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2019-04-25 | Low damping magnetic properties and perpendicular magnetic anisotropy with strong volume contribution in the Heusler alloy Fe1.5CoGe | We present a study of the dynamic magnetic properties of TiN-buffered
epitaxial thin films of the Heusler alloy Fe$_{1.5}$CoGe. Thickness series
annealed at different temperatures are prepared and the magnetic damping is
measured, a lowest value of $\alpha=2.18\times 10^{-3}$ is obtained. The
perpendicular magnetic anisotropy properties in Fe$_{1.5}$CoGe/MgO are also
characterized. The evolution of the interfacial perpendicular anisotropy
constant $K^{\perp}_{\rm S}$ with the annealing temperature is shown and
compared with the widely used CoFeB/MgO interface. A large volume contribution
to the perpendicular anisotropy of $(4.3\pm0.5)\times 10^{5}$ $\rm J/m^3$ is
also found, in contrast with vanishing bulk contribution in common Co- and
Fe-based Heusler alloys. | 1904.11247v1 |
2018-02-07 | Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy | Future spintronics requires the realization of thin film of half-metallic
ferromagnets having high Curie temperature and 100\% spin polarization at the
Fermi level for potential spintronics applications. In this paper, we report
the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO
(001) substrate using pulsed laser deposition system, along with the study of
structural, magnetic and transport properties. The magnetic property
measurements of the thin film suggest a soft ferromagnetic state at room
temperature with an in-plane magnetic anisotropy and a Curie temperature well
above the room temperature. Anisotropic magnetoresistance (AMR) ratio and
temperature dependent electrical resistivity measurements of the thin film
indicate the compound to be half-metallic in nature and therefore suitable for
the fabrications of spintronics devices. | 1802.02413v1 |
2018-02-17 | FeTaSb and FeMnTiSb as promising thermoelectric materials: An ab initio approach | Thermoelectricity in principle provides a pathway to put waste heat to good
use. Motivated by this we investigate thermal and electrical transport
properties of two new Fe-based Heusler alloys, FeTaSb and FeMnTiSb, by a first
principles approach and semiclassical Boltzmann transport theory within the
constant relaxation-time approximation. We find a high power factor of
\textit{p}-doped FeTaSb, competitive with best performing Heusler alloy FeNbSb
at 1100 K. The obtained power factor of \textit{n}-doped FeMnTiSb at room
temperature is higher than that of both FeNbSb and FeTaSb. Remarkably, FeMnTiSb
can be used for both \textit{n}-type and \textit{p}-type legs in a
thermoelectric module. The Seebeck coefficients of the two proposed systems are
in line with those of earlier reported Heusler alloys. We also provide
conservative estimates of the figure of merit for the two systems. Overall, our
findings suggest a high temperature thermoelectric potential of FeTaSb while
the low cost FeMnTiSb is a viable room temperature thermoelectric candidate
material. | 1802.06254v1 |
2018-12-13 | Current-induced nucleation and dynamics of skyrmions in a Co-based Heusler alloy | We demonstrate room-temperature stabilization of dipolar magnetic skyrmions
with diameters in the range of $100$ nm in a single ultrathin layer of the
Heusler alloy Co$_2$FeAl (CFA) under moderate magnetic fields. Current-induced
skyrmion dynamics in microwires is studied with a scanning Nitrogen-Vacancy
magnetometer operating in the photoluminescence quenching mode. We first
demonstrate skyrmion nucleation by spin-orbit torque and show that its
efficiency can be significantly improved using tilted magnetic fields, an
effect which is not specific to Heusler alloys and could be advantageous for
future skyrmion-based devices. We then show that current-induced skyrmion
motion remains limited by strong pinning effects, even though CFA is a magnetic
material with a low magnetic damping parameter. | 1812.05345v1 |
2020-04-03 | Improved magnetostructural and magnetocaloric reversibility in magnetic Ni-Mn-In shape-memory Heusler alloy by optimizing the geometric compatibility condition | We report an improved reversibility of magnetostriction and inverse
magnetocaloric effect (MCE) for the magnetic shape-memory Heusler alloy
Ni$_{1.8}$Mn$_{1.8}$In$_{0.4}$. We show that the magnetostriction and MCE
crucially depends on the geometrical compatibility of the austenite and
martensite phases. Detailed information on the compatibility of both phases has
been obtained from the transformation matrix calculated from x-ray diffraction
data. The uniqueness of the lattice parameters results in an improved
reversibility of the magnetostriction and the MCE. In the thermal hysteresis
region of the martensitic transformation, the maximum relative length change is
0.3% and the adiabatic temperature change $\Delta T_{ad}\approx -10$ K in
pulsed magnetic fields. Our results reveal that the approach of geometric
compatibility will allow one to design materials with reversible
magnetostriction and reversible inverse MCE at a first-order magnetostructural
phase transition in shape-memory Heusler alloys. | 2004.01527v1 |
2019-08-20 | Coexistence of spin frustration and spin unfrustration induced spontaneous exchange bias in Heusler alloys | The mechanism of spontaneous exchange bias (SEB) and the dominant factor of
its blocking temperature are still unclear in Heusler alloys. Here, the related
investigations are performed in Mn2Ni1.5Al0.5 Heusler alloys with SEB. The
results of both magnetic measurements and first-principles calculations
confirmed that spin frustrated and unfrustrated antiferromagnetic (AFM) states
coexist there and they have different magnetic anisotropies, which are
essential for SEB. Based on a series of measurement strategies, we demonstrate
that the frustrated AFM state undergoes a first-order magnetic transition to
the superferromagnet (SFM) state with the help of an external magnetic field,
and SFM is retained due to the first-order property of the magnetic transition.
SEB originates from the interface coupling of multiple sublattices between the
unfrustrated AFM state and SFM state. By analyzing the Arrott plot using the
Landau model, we found that the internal field of the system dominates the
blocking temperature of SEB, which paves the way for improving the blocking
temperature. | 1908.07149v1 |
2020-09-09 | Structural, Elastic, Electronic and Magnetic Properties of MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) Semi-Heusler Alloys | The study of structural, electronic, magnetic, and elastic properties of new
series of semi-Heusler alloys MnNbZ (Z=As, Sb) and FeNbZ (Z=Sn, Pb) has been
performed by density functional theory. The magnetic phase and hence the
structural stability of the alloys were considered wherein ferromagnetic state
is found to stable. The half-metallic states are observed from the density of
states and band structure calculations. The total magnetic moments found for
all studied compounds are 1 $\mu_B$/f.u., which obey Slating-Pauling rule for
semi-Heusler with ferromagnetic behavior. The calculated elastic constant
C$_{ij}$, cohesive energy, and formation energy confirmed that these materials
are mechanically stable. Among the four system, MnNbAs is found to have the
highest ductility while the remaining systems are found to be brittle in
nature. These properties confirmed that among others, MnNbAs is one of the
novel candidate for spintronic devices applications. | 2009.04123v1 |
2020-12-22 | Structural insight using anomalous XRD into Mn2CoAl Heusler alloy films grown by magnetron sputtering, IBAS and MBE techniques | Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless
semiconductor (SGS), grown by three different methods: ultra-high vacuum
magnetron spattering, Ar-ion beam assisted sputtering, and molecular beam
epitaxy, are investigated by comparing their electric transport properties,
microstructures and atomic-level structures. Of the samples, the Mn2CoAl thin
film grown by MBE consists of Mn- and Co-rich phases, the structures of which
are determined to be the L21B-type and disordered L21-type, respectively,
according to anomalous XRD analysis. None of them forms the XA-type structure
expected for SGS Heusler alloy, although they all show SGS characteristics. We
suggest, to validate SGS characteristics, it is necessary to extract not only
magnetic and electric transport properties but also information about
microstructures and atomic-scale structures of the films including defects such
as atomic swap. | 2012.12282v1 |
2021-02-01 | Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: possible states of a half-metallic ferromagnet and spin gapless semiconductor | Parameters of the energy gap and, consequently, electronic, magnetic and
galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite
strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless
semiconductors (SGSs) with almost 100% spin polarization of charge carriers are
promising materials for spintronics. The changes in the electrical, magnetic
and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and
Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states
were followed and their interconnection was established. Significant changes in
the values of the magnetization and residual resistivity were found. At the
same time, the correlations between the changes in these electronic and
magnetic characteristics depending on the number of valence electrons and spin
polarization are observed. | 2102.00952v1 |
2021-09-23 | Tuning magnetic antiskyrmion stability in tetragonal inverse Heusler alloys | The identification of materials supporting complex, tunable magnetic order at
ambient temperatures is foundational to the development of new magnetic device
architectures. We report the design of Mn2XY tetragonal inverse Heusler alloys
that are capable of hosting magnetic antiskyrmions whose stability is sensitive
to elastic strain. We first construct a universal magnetic Hamiltonian
capturing the short- and long- range magnetic order which can be expected in
these materials. This model reveals critical combinations of magnetic
interactions that are necessary to approach a magnetic phase boundary, where
the magnetic structure is highly susceptible to small perturbations such as
elastic strain. We then computationally search for quaternary Mn2(X1,X2)Y
alloys where these critical interactions may be realized and which are likely
to be synthesizable in the inverse Heusler structure. We identify the
Mn2Pt(1-z)X(z)Ga family of materials with X=Au, Ir, Ni as an ideal system for
accessing all possible magnetic phases, with several critical compositions
where magnetic phase transitions may be actuated mechanically. | 2109.11423v1 |
2007-07-03 | Effect of Co and Fe on the inverse magnetocaloric properties of Ni-Mn-Sn | At certain compositions Ni-Mn-$X$ Heusler alloys ($X$: group IIIA-VA
elements) undergo martensitic transformations, and many of them exhibit inverse
magnetocaloric effects. In alloys where $X$ is Sn, the isothermal entropy
change is largest among the Heusler alloys, particularly in
Ni$_{50}$Mn$_{37}$Sn$_{13}$ where it reaches a value of 20 Jkg$^{-1}$K$^{-1}$
for a field of 5T. We substitute Ni with Fe and Co in this alloy, each in
amounts of 1 at% and 3 at% to perturb the electronic concentration and examine
the resulting changes in the magnetocaloric properties. Increasing both Fe and
Co concentrations causes the martensitic transition temperature to decrease,
whereby the substitution by Co at both compositions or substituting 1 at% Fe
leads to a decrease in the magnetocaloric effect. On the other hand, the
magnetocaloric effect in the alloy with 3 at% Fe leads to an increase in the
value of the entropy change to about 30 Jkg$^{-1}$K$^{-1}$ at 5T. | 0707.0360v1 |
2015-01-21 | Antiferromagnetism in Ru2MnZ (Z=Sn, Sb, Ge, Si) full Heusler alloys: effects of magnetic frustration and chemical disorder | We present systematic theoretical investigations to explore the microscopic
mechanisms leading to the formation of antiferromagnetism in Ru2MnZ (Z=
Sn,Sb,Ge,Si) full Heusler alloys. Our study is based on first-principles
calculations of inter-atomic Mn-Mn exchange interactions to set up a suitable
Heisenberg spin-model and on subsequent Monte-Carlo simulations of the magnetic
properties at finite temperature. The exchange interactions are derived from
the paramagnetic state, while a realistic account of long-range chemical
disorder is made in the framework of the Coherent Potential Approximation. We
find that in case of the highly ordered alloys (Z=Sn and Sb) the exchange
interactions derived from the perfectly ordered L21 structure lead to N\'eel
temperatures in excellent agreement with the experiments, whereas, in
particular, in case of Si the consideration of chemical disorder is essential
to reproduce the experimental N\'eel temperatures. Our numerical results
suggest that improving a heat treatment of the samples to suppress the
intermixing between the Mn and Si atoms, the N\'eel temperature of the Si-based
alloys can potentially be increased by more than 30%. Furthermore, we show that
in strongly disordered Ru2MnSi alloys a distinct change in the
antiferromagnetic ordering occurs. | 1501.05116v1 |
2015-06-10 | A first-principle study of half-Heusler alloys CKMg and SiKMg | The structural, electronic, and magnetic properties of half-Heusler alloys
CKMg and SiKMg are studied by using first-principle density functional theory.
The calculations reveal the SiKMg alloy is a half-metallic ferromagnet with the
magnetic moment of 1 $\mu_B$ per formula unit at equilibrium lattice constant.
The magnetic moment mainly originates from the strong spin-polarization of $p$
electrons of Si atom and partial involvement of $d$ electrons of K atom. The
half-metallic gap is 0.105 eV. The robustness of half-metallic against the
lattice constants for SiKMg is also calculated. CKMg alloy is nearly
half-metallic with a spin polarization of 99.99 \%\ at equilibrium lattice
constant, but it is a good half-metallic alloy when a low pressure is applied.
