are identified. We find that in
the case of a large conduction electron spin polarization and the unoccupied Mn
3d states lying far above the Fermi level, an RKKY-like ferromagnetic
interaction is dominating. On the other hand, the antiferromagnetic
superexchange becomes important in the presence of large peaks of the
unoccupied Mn 3d states lying close to the Fermi energy. The overall magnetic
behavior depends on the competition of these two exchange mechanisms. The
obtained results are in very good agreement with the available experimental
data. | 0609001v1 |
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 |
2008-01-13 | 3d-electron induced magnetic phase transition in half-metallic semi-Heusler alloys | We study the effect of the non-magnetic 3\textit{d} atoms on the magnetic
properties of the half-metallic (HM) semi-Heusler alloys Co$_{1-x}$Cu$_{x}$MnSb
and Ni$_{1-x}$Cu$_{x}$MnSb ($0 \leq x \leq 1$) using first-principles
calculations. We determine the magnetic phase diagram of both systems at zero
temperature and obtain a phase transition from a ferromagnetic to an
antiferromagnetic state. For low Cu concentrations the ferromagnetic RKKY-like
exchange mechanism is dominating, while the antiferromagnetic superexchange
coupling becomes important for larger Cu content leading to the observed
magnetic phase transition. A strong dependence of the magnetism in both systems
on the position of the Fermi level within the HM gap is obtained. Obtained
results are in good agreement with the available experimental data. | 0801.1968v1 |
2008-01-15 | Structural and magnetic properties of half-heusler alloys NiCrZ (Z = Si, P, Ge, As, Te): First principle study | We present a first principle study of new class of high-$T_c$ half-heusler
ferromagnets NiCrZ (Z = Si, P, Ge, As, Te). The structure and magnetic
properties are investigated through the calculation of the electronic
structure, equilibrium lattice constant, magnetic exchange interaction $J_{ij}$
and Curie temperature $T_c$. The role of $sp$-elements and the influence of
lattice expansion/compression are also studied. In alloys having 20 valence
electrons, a pseudo-gap of the majority band can be formed at Fermi level.
Otherwise, the half-metallicity and ferromagnetism at temperatures much higher
than room temperature are found to be stable in a wide range of lattice
expansion. Based on these results, NiCrZ can be expected to be promising
materials for spintronics. | 0801.2222v1 |
2008-01-15 | New High-$T_c$ Half-Heusler Ferromagnets NiMnZ (Z = Si, P, Ge, As) | Based on the first principle calculation, we propose a new class of
high-$T_c$ half-heusler ferromagnets NiMnZ (Z = Si, P, Ge, As). The structural
and magnetic properties are investigated through the calculation of the
electronic structure, phase stability, equilibrium lattice constant, magnetic
exchange interaction $J_{ij}$ and Curie temperature $T_c$. It is found that all
alloys show half-metallicity and ferromagnetism at temperatures much higher
than room temperature in a wide range of lattice expansion (compression). At
the equilibrium lattice constant, $T_c$ of 715K, 840K, 875K and 1050K are
predicted by Monte Carlo simulation for NiMnP, NiMnAs, NiMnGe and NiMnSi,
respectively. Following these results, these alloys are strongly expected to be
promising candidates for spintronic applications. | 0801.2225v1 |
2008-11-20 | Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes | We report the current-perpendicular-to-plane giant magnetoresistance of a
spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A
multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a
MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown
on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after
annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu
spacer layer despite the large lattice mismatch between Cu and CMS. The highest
MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6
K, respectively. The high spin polarization of the epitaxial CMS layers is the
most likely origin of the high MR ratio. | 0811.3282v1 |
2009-05-24 | Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa | The structural and elastic properties as well as phonon-dispersion relations
of the Heusler-type alloys Fe$_2$VAl and Fe$_2$VGa are computed using
density-functional and density-functional perturbation theory within the
generalized-gradient approximation. The calculated equilibrium lattice
constants agree well with the experimental values. The elastic constants of
Fe$_2$VAl and Fe$_2$VGa are predicted for the first time. From the elastic
constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities
and Debye temperatures are obtained. By analyzing the ratio between the bulk
and shear modulii, we conclude that both Fe$_2$VAl and Fe$_2$VGa are brittle in
nature. The computed phonon-dispersion relation shows that both compounds are
dynamically stable in the L1$_2$ structure without any imaginary phonon
frequencies. The isomer shifts of Fe in the two compounds are discussed in
terms of the Fe s partial density of states, which reveal larger ionicity/less
hybridization in Fe$_2$VGa than in Fe$_2$VAl. For the same reason the Cauchy
pressure is negative in Fe$_2$VAl but positive in Fe$_2$VGa | 0905.3909v1 |
2010-06-01 | Pressure induced magnetic and magnetocaloric properties in NiCoMnSb Heusler alloy | The effect of pressure on the magnetic and the magnetocaloric properties
around the martensitic transformation temperature in NiCoMnSb Heusler alloy has
been studied. The martensitic transition temperature has significantly shifted
to higher temperatures with pressure, whereas the trend is opposite with the
application of applied magnetic field. The maximum magnetic entropy change
around the martensitic transition temperature for Ni45Co5Mn38Sb12 is 41.4 J/kg
K at the ambient pressure, whereas it is 33 J/kg K at 8.5 kbar. We find that by
adjusting the Co concentration and applying suitable pressure, NiCoMnSb system
can be tuned to achieve giant magnetocaloric effect spread over a large
temperature span around the room temperature, thereby making it a potential
magnetic refrigerant material for applications. | 1006.0067v1 |
2010-06-01 | Giant inverse magnetocaloric effect near room temperature in Co substituted NiMnSb Heusler alloys | The effect of Co on the structural, magnetic and magnetocaloric effect (MCE)
of Ni50-xCoxMn38Sb12 (x=0,2,3,4,5) Heusler alloys was studied. Using x-ray
diffraction, we show the evolution of the martensitic phase from the austenite
phase. The martensitic transition temperature is found to decrease
monotonically with Co concentration. Remarkable enhancement of MCE is observed
near room temperature upon Co substitution. The maximum magnetic entropy change
of 34 Jkg-1K-1 was achieved in x=5 at 262 K in a field of 50 kOe and a value of
29 Jkg-1K-1 found near room temperature. The significant increase in the
magnetization associated with the reverse martensitic transition is responsible
for the giant MCE in these compounds. | 1006.0072v1 |
2010-10-15 | Direct measurements of the magnetocaloric effect in ribbon samples of Heusler alloys Ni - Mn - M (M = In, Sn) | Direct measurements of the magnetocaloric effect in samples of rapidly
quenched ribbons of Mn50Ni40In10 and Ni50Mn37Sn13 Heusler alloys, with
potential applications in magnetic refrigeration technology, are carried out.
