Tailoring and controlling magnetic properties is an important factor for materials design. Here, we present a case study for Ni-based Heusler compounds of the type Ni$_2$YZ with Y = Mn, Fe, Co and Z = B, Al, Ga, In, Si, Ge, Sn based on first principles electronic structure calculations. These compounds are interesting since the materials properties can be quite easily tuned by composition and many of them possess a non-cubic ground state being a prerequisite for a finite magnetocrystalline anisotropy (MAE). We discuss systematically the influence of doping at the Y and Z sublattice as well of lattice deformation on the MAE. We show that in case of Ni$_2$CoZ the phase stability and the MAE can be improved using quaternary systems with elements from group 13 and 14 on the Z sublattice whereas changing the Y sublattice occupation by adding Fe does not lead to an increase of the MAE. Furthermore, we studied the influence of the lattice ratio on the MAE. Showing that small deviations can lead to a doubling of the MAE as in case of Ni$_2$FeGe. Even though we demonstrate this for a limited set of systems the findings may carry over to other related systems.
This work reports on first principles calculations of the electronic and magnetic structure of tetragonal Heusler compounds with the composition Rh$_2$Fe$_{x}$Co$_{1-x}$Sb ($0\leq x\leq1$). It is found that the magnetic moments increase from 2 to 3.4~$μ_B$ and the Curie temperature decreases from 500 to 464~K with increasing Fe content $x$. The $3d$ transition metals make the main contribution to the magnetic moments, whereas Rh contributes only approximately 0.2~$μ_B$ per atom, independent of the composition. The paper focuses on the magnetocrystalline anisotropy of the borderline compounds R…
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 stru…
On the basis of the density functional calculations in combination with the supercell approach, we report on a complete study of the influences of atomic arrangement and Ni substitution for Al on the ground state structural and magnetic properties for Fe$_2$Ni$_{1+x}$Al$_{1-x}$ Heusler alloys. We discuss systematically the competition between five cubic Heusler-type structures formed by shuffles of Fe and Ni atoms to reveal routes for improving the phase stability and magnetic properties, in particular magnetocrystalline anisotropy~(MAE). We predict that in case of Fe$_2$NiAl the ground state …
With a view to the design of hard magnets without rare earths we explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion. We consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is always, at $T=0$, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for…
Magnetocrystalline anisotropy at Heusler alloy$|$MgO interfaces have been studied using first principles calculations. It is found that Co terminated Co$_{2}$FeAl$|$MgO interfaces show perpendicular magnetic anisotropy up to 1.31 mJ/m$^2$, while those with FeAl termination exhibit in-plane magnetic anisotropy. Atomic layer resolved analysis indicates that the origin of perpendicular magnetic anisotropy in Co$_{2}$FeAl$|$MgO interfaces can be attributed to the out-of-plane orbital contributions of interfacial Co atoms. At the same time, Co$_{2}$MnGe and Co$_{2}$MnSi interfaced with MgO tend to …
We report the magnetotransport properties of ferromagnet (FM)/antiferromagnet (AFM) Fe$_2$CrSi/Ru$_2$MnGe epitaxial bilayers using current-in-plane configurations. Above the critical thickness of the Ru$_2$MnGe layer to induce exchange bias, symmetric and asymmetric curves were observed in response to the direction of FM magnetocrystalline anisotropy. Because each magnetoresistance curve showed full and partial AFM rotation, the magnetoresistance curves imply the impact of the Fe$_2$CrSi magnetocrystalline anisotropy to govern the AFM rotation. The maximum magnitude of the angular-dependent re…
A comprehensive study of the total energy of manganese-rich Heusler compounds using density functional theory is presented. Starting from a large set of cubic parent systems, the response to tetragonal distortions is studied in detail. We single out the systems that remain cubic from those that most likely become tetragonal. The driving force of the tetragonal distortion and its effect on the magnetic properties, especially where they deviate from the Slater--Pauling rule, as well as the trends in the Curie temperatures, are highlighted. By means of partial densities of states, the electronic …
We investigate the structural stability and magnetic properties of cubic, tetragonal and hexagonal phases of Mn3Z (Z=Ga, Sn and Ge) Heusler compounds using first-principles density-functional theory. We propose that the cubic phase plays an important role as an intermediate state in the phase transition from the hexagonal to the tetragonal phases. Consequently, Mn3Ga and Mn3Ge behave differently from Mn3Sn, because the relative energies of the cubic and hexagonal phases are different. This result agrees with experimental observations from these three compounds. The weak ferromagnetism of the h…
We determine experimentally the spin structure of half-metallic Co2FeAl0.4Si0.6 Heusler alloy elements using magnetic microscopy. Following magnetic saturation, the dominant magnetic states consist of quasi-uniform configurations, where a strong influence from the magnetocrystalline anisotropy is visible. Heating experiments show the stability of the spin configuration of domain walls in confined geometries up to 800 K. The switching temperature for the transition from transverse to vortex walls in ring elements is found to increase with ring width, an effect attributed to structural changes a…