This shows CKMg is a very promising spintronic functional material. | 1506.03297v1 |
2015-09-16 | Structural and magnetic properties of a new and ordered quaternary alloy MnNiCuSb (SG: F-43m) | We have synthesized a new crystallographically ordered quaternary Heusler
alloy, MnNiCuSb. The crystal structure of the alloy has been determined by
Rietveld refinement of the powder x-ray diffraction data. This alloy
crystallizes in the LiMgPdSb type structure with F-43m space group. MnNiCuSb is
a ferromagnet with a high TC ~ 690K and magnetic moment of 3.85MuB/f.u. Besides
this we have also studied two other off-stoichiometric compositions; one Cu
rich and the other Ni rich (MnNi0.9Cu1.1Sb and MnNi1.1Cu0.9Sb) which are also
ferromagnets. It must be stressed that MnNiCuSb is one of the very few known,
non-Fe containing quaternary Heusler alloys with 1: 1: 1: 1 composition. | 1509.04833v1 |
2022-05-07 | First-principle calculations on Li2CuSb: A novel material for lithium-ion batteries | We investigate the Li2CuSb full-Heusler alloy using the first-principles
electronic structure calculations and propose the electrochemical lithiation in
this alloy. Band structure calculations suggest the presence of metallic nature
in this alloy contrary to half-metallic nature as predicted for most of the
members of the full-Heusler alloy family. This alloy is found to be a promising
anode material for high-capacity rechargeable batteries based on lithium-ion.
We found a removal voltage of 2.48 V for lithium ions in the Li2CuSb/Cu cell,
which is in good agreement with the experimentally obtained result for a
similar kind of material Cu3Sb. During charge and discharge cycles of the
Li2CuSb/Cu cell, the formation of a non-stoichiometric compound Li2-yCu1+xSb
having a similar structure as Li2CuSb suggests a better performance as well as
stabilitty of this cell. | 2205.03631v1 |
2020-07-15 | Experimentally correlating thermal hysteresis and phase compatibility in multifunctional Heusler alloys | Thermal hysteresis is recognized as one of the main drawbacks for cyclical
applications of magnetocaloric and ferromagnetic shape memory materials with
first order transformations. As such, the challenge is to develop strategies
that improve the compatibility between the phases involved in the transitions
and study its influence on thermal hysteresis. With this purpose, we explore
the thermal, structural and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16
Heusler alloys. The alloys present a thermal hysteresis reduction of ~60% when
the Cu content in the compound varies from x = 0.10 to x = 0.25, with a minimum
hysteresis width of 6 K being achieved. We applied the geometric non-linear
theory of martensite to address the phase compatibility, quantified by the
parameter lambda2, the middle eigenvalue of the transformation stretch tensor,
and found that the minimum of hysteresis is associated with a better
crystallographic compatibility (lambda2 closer to 1) between the austenite and
martensite phases. In addition, we show that the valley-like properties of
hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several
other alloys in the literature. These results provide new pathways to
understand as well as to masters the phase compatibility and ultimately achieve
a low thermal hysteresis in multifunctional Heusler alloys. | 2007.07485v1 |
2023-05-04 | 4d-element induced improvement of structural disorder and development of weakly re-entrant spin-glass behaviour in NiRuMnSn | The pursuit of efficient spin-polarization in quaternary Heusler alloys with
the general formula $XX'YZ$ (where X, $X'$, and Y are transition metals and Z
is a p-block element), has been a subject of significant scientific interest.
While previous studies shows that isoelectronic substitution of 4d element in
place of 3d element in quaternary Heusler alloy, improves the half-metallic
ferromagnetic characteristics, our research on the quaternary Heusler alloy
NiRuMnSn reveals a strikingly different scenario. In this study, we present a
detailed structural analysis of the material using X-ray absorption fine
structure (EXAFS) and neutron diffraction (ND) techniques, which confirms the
formation of a single-phase compound with 50:50 site disorder between Ni/Ru
atoms at 4c/4d sites. Contrary to expectations, our DFT calculations suggests a
considerable decrease in spin-polarization even in the ordered structure.
Additionally, we report on the compound's exceptional behavior, displaying a
rare re-entrant spin glass property below $\sim$60 K, a unique and intriguing
feature for quaternary Heusler-type compounds. | 2305.03087v1 |
2012-10-22 | Structure, magnetism and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys | The structure, magnetism, magnetic compensation behavior, exchange
interaction and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25
(x=0-25) alloys have been systematically investigated by both experiments and
first-principles calculations. We found that all the samples exhibited body
centered cubic structures with a high degree of atomic ordering. With
increasing Ga content, the composition dependence of lattice parameters shows a
kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be
attributed to the enhanced covalent effect between the Ga and the transition
metals. Furthermore, a complicated magnetic competition has been revealed in
Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically
decrease and results in a magnetic moment compensation behavior. In
Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional
ferrimagnetic configuration was established in the native ferromagnetic matrix,
which causes the molecular moment monotonously decreases and the exchange
interaction enhances gradually. The electronic structure calculations indicate
that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the
itinerant and localized magnetism. Our study will be helpful to understand the
nature of magnetic ordering as well as to tune magnetic compensation and
electronic properties of Heusler alloys. | 1210.5810v1 |
2019-02-20 | Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe$_{45}$Mn$_{26}$Ga$_{29}$ alloy on its electronic structure and physical properties | Effect of the temperature and magnetic field induced martensitic
transformation (MT) on the electronic structure and some physical properties of
bulk Fe$_{45.2}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy has been investigated.
{According to the experimental results of DSC, magnetic and transport
measurements direct and reverse martensitic transformation without external
magnetic field takes place within 194 $\leq T \leq$ 328 K temperature range
with a hysteresis up to $\Delta T \approx$ 100 K defined as $\Delta T$ =
$A_{f,s}$ - $M_{s,f}$, where $A_{f,s}$ and $M_{s,f}$ are the critical
temperatures of direct and reverse martensitic transformation. External
magnetic field of $\mu_{0}H$ = 5 T causes a high-temperature shift of MT
temperatures.} MT from parent austenite L2$_{1}$ phase to martensitic
tetragonally distorted L2$_{1}$ one (i. e. to L1$_{0}$) causes significant
changes in the electronic structure of alloy, a drastic increase in alloy
magnetization, a decrease in the alloy resistivity, and a reversal of the sign
of the temperature coefficient of resistivity from negative to positive. At the
same time experimentally determined optical properties of
Fe$_{45.6}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy in austenitic and martensitic
states look visually rather similar being noticeable different in microscopic
nature as can be concluded from first-principle calculations. Experimentally
observed changes in the physical properties of the alloy are discussed in terms
of the electronic structures of an austenite and martensite phases. | 1902.07462v1 |
2007-06-29 | Role of the exchange and correlation potential into calculating the x-ray absorption spectra of half-metallic alloys: the case of Mn and Cu K-edge XANES in Cu$_2$MnM (M = Al, Sn, In) Heusler alloys | This work reports a theoretical study of the x-ray absorption near-edge
structure spectra at both the Cu and the Mn K-edge in several Cu$_2$MnM (M= Al,
Sn and In) Heusler alloys. Our results show that {\it ab-initio} single-channel
multiple-scattering calculations are able of reproducing the experimental
spectra. Moreover, an extensive discussion is presented concerning the role of
the final state potential needed to reproduce the experimental data of these
half-metallic alloys. In particular, the effects of the cluster-size and of the
exchange and correlation potential needed in reproducing all the experimental
XANES features are discussed. | 0706.4370v3 |
2011-04-21 | Effect of Fe substitution on the magnetic, transport, thermal and magnetocaloric properties in Ni50Mn38-xFexSb12 Heusler alloys | The structural, magnetic, transport, thermal and magnetothermal properties of
quaternary Heusler alloys Ni50Mn38-xFexSb12 have been studied. Powder x-ray
diffraction and temperature dependence of magnetization studies reveal that
with addition of Fe in Mn site, the martensitic transition shifts to lower
temperatures. It is also found that the martensitic transition becomes broader
for the higher Fe concentrations. The metamagnetic transition in M(H) isotherms
becomes very prominent in x=2 and vanishes for x=3 and 4. A maximum positive
magnetic entropy change of 14.2 J/kg K is observed for x=2 at 288 K for 50 kOe.
Resistivity shows an abrupt decrease across the martensitic transition in all
the alloys, except x=6, which does not have the martensitic transition. Maximum
negative magnetoresistance of 21% has been obtained for x=2 at 50 kOe. The same
alloy also shows an exchange bias field of 288 Oe. | 1104.4214v1 |
2012-12-08 | $Ab~initio$ studies of Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys | We present results of extensive theoretical studies of
Co$_2$FeAl$_{1-x}$Si$_x$ Heusler alloys, which have been performed in the
framework of density functional theory employing the all-electron
full-potential linearized augmented plane-wave scheme. It is shown that the
Si-rich alloys are more resistive to structural disorder and as a consequence
Si stabilizes the $L2_1$ structure. Si alloying changes position of the Fermi
level, pushing it into the gap of the minority spin-band. It is also shown that
the hyperfine field on Co nuclei increases with the Si concentration, and this
increase originates mostly from the changes in the electronic density of the
valence electrons. | 1212.1781v2 |
2013-07-08 | Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds | Half-Heusler (HH) alloys have attracted considerable interest as promising
thermoelectric (TE) materials in the temperature range around 700 K and above,
which is close to the temperature range of most industrial waste heat sources.
The past few years have seen nanostructuing play an important role in
significantly enhancing the TE performance of several HH alloys. In this
article, we briefly review the recent progress and advances in these HH
nanocomposites. We begin by presenting the structure of HH alloys and the
different strategies that have been utilized for improving the TE properties of
HH alloys. Next, we review the details of HH nanocomposites as obtained by
different techniques. Finally, the review closes by highlighting several
promising strategies for further research directions in these very promising TE
materials. | 1307.2156v1 |
2015-10-17 | Direct evidence for minority spin gap in the Co2MnSi Heusler alloy | Half Metal Magnets are of great interest in the field of spintronics because
of their potential full spin-polarization at the Fermi level and low
magnetization damping. The high Curie temperature and predicted 0.7eV minority
spin gap make the Heusler alloy Co2MnSi very promising for applications.We
investigated the half-metallic magnetic character of this alloy using
spin-resolved photoemission, ab initio calculation and ferromagnetic resonance.
At the surface of Co2MnSi, a gap in the minority spin channel is observed,
leading to 100% spin polarization. However, this gap is 0.3 eV below the Fermi
level and a minority spin state is observed at the Fermi level. We show that a
minority spin gap at the Fermi energy can nevertheless be recovered either by
changing the stoichiometry of the alloy or by covering the surface by Mn, MnSi
or MgO. This results in extremely small damping coefficients reaching values as
low as 7x 10-4. | 1510.05085v1 |
2018-02-28 | Magnetocaloric effect in some magnetic materials in alternating magnetic fields up to 22 Hz | Direct measurements of the magnetocaloric effect (MCE) in different materials
(Gd, Fe48Rh52, Ni43Mn37.9In12.1Co7 and Ni2.07Co0.09Mn0.84Ga) in alternating
magnetic fields with frequencies f < 22 Hz and an amplitude deltaH = 6.2 kOe
are carried out. The MCE in Gd shows inconsiderable changes with field
frequency. Near paramagnetic-ferromagnetic phase transition in
Ni43Mn37.9In12.1Co7 Heusler alloy a slight reduction of MCE with frequency is
observed. In weak alternating fields in materials with AFM-FM
magneto-structural phase transitions (Fe48Rh52, Ni43Mn37.9In12.1Co7) it is not
possible to get a structural contribution to overall MCE because of
irreversibility of the transitions in these fields. Near magneto-structural
phase transitions the MCE in these alloys has only magnetic contribution, and
does not show a significant dependence on the magnetic field frequency. In
Ni2.07Co0.09Mn0.84Ga Heusler alloy the MCE vanishes at frequencies about 20 Hz.
The obtained results show the increase of frequencies of operating cycles is
one of the powerful methods to improve the efficiency of magnetic refrigerators
in case of Gd as a refrigerant. | 1802.10391v1 |
2020-04-13 | Half-metallic compositional ranges for selected Heusler alloys | For a material that is a half-metal, there should exist a range of
compositions for half-metallicity. This compositional range can be expressed in
terms of electron count and computed. We investigate electronic and magnetic
properties of doped full- and half-Heusler alloys (stoichiometry XYZ2 and XYZ,
respectively) with elements X from groups 13-16 and periods 3-6 of the Periodic
Table, Y={Mn, Fe}, and Z={Co, Ni}. Using spin density functional theory, we
predict shifts of the Fermi energy in the doped and solid-solution alloys.