The measurements were made by a precise method based on the measurement of the
oscillation amplitude of the temperature in the sample while is subjected to a
modulated magnetic field. In the studied compositions both direct and inverse
magnetocaloric effects associated with magnetic (paramagnet - ferromagnet -
antiferromagnet) and structural (austenite - martensite) phase transitions are
found. Additional inverse magnetocaloric effects of small value are observed
around the ferromagnetic transitions. | 1010.3135v1 |
2010-12-09 | Epitaxial germanidation of full-Heusler Co2FeGe alloy thin films formed by rapid thermal annealing | The authors demonstrated that a full-Heusler Co2FeGe (CFG) alloy thin film
was epitaxially grown by rapid-thermal-annealing-induced germanidation of an
Fe/Co/pseudo-Ge(001)-on-insulator (GOI) multilayer formed on a Si-on-insulator
(SOI) substrate. X-ray diffraction (XRD) measurements with the out-of-plane and
in-plane configurations revealed that the CFG film was epitaxially grown along
the [001] direction with the in-plane epitaxial relation of CFG[100]||GOI[100],
although the film slightly contained a texture component. The strong (111) and
(200) superlattice diffraction intensities indicated that the CFG film had a
high degree of order for the L21 structure. Cross-sectional high-resolution
transmission electron microscopy images of the film implied that the film had
the dominant epitaxial and slight texture components, which was consistent with
the XRD measurements. The epitaxial component was grown directly on the BOX
layer of the SOI substrate without the formation of any interfacial layer. | 1012.1917v1 |
2010-12-13 | Effect of Si and Ga substitutions on the magnetocaloric properties of NiCoMnSb quaternary Heusler alloys | The effect of Si and Ga substitutions on the magnetic and the magnetocaloric
properties in Heusler based system Ni46Co4Mn38Sb12-xZx (Z=Si and Ga) has been
studied. From the M(T) plots it is found that Si substitution stabilizes the
austenite phase, whereas, Ga substitution stabilizes the martensite phase.
Strong metamagnetic behaviour is observed in the M(H) isotherms for Si=0.75 and
1, whereas, such a behaviour is absent in the Ga substituted alloys. Associated
with magneto-structural transition, large MCE of 58 J/kg K and 70 J/kg K is
observed for x=0.75 and 1, respectively in the case of Si. Though the MCE
observed in x=0.5 and 1 in the case of Ga is much lower, the MCE peak is found
to be quite broad. | 1012.2684v1 |
2011-11-19 | Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars | We have studied microwave emission from a current-perpendicular-to-plane
pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes.
Large emission amplitude exceeding 150 nV/Hz^0.5, partly owing to the large
magnetoresistance, and narrow generation linewidth below 10 MHz are observed.
We also find that the linewidth shows significant dependence on the applied
field magnitude and its angle within the film plane. A minimum in the linewidth
is observed when the slope of the frequency versus current becomes near zero.
This agrees with theoretical prediction that takes into account non-linear
phase noise as a source for linewidth broadening. | 1111.4539v1 |
2012-10-22 | Thickness-dependent structural, magnetic and transport properties of epitaxial Co2FeAl Heusler alloy thin films | We report on a systematic study of the structural, magnetic properties and
the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films
on MgO(001), as a function of film thickness. It was found that the epitaxial
CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic
anisotropy. An analysis of the electrical transport properties reveals that the
lattice and magnon scattering contributions to the longitudinal resistivity.
Independent on the thickness of films, the anomalous Hall resistivity of CFA
films is found to be dominated by skew scattering only. Moreover, the anomalous
Hall resistivity shows weakly temperature dependent behavior, and its absolute
value increases as the thickness decreases. We attribute this temperature
insensitivity in the anomalous Hall resistivity to the weak temperature
dependent of tunneling spin-polarization in the CFA films, while the thickness
dependence behavior is likely due to the increasing significance of interface
or free surface electronic states. | 1210.5807v1 |
2013-11-28 | Local magnetism and structural properties of Heusler Ni$_2$MnGa alloys | We present a detailed experimental study of bulk and powder samples of the
Heusler shape memory alloy Ni$_2$MnGa, including zero-field static and dynamic
$^{55}$Mn NMR experiments, X-ray powder diffraction and magnetization
experiments. The NMR spectra give direct access to the sequence of structural
phase transitions in this compound, from the high-T austenitic phase down to
the low-T martensitic phase. In addition, a detailed investigation of the
so-called rf-enhancement factor provides local information for the magnetic
stiffness and restoring fields for each separate coordination, structural,
crystallographic environment, thus differentiating signals coming from
austenitic and martensitic components. The temperature evolution of the NMR
spectra and the rf-enhancement factors shows strong dependence on sample
preparation. In particular, we find that sample powderization gives rise to a
significant portion of martensitic traces inside the high-T austenitic region,
and that these traces can be subsequently removed by annealing. | 1311.7414v1 |
2015-05-12 | Examining the thermal conductivity of half-Heusler alloy TiNiSn by first-principles calculations | The thermoelectric properties of half-Heusler alloy TiNiSn have been studied
for decade, however, theoretical report on its thermal conductivity is still
little known, because it is difficult to estimate effectively the lattice
thermal conductivity. In this work, we use the ShengBTE code developed recently
to examine the lattice thermal conductivity of TiNiSn. The calculated lattice
thermal conductivity at room temperature is 7.6 W/mK, which is close to the
experimental value of 8 W/mK. We also find that the total and lattice thermal
conductivities dependent temperature are in good agreement with available
experiments, and the total thermal conductivity is dominated by the lattice
contribution. The present work is useful for the theoretical prediction of
lattice thermal conductivity and the optimization of thermoelectric
performance. | 1505.02845v1 |
2015-05-28 | Large ground state magnetic moment and magnetocaloric effect in Ni2Mn1.4In0.6 | A large conventional magnetocaloric effect at the second order magnetic
transition in cubic Ni2Mn1.4In0.6 Heusler alloy is reported. The isothermal
magnetization at 2K shows a huge ground state magnetic moment of about 6.17
{\mu}B/f.u. The theoretical calculations show that the origin of the large
magnetic moment in cubic Ni2Mn1.4In0.6 results from the strong ferromagnetic
interaction between Mn- Ni and Mn-Mn sublattices. The experimental magnetic
moment is in excellent agreement with the moment calculated from the theory.
The large magnetic moment gives rise to considerably high adiabatic temperature
and entropy changes at the magnetic transition. The present study opens up the
possibility to explore cubic Heusler alloys for magnetocaloric applications. | 1505.07677v2 |
2015-10-23 | Resonant impurity states in chemically disordered half-Heusler Dirac semimetals | We address the electron transport characteristics in bulk half-Heusler alloys
with their compositions tuned to the borderline between topologically
nontrivial semi-metallic and trivial semiconducting phases. The precise
first-principles calculations based on the coherent potential approximation
(CPA) reveal that all the studied systems exhibit sets of dispersionless
impurity-like resonant levels, with one of them being located right at the
Dirac point. By means of the Kubo formalism we reveal that the residual
conductivity of these alloys is strongly suppressed by impurity scattering,
whereas the spin Hall conductivity exhibits a large value which is comparable
to that of Pt, thereby leading to divergent spin Hall angles. | 1510.06935v1 |
2015-12-04 | Suppression of the ferromagnetic order in the Heusler alloy Ni50Mn35In15 by hydrostatic pressure | We report the effect of hydrostatic pressure on the magnetic and structural
properties of the shape-memory Heusler alloy Ni50Mn35In15. Magnetization and
x-ray diffraction experiments were performed at hydrostatic pressures up to 5
GPa using diamond anvil cells. Pressure stabilizes the martensitic phase,
shifting the martensitic transition to higher temperatures and suppresses the
ferromagnetic austenitic phase. Above ~3 GPa, where the martensitic-transition
temperature approaches the Curie temperature in the austenite, the
magnetization shows no indication of ferromagnetic ordering anymore. We further
find an extremely large temperatureregion with a mixture of martensite and
austenite phases, which directly relates to the magnetic properties. | 1512.01407v1 |
2016-06-14 | Defect-induced magnetic structure of CuMnSb | Ab initio total energy calculations show that the antiferromagnetic (111)
order is not the ground state for the ideal CuMnSb Heusler alloy in contrast to
the results of neutron diffraction experiments. It is known, that Heusler
alloys usually contain various defects depending on the sample preparation. We
have therefore investigated magnetic phases of CuMnSb assuming the most common
defects which exist in real experimental conditions. The full-potential
supercell approach and a Heisenberg model approach using the coherent potential
approximation are adopted. The results of the total energy supercell
calculations indicate that defects that bring Mn atoms close together promote
the antiferromagnetic (111) structure already for a low critical defect
concentrations ($\approx$ 3%). A detailed study of exchange interactions
between Mn-moments further supports the above stabilization mechanism. Finally,
the stability of the antiferromagnetic (111) order is enhanced by inclusion of
electron correlations in narrow Mn-bands. The present refinement structure
analysis of neutron scattering experiment supports theoretical conclusions. | 1606.04238v1 |
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 |
2017-01-06 | Modulations in martensitic Heusler alloys originate from nanotwin ordering | Heusler alloys exhibiting magnetic and martensitic transitions enable
applications like magnetocaloric refrigeration and actuation based on the
magnetic shape memory effect. Their outstanding functional properties depend on
low hysteresis losses and low actuation fields. These are only achieved if the
atomic positions deviate from a tetragonal lattice by periodic displacements.
The origin of the so-called modulated structures is the subject of much
controversy: They are either explained by phonon softening or adaptive
nanotwinning. Here we used large-scale density functional theory calculations
on the Ni2MnGa prototype system to demonstrate interaction energy between twin
boundaries. Minimizing the interaction energy resulted in the experimentally
observed ordered modulations at the atomic scale, it explained that a/b twin
boundaries are stacking faults at the mesoscale, and contributed substantially
to the macroscopic hysteresis losses. Furthermore, we found that phonon
softening paves the transformation path towards the nanotwinned martensite
state. This unified both opposing concepts to explain modulated martensite. | 1701.01562v2 |
2017-01-29 | $d^0$-$d$ half-Heusler alloys: A class of future spintronic materials | It is shown by rigorous ab initio calculations that half-Heusler alloys of
transition metals and $d^0$ metals, defined by the valence electronic
configuration $ns^{1,2},(n-1)d^0$, can produce all kinds of half-metallic
behavior including the elusive Dirac half-semimetallicity that is reported for
the first time in the real 3D material CoKSb. Together with the predicted
magnetic and chemical stability, this paves the way for massless and
dissipationless spintronics of the future. Furthermore, the introduction of
$d^0$ atoms is shown to stabilize the otherwise instable chemical structure of
zinc-blende transition metal pnictides and chalcogeneides without altering the
$p$-$d$ exchange that is mainly responsible for their half-metallicity,
therefore, making their application in spintronic devices feasible. | 1701.08397v3 |
2017-07-17 | Possible spin gapless semiconductor type behaviour in CoFeMnSi epitaxial thin films | Spin-gapless semiconductors with their unique band structures have recently
attracted much attention due to their interesting transport properties that can
be utilized in spintronics applications. We have successfully deposited the
thin films of quaternary spin-gapless semiconductor CoFeMnSi Heusler alloy on
MgO (001) substrates using a pulsed laser deposition system. These films show
epitaxial growth along (001) direction and display uniform and smooth
crystalline surface. The magnetic properties reveal that the film is
ferromagnetically soft along the in-plane direction and its Curie temperature
is well above 400 K. The electrical conductivity of the film is low and
exhibits a nearly temperature independent semiconducting behaviour. The
estimated temperature coefficient of resistivity for the film is -7x10^-10
Ohm.m/K, which is comparable to the values reported for spin-gapless