These predictions can be used for band-gap engineering of multicomponent
half-metals and provide the viable range of compositions, such as for a range
of n=x+y+z in (Co$_{2-z}Ni_z)$(Mn$_{1-y}$Fe$_{y}$)(Sn$_{1-x}$Sb$_{x}$). This
methodology for doped and chemically disordered half-metallic alloys offers a
design approach to electronic-structure engineering that can accelerate
development of half-metals for novel electronic and spintronic applications. | 2004.06233v1 |
2016-12-21 | Volume dependence of magnetic properties in Co2Cr1-xYxGa (Y=Ti-Ni) Heusler alloys: a first-principles study | The magnetic properties tuning and volume dependence in the series of
quaternary full Heusler alloys with formula Co2Cr1-xYGa (Y = Ti, V, Mn, Fe, Co,
Ni) were studied with a detailed first-principles exploration. We employ the
density functional KKR method with the coherent potential approximation,
estimating effective Heisenberg exchange constants via the magnetic force
theorem together with mean-field Curie temperature (TC) and magnetic moment for
compositions in the whole concentration range. The volumetric dependency of
these magnetic properties is studied, particularly the pressure derivatives of
TC at equilibrium. Our ternary alloy calculations show good agreement with
local-density and generalized gradient approximations in the literature. The
quaternary alloys show a wide range of tunable magnetic properties, where
magnetic moments range from 0.8 to 4.9 mu_B, TC from 130 K to 1250 K, and
dTC/dV values range from -7 to +6.3 K A-3. | 1612.07071v1 |
2017-10-07 | Effect of multinary substitution on electronic and transport properties of TiCoSb based half-Heusler alloys | The electronic structures of TixZrx/2CoPbxTex, TixZrx/2Hfx/2CoPbxTex (x =
0.5), and the parent compound TiCoSb were investigated using the full potential
linearized augmented plane wave method. The thermoelectric transport properties
of these alloys are calculated on the basis of semi-classical Boltzmann
transport theory. From the band structure calculations we show that the
substitution of Zr,Hf in the Ti site and Pb and Te in the Sb site lower the
band gap value and also change the indirect band (IB) gap of TiCoSb to the
direct band (DB) gap. The calculated band gap of TiCoSb, TixZrx/2CoPbxTex, and
TixZrx/2Hfx/2CoPbxTex are 1.04 eV (IB), 0.92 eV (DB), and 0.93 eV (DB),
respectively. All these alloys follow the empirical rule of 18 valence-electron
content which is essential for bringing semiconductivity in half Heusler
alloys. It is shown that the substitution of Hf at the Ti site improve the ZT
value (~1.05) at room temperature, whereas there is no significant difference
in ZT is found at higher temperature. Based on the calculated thermoelectric
transport properties, we conclude that the appropriate concentration of Hf
substitution can further improve the thermoelectric performance of
TixZrx/2Hfx/2CoPbxTex. | 1710.02639v1 |
2020-10-19 | Investigation on structural, electronic and magnetic properties of Co2FeGe Heusler alloy: experiment and theory | Experimental and computational studies were performed on Co2FeGe Heusler
alloy. It was found that the alloy has very high experimental magnetic moment
of 6.1 muB/f.u., curie temperature of 1073K and very high spin-wave stiffness
constant of 10.4 nm2-meV, which indicates that the magnetic moment is very high
and do not vary with change in temperature in the range 0-300K. The alloy
strictly follows Slater-Pauling (SP) rule and the minor experimental deviation
from its SP value is justified by doing full-potential density functional
calculations which gives more accurate result when electron-electron
correlation parameter (U) is taken into account with conventional GGA method.
Effect of lattice strain and electron correlation on individual atomic moments,
total magnetic moment and spin-polarization is studied in detail and can be
concluded that they have a role in the deviation of the experimental results
from the expected theoretical values. | 2010.09590v1 |
2021-06-18 | Atomistic spin model of single pulse toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys | Single femtosecond pulse toggle switching of ferrimagnetic alloys is an
essential building block for ultrafast spintronics. Very different
element-specific demagnetization dynamics is believed to be a hard limit for
switching in ferrimagnets. This suggests that ferrimagnets composed of two ions
of different nature, such as rare earth transition metal alloys, are necessary
for switching. However, experimental observation of toggle switching in
Mn$_2$Ru$_x$Ga Heusler alloys, has contested this limit since Mn ions are of
the same nature. To shed some light into this question, we present an atomistic
spin model for the simulation of single pulse toggle switching of
Mn$_2$Ru$_x$Ga. The magnetic parameters entering in our model are extracted
from previous experimental observations. We show that our model is able to
quantitatively reproduce measured magnetization dynamics of single pulse toggle
switching. We demonstrate that differently to previous understanding toggle
switching in Mn$_2$Ru$_x$Ga is possible even when both Mn sublattices
demagnetization at very similar rate. | 2106.10111v2 |
2021-07-24 | Randomly packed Ni$_2$MnIn and NiMn structural units in off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys | Ni$_2$Mn$_{2-y}$In$_y$ alloys transform from the martensitic $L1_0$
antiferromagnetic ground state near $y = 0$ to austenitic ferromagnetic $L2_1$
Heusler phase near $y = 1$ due to doping of In impurity for Mn. The off
stoichiometric alloys prepared by rapid quenching are structurally metastable
and dissociate into a mixture of $L2_1$ (Ni$_2$MnIn) and $L1_0$ (NiMn) phases
upon temper annealing. Despite this structural disintegration, the martensitic
transformation temperature remains invariant in the temper annealed alloys.
Investigations of the local structure of the constituent atoms reveal the
presence of strongly coupled Ni$_2$MnIn and NiMn structural units in the temper
annealed as well as the rapidly quenched off stoichiometric
Ni$_2$Mn$_{2-y}$In$_y$ alloys irrespective of their crystal structure. This
random packing of the $L2_1$ and $L1_0$ structural units seems to be
responsible for invariance of martensitic transition temperature in the temper
annealed alloys as well as the absence of strain glass transition in rapidly
quenched alloys. | 2107.11551v1 |
2006-03-24 | Structural and magneto-transport characterization of Co_2Cr_xFe_(1-x)Al Heusler alloy films | We investigate the structure and magneto-transport properties of thin films
of the Co_2Cr_xFe_(1-x)Al full-Heusler compound, which is predicted to be a
half-metal by first-principles theoretical calculations. Thin films are
deposited by magnetron sputtering at room temperature on various substrates in
order to tune the growth from polycrystalline on thermally oxidized Si
substrates to highly textured and even epitaxial on MgO(001) substrates,
respectively. Our Heusler films are magnetically very soft and ferromagnetic
with Curie temperatures up to 630 K. The total magnetic moment is reduced
compared to the theoretical bulk value, but still comparable to values reported
for films grown at elevated temperature. Polycrystalline Heusler films combined
with MgO barriers are incorporated into magnetic tunnel junctions and yield 37%
magnetoresistance at room temperature. | 0603649v1 |
2013-01-31 | A New Spin Gapless Semiconductors Family: Quaternary Heusler Compounds | Using first-principles calculations, we investigate the band structures of a
series of quaternary LiMgPdSn-type Heusler compounds. Our calculation results
show that five compounds CoFeMnSi, CoFeCrAl, CoMnCrSi, CoFeVSi and FeMnCrSb
possess unique electronic structures characterized by a half-metallic gap in
one spin direction while a zero-width gap in the other spin direction showing
spin gapless semiconducting behavior. We further analysis the electronic and
magnetic properties of all quaternary Heusler alloys involved, and reveal a
semi-empirical general rule (total valence electrons number being 26 or 28) for
indentifying spin gapless semiconductors in Heusler compounds. The influences
of lattice distortion and main-group element change have also been discussed. | 1301.7488v1 |
2016-03-17 | Ultrafast Local Magnetization and Demagnetization in Heusler Alloys | With the goal of pushing Spintronic devices towards faster and faster
timescales, we demonstrate, using ab-intio time-dependent density functional
theory simulations of bulk Heusler compounds subject to ultrashort intense
laser pulses, that the local magnetic moment can increase or decrease in a few
femtoseconds. This speed is due to the all optical nature of the process, which
transfers spin moment from one sublattice to another. This transfer depends on
easily tunable laser parameters. By comparing the spin dynamics of a variety of
Heusler (or half-Heusler) compounds, we demonstrate that the density of states
explains the observed moment transfer; most the physics of inter sublattice
moment transfer is due to the flow of spin current which is governed by
availability of states above the Fermi level. | 1603.05603v1 |
2009-10-26 | Direct determination of the surface termination in full Heusler alloys by means of low energy electron diffraction | The performance of Heusler based magnetoresistive multilayer devices depends
crucially on the spin polarization and thus on the structural details of the
involved surfaces. Using low energy electron diffraction (LEED), one can
non-destructively distinguish between important surface terminations of Co2XY
full-Heusler alloys. We present an analysis of the LEED patterns of the Y-Z
,the vacancy-Z, the Co and the disordered B2 and A2 terminations. As an
example, we show that the surface geometries of bulk L21 ordered Co2MnSi and
bulk B2 disordered Co2Cr0.6Fe0.4Al can be determined by comparing the
experimental LEED patterns with the presented reference patterns. | 0910.4909v2 |
2013-04-09 | Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi | In this paper, we investigate the half-metallicity of Heusler alloys
Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance
measurements. It is found that, with the increase of Cr content x, the Fermi
level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of
conduction band, and a large half-metallic band gap of 0.75 eV is obtained for
x=0.75. We then successfully synthesized a series Heusler Fe2Co1-xCrxSi
polycrystalline ribbon samples. The results of X-ray diffraction indicate that
the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order
and the saturation magnetic moment follows half-metallic Slater-Pauling rule.
Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic
magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, 0.75) show a negative value
suggesting they are stable half-metallic ferromagnets. | 1304.2602v1 |
2014-02-18 | Interplay of growth mode and thermally induced spin accumulation in epitaxial Al/Co$_2$TiSi/Al and Al/Co$_2$TiGe/Al contacts | The feasibility of thermally driven spin injectors built from half-metallic
Heusler alloys inserted between aluminum leads was investigated by means of
{\em ab initio} calculations of the thermodynamic equilibrium and electronic
transport. We have focused on two main issues and found that: (i) the interface
between Al and the closely lattice-matched Heusler alloys of type Co$_2$Ti$Z$
($Z=$ Si or Ge) is stable under various growth conditions; and (ii) the
conventional and spin-dependent Seebeck coefficients in such heterojunctions
exhibit a strong dependence on both the spacer and the atomic composition of
the Al/Heusler interface. The latter quantity gives a measure of the spin
accumulation and varies between $+8$~$\mu$V/K and $-3$~$\mu$V/K near $300$~K,
depending on whether a Ti-Ge or a Co-Co plane makes the contact between Al and
Co$_2$TiGe in the trilayer. Our results show that it is in principle possible
to tailor the spin-caloric effects by a targeted growth control of the samples. | 1402.4396v2 |
2016-04-19 | Half Heusler Alloys for Efficient Thermoelectric Power Conversion | Half-Heusler (HH) phases (space group F43m, Clb) are increasingly gaining
attention as promising thermoelectric materials in view of their thermal
stability, scalability, and environmental benignity as well as efficient power
output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH
phases has remained moderate near 1, which limits the power conversion
efficiency of these materials. We report herein ZT~1.3 in n-type (Hf,Zr)NiSn
alloys near 850 K developed through elemental substitution and simultaneously
embedment of nanoparticles in the HH matrix, obtained by annealing the samples
close to their melting temperatures. Introduction of mass fluctuation and
scattering centers play a key role in the high ZT measured, as shown by the
reduction of thermal conductivity and increase of thermopower. Based on
computation, the power conversion efficiency of a n-p couple module based on
the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently
reported high-ZT p-type HH phases is expected to reach 13%, comparable to that
of state-of-the-art materials, but with the mentioned additional materials and
environmental attributes. Since the high efficiency is obtained without tuning
the microstructure of the Half-Heusler phases, it leaves room for further
optimization. | 1604.05397v2 |
2016-12-29 | Magnetovolume Effects in Heusler Compounds via First-Principles Calculations | Heusler alloys are promising for several applications, including magnetic
refrigeration, due to high magnetocaloric and magnetovolume effects. One way to
optimize this potential is by increasing the magnetovolume effect. Using
density functional theory with the Korringa-Kohn-Rostoker method, we calculate
the effective exchange interaction energies and corresponding mean field Curie
temperature as a function of the volume (hydrostatic pressure) in several L2 1
-type Co 2 YZ Heusler alloys. Different qualitative trends and signs of the
pressure derivatives of the Curie temperature and moments are found among these
compounds, discussed and compared with previous calculations and experiments. | 1612.09133v1 |
2020-03-20 | A ternary map of Ni-Mn-Ga Heusler alloys from ab initio calculations | In the present work, the aspects of magnetic and structural properties of
Ni-Mn-Ga alloys are described in the framework of fist-principles approach and
mapped into ternary composition diagrams. The stable atomic arrangement and
magnetic alignment for compositions with cubic austenite and tetragonal
martensite structures across phase diagrams are predicted. It is shown that Ni-
and Ga-rich compositions possess the regular Heusler structure in contrast to
Mn-rich compositions with inverse Heusler structure as favorable one.