semiconductors. | 1707.05078v2 |
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 |
2018-03-05 | Measurement independent magnetocaloric effect in Mn-rich Mn-Fe-Ni-Sn(Sb/In) Heusler alloys | We report a systematic study on the magneto-structural transition in Mn-rich
Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence
electron concentration (e/a ratio) fixed. The martensitic transition (MT)
temperature is found to shift by following a proportional relationship with the
e/a ratio of the magnetic elements alone. The magnetic entropy change across MT
for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different
measurement methods (isofield magnetization (M) vs temperature (T), isothermal
M vs field (H) and heat capacity (HC) vs T). We observed that though the peak
value of magnetic entropy change changes with the measurement methods, the
broadened shape of the magnetic entropy change vs T curves and the
corresponding cooling power (~140 Jkg-1) remains invariant. The equivalent
adiabatic temperature change ~ -2.6 K has been obtained from indirect
measurements of temperature change. Moreover, an exchange bias field ~ 783 Oe
at 5 K and a magnetoresistance of -30% are also obtained in one of these
materials. | 1803.01566v3 |
2018-11-15 | LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys for topological superconductivity | Based on the first-principles electronic structure calculations and the
symmetry analysis, we predict that the topological superconductivity may occur
on the surface of the LnPd$_{2}$Sn (Ln=Sc, Y, Lu) class of Heusler alloys. The
calculated electronic band structure and topological invariant demonstrate that
the LnPd$_{2}$Sn family is topologically nontrivial. The further slab
calculations show that the nontrivial topological surface states of
LnPd$_{2}$Sn exist within the bulk band gap and meanwhile they cross the Fermi
level. Considering that the LnPd$_{2}$Sn class of compounds were all found
experimentally to be superconducting at low temperature, the surface
topological superconductivity is likely to be generated via the proximity
effect. Thus the LnPd$_{2}$Sn class of compounds shall be a promising platform
for exploring novel topological superconductivity and handling Majorana zero
modes. | 1811.06401v1 |
2019-11-06 | High spin mixing conductance and spin interface transparency at $Co_2Fe_{0.4}Mn_{0.6}Si$ Heusler alloy and Pt interface | Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and
moderately high saturation magnetization are required from the viewpoints of
generation, transmission and detection of spin wave. Since spin-to-charge
conversion efficiency is another important parameter, high spin mixing
conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient
spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$
(CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$.
However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a
paramagnet has not fully been understood. Here, we report the investigations of
spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping
analysis indicates the presence of significant spin pumping at the interface of
CFMS and Pt, which is also confirmed by the detection of inverse spin Hall
voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$
(1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher
compared to values reported for other ferromagnet/heavy metal systems. | 1911.02230v1 |
2019-04-04 | \textit{Ab initio} study of Bi-based half Heusler alloys as potential thermoelectric prospects | We investigated six heavy element bismuth-based 18-VEC half-Heusler alloys
CoTiBi, CoZrBi, CoHfBi, FeVBi, FeNbBi, and FeTaBi by first principles approach,
in search of better thermoelectric prospects. The motivation is driven by
expected lower thermal conductivity and the recent discovery of CoZrBi-based
materials. Significantly, our calculated power factor values of all the systems
show an increment of $\sim$40\% in comparison to the reported \textit{p}-type
CoTiSb. We propose that doping at Bi-site, on account of electronic features,
will be helpful in achieving the proposed power factor values. Interestingly,
the thermal conductivity of CoTiBi and CoZrBi was found to be lower and that of
CoHfBi was almost parallel, in comparison to the reported CoTiSb. We also
provide conservative estimates of the figure of merit, exceeding the reported
CoTiSb and comparable to FeNbSb. Overall, our results suggest potential new
candidates of bismuth-based ternary compounds for high thermoelectric
performance. | 1904.02488v1 |
2012-09-12 | Spin configurations in Co2FeAl0.4Si0.6 Heusler alloy thin film elements | We determine experimentally the spin structure of half-metallic
Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following
magnetic saturation, the dominant magnetic states consist of quasi-uniform
configurations, where a strong influence from the magnetocrystalline anisotropy
is visible. Heating experiments show the stability of the spin configuration of
domain walls in confined geometries up to 800 K. The switching temperature for
the transition from transverse to vortex walls in ring elements is found to
increase with ring width, an effect attributed to structural changes and
consequent changes in magnetic anisotropy, which start to occur in the narrower
elements at lower temperatures. | 1209.2702v1 |
2014-06-13 | Investigation of the electronic and thermoelectric properties of Fe2 ScX (X = P, As and Sb) full Heusler alloys by using first principles calculations | By using ab initio electronic structure calculations here we report the three
new full Heusler alloys which are possessing very good thermoelectric behavior
and expected to be synthesized in the laboratories. These are Fe2 ScP, Fe2 ScAs
and Fe2 ScSb compound. First two compounds are indirect band gap semiconductors
and the last one shows semimetallic ground state. The value of band gap of Fe2
ScP and Fe2 ScAs is 0.3 and 0.09 eV, respectively. These compounds show the
presence of flat conduction bands along {\Gamma} - X-direction suggesting for
the large electron like effective mass and promising for very good
thermoelectric behavior of the compounds. At 200 K, the Seebeck coefficients of
Fe2 ScP, Fe2 ScAs and Fe2 ScSb compounds are -770, -386 and -192{\mu}V/K,
respectively. The maximum power factor (P F ) is expected for the n-type doping
in these materials. The heavily doped Fe2 ScP and Fe2 ScAs have P F >60 for a
wide temperature range, which is comparable to the PF of Bi2 Te3 - a well known
and one of the best commercially used thermoelectric material. Present work
suggests the possible thermoelectric applicability of these materials in a wide
temperature range. | 1406.3425v1 |
2019-02-05 | Co-existence of spin semi-metallic and Weyl semi-metallic behavior in FeRhCrGe | In this letter, we report the discovery of a new class of spintronic
materials, namely spin semi-metals (SSM), employing both theoretical and
experimental tools. The band structure of this class of materials is such that
one of the spin bands resembles that of a semi-metal, while the other is
similar to that of an insulator/semiconductor. This report is the experimental
verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a
magnetic moment 3 $\mu_B$ and a Curie temperature of 550 K. The measurement
below 300 K shows nearly temperature independent conductivity and a relatively
moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous
first principles calculations. Band structure calculations also reveal that the
spin up (semi metallic) band has combined features of type II Weyl and nodal
line semimetal. As such, this study opens up the possibility of a new class of
material with combined spintronic and topological properties, which is
important both from fundamental and applied point of view. | 1902.01593v2 |
2020-04-15 | Effect of chemical and hydrostatic pressure on the coupled magnetostructural transition of Ni-Mn-In Heusler alloys | Ni-Mn-In magnetic shape-memory Heusler alloys exhibit generally a large
thermal hysteresis at their first-order martensitic phase transition which
hinder a technological application in magnetic refrigeration. By optimizing the
Cu content in Ni$_2$Cu$_x$Mn$_{1.4-x}$In$_{0.6}$, we obtained a thermal
hysteresis of the martensitic phase transition in
Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ of only 6 K. We can explain this very
small hysteresis by an almost perfect habit plane at the interface of
martensite and austenite phases. Application of hydrostatic pressure does not
reduce the hysteresis further, but shifts the martensitic transition close to
room temperature. The isothermal entropy change does not depend on warming or
cooling protocols and is pressure independent. Experiments in pulsed-magnetic
fields on Ni$_{2}$Cu$_{0.2}$Mn$_{1.2}$In$_{0.6}$ find a reversible
magnetocaloric effect with a maximum adiabatic temperature change of -13 K. | 2004.07145v1 |
2021-03-29 | Prediction of electronic and half metallic properties of Mn$_2$YSn (Y = Mo, Nb, Zr) Heusler alloys | We investigate the structural, electronic and magnetic properties of the full
Heusler compounds Mn$_2$YSn (Y = Mo, Nb, Zr) by first-principles density
functional theory using the generalized gradient approximation. It is found
that the calculated lattice constants are in good agreement with the
theoretical values. We observe that the Cu$_2$MnAl-type structure is more
stable than the Hg$_2$CuTi type. The calculated total magnetic moments of
Mn$_2$NbSn and Mn$_2$ZrSn are 1 $\mu_{\text{B}}$ and 2 $\mu_{\text{B}}$ at the
equilibrium lattice constant of 6.18 \AA and 6.31 \AA, respectively, for the
Cu$_2$MnAl-type structure. Mn$_2$MoSn have a metallic character in both
Hg$_2$CuTi and Cu$_2$MnAl type structures. The total spin magnetic moment obeys
the Slater-Pauling rule. Half-metal exhibits 100% spin polarization at the
Fermi level. Thus, these alloys are promising magnetic candidates in spintronic
devices. | 2103.15542v1 |
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 |
2022-03-22 | Lattice Dynamics, Mechanical Properties, Electronic Structure and Magnetic Properties of Equiatomic Quaternary Heusler Alloys CrTiCoZ (Z =Al,Si) using first principles calculations | First principles calculations are performed to investigate the
thermodynamical stability, dynamical, mechanical, electronic and magnetic
properties of CrTiCoZ (Z= Al/Si) novel quaternary Heusler alloys. Y-type III
atomic configuration is found to be the most stable structure for both
compounds. The melting temperatures of both compounds are as high as 2142 K and
2420 K for CrTiCoAl and CrTiCoSi, respectively. The electronic structure
calculations using GGA-PBE approach show a half metallic behavior of CrTiCoAl.
The spin-down channel exhibits a direct band gap of 0.15 eV, whereas the
spin-up channel is metallic making CrTiCoAl a half metallic ferromagnet with
100% spin polarization and an appreciable magnetic moment of -2 Bohr Magnetons.
The Curie temperature of CrTiCoAl is well above the room temperature (385K),
whereas that of CrTiCoSi is below the room temperature (203K). | 2203.11858v1 |
2022-03-23 | Effective decoupling of ferromagnetic sublattices by frustration in Heusler alloys | Magnetic frustration in ferromagnetic metallic systems is unusual due to the
long-range and symmetric nature of the exchange interactions. In this work we
prove that it is possible to obtain a highly frustrated ferromagnetic phase in
a multi-sublattices cubic structure through a fine tuning of the magnetic
interactions. This peculiar state is achieved in Ni-Mn-(In, Sn) Heusler alloys
and results in the effective decoupling of their two intertwined ferromagnetic
sublattices. One sublattice is ferromagnetic long range ordered below the
macroscopic Curie temperature (TC ) whereas the second one remains disordered
until a crossover to a polarized state occurs at T << TC . This result points
out that a fine engineering of the magnetic interactions in metallic systems
can lead to interesting novel and emergent phenomena. | 2203.12498v2 |
2016-03-29 | Revealing the nature of magnetic phases in the semi-Heusler alloy Cu0.85Ni0.15MnSb | We report the magnetic, magnetocaloric, and magnetotransport properties of
the semi-Heusler alloy Cu0.85Ni0.15MnSb, which exhibits coexistence of
antiferromagnetic (AFM) and ferromagnetic (FM) phases. A broad magnetic phase
transition is evident from the temperature variations of magnetization, heat
capacity, and isothermal magnetic entropy change. This is due to the presence
of both AFM and FM phases at low temperatures. The variation of electrical
resistivity with temperature shows three distinct regions of magnetic phases.