Compositions with unstable austenite structure are concentrated in the left and
right sides of diagram whereas compositions with unstable martensite structure
are located in the low-middle part of diagram. The magnetic phase diagrams
showing regions with the ferromagnetic order and the complex ferrimagnetic
order for austenitic and martensitic compositions are obtained. The results of
calculations are in a good agreement with available experimental data. | 2003.09128v1 |
2020-09-24 | Electronic Structure and Thermoelectric Properties of Half-Heusler Alloys NiTZ | We have investigated the electronic and thermoelectric properties of
half-Heusler alloys NiTZ (T = Sc, and Ti; Z = P, As, Sn, and Sb) having 18
valence electron. Calculations are performed by means of density functional
theory and Boltzmann transport equation with constant relaxation time
approximation, validated by NiTiSn. The chosen half-Heuslers are found to be an
indirect band gap semiconductor, and the lattice thermal conductivity is
comparable with the state-of-the-art thermoelectric materials. The estimated
power factor for NiScP, NiScAs, and NiScSb reveals that their thermoelectric
performance can be enhanced by appropriate doping rate. The value of ZT found
for NiScP, NiScAs, and NiScSb are 0.46, 0.35, and 0.29, respectively at 1200 K. | 2009.11916v4 |
2021-05-11 | First-principles calculations and experimental studies on Co2FeGe Heusler alloy nanoparticles for spintronics applications | Here, we report the synthesis and physical properties of Co2FeGe (CFG)
Heusler alloy (HA) nanoparticles (NPs). The NPs of size 23 nm are prepared
using the co-precipitation method. X-ray and selected area electron diffraction
patterns have confirmed the cubic Heusler phase of the NPs with the
A2-disorder. These NPs are soft ferromagnetic, and exhibit a high saturation
magnetization (Ms) along with a very high Curie temperature (Tc) of 1060 K. The
observed Tc value matches closely with the theoretically calculated one
following a model provided by Wurmehl et al. [1]. The high Ms and Tc make the
present system a potential candidate for magnetically activated nano-devices
working at high temperatures. The near-integral value 5.9 mehoB/f.u. of Ms at
low temperatures indicates that the half-metallic ferromagnetism is preserved
even in the particles even on the 20 nm length scale. Additionally, we have
facilitated the existing HA-NP preparation method, which can be used in
synthesizing other HA-NPs. The first-principles density functional theory
computations complement the experimental results. | 2105.05200v1 |
2021-09-24 | Impact of local arrangement of Fe and Ni on the phase stability and magnetocrystalline anisotropy in Fe-Ni-Al Heusler alloys | On the basis of density functional calculations, we report on a comprehensive
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
Heusler-type structures formed by shuffles of Fe and Ni atoms and their
thermodynamic stability. All~Ni-rich Fe$_2$Ni$_{1+x}$Al$_{1-x}$ tend to
decompose into a dual-phase mixture consisting of Fe$_2$NiAl and~FeNi.
The~successive replacement of Ni by Al leads to a change of ground state
structure and eventually an increase in magnetocrystalline anisotropy
energy~(MAE). We predict for stoichiometric Fe$_2$NiAl a ground state structure
with nearly cubic lattice parameters but alternating layers of Fe and Ni
possessing an uniaxial MAE which is even larger than tetragonal L1$_0$-FeNi.
This opens an alternative route for improving the phase stability and magnetic
properties in FeNi-based permanent magnets. | 2109.12005v2 |
2022-08-31 | Unusual kinetic properties of usual Heusler alloys | The review considers various groups of Heusler compounds, which can have the
properties of a semiconductor, a half-metallic ferromagnet, a spin gapless
semiconductor, a topological semimetal, and a noncollinear antiferromagnet. In
these Heusler compounds, "conventional" from the point of view of the crystal
structure, unusual kinetic and magnetic properties can be observed, which are
caused by the features of their electronic structure (e.g., presence of an
energy gap for one spin projection) and magnetic state (e.g., strong
ferromagnetism, compensated ferrimagnetism, etc.). Their magnetic and kinetic
characteristics are very sensitive to external influences. Depending on the
alloy composition and external parameters, transitions between the considered
states can be realized. All this opens up further prospects for controlling the
electronic and magnetic characteristics of such compounds and their practical
application. | 2208.14868v1 |
2024-03-13 | Study of Physical Characteristics of the New Half-Heusler Alloy BaHgSn by DFT Analysis | To investigate the physical characteristics of the half-Heusler BaHgSn
molecule, we used theoretical calculations within the Density Functional Theory
(DFT) framework utilizing the LSDA+mBJ technique in this study. Using the
optimal lattice parameters, we discover that half-Heusler BaHgSn exhibits a
Dirac semimetal behavior with a band gap of 0.1 eV. Thomas Charpin's numerical
first-principles calculation approach was applied to determine the elastic
constants of hexagonal BaHgSn alloys. The material's optical characteristics
verified its prospective use in infrared-visible devices. According to a
thermo-electric properties analysis, at 20x10^18 {\Omega}-1.m-1.s-1, the
electrical conductivity reaches its maximum after increasing gradually up to
500 K. Compared to other compounds, these results indicate that BaHgSn has
potential for use in opto-electronic and thermo-electric devices. | 2403.08483v1 |
2019-11-12 | Formation and magnetic properties of spark plasma sintered Mn$_{3-δ}$ ($δ$ = 0, 1) alloys | We present the synthesis of D0$_{22}$ Mn$_{3 - \delta}$Ga ($\delta$ = 0, 1)
Heusler alloys by Spark Plasma Sintering method. The single phase Mn$_3$Ga
(T$_\mathrm{c}$ $\simeq$ 780 K) is synthesized, while Mn$_2$Ga (T$_\mathrm{c}$
$\simeq$ 710 K) is found to coexist with a near-stoichiometric room temperature
paramagnetic Mn$_9$Ga$_5$~($\approx$ 15 \%) phase due to its lower formation
energy, as confirmed from our density functional theory (DFT) calculations. The
alloys show hard magnetic behavior with large room temperature spontaneous
magnetization m$_s$(80 kOe) = 1.63 (0.83) $\mu_\mathrm{B}$/f.u. and coercivity
H$_\mathrm{c}$ = 4.28 (3.35) kOe for Mn$_3$Ga (Mn$_2$Ga). The magnetic
properties are further investigated till T$_\mathrm{c}$ and the H$_\mathrm{c}$
(T) analysis by Stoner-Wohlfarth model shows the nucleation mechanism for the
magnetization reversal. The experimental results are well supported by DFT
calculations, which reveal that the ground state of D0$_{22}$ Mn$_2$Ga is
achieved by the removal of Mn-atoms from full Heusler Mn$_3$Ga structure in
accordance with half Heusler alloy picture. | 1911.05040v1 |
1999-10-15 | Electronic structure and magnetism of Fe$_{3-x}$V$_{x}$X (X = Si, Ga and Al) alloys by the KKR-CPA method | We present first principles charge- and spin-selfconsistent electronic
structure computations on the Heusler-type disordered alloys Fe$_{3-x}$V$_{x}$X
for three different metalloids X=(Si, Ga and Al). In these calculations we use
the methodology based on the Korringa-Kohn- Rostoker formalism and the
coherent-potential approximation (KKR-CPA), generalized to treat disorder in
multi-component complex alloys. | 9910249v1 |
2003-09-11 | An efficient control of Curie temperature $T_C$ in Ni-Mn-Ga alloys | We have studied the influence of alloying with a fourth element on the
temperature of ferromagnetic ordering $T_C$ in Ni-Mn-Ga Heusler alloys. It is
found that $T_C$ increases or decreases, depending on the substitution. The
increase of $T_C$ is observed when Ni is substituted by either Fe or Co. On the
contrary, the substitution of Mn for V or Ga for In strongly reduces $T_C$. | 0309271v1 |
2020-04-25 | Mechanical and thermodynamical properties of $β-Cu-Al-Mn$ alloys along the $Cu_3Al \to Cu_2AlMn$ compositional line | The elastic properties of $Cu-Al-Mn$ alloys with compositions along the
$Cu_3Al \to Cu_2AlMn$ line and $bcc$-based structures, are studied by means of
first-principles calculations. From the calculated elastic constants, the
Zener's anisotropy, sound velocities and Debye temperature are determined. The
theoretical results compare well with the available experimental data. The
influence of vibrations is introduced through the quasi-harmonic Debye model,
and different properties are studied as functions of temperature and
composition. | 2004.12253v1 |
2004-07-01 | Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al | The Heusler alloy is used as an electrode of magnetic tunneling junctions.
The junctions are deposited by magnetron dc sputtering using shadow mask
techniques with AlO_{x} as a barrier and cobalt as counter electrode.
Measurements of the magnetoresistive differential conductivity in a temperature
range between 4K and 300K are shown. An analysis of the barrier properties
applying the Simmons model to the bias dependent junction conductivity is
performed. VSM measurements were carried out to examine the magnetic properties
of the samples. | 0407034v1 |
2011-02-18 | Perpendicular magnetic anisotropy of full-Heusler films in Pt/Co2FeAl/MgO trilayers | We report on perpendicular magnetic anisotropy (PMA) in a Pt/Co2FeAl/MgO
sandwiched structure with a thick Co2FeAl layer of 2-2.5 nm. The PMA is
thermally stable that the anisotropy energy density Ku is 1.3{\times}106
erg/cm3 for the structure with 2 nm Co2FeAl after annealing at 350 oC. The
thicknesses of Co2FeAl and MgO layers greatly affect the PMA. Our results
provide an effective way to realize relative thick perpendicularly magnetized
Heusler alloy films. | 1102.3802v1 |
2013-09-25 | Prediction of half metallic properties in Ti\raisebox{-.2ex}{\scriptsize 2}CoSi Heusler alloy based on density functional theory | The electronic and magnetic properties of Ti\raisebox{-.2ex}{\scriptsize
2}CoSi Heusler compound are investigated using density functional calculations.
The optimized lattice constant is found to be 6.030 A. The compound is a
half-metallic ferromagnet with an energy gap in minority spin channel of 0.652
eV at equilibrium lattice constant, which leads to a 100% spin-polarization.
The obtained total magnetic moment from spin-polarized calculations is 3.0
$\mu_{B}$ for values of lattice constants higher than 5.941 A. The
half-metallicity is spoiled for a compressed volume of 4%, suggesting a
possible application as pressure sensitive material. | 1309.6427v1 |
2013-12-20 | Multiple phases in sputtered Cr2CoGa films | By magnetron co-sputtering, thin films of a nominal Cr2CoGa compound were
deposited on MgO and MgAl2O4. To achieve crystallisation in the inverse Heusler
structure, different heat treatments were tested. Instead of the inverse
Heusler structure, we observed phase separation and precipitate formation in
dependence on the heat treatment. The main precipitate is Cr3Ga in A15
structure. The remainder forms Co-rich CoGa in the B2 structure and possibly
Cr-rich CoCr in the sigma-phase. | 1312.6014v2 |
2022-01-14 | Antisite disorder and phase segregation in Mn$_{2}$NiSn | A systematic study of crystal structure, local structure, magnetic and
transport properties in quenched and temper annealed Ni$_{2-x}$Mn$_{1+x}$Sn
alloys indicate the formation of Mn$_3$Sn type structural defects caused by an
antisite disorder between Mn and Sn occupying the Y and Z sublattices of
X$_2$YZ Heusler structure. The antisite disorder is caused by the substitution
of Ni by Mn at the X sites. On temper annealing, these defects segregate and
phase separate into $L2_1$ Heusler and $D0_{19}$ Mn$_3$Sn type phases. | 2201.05283v1 |
2016-03-30 | Probing the possibility of coexistence of martensite transition and half-metallicity in Ni and Co-based full Heusler Alloys : An ab initio Calculation | Using first-principles calculations based on density functional theory, we
have studied the mechanical, electronic, and magnetic properties of Heusler
alloys, namely, Ni$_{2}BC$ and Co$_{2}BC$ ($B$ = Sc, Ti, V, Cr and Mn as well
as Y, Zr, Nb, Mo and Tc; $C$ = Ga and Sn). On the basis of electronic structure
(density of states) and mechanical properties (tetragonal shear constant), as
well as magnetic interactions (Heisenberg exchange coupling parameters), we
probe the properties of these materials in detail. We calculate the formation
energy of these alloys in the (face-centered) cubic austenite structure to
probe the stability of all these materials. From the energetic point of view,
we have studied the possibility of the electronically stable alloys having a
tetragonal phase lower in energy compared to the respective cubic phase. A
large number of the magnetic alloys is found to have the cubic phase as their
ground state. On the other hand, for another class of alloys, the tetragonal
phase has been found to have lower energy compared to the cubic phase. Further,
we find that the values of tetragonal shear constant show a consistent trend :
a high positive value for materials not prone to tetragonal transition and low
or negative for others. In the literature, materials, which have been seen to
undergo the martensite transition, are found to be metallic in nature. We probe
here if there is any Heusler alloy which has a tendency to undergo a tetragonal
transition and at the same time possesses a high spin polarization at the Fermi
level. From our study, it is found that out of the four materials, which
exhibit a martensite phase as their ground state, three of these, namely,
Ni$_{2}$MnGa, Ni$_{2}$MoGa and Co$_{2}$NbSn have a metallic nature; on the
contrary, Co$_{2}$MoGa exhibits a high spin polarization. | 1603.09112v1 |
2008-04-23 | Hybridization Effects in Ni-Mn based Shape Memory Alloys: XAFS Study | Martensitic and magnetic properties of ferromagnetic shape memory alloys are
known to depend up on structural modulations and associated changes in the
Fermi surface. These modulations although periodic and spanning over multiple
unit cells, involve movement of atoms typically of the order of 0.01A.
Therefore X-ray Absorption Fine Structure (XAFS) is an ideal tool to map both,
local atomic movements and changes in density of states (DOS) due to changing
hybridization as the system transforms from austenitic to martensitic phase.
This paper presents a compilation of our XAFS studies on the Ni-Mn based shape
memory alloys. A complete description of the changes in local structure around
the constituent metal ions in the following alloy compositions: Ni2+xMn1-xGa,
Ni2Mn1.4Sn0.6 and Ni2Mn1.4In0.6 in the austenitic and martensitic phases have
been obtained. The results give the new experimental evidence for the crucial
hybridization component that influences and leads to structural transition in
these Ni-Mn based Heusler alloys. | 0804.3663v1 |
2018-12-03 | Mn2V0.5Co0.5Z (Z= Ga, Al) Heusler alloys: Fully compensated ferrimagnets with high Tc and compensation temperature | High TC fully compensated ferrimagnets are potential candidates for spin
transfer torque based spintronic devices. We report the structural and magnetic
properties of high TC fully compensated ferrimagnets Mn2V0.5Co0.5Z where Z is
Ga, Al, in the melt spun ribbon and arc melted bulk form. While the parent
alloys Mn2YZ where Y is V, Co and Z is Ga, Al exhibits a magnetic moment value
around 2 muB per f.u, the Mn2V0.5Co0.5Ga alloy exhibits room temperature nearly
fully compensated moment value of 0.09 and 0.13 muB per f.u. in the bulk and
ribbon form respectively. For Mn2V0.5Co0.5Al this turned out to be 0.04 and
0.08 muB per f.u. In Contrast to the bulk sample's Neel P type ferrimagnetic
behaviour, ribbon samples exhibit Neel N type ferrimagnetic characteristic with
a high compensation temperature of 420 K for Ga alloy and 275 K for Al alloy.
The observed TC values are more than 640 K for all samples. The differences in
the magnetic properties of arc melted and melt spun alloys indicates that even
a slight variation in stoichiometry and sample preparation method can influence
the physical properties of a compensated system. | 1812.00714v1 |
2021-11-12 | First-principles investigations of the electronic, magnetic and thermoelectric properties of VTiRhZ (Z= Al, Ga, In) Quaternary Heusler Alloys | Calculations using density functional theory (DFT) were performed to
investigate the structural, dynamical, mechanical, electronic, magnetic, and
thermoelectric properties of VTiRhZ (Z = Al, Ga, In) alloys. The most stable
structure of these alloys was found to be the type-I configuration. Using
GGA-PBE functional, VTiRhGa, and VTiRhIn alloys are predicted as half-metallic
ferromagnets with a 100% spin-polarization and a total magnetic moment of
3{\mu}B, which is promising for spintronic applications. The thermoelectric
properties and lattice thermal conductivity of VTiRhZ alloys were obtained
using the Boltzmann transport theory within the constant relaxation time and
Slack equation, respectively. The figure-of-merit (ZT) values of VTiRhAl,
VTiRhGa, and VTiRhIn alloys were found to be 0.96, 0.88 and 0.64, respectively,
which are promising for future thermoelectric applications. | 2111.06915v1 |
2022-10-24 | Ab-initio calculation of the Hubbard $U$ and Hund exchange $J$ in local moment magnets: The case of Mn-based full Heusler compounds | Mn-based full Heusler compounds possess well-defined local atomic Mn moments,
and thus the correlation effects between localized d electrons are expected to
play an important role in determining the electronic and magnetic properties of
these materials. Employing ab-initio calculations in conjunction with the
constrained random-phase approximation (cRPA) method, we calculate the strength
of the effective on-site Coulomb interaction parameters (Hubbard U and Hund
exchange J) in the case of X2MnZ full Heusler compounds with X being one of Ni,
Pd or Cu, and Z being one of In, Sn, Sb or Te. We show that the Z element (or
sp element) in Heusler compounds significantly reduces the strength of the
Hubbard U parameter for Mn 3d electrons compared to the elementary bulk Mn. On
the contrary, the effect of the sp-atom on the strength of the U parameter of
Ni, Cu or Pd valence d electrons is not so substantial with respect to the
elementary bulk values. The U values for all transition metal atoms decrease
with increasing sp electron number in the In-Sn-Sb-Te sequence. Our cRPA
calculations reveal that despite their well-defined local magnetic moments, the
Mn-based full Heusler alloys fall into the category of the weakly correlated
materials. | 2210.13061v1 |
2023-03-04 | Giant anomalous Hall and Nernst conductivities in magnetic all-$d$ metal Heusler alloys | All-$d$ Heuslers are a category of novel compounds combining versatile
functionalities such as caloric responses and spintronics with enhanced
mechanical properties. Despite the promising transport properties (anomalous
Hall (AHC) and anomalous Nernst (ANC) conductivities) shown in the conventional
Co$_2$XY Heuslers with $p$-$d$ hybridization, the all-$d$ Heuslers with only
$d$-$d$ hybridization open a new horizon to search for new candidates with
outstanding transport properties. In this work, we evaluate the AHC and ANC for
thermodynamically stable ferro/ferri-magnetic all-$d$-metal regular Heusler
compounds based on high-throughput first-principles calculations. It is
observed that quite a few materials exhibit giant AHCs and ANCs, such as cubic
Re$_2$TaMn with an AHC of 2011 S/cm, and tetragonal Pt$_2$CrRh with an AHC of
1966 S/cm and an ANC of 7.50 A/mK. Comprehensive analysis on the electronic
structure reveals that the high AHC can be attributed to the occurrence of the
Weyl nodes or gapped nodal lines in the neighbourhood of the Fermi level. The
correlations between such transport properties and the number of valence
electrons are also thoroughly investigated, which provides a practical guidance
to tailor AHC and ANC via chemical doping for transverse thermoelectric
applications. | 2303.02351v1 |
2005-12-15 | Search for half-metallic ferrimagnetism in V-based Heusler alloys Mn$_2$VZ (Z$=$Al, Ga, In, Si, Ge, Sn) | Using a state-of-the-art full-potential electronic structure method within
the local spin density approximation, we study the electronic and magnetic
structure of Mn$_2$V-based full Heusler alloys: Mn$_2$VZ (Z=Al, Ga, In, Si, Ge,
and Sn). We show that small expansion of the calculated theoretical equilibrium
lattice constants restores the half-metallic ferrimagnetism in these compounds.
Moreover a small degree of disorder between the V and Z atoms, although iduces
some states within the gap, it preserves the Slater-Pauling behaviour of the
spin magnetic moments and the alloys keep a high degree of spin-polarisation at
the Fermi level opening the way for a half-metallic compensated ferrimagnet. | 0512361v1 |
2006-01-24 | Lattice dynamics and phonon softening in Ni-Mn-Al Heusler alloys | Inelastic and elastic neutron scattering have been used to study a single
crystal of the Ni$_{54}$Mn$_{23}$Al$_{23}$ Heusler alloy over a broad
temperature range. The paper reports the first experimental determination of
the low-lying phonon dispersion curves for this alloy system. We find that the
frequencies of the TA$_2$ modes are relatively low. This branch exhibits an
anomaly (dip) at a wave number $\xi_{0} ={1/3}\approx 0.33$, which softens with
decreasing temperature. Associated with this anomalous dip at $\xi_{0}$, an
elastic central peak scattering is also present. We have also observed
satellites due to the magnetic ordering. | 0601546v1 |
2006-06-02 | Temperature and magnetic field dependences of the elastic constants of Ni-Mn-Al magnetic Heusler alloys | We report on measurements of the adiabatic second order elastic constants of
the off-stoichiometric Ni$_{54}$Mn$_{23}$Al$_{23}$ single crystalline Heusler
alloy. The variation in the temperature dependence of the elastic constants has
been investigated across the magnetic transition and over a broad temperature
range. Anomalies in the temperature behaviour of the elastic constants have
been found in the vicinity of the magnetic phase transition. Measurements under
applied magnetic field, both isothermal and variable temperature, show that the
value of the elastic constants depends on magnetic order, thus giving evidence
for magnetoelastic coupling in this alloy system. | 0606065v1 |
2006-06-28 | The study of electronic and magnetic properties of the partially disordered pseudo-Heusler alloy Co2Fe0.4Cr0.6Al : an augmented space approach | In this communication we present a study of the electronic structure of
partially disordered bulk and (100) thin film of quaternary pseudo-Heusler
alloy Co$_2$Fe$_{0.4}$Cr$_{0.6}$Al in the L2$_1$ phase using the Augmented
Space recursion (ASR) in a scalar-relativistic tight binding linear muffin-tin
orbitals (TB-LMTO) basis. We study the orbital resolved magnetic moment
contributions of the constituents of the alloy. Our theoretical predictions
match well with the available experimental observations for the magnetic
moments of Fe and Co but they overestimate that of Cr. For a (100) thin film,
layer as well as orbital resolved properties have been studied. | 0606737v2 |
2009-04-17 | Ferromagnetism and Electronic Structures of Nonstoichiometric Heusler-Alloy Fe_3-xMn_xSi Epilayers Grown on Ge(111) | For the study of ferromagnetic materials which are compatible with group-IV
semiconductor spintronics, we demonstrate control of the ferromagnetic
properties of Heusler-alloys Fe_3-xMn_xSi epitaxially grown on Ge(111) by
tuning the Mn composition x. Interestingly, we obtain L2_1-ordered structures
even for nonstoichiometric atomic compositions. The Curie temperature of the
epilayers with x ~ 0.6 exceeds 300 K. Theoretical calculations indicate that
the electronic structures of the nonstoichiometric Fe_3-xMn_xSi alloys become
half-metallic for 0.75 < x < 1.5. We discuss the possibility of
room-temperature ferromagnetic Fe_3-xMn_xSi/Ge epilayers with high spin
polarization. | 0904.2610v1 |
2010-08-24 | Magnetism of mixed quaternary Heusler alloys: (Ni,T)$_{2}$MnSn (T=Cu,Pd) as a case study | The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler Ni$_{2}$MnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity. | 1008.4060v1 |
2012-08-10 | Electronic structure, optical and magnetic properties of Co$_{2}$FeGe Heusler alloy films | Optical properties of ferromagnetic half-metallic full-Heusler Co$_{2}$FeGe
alloy are investigated experimentally and theoretically. Co$_{2}$FeGe thin
films were obtained by DC magnetron sputtering and show the saturation
magnetization at $T$=10 K of $m\approx$5.6 $\mu_{B}$/f.u., close to the value
predicted by the Slater-Pauling rule. First-principles calculations of the
electronic structure and the dielectric tensor are performed using the
full-potential linearized-augmented-plane-wave method in the generalized
gradient (GGA) and GGA+U approximations. The measured interband optical
conductivity spectrum for the alloy exhibits a strong absorption band in the 1
- 4 eV energy range with pronounced fine structure, which agrees well with the
calculated half-metallic spectrum of the system, suggesting a near perfect
spin-polarization in the material. | 1208.2193v1 |
2013-01-31 | Structure and magnetic properties of Heusler alloy Fe2NiZ (Z=Al, Ga, Si and Ge) | The Heusler alloys Fe2NiZ (Z=Al, Ga, Si and Ge) have been synthesized and
investigated focusing on the phase stability and the magnetic properties. The
experimental and theoretical results reveal the covalent bonding originated
from p-d hybridization takes an important role in these alloys, which dominates
the stability of ordered structure but leads to the decline of the band
splitting. The electronic structure shows the IV group main group element (Si
and Ge) provides stronger covalent effect than that of the III group element
(Al and Ga). It has been found that the variations of the physical parameters,
lattice constants, critical ordering temperature, magnetic moments and Curie
temperature, precisely follow these covalent characters. | 1301.7489v1 |
2013-04-20 | Antiferromagnetic Exchange Interactions in Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ ferromagnetic Heusler alloy | Magnetism in Ni-Mn-Z (Z = Ga,In,Sn,Sb) Heusler alloys has so far been
predominantly attributed to Rudermann-Kittel-Kasuya-Yoshida type interactions
between Mn atoms. We investigate magnetic interactions in one such alloy,
Ni$_{2}$Mn$_{1.4}$In$_{0.6}$ and attempt to explain the origin of
antiferromagnetic (AFM) interactions that coexist with ferromagnetic ones.