The magnetoresistance (MR) results also show the presence of AFM and FM phases
at temperatures below 45 K, and a FM phase at temperature above 45K. Though
there is no signature of a spin-glass state at low temperatures, various
results point towards the presence of short-range magnetic correlations at low
temperatures. | 1603.08618v1 |
2017-02-03 | Field dependent neutron diffraction study in Ni50Mn38Sb12 Heusler alloy | In this paper, we present temperature and field dependent neutron diffraction
(ND) study to unravel the structural and the magnetic properties in
Ni50Mn38Sb12 Heusler system. This alloy shows martensitic transition from high
temperature austenite cubic phase to low temperature martensite orthorhombic
phase on cooling. At 3 K, the lattice parameters and magnetic moments are found
to be almost insensitive to field. Just below the martensitic transition
temperature, the martensite phase fraction is found to be 85%. Upon applying
the field, the austenite phase becomes dominant, and the field induced reverse
martensitic transition is clearly observed in the ND data. Therefore, the
present study gives an estimate of the strength of the martensite phase or the
sharpness of the martensitic transition. Variation of individual moments and
the change in the phase fraction obtained from the analysis of the ND data
vividly show the change in the magneto-structural state of the material across
the transition. | 1702.00940v1 |
2019-05-21 | Competition of L21 and XA Ordering in Fe2CoAl Heusler Alloy: A First-Principles Study | The physical properties of Fe2CoAl (FCA) Heusler alloy are systematically
investigated using the first-principles calculations within generalized
gradient approximation (GGA) and GGA+U. The influence of atomic ordering with
respect to the Wyckoff sites on the phase stability, magnetism and half
metallicity in both the conventional L21 and XA phases of FCA is focused in
this study. Various possible hypothetical structures viz., L21, XA-I, and XA-II
are prepared by altering atomic occupancies at their Wyckoff sites. At first,
we have determined the stable phase of FCA considering various non-magnetic (or
paramagnetic), ferromagnetic (FM) and antiferromagnetic (AFM) configurations.
Out of these, the ferromagnetic (FM) XA-I structure is found to be
energetically most stable. The total magnetic moments per cell are not in
agreement with the Slater-Pauling (SP) rule in any phases; therefore, the
half-metallicity is not observed in any configurations. However, FM ordered
XA-I type FCA shows 78% spin polarization at EF. Interestingly, the results of
XA-I type FCA are closely matched with the experimental results. | 1905.08476v2 |
2019-09-07 | Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping | Based on high-throughput density functional theory calculations, we
investigated the effects of light interstitial H, B, C, and N atoms on the
magnetic properties of cubic Heusler alloys, with the aim to design new
rare-earth free permanent magnets. It is observed that the interstitial atoms
induce significant tetragonal distortions, leading to 32 candidates with large
($>$ 0.4 MJ/m$^3$) uniaxial magneto-crystalline anisotropy energies (MAEs) and
10 cases with large in-plane MAEs. Detailed analysis following the the
perturbation theory and chemical bonding reveals the strong MAE originates from
the local crystalline distortions and thus the changes of the chemical bonding
around the interstitials. This provides a valuable way to tailor the MAEs to
obtain competitive permanent magnets, filling the gap between high performance
Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials. | 1909.03275v1 |
2019-09-23 | Giant magnetocaloric effect in Co2FeAl Heusler alloy nanoparticles | A giant magnetocaloric effect across the ferromagnetic (FM) to paramagnetic
(PM) phase transition was observed in chemically synthesized Co2FeAl Heusler
alloy nanoparticles with a mean diameter of 16 nm. In our previous report, we
have observed a significant enhancement in its saturation magnetization (Ms)
and Curie temperature (Tc) as compared with the bulk counterpart. Motivated
from those results, here, we aim to explore its magnetocaloric properties near
the Tc. The magnetic entropy change shows a positive anomaly at 1252 K.
Magnetic entropy change increases linearly with the magnetic field, and a large
value of ~15 J/Kg-K is detected under a moderate field of 14 kOe. It leads to a
net relative cooling power of 89 J/Kg for the magnetic field change of 14 kOe.
To confirm the nature of magnetic phase transition, a detailed study of its
magnetization is performed. The Arrott plot and nature of the universal curve
conclude that FM to PM phase transition in the present system is of
second-order. | 1909.10201v4 |
2020-02-27 | Ultrafast magnetization dynamics in half-metallic Co$_2$FeAl Heusler alloy | We report on optically induced, ultrafast magnetization dynamics in the
Heusler alloy $\mathrm{Co_{2}FeAl}$, probed by time-resolved magneto-optical
Kerr effect. Experimental results are compared to results from electronic
structure theory and atomistic spin-dynamics simulations. Experimentally, we
find that the demagnetization time ($\tau_{M}$) in films of
$\mathrm{Co_{2}FeAl}$ is almost independent of varying structural order, and
that it is similar to that in elemental 3d ferromagnets. In contrast, the
slower process of magnetization recovery, specified by $\tau_{R}$, is found to
occur on picosecond time scales, and is demonstrated to correlate strongly with
the Gilbert damping parameter ($\alpha$). Our results show that
$\mathrm{Co_{2}FeAl}$ is unique, in that it is the first material that clearly
demonstrates the importance of the damping parameter in the remagnetization
process. Based on these results we argue that for $\mathrm{Co_{2}FeAl}$ the
remagnetization process is dominated by magnon dynamics, something which might
have general applicability. | 2002.12255v1 |
2020-07-12 | Magnetocaloric effect in Ni2(Mn,Cu)Ga0.84Al0.16 Heusler alloys | Polycrystalline Heusler compounds Ni2Mn0.75Cu0.25Ga0.84Al0.16 with a
martensitic transition between ferromagnetic phases and
Ni2Mn0.70Cu0.30Ga0.84Al0.16 with a magnetostructural transformation were
investigated by magnetization and thermal measurements, both as a function of
temperature and magnetic field. The compound Ni2Mn0.75Cu0.25Ga0.84Al0.16
presents a large magnetocaloric effect among magnetically aligned structures
and its causes are explored. In addition, Ni2Mn0.70Cu0.30Ga0.84Al0.16 shows
very high, although irreversible, entropy and adiabatic temperature change at
room temperature under a magnetic field change 0-1 T. Improved refrigerant
capacity is also a highlight of the 30% Cu material when compared to similar
Ni2MnGa-based alloys. | 2007.05899v2 |
2020-10-16 | Visualizing half-metallic bulk band structure with multiple Weyl cones of the Heusler ferromagnet | Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved
photoelectron spectroscopy was applied to a full-Heusler-type Co$_2$MnGe alloy
to elucidate its bulk band structure. A large parabolic band at the Brillouin
zone center and several bands that cross the Fermi level near the Brillouin