Through the combination of x-ray absorption spectroscopy and x-ray magnetic
circular dichroism (XMCD), we find that Ni plays an important role along with
Mn in the overall magnetism. A significant hybridization that develops between
Mn and Ni orbitals results in a small antiferromagnetic moment at Ni sites. The
shift in the XMCD hysteresis loops in the martensitic phase suggests that
antiferromagnetism results from superexchange like interactions between Mn
atoms mediated by Ni. | 1304.5580v1 |
2014-05-26 | Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa | Magnetic shape memory Heusler alloys are multiferroics stabilized by the
correlations between electronic, magnetic and structural order. To study these
correlations we use time resolved x-ray diffraction and magneto-optical Kerr
effect experiments to measure the laser induced dynamics in a Heusler alloy
Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We
observe a coherent phonon which we identify as the amplitudon of the modulated
structure and an ultrafast phase transition leading to a quenching of the
incommensurate modulation within 300~fs with a recovery time of a few ps. The
thermally driven martensitic transition to the high temperature cubic phase
proceeds via nucleation within a few ps and domain growth limited by the speed
of sound. The demagnetization time is 320~fs, which is comparable to the
quenching of the structural modulation. | 1405.6534v1 |
2014-08-11 | High spin polarization in CoFeMnGe quaternary Heusler alloy | We report the structure, magnetic property and spin polarization of CoFeMnGe
equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21
structure with considerable amount of DO3 disorder. Thermal analysis result
indicated the Curie temperature is about 711K without any other phase
transformation up to melting temperature. The magnetization value was close to
that predicted by the Slater-Pauling curve. Current spin polarization of P =
0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR)
measurements. Half-metallic trend in the resistivity has also been observed in
the temperature range of 5 K to 300 K. Considering the high spin polarization
and Curie temperature, this material appears to be promising for spintronic
applications. | 1408.2408v2 |
2015-01-19 | Direct measurements of the magnetocaloric effect in pulsed magnetic fields: The example of the Heusler alloy Ni$_{50}$Mn$_{35}$In$_{15}$ | We have studied the magnetocaloric effect (MCE) in the shape-memory Heusler
alloy Ni$_{50}$Mn$_{35}$In$_{15}$ by direct measurements in pulsed magnetic
fields up to 6 and 20 T. The results in 6 T are compared with data obtained
from heat-capacity experiments. We find a saturation of the inverse MCE,
related to the first-order martensitic transition, with a maximum adiabatic
temperature change of $\Delta T_{ad} = -7$ K at 250 K and a conventional
field-dependent MCE near the second-order ferromagnetic transition in the
austenitic phase. The pulsed magnetic field data allow for an analysis of the
temperature response of the sample to the magnetic field on a time scale of
$\sim 10$ to 100 ms which is on the order of typical operation frequencies (10
to 100 Hz) of magnetocaloric cooling devices. Our results disclose that in
shape-memory alloys the different contributions to the MCE and hysteresis
effects around the martensitic transition have to be carefully considered for
future cooling applications. | 1501.04430v1 |
2015-04-14 | Effect of ball milling and post annealing on structural and magnetic properties in Ni50Mn36Fe2Sb12 Heusler alloy | The effect of ball milling on the structural, magnetic and exchange bias
properties of Ni50Mn36Fe2Sb12 Heusler alloys was studied. The ball milled
samples exhibited coexisting austenite and martensite phases at room
temperature, while annealing supresses the austenite phase completely. Ball
milling was found to reduce the grain size, which resulted in the weakening of
the ferromagnetic properties. An exchange bias field of 111 Oe and coercivity
of 826 Oe were observed at 5 K in the as-milled sample, in contrast to the bulk
alloy values of 288 Oe and 292 Oe, respectively. Annealing causes an increase
in the ferromagnetic ordering and a decrease in the interfacial exchange
coupling, resulting in a decrease of both exchange bias and coercivity. | 1504.03460v1 |
2015-06-23 | Spin polarization studies in half-metallic Co2TiX (X = Ge and Sn) Heusler alloys | In this paper, we investigated the Co2TiX (X = Ge, Sn) Heusler alloys by
structural, magnetic and spin polarization measurements to probe the
half-metallic nature. Alloys are synthesized using the arc melting technique,
and found to exist in L21 crystal structure with Fm-3m space group. Curie
temperature (TC) is found to be 384 and 371 K for Co2TiGe and Co2TiSn
respectively. The saturation magnetization (MS) value of 1.8 and 2.0 Bohr
magneton/f.u. are obtained at 5 K for for Co2TiGe and Co2TiSn respectively,
compared to 2.0 Bohr magneton/f.u. calculated by Slater-Pauling rule. To obtain
the spin polarization value, differential conductance curves are recorded at
the ferromagnetic/superconducting point contact at 4.2 K. The current spin
polarization (P) value of 0.63 and 0.64 are deduced for Co2TiGe and Co2TiSn
respectively. Considering the high current spin polarization and TC, these
materials appear to be promising for spintronic devices. | 1506.07109v1 |
2015-09-20 | Electronic structure, magnetism and antisite disorder in CoFeCrGe and CoMnCrAl quaternary Heusler alloys | We present a combined theoretical and experimental study of two quaternary
Heusler alloys CoFeCrGe (CFCG) and CoMnCrAl (CMCA), promising candidates for
spintronics applications. Magnetization measurement shows the saturation
magnetization and transition temperature to be $3\; \mu_B$, $866$ K and $0.9 \;
\mu_B$, $358$ K for CFCG and CMCA respectively. The magnetization values agree
fairly well with our theoretical results and also obey the Slater-Pauling rule,
a prerequisite for half metallicity. A striking difference between the two
systems is their structure; CFCG crystallizes in fully ordered Y-type structure
while CMCA has L2$_1$ disordered structure. The antisite disorder adds a
somewhat unique property to the second compound, which arises due to the
probabilistic mutual exchange of Al positions with Cr/Mn and such an effect is
possibly expected due to comparable electronegativities of Al and Cr/Mn. {\it
Ab-initio} simulation predicted a unique transition from half metallic
ferromagnet to metallic antiferromagnet beyond a critical excess amount of Al
in the alloy. | 1509.05971v2 |
2016-08-22 | Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys | The all-d-metal Mn2-based Heusler ferromagnetic shape memory alloys
Mn50Ni40-xCoxTi10 (x = 8 and 9.5) are realized. With a generic comparison
between d-metal Ti and main-group elements in lowering the transformation
temperature, the magnetostructural martensitic transformations are established
by further introducing Co to produce local ferromagnetic Mn-Co-Mn
configurations. A 5-fold modulation and (3, -2) stacking of [00 10] of
martensite are determined by XRD and HRTEM analysis. Based on the
transformation, a large magneto-strain of 6900 ppm and a large volume change of
-2.54% are observed in polycrystalline samples, which makes the all-d-metal
magnetic martensitic alloys of interest for magnetic/pressure multi-field
driven applications. | 1608.06301v1 |
2017-08-28 | Deciphering M-T diagram of shape memory Heusler alloys: reentrance, plateau and beyond | We present our recent results on temperature behaviour of magnetization
observed in Ni_47Mn_39In_14 Heusler alloys. Three regions can be distinguished
in the M-T diagram: (I) low temperature martensitic phase (with the Curie
temperature T_CM = 140 K), (II) intermediate mixed phase (with the critical
temperature T_MS = 230 K) exhibiting a reentrant like behavior (between T_CM
and T_MS) and (III) high temperature austenitic phase (with the Curie
temperature T_CA = 320 K) exhibiting a rather wide plateau region (between T_MS
and T_CA). By arguing that powerful structural transformations, causing drastic
modifications of the domain structure in alloys, would also trigger strong
fluctuations of the order parameters throughout the entire M-T diagram, we were
able to successfully fit all the data by incorporating Gaussian fluctuations
(both above and below the above three critical temperatures) into the
Ginzburg-Landau scenario. | 1708.08368v1 |
2018-06-04 | Atomistic Study of the Electronic Contact Resistivity Between the Half-Heusler Alloys (HfCoSb, HfZrCoSb, HfZrNiSn) and the Metal Ag | Half-Heusler(HH) alloys have shown promising thermoelectric properties in the
medium and high temperature range. To harness these material properties for
thermoelectric applications, it is important to realize electrical contacts
with low electrical contact resistivity. However, little is known about the
detailed structural and electronic properties of such contacts, and the
expected values of contact resistivity. Here, we employ atomistic ab initio
calculations to study electrical contacts in a subclass of HH alloys consisting
of the compounds HfCoSb, HfZrCoSb, and HfZrNiSn. By using Ag as a prototypical
metal, we show that the termination of the HH material critically determines
the presence or absence of strong deformations at the interface. Our study
includes contacts to doped materials, and the results indicate that the p-type
materials generally form ohmic contacts while the n-type materials have a small
Schottky barrier. We calculate the temperature dependence of the contact
resistivity in the low to medium temperature range and provide quantitative
values that set lower limits for these systems. | 1806.01375v1 |
2020-01-03 | Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1-xCoxGa Heusler alloys | Neutron diffraction and ab initio studies were carried out on Mn2V1-xCoxGa
(x=0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high TC fully
compensated ferrimagnetic characteristic for x=0.5. A combined analysis of
neutron diffraction and ab initio calculations revealed the crystal structure
and magnetic configuration which could not be determined from the X-ray
diffraction and magnetic measurements. As reported earlier, Rietveld refinement
of neutron diffraction data confirmed L21 structure for Mn2VGa and Xa structure
for Mn2CoGa. The alloys with x=0.25 and 0.5 possess L21 structure with Mn(C)-Co
disorder. As the Co concentration reaches 0.75, a structural transition has
been observed from disordered L21 to disordered Xa. Detailed ab initio studies
also confirmed this structural transition. The reason for the magnetic moment
compensation in Mn2(V1-xCox)Ga was identified to be different from that of the
earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of
neutron diffraction and ab initio studies, it is identified that the disordered
L21 structure with antiparallel coupling between the ferromagnetically aligned
magnetic moments of (Mn(A)-Mn(C)) and (V-Co) atom pairs enables the
compensation in Mn2V1-xCoxGa. | 2001.00707v1 |
2020-08-11 | Effect of doping on SGS and weak half-metallic properties of inverse Heusler Alloys | Heusler alloys with Mn and Co have been found to exhibit interesting
electronic and magnetic properties. Mn$_2$CoAl is well known SGS compound while
Mn$_2$CoGa has weak half metallic character. By using plane wave
pseudo-potential method, we studied the effect of Fe and Cr doping on
half-metalicity and magnetism of these compounds. The doping destroys the SGS
nature of Mn$_2$CoAl while the small-scale doping enhance the half-metallicity
of Mn$_2$CoGa making it perfect half-metal. In case of Mn$_2$CoAl, the doping
decrease the band gap while increase in band width is noticed for Mn$_2$CoGa.