zone boundary were identified in line with the results from first-principles
calculations. These Fermi level crossings are ascribed to majority spin bands
that are responsible for electron transport with extremely high spin
polarization especially along the direction being perpendicular to the
interface of magneto-resistive devices. The spectroscopy confirms there is no
contribution of the minority spin bands to the Fermi surface, signifying
half-metallicity for the alloy. Furthermore, two topological Weyl cones with
band crossing points were identified around the $X$ point, yielding the
conclusion that Co$_2$MnGe could exhibit topologically meaningful behavior such
as large anomalous Hall and Nernst effects driven by the Berry flux in its
half-metallic band structure. | 2010.08415v1 |
2021-02-15 | Prediction of a Heusler alloy with switchable metal-to-half-metal behavior | We propose a ferromagnetic Heusler alloy that can switch between a metal and
a half-metal. Thiseffect can provide tunable spintronics properties. Using the
density functional theory (DFT) withreliable implementations of the electron
correlation effects, we find Mn2ScSi total energy curvesconsisting of distinct
branches with a very small energy difference. The phase at low lattice
crystalvolume is a low magnetic half-metallic state while the phase at high
lattice crystal volume is a highmagnetic metallic state. We suggest that the
transition between half-metallic and metallic statescan be triggered by a
triaxial contraction/expansion of the crystal lattice or by an external
magneticfield if we assume that the lattice is cubic and remains cubic under
expansion/contraction. However,the phase at high volume can also undergo an
austenite-martensite phase transition because of thepresence of Jahn-Teller
active3delectrons on the Mn atoms. | 2102.07447v1 |
2021-06-06 | Prediction of half-metallicity and spin-gapless semiconducting behavior in the new series of FeCr-based quaternary Heusler alloys: an ab initio study | This paper presents a detailed investigation of FeCr-based quaternary Heusler
alloys. By using ultrasoft pseudopotential, electronic and magnetic properties
of the compounds are studied within the framework of Density Functional Theory
(DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and
dynamical stability of the compounds is established through the comprehensive
study of different mechanical parameters and phonon dispersion curves. The
meticulous study of elastic parameters such as bulk, Young's, shear moduli,
etc. is done to understand different mechanical properties. The FeCr-based
compounds containing also Yttrium are studied to redress the contradictory
electronic and magnetic properties observed in the literature. The interesting
properties like half-metallicity and spin-gapless semiconducting (SGS) behavior
are realized in the compounds under study. | 2106.03026v1 |
2021-11-29 | Half-metallic Ferromagnets, Spin Gapless Semiconductors, and Topological Semimetals Based on Heusler Alloys | A review of theoretical and experimental studies of the electronic structure,
electronic and magnetic properties of various systems of Heusler alloys in the
states of a half-metallic ferromagnet, a spin gapless semiconductor, and a
topological semimetal is presented. These substances have unusual, highly
sensitive to external influences, magnetic and electronic characteristics,
which is associated with the presence of energy gaps and exotic excitations in
them. The features of the behavior and evolution of the electronic structure
and properties in each of these states, as well as during the transition
between them, are considered. The possibility to purposefully control the
properties of such materials is prospective for their practical application. | 2111.14537v1 |
2022-08-06 | Giant spin Hall effect in half-Heusler alloy topological semimetal YPtBi grown at low temperature | Half-Heusler alloy topological semimetal YPtBi is a promising candidate for
an efficient spin source material having both large spin Hall angle
${\theta}$$_{SH}$ and high thermal stability. However, high-quality YPtBi thin
films with low bulk carrier density are usually grown at 600${\deg}$C, which
exceeds the limitation of 400${\deg}$C for back end of line (BEOL) process.
Here, we investigate the crystallinity and spin Hall effect of YPtBi thin films
grown at lower growth temperature down to 300${\deg}$C. Although
${\theta}$$_{SH}$ degraded with lowering the growth temperature to 300${\deg}$C
due to degradation of the crystallinity, it was recovered by reducing the
sputtering Ar gas pressure. We achieved a giant ${\theta}$$_{SH}$ up to 8.2 and
demonstrated efficient spin-orbit torque magnetization switching by ultralow
current density of ~10$^5$ A/cm$^2$ in YPtBi grown at 300${\deg}$C with the Ar
gas pressure of 1 Pa. Our results provide the recipe to achieve giant
${\theta}$$_{SH}$ in YPtBi grown at lower growth temperature suitable for BEOL
process. | 2208.03413v1 |
2022-09-18 | Superparamagnetic and metal-like Ru2TiGe: a propitious thermoelectric material | We report a study of structural, magnetic, heat capacity and thermoelectric
properties of a Rubased Heusler alloy, Ru2TiGe. The magnetic measurements
reveal that at higher temperatures, diamagnetic and Pauli paramagnetic
contributions dominate the magnetic behaviour whereas, at lower temperatures
(T<= 20 K), superparamagnetic interaction among clusters is observed. Effect of
such magnetic defects is also evident in the electrical resistivity behaviour
at lower temperatures. Though the temperature dependence of resistivity
exhibits a metal-like nature, the large value of Seebeck coefficient leads to
an appreciable power factor of the order of 1 mW/mK2 at 300 K. Large power
factor as well as low thermal conductivity results in a value of ZT = 0.025 at
390 K for Ru2TiGe that is orders of magnitude higher than that of the other
pure Heusler alloys and point towards its high potential for practical
thermoelectric applications. | 2209.08474v1 |
2022-11-22 | Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl | Heusler alloys based magnetic tunnel junctions can potentially provide high
magnetoresistance, small damping and fast switching. Here junctions with
Co2FeAl as a ferromagnetic electrode are fabricated by room temperature
sputtering on Si/SiO2 substrates. The doping of Boron in Co2FeAl is found to
have a large positive impact on the structural, magnetic and transport
properties of the junctions, with a reduced interfacial roughness and
substantial improved tunneling magnetoresistance. A two-level magnetoresistance
is also observed in samples annealed at low temperature, which is believed to
be related to the memristive effect of the tunnel barrier with impurities. | 2211.12448v1 |
2023-09-11 | Experimental realization of a high Curie temperature CoFeRuSn quaternary Heusler alloy for spintronic applications | We synthesize CoFeRuSn equiatomic quaternary Heusler alloy using arc-melt
technique and investigate its structural, magnetic and transport properties.
The room temperature powder X-ray diffraction analysis reveals that CoFeRuSn
crystallizes in cubic crystal structure with small amount of DO3 - disorder.
The field dependence of magnetization shows non-zero but small hysteresis and
saturation behavior up to room temperature, indicating soft ferromagnetic
nature of CoFeRuSn. The magnetic moment estimated from the magnetization data
is found to be 4.15 {\mu}B / f.u., which is slightly less than the expected
Slater-Pauling rule. The deviation in the value of experimentally observed
moment from the theoretical value might be due to small disorder in the
crystal. The low temperature fit to electrical resistivity data show absence of
quadratic temperature dependence of resistivity, suggesting half-metallic
behavior of CoFeRuSn. The high Curie temperature and possible half-metallic
behavior of CoFeRuSn make it a highly promising candidate for room temperature
spintronic applications. | 2309.05493v1 |
2023-11-26 | Machine Learning-based estimation and explainable artificial intelligence-supported interpretation of the critical temperature from magnetic ab initio Heusler alloys data | Machine Learning (ML) has impacted numerous areas of materials science, most
prominently improving molecular simulations, where force fields were trained on
previously relaxed structures. One natural next step is to predict material
properties beyond structure. In this work, we investigate the applicability and
explainability of ML methods in the use case of estimating the critical
temperature for magnetic Heusler alloys calculated using ab initio methods
determined materials-specific magnetic interactions and a subsequent Monte
Carlo (MC) approach. We compare the performance of regression and
classification models to predict the range of the critical temperature of given
compounds without performing the MC calculations. Since the MC calculation
requires computational resources in the same order of magnitude as the
density-functional theory (DFT) calculation, it would be advantageous to
replace either step with a less computationally intensive method such as ML. We
discuss the necessity to generate the magnetic ab initio results to make a
quantitative prediction of the critical temperature. We used state-of-the-art
explainable artificial intelligence (XAI) methods to extract physical relations
and deepen our understanding of patterns learned by our models from the
examined data. | 2311.15423v1 |
2024-03-27 | THz probing of non-trivial topological states in Co2MnGe Heusler alloy thin films | Co2MnGe (CMG) has been demonstrated recently as a half-metallic ferromagnetic
Heusler alloy which possesses a topologically non-trivial band structure. This
behavior is unique to such systems and hence warrants extensive experimental
exploration for potential spintronic and chirality sensitive optoelectonic
applications. Here, we demonstrate that an epitaxial thin film of CMG acts as a
source of THz radiation upon photoexcitation by optical femtosecond laser
pulses. Detailed experiments have revealed that a large contribution to THz
emission occurs due to nonmagnetic or spin-independent origin, however,
significant contribution in the THz generation is evidenced through excitation
light helicity dependent circular photogalvanic effect (CPGE) confirming the
presence of topologically non-trivial carriers. Furthermore, we show that not
only the topological contribution is easily suppressed but also the overall THz
generation efficiency is also affected adversely for the epitaxial films grown
at high substrate temperatures. | 2403.18332v1 |
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 |
2021-07-19 | Impact of local arrangement of Fe and Ni in Fe-Ni-Al Heusler alloys on the phase stability and magnetocrystalline anisotropy | On the basis of the density functional calculations in combination with the
supercell approach, we report on a complete study of the influences of atomic
arrangement and Ni substitution for Al on the ground state structural and
magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss
systematically the competition between five cubic Heusler-type structures
formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase
stability and magnetic properties, in particular magnetocrystalline
anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state cubic
structure with alternated layers of Fe and Ni possesses the highest uniaxial
MAE which twice larger than that for the tetragonal L1$_0$ FeNi. The successive
Ni doping at Al sublattice leads to a change of ground state structure and to
reduce of the MAE. In addition, the phase stability against the decomposition
into the stable systems at finite-temperatures is discussed. All~Ni-rich
Fe$_2$Ni$_{1+x}$Al$_{1-x}$ are turned to be decomposed into a dual-phase
consisting of Fe$_2$NiAl and FeNi. | 2107.08804v2 |
2019-07-05 | Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy | Materials suitable for magnonic crystals demand low magnetic damping and long
spin wave (SW) propagation distance. In this context Co based Heusler compounds
are ideal candidates for magnonic based applications. In this work, antidot
arrays (with different shapes) of epitaxial
$\mathrm{Co}_2\mathrm{Fe}_{0.4}\mathrm{Mn}_{0.6}\mathrm{Si}$ (CFMS) Heusler
alloy thin films have been prepared using e-beam lithography and sputtering
technique. Magneto-optic Kerr effect and ferromagnetic resonance analysis have
confirmed the presence of dominant cubic and moderate uniaxial magnetic
anisotropies in the thin films. Domain imaging via x-ray photoemission electron
microscopy on the antidot arrays reveals chain like switching or correlated
bigger domains for different shape of the antidots. Time-resolved MOKE
microscopy has been performed to study the precessional dynamics and magnonic
modes of the antidots with different shapes. We show that the optically induced
spin-wave spectra in such antidot arrays can be tuned by changing the shape of
the holes. The variation in internal field profiles, pinning energy barrier,
and anisotropy modifies the spin-wave spectra dramatically within the antidot
arrays with different shapes. We further show that by combining the
magnetocrystalline anisotropy with the shape anisotropy, an extra degree of
freedom can be achieved to control the magnonic modes in such antidot lattices. | 1907.02746v1 |
2014-02-07 | Fermi sea term in the relativistic linear muffin-tin-orbital transport theory for random alloys | We present a formulation of the so-called Fermi sea contribution to the
conductivity tensor of spin-polarized random alloys within the fully
relativistic tight-binding linear muffin-tin-orbital (TB-LMTO) method and the
coherent potential approximation (CPA). We show that the configuration
averaging of this contribution leads to the CPA-vertex corrections that are
solely due to the energy dependence of the average single-particle propagators.
Moreover, we prove that this contribution is indispensable for the invariance
of the anomalous Hall conductivities with respect to the particular LMTO
representation used in numerical implementation. Ab initio calculations for
cubic ferromagnetic 3d transition metals (Fe, Co, Ni) and their random binary
alloys (Ni-Fe, Fe-Si) indicate that the Fermi sea term is small against the
dominating Fermi surface term. However, for more complicated structures and
systems, such as hexagonal cobalt and selected ordered and disordered Co-based
Heusler alloys, the Fermi sea term plays a significant role in the quantitative
theory of the anomalous Hall effect. | 1402.1643v1 |
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 |
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