The half-metallicity is destroyed in both cases when the doping level is beyond
certain degree. Moreover, we have also computed magnetic behavior of Mn$_2$CoZ
alloys and we found that total magnetic moments of dopped samples have higher
values than that of pristine compounds. | 2008.04536v1 |
2018-04-23 | Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations | Structural, electronic, and transport properties of ScNiSb, ScPdSb, and
ScPtSb were investigated from first principles. Electronic band structures
derived within the fully relativistic MBJLDA approach were compared with those
obtained from the standard GGA calculations. All the compounds studied exhibit
indirect narrow band gaps (0.24-0.63 eV). The effective masses of hole-like
carriers are relatively small (0.27-0.36), and decrease with an increasing
atomic number of the transition metal component. The carrier relaxation time,
required for realistic calculations of the electrical conductivity, was
approximated within the deformation potential theory. The GGA approach yielded
overestimated transport characteristics with respect to those derived within
the MBJLDA analysis. The largest power factor of 4-6 mWK^-2m^-1 ) at high
temperatures was obtained for ScPtSb. This value is comparable with those
observed experimentally for Fe-Nb-Sb half-Heusler alloys, and hence makes
ScPtSb a very good candidate material for thermoelectric applications. | 1804.08423v1 |
2019-08-16 | Scaling Analysis of Anomalous Hall Resistivity in the Co$_{2}$TiAl Heusler Alloy | A comprehensive magnetotransport study including resistivity ($\rho_{xx}$) at
various fields, isothermal magnetoresistance and Hall resistivity ($\rho_{xy}$)
has been carried out at different temperatures on the Co$_{2}$TiAl Heusler
alloy. Co$_{2}$TiAl alloy shows a paramagnetic (PM) to ferromagnetic (FM)
transition below the curie temperature (T$_{C}$) $\sim$ 125 K. In the FM
region, resistivity and magnetoresistance reveals a spin flip electron-magnon
scattering and the Hall resistivity unveils the anomalous Hall resistivity
($\rho_{xy}^{AH}$). Scaling of anomalous Hall resistivity with resistivity
establishes the extrinsic scattering process responsible for the anomalous hall
resistivity; however Skew scattering is the dominant mechanism compared to the
side-jump contribution. A one to one correspondence between magnetoresistance
and side-jump contribution to anomalous Hall resistivity verifies the
electron-magnon scattering being the source of side-jump contribution to the
anomalous hall resistivity. | 1908.05974v1 |
2021-06-25 | First-principles investigation of half-metallic ferromagnetism of Fe$_2$YSn (Y = Mn, Ti and V) Heusler alloys | In this paper, we use the first-principles calculations based on the density
functional theory to investigate structural, electronic and magnetic properties
of Fe$_{2}$YSn with (Y = Mn, Ti and V). The generalized gradient approximation
(GGA) method is used for calculations. The Cu$_{2}$MnAl type structure is
energetically more stable than the Hg$_{2}$CuTi type structure. The negative
formation energy is shown as the evidence of thermodynamic stability of the
alloy. The calculated total spin moment is found as 3$\mu_\text{B}$ and
0$\mu_\text{B}$ at the equilibrium lattice constant for Fe$_{2}$MnSn and
Fe$_{2}$TiSn respectively, which agrees with the Slater-Pauling rule of $M_t=
Z_t-24$. The study of electronic and magnetic properties proves that
Fe$_{2}$MnSn and Fe$_{2}$TiSn full-Heusler alloys are complete half-metallic
ferromagnetic materials. | 2106.13604v1 |
2021-08-11 | Critical Magnetic Behavior of the Half Heusler Alloy RhCrSi: Monte Carlo Study | In this paper, we study the critical magnetic properties of the Half Heusler
alloy RhCrSi, using Monte Carlo simulations (MCS) under the Metropolis
algorithm. In fact, to study this alloy, we apply an Ising model using the MCS
simulations, we concentrate only on the magnetic atoms: Rh and Cr. For this
purpose, these magnetic atoms are modeled by the spin moments S=5/2 for Rh
atoms and sigma=2 for Cr atoms, respectively. In addition, we discuss the
ground state phase diagrams in different planes corresponding to different
physical parameters. On the other hand, for non-null temperature values, we
perform the Monte Carlo simulations (MCS) to study the critical behavior of the
compound RhCrSi, in the Ising approximation. Indeed, we present a detailed
discussion of the obtained results for the magnetizations as a function of the
temperature, the crystal field and the exchange coupling interactions.
Additionally, we give the reliance of the basic temperature as an element of
precious crystal field when fixing the exchange coupling interactions. To
finish this work, we built up and examined the magnetic hysteresis cycles and
the relating coercive fields as a part of the external magnetic field. | 2108.05162v1 |
2023-02-15 | Magnetic phase diagram of the austenitic Mn-rich Ni-Mn-(In,Sn) Heusler alloys | Heusler compounds have been intensively studied owing to the important
technological advancements that they provide in the field of shape memory,
thermomagnetic energy conversion and spintronics. Many of their intriguing
properties are ultimately governed by their magnetic states and understanding
and possibly tuning them is evidently of utmost importance. In this work we
examine the \alloys alloys with Density Functional Theory simulations and
$^{55}$Mn Nuclear Magnetic Resonance and combine these two methods to carefully
describe their ground state magnetic order. In addition, we compare the results
obtained with the conventional generalized gradient approximation with the ones
of strongly constrained and appropriately normed (SCAN) semilocal functionals
for exchange and correlation. Experimental results eventually allow to
discriminate between two different scenarios identified by ab initio
simulations. | 2302.07550v1 |
2008-10-29 | Thermodynamics of the Heusler alloy Co_2-xMn_1+xSi: a combined density functional theory and cluster expansion study | Previous studies indicated that intrinsic point defects play a crucial role
for the density of states of ferromagnetic half-metals in the band gap region:
At large concentrations, defect-derived bands might close the gap at the Fermi
energy in the minority spin channel. In this work, structural disorder in the
Co- and Mn-sublattices of the full Heusler alloy Co_2-xMn_1+xSi (-1 < x < 2) is
investigated with a cluster expansion approach, parametrized using all-electron
density functional theory calculations. By establishing two separate cluster
expansions, one for the formation energy and one for the total spin moment, we
are in position to determine the stability of different configurations, to
predict new (also half-metallic) ground states and to extend the known
Slater-Pauling rule for ideally stoichiometric Heusler alloys to
non-stoichiometric, Mn-rich compositions. This enables us to identify
potentially half-metallic structures in the Mn-rich region. With the help of
Monte Carlo simulations based on the cluster expansion, we establish
theoretically that Co_2-xMn_1+xSi close to the stoichiometric composition ought
to show a high degree of structural order in thermodynamic equilibrium. Hence,
samples prepared with the correct stoichiometry should indeed be half-metallic
after thermal annealing. Moreover, we predict that adding a small amount of Mn
to stoichiometric Co_2MnSi allows to suppress the thermally activated formation
of detrimental Co antisites. At Mn-rich compositions (x>1), the ordered ground
state structures predicted for zero temperature are found to be thermally
unstable and to decompose into Co2MnSi and Mn3Si above room temperature. | 0810.5354v2 |
2014-10-01 | Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy | Spin gapless semiconductors (SGS) form a new class of magnetic
semiconductors, which has a band gap for one spin sub band and zero band gap
for the other, and thus are useful for tunable spin transport based
applications. In this paper, we report the first experimental evidence for spin
gapless semiconducting behavior in CoFeMnSi Heusler alloy. Such a behavior is
also confirmed by first principles band structure calculations. The most stable
configuration obtained by the theoretical calculation is verified by
experiment. The alloy is found to crystallize in the cubic Heusler structure
(LiMgPdSn type) with some amount of disorder and has a saturation magnetization
of 3.7 Bohr's magneton/f.u.. and Curie temperature of 620 K. The saturation
magnetization is found to follow the Slater-Pauling behavior, one of the
prerequisites for SGS. Nearly temperature-independent carrier concentration and
electrical conductivity is observed from 5 to 300 K. An anomalous Hall
coefficient of 162 S/cm is obtained at 5 K. Point contact Andreev reflection
data has yielded the current spin polarization value of 0.64, which is found to
be robust against the structural disorder. All these properties are quite
promising for the spintronic applications such as spin injection and can bridge
a gap between the contrasting behavior of half-metallic ferromagnets and
semiconductors. | 1410.0177v1 |
2019-03-11 | Evidence for the formation of nanoprecipitates with magnetically disordered regions in bulk $\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys | Shell ferromagnetism is a new functional property of certain Heusler alloys
which has been recently observed in
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$. We report the results of a
comparative study of the magnetic microstructure of bulk
$\mathrm{Ni}_{50}\mathrm{Mn}_{45}\mathrm{In}_{5}$ Heusler alloys using
magnetometry, synchrotron x-ray diffraction, and magnetic small-angle neutron
scattering (SANS). By combining unpolarized and spin-polarized SANS (POLARIS)
we demonstrate that a number of important conclusions regarding the mesoscopic
spin structure can be made. In particular, the analysis of the magnetic neutron
data suggests that nanoprecipitates with an effective ferromagnetic component
form in an antiferromagnetic matrix on field annealing at $700 \, \mathrm{K}$.
These particles represent sources of perturbation, which seem to give rise to
magnetically disordered regions in the vicinity of the particle-matrix
interface. Analysis of the spin-flip SANS cross section via the computation of
the correlation function yields a value of $\sim 55 \, \mathrm{nm}$ for the
particle size and $\sim 20 \, \mathrm{nm}$ for the size of the spin-canted
region. | 1903.04183v1 |
2021-05-05 | Rhodium based half-Heusler alloys as possible optoelectronic and thermoelectric materials | On the basis of density functional theory and semi-classical Boltzmann
theory, we have investigated the structural, elastic, electronic, optical and
thermoelectric properties of 18--valence electron count rhodium based
half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The absence
of imaginary frequencies in the phonon dispersion curve for these system
verifies that they are structurally stable. RhTiP is ductile in nature, while
others are brittle. The alloys are found to be semiconducting with indirect
band gaps ranging from 0.94 to 1.01 eV. Our calculations suggest these
materials to have high absorption coefficient and optical conductivity in the
ultraviolet as well as visible region. While considering thermoelectricity, we
found that $p$--type doping is more favorable in improving the thermoelectric
properties. The calculated values of power factor with $p$-type doping are
comparable to some of the reported half-Heusler materials. The optimum figure
of merit \zt\ is $\sim1$ for RhTiBi suggesting it as a promising candidate for
thermoelectric applications while RhTiP, RhTiAs, and RhTiSb with optimum \zt \
values between 0.38 to 0.67 are possible candidates for use in thermoelectric
devices. | 2105.02177v1 |
2022-04-07 | First Principles Study of the Structural, Mechanical, Electronic, and Lattice Dynamical Properties of the Half-Heusler Alloys ZrCoY (Y=Sb, Bi ) | First-principles calculation has led to significant discoveries in materials
science. Half heusler (HH) alloys, which are potential thermoelectric materials
have demonstrated significant improvements in thermoelectric performance owing
to their thermal stability, mechanical strength, and moderate ZT. Using Density
Functional Theory (DFT), the structural, mechanical, electronic, and lattice
dynamical properties of cubic Half Heusler alloys ZrCoY (Y=Sb, Bi) have been
investigated. The unknown exchange-correlation functional is approximated using
the generalized gradient approximation (GGA) pseudopotential plane-wave
approach. The structural parameters, that is, equilibrium lattice constant,
elastic constants, and their derivatives are consistent with reported
experimental and theoretical studies where available. Mechanical properties
such as anisotropy factor A, shear modulus G, bulk modulus B, Youngs modulus E,
and Poisons ratio n, are calculated using the Voigt-Reuss-Hill average approach
based on elastic constants. The Debyes temperature, as well as longitudinal and
transverse sound velocities, are predicted from elastic constants at GGA-PBE
and GW approximations. The study of elastic constants showed that the compounds
are mechanically stable, and the phonon dispersion study showed that they are
dynamically stable as well. The ductility and anisotropic nature of the
compounds are confirmed by the elastic constants and mechanical properties. | 2204.03759v1 |
2023-03-08 | Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa | Spin semimetals are amongst the most recently discovered new class of
spintronic materials, which exhibit a band gap in one spin channel and
semimetallic feature in the other, thus facilitating tunable spin transport.
Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along
with giant coercivity and spin-valve characteristics using a combined
experimental and theoretical study. The alloy crystallizes in an inverse
Heusler structure (without any martensitic transition) with a para- to
ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant
coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient,
relatively low magnitude and weak temperture dependance of electrical
resistivity suggest the semimetallic character of the alloy. This is further
supported by our specific heat measurement. Magnetoresistance (MR) confirms an
irreversible nature (with its magnitude $\sim$1\%) along with a change of sign
across the magnetic transition indicating the potentiality of Mn$_2$IrGa in
magnetic switching applications. In addition, asymmetric nature of MR in the
positive and negative field cycles is indicative of spin-valve characteristics.
Our ab-initio calculations confirm the inverse Heusler structure with
ferrimagnetic ordering to be the lowest energy state, with a saturation
magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic
axis with considerable magneto-crystalline anisotropy energy. A large positive
Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall
conductivity ($\sim$-180 S/cm). | 2303.04649v2 |
2023-07-18 | Effect of Spin Orbit Coupling in non-centrosymmetric half-Heusler alloys | Spin-orbit coupled electronic structure of two representative non-polar
half-Heusler alloys, namely 18 electron compound CoZrBi and 8 electron compound
SiLiIn have been studied in details. An excursion through the Brillouin zone of
these alloys from one high symmetry point to the other revealed rich local
symmetry of the associated wave vectors resulting in non-trivial spin splitting
of the bands and consequent diverse spin textures in the presence of spin-orbit
coupling. Our first principles calculations supplemented with low energy
$\boldsymbol{k.p}$ model Hamiltonian revealed the presence of linear
Dresselhaus effect at the X point having $D_{2d}$ symmetry and Rashba effect
with both linear and non-linear terms at the L point with $C_{3v}$ point group
symmetry. Interestingly we have also identified non-trivial Zeeman spin
splitting at the non-time reversal invariant W point and a pair of
non-degenerate bands along the path $\Gamma$ to L displaying vanishing spin
polarization due to the non-pseudo polar point group symmetry of the wave
vectors. Further a comparative study of CoZrBi and SiLiIn suggest, in addition,
to the local symmetry of the wave vectors, important role of the participating
orbitals in deciding the nature and strength of spin splitting. Our
calculations identify half-Heusler compounds with heavy elements displaying
diverse spin textures may be ideal candidate for spin valleytronics where spin
textures can be controlled by accessing different valleys around the high
symmetry k-points. | 2308.03760v2 |
2020-04-04 | Improved crystallographic compatibility and magnetocaloric reversibility in Pt substituted Ni2Mn1.4In0.6 magnetic shape memory Heusler alloy | We present here the improved crystallographic/geometric compatibility and
magnetocaloric reversibility by measurement of magnetic entropy change using
different protocols in 10% Pt substituted Ni2Mn1.4In0.6 magnetic shape memory
alloy. The substitution of Pt reduces the thermal hysteresis about 50% to the
Ni2Mn1.4In0.6. The origin of the reduced thermal hysteresis is investigated by
the crystallographic compatibility of the austenite and martensite phases. The
calculated middle eigenvalue of the transformation matrix turned out to be
0.9982, which is very close to 1 (deviation is only 0.18%) suggests for the
crystallographic compatibility between the austenite and martensite phases in
Ni1.9Pt0.1Mn1.4In0.6. A very small thermal hysteresis and crystallographic
compatibility between two phases in this alloy system indicate a stress-free
transition layer (i.e. perfect habit plane) between the austenite and
martensite phase, which is expected to give reversible martensite phase
transition and therefore reversible magnetocaloric effect (MCE) as well. The
calculated value of the isothermal entropy change ({\Delta}Siso) using the
magnetization curve under three different measurement protocols (i.e.
isothermal, loop, and isofield measurement protocol) is found to be nearly same
indicating a reversible MCE in the present alloy system. Our work provides a
path to design new magnetic shape memory Heusler alloys for magnetic
refrigeration and also suggest that any of the above measurement protocol can
be used for the calculation of {\Delta}Siso for materials satisfying
geometrical compatibility condition. | 2004.01854v1 |
2017-06-06 | Structural, electronic, magnetic and transport properties of equiatomic quaternary Heusler Alloy CoRhMnGe: Theory and Experiment | In this work, we present structural, electronic, magnetic, mechanical and
transport properties of equiatomic quaternary Heusler alloy, CoRhMnGe using
both theoretical and experimental techniques. A detailed structural analysis is
performed using X-ray diffraction(XRD) and extended X-ray absorption fine
structure(EXAFS) spectroscopy. The alloy is found to crystallize in Y-type
structure having space group $F\bar{4}3m$ (\# 216). The ab-initio simulation
pedict half-metallic ferromagnetic characteristics leading to large spin
polarization. The calculated magnetization is found to be in fair agreement
with experiment as well as those predicted by the Slater-Pauling rule, which is
a prerequisite for half-metallicity. The magnetic transition
temperature($\mathrm{T_{C}}$) is found to be $\sim 760$ K. Measured electrical
resistivity in the temperature range 2-400 K also gives an indication of
half-metallic behavior. Simulated resistivity matches fairly well with those
measured, with the temperature dependant carrier relaxation time lying in the
range $1-2$ fs. Effect of hydrostatic pressure on electronic structure,
magnetic and mechanical properties are investigated in detail. The alloy is
found to preserve half-metallic characteristics upto 30.27 GPa beyond which it
transit to metallic phase. No magnetic phase transition is found to occur in
the whole range of pressure. The system also satisfies the Born-Huang criteria
for mechanical stability upto a limited range of pressure. All these properties
make CoRhMnGe alloy promising for spintronics devices. | 1706.01624v1 |
2023-06-26 | Large saturation moment and high ferromagnetic transition temperature in a structurally disordered inverse Heusler alloy Fe2RuGe | We report the successful synthesis of a new 4$d$ based polycrystalline
inverse Heusler alloy Fe$_2$RuGe by an arc melting process and have studied in
detail its structural, magnetic and transport properties complemented with
first principle calculations. X-ray and neutron diffraction, Extended X-ray
Absorption Fine Structure and $^{57}$Fe M\"{o}ssbauer spectroscopic studies
confirm the single phase nature of the system where the Fe and Ru atoms are
randomly distributed in the 4$c$ and 4$d$ Wyckoff positions in a ratio close to
50:50. The formation of the disordered structure is also confirmed by the
theoretical energy minimization calculation. Despite the random cross-site
disorder of Fe and Ru atoms, magnetic measurements suggest not only a high
Curie temperature of $\sim$860\,K, but also a large saturation magnetic moment
$\sim$4.9\,$\mu_B$ per formula unit at 5\,K, considerably exceeding the
theoretical limit (4\,$\mu_B$ per formula unit) predicted by the Slater-Pauling
rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high
Curie temperatures. Neutron diffraction analysis coupled with the isothermal
magnetization value indicates that the magnetic moments in Fe$_2$RuGe are
associated with Fe-atoms only, which is also confirmed by M\"ossbauer
spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of
the parent compound, Fe$_3$Ge, the Curie temperature of Fe$_2$RuGe has
increased significantly despite the substitution of the nonmagnetic, yet
isoelectronic element Ru in this structurally disordered compound. Our
theoretical calculation reveals that the large Fe moment ($\sim2.8\mu_B$/Fe) on
the 4$b$ site can be attributed to a charge transfer from this Fe site towards
its Ru neighbours. Such a substantial increase in magnetic moment due to
electron charge transfer has not previously been reported in a Heusler alloy
system. | 2306.14831v1 |
2013-11-04 | Magnetic interactions in the Martensitic phase of Mn rich Ni-Mn-In shape memory alloys | The magnetic properties of Mn$_{2}$Ni$_{(1+x)}$In$_{(1-x)}$ ($x$ = 0.5, 0.6,
0.7) and Mn$_{(2-y)}$Ni$_{(1.6+y)}$In$_{0.4}$ ($y$ = -0.08, -0.04, 0.04, 0.08)
shape memory alloys have been studied. Magnetic interactions in the martensitic
phase of these alloys are found to be quite similar to those in
Ni$_2$Mn$_{(1+x)}$In$_{(1-x)}$ type alloys. Doping of Ni for In not only
induces martensitic instability in Mn$_2$NiIn type alloys but also affects
magnetic properties due to a site occupancy disorder. Excess Ni preferentially
occupies X sites forcing Mn to the Z sites of X$_2$YZ Heusler composition
resulting in a transition from ferromagnetic ground state to a state dominated
by ferromagnetic Mn(Y) - Mn(Y) and antiferromagnetic Mn(Y)-Mn(Z) interactions.
These changes in magnetic ground state manifest themselves in observation of
exchange bias effect even in zero field cooled condition and virgin
magnetization curve lying outside the hysteresis loop. | 1311.0579v1 |
2017-01-30 | Effect of site occupancy disorder on Martensitic properties of Mn$_{2}$NiIn type alloys: x-ray absorption fine structure study | We have carried out \textit{ab-initio} calculations of local structure of Mn
and Ni in Mn$_{2}$Ni$_{1.5}$In$_{0.5}$ alloy with different site occupancies in
order to understand the similarities in martensitic and magnetic properties of
Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ and Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Our results
show that in Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ alloys there is a strong possibility
of Mn atoms occupying all the three, X, Y and Z sites of X$_2$YZ Heusler
structure while Ni atoms preferentially occupy the X sites. Such a site
occupancy disorder of Mn atoms is in addition to a local structural disorder
due to size differences between Mn and In atoms which is also present in
Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Further, a comparison of the calculations
with experimental XAFS at the Mn and Ni K edges in
Mn$_{2-y}$Ni$_{1.6+y}$In$_{0.4}$ ($-0.08 \le y \le 0.08$) indicate a strong
connection between martensitic transformation and occupancy of Z sites by Mn
atoms. | 1701.08561v1 |
2019-11-09 | Multi-Principal-Element Approach to High-Performance Thermoelectric Materials | High-entropy alloys are characterized by high configurational entropy. Since
the discovery of high-entropy alloys (HEA) in 2004, entropy engineering has
provided a promising direction for exploiting composition, lattice disorder,
band structure, and microstructure effects to advance thermoelectric
performance. This review discusses the impact of entropy on thermoelectric
properties and looks back at the role of multi-principal-element alloys, a
weaker version of HEA, on the development of compositionally complex
thermoelectric alloys in achieving high thermoelectric performance. The
experimental and theoretical efforts in a wide range of material systems such
as TAGS, LAST, half-Heusler, liquid-like copper chalcogenides, SnTe, and
CuInTe2 chalcopyrites provide insights into the entropy engineering approach
and also promise an emerging paradigm of high-entropy thermoelectrics. | 1911.03797v1 |
2019-07-05 | Thermoelectric transport trends in group 4 half-Heusler alloys | The thermoelectric properties of 54 different group 4 half-Heusler (HH)
alloys have been studied from first principles. Electronic transport was
studied with density functional theory using hybrid functionals facilitated by
the $\mathbf{k} \cdot \mathbf{p}$ method, while the temperature dependent
effective potential method was used for the phonon contributions to the figure
of merit $ZT$. The phonon thermal conductivity was calculated including
anharmonic phonon-phonon, isotope, alloy and grain-boundary scattering. HH
alloys have an ${\it XYZ}$ composition and those studied here are in the group
4-9-15 (Ti,Zr,Hf)(Co,Rh,Ir)(As,Sb,Bi) and group 4-10-14
(Ti,Zr,Hf)(Ni,Pd,Pt)(Ge,Sn,Pb). The electronic part of the thermal conductivity
was found to significantly impact $ZT$ and thus the optimal doping level.
Furthermore, the choice of functional was found to significantly affect
thermoelectric properties, particularly for structures exhibiting band
alignment features. The intrinsic thermal conductivity was significantly
reduced when alloy and grain boundary scattering were accounted for, which also
reduced the spread in thermal conductivity. It was found that sub-lattice
disorder on the ${\it Z}$-site, i.e. the site occupied by group 14 or 15
elements, was more effective than ${\it X}$-site substitution, occupied by
group 4 elements. The calculations confirmed that ZrNiSn, ZrCoSb and ZrCoBi
based alloys display promising thermoelectric properties. A few other n-type
and p-type compounds were also predicted to be potentially excellent
thermoelectric materials, given that sufficiently high charge carrier
concentrations can be achieved. This study provides insight into the
thermoelectric potential of HH alloys and casts light on strategies to optimize
thermoelectric performance of multicomponent alloys. | 1907.02845v1 |
2019-03-18 | Experimental and Theoretical Investigation on the Possible Half-metallic Behaviour of Equiatomic Quaternary Heusler Alloys: CoRuMnGe and CoRuVZ (Z = Al, Ga) | In this report, structural, electronic, magnetic and transport properties of
quaternary Heusler alloys CoRuMnGe and CoRuVZ (Z = Al, Ga) are investigated.
All the three alloys are found to crystallize in cubic structure. CoRuMnGe
exhibits L2$_1$ structure whereas, the other two alloys have B2-type disorder.
For CoRuMnGe and CoRuVGa, the experimental magnetic moments are in close
agreement with the theory as well as those predicted by the Slater-Pauling
rule, while for CoRuVAl, a relatively large deviation is seen. The reduction in
the moment in case of CoRuVAl possibly arises due to the anti-site disorder
between Co and Ru sites as well as V and Al sites. Among these alloys, CoRuMnGe
has the highest T$\mathrm{_C}$ of 560 K. Resistivity variation with temperature
reflects the half-metallic nature in CoRuMnGe alloy. CoRuVAl shows metallic
character in both paramagnetic and ferromagnetic states, whereas the
temperature dependence of resistivity for CoRuVGa is quite unusual. In the last
system, $\rho$ vs. T curve shows an anomaly in the form of a maximum and a
region of negative temperature coefficient of resistivity (TCR) in the
magnetically ordered state. The ab initio calculations predict nearly
half-metallic ferromagnetic state with high spin polarization of 91, 89 and 93
\% for CoRuMnGe, CoRuVAl and CoRuVGa respectively. To investigate the
electronic properties of the experimentally observed structure, the Co-Ru swap
disordered structures of CoRuMnGe alloy are also simulated and it is found that
the disordered structures retain half-metallic nature, high spin polarization
with almost same magnetic moment as in the ideal structure. Nearly
half-metallic character, high T$\mathrm{_C}$ and high spin polarization make
CoRuMnGe alloy promising for room temperature spintronic applications. | 1903.07265v2 |
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