We report first-principles investigations of magnetocrystalline anisotropy energy (MCAE) oscillations as a function of capping layer thickness in Heusler alloy Co\textsubscript{2}FeAl/Ta heterostructures. Substantial oscillation is observed in FeAl-interface structure. According to $k$-space and band-decomposed charge density analyses, this oscillation is mainly attributed to the Fermi-energy-vicinal quantum well states (QWS) which are confined between Co\textsubscript{2}FeAl/Ta interface and Ta/vacuum surface. The smaller oscillation magnitude in the Co-interface structure can be explained by…
The ferromagnetic Heusler alloy $Ni_2MnGa$ had been of major interest in the past few years because of its magnetic properties which can be easily tuned. The $Ni_2MnGa$ Heusler alloys are intermetallic alloy with $L2_1$ structure. Here we report a detailed investigation of the effect of doping of Co and Mn in Ni2MnGa. Magnetic properties and electronic structure of $Ni_{2-x}Co_xMnGa_{1-y}Mn_y$ Heusler alloys have been studied by using Green's function-based KKR-CPA method based DFT calculations. We will show the magnetization can be tuned depending on the Co and Mn occumencies. We will also di…
Perpendicular magnetization is essential for high-density memory application using magnetic materials. High-spin polarization of conduction electrons is also required for realizing large electric signals from spin-dependent transport phenomena. Heusler alloy is a well-known material class showing the half-metallic electronic structure. However, its cubic lattice nature favors in-plane magnetization and thus minimizes the perpendicular magnetic anisotropy (PMA), in general. This study focuses on an inverse-type Heusler alloy, Mn$_{2-δ}$CoGa$_{1+δ}$ (MCG) with a small off-stoichiometry ($δ$) , w…
Influence of chemical ordering on magnetocrystalline anisotropy and magnetoelastic properties in Weyl magnetic semimetal Co2MnGa thin films
Institute of Physics PAS（波兰科学院物理研究所）；Institute for Materials Research, Tohoku University（东北大学物质材料研究所）；Innovative Functional Materials Research Institute, National Institute of Advanced Industrial Science and Technology（产业技术综合研究所创新功能材料研究所）；Advanced Science Research Center, Japan Atomic Energy Agency（日本原子能机构先进科学研究中心）
The anomalous Hall effect (AHE) in the Heusler compounds Co$_{2}$FeSi and Co$_{2}$FeAl is studied in dependence of the annealing temperature to achieve a general comprehension of its origin. We have demonstrated that the crystal quality affected by annealing processes is a significant control parameter to tune the electrical resistivity $ρ_{xx}$ as well as the anomalous Hall resistivity $ρ_{ahe}$. Analyzing the scaling behavior of $ρ_{ahe}$ in terms of $ρ_{xx}$ points to a temperature-dependent skew scattering as the dominant mechanism in both Heusler compounds.
Search for ultrathin magnetic film with large perpendicular magnetocrystalline anisotropy (PMA) has been inspired for years by the continuous miniaturization of magnetic units in spintronics devices. The common magnetic materials used in research and applications are based on Fe because the pure Fe metal is the best yet simple magnetic material from nature. Through systematic first-principles calculations, we explored the possibility to produce large PMA with ultrathin Fe on non-noble and non-magnetic Pb(001) substrate. Interestingly, huge magnetocrystalline anisotropy energy (MAE) of 7.6 meV …
The development of high-density magnetic recording media is limited by the superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat assisted magnetic recording (HAMR) has been developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here we introduce Rh2CoSb as …
Since the discovery of the anomalous Hall effect (AHE), the anomalous Hall conductivity (AHC) has been thought to be zero when there is no net magnetization. However, the recently found relation between the intrinsic AHE and the Berry curvature predicts other possibilities, such as a large AHC in non-colinear antiferromagnets with no net magnetization but net Berry curvature. Vice versa, the AHE in principle could be tuned to zero, irrespective of a finite magnetization. Here, we experimentally investigate this possibility and demonstrate that, the symmetry elements of Heusler magnets can be c…
The electronic structures of tetragonally distorted half-Heuselr compound LaPtBi in the C1b structure are investigated in the framework of density functional theory using the full potential linearized augmented plane with local spin density approximation method. The calculation results show that both the band structures and the Fermi level can be tuned by using either compressive or tensile in-plane strain. A large bulk band gap of 0.3 eV can be induced through the application of a compressive in-pane strain in LaPtBi with the assumption of a relaxed volume of the unit cell. Our results could …
Heusler compounds having $\textit{D}$${}_{2d}$ crystal symmetry gained much attention recently due to the stabilization of a vortex-like spin texture called antiskyrmions in thin lamellae of Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn as reported in the work of Nayak $\textit{et al.}$ [Nature (London) 548, 561 (2017)]. Here we show that bulk Mn${}_{1.4}$Pt${}_{0.9}$Pd${}_{0.1}$Sn undergoes a spin-reorientation transition from a collinear ferromagnetic to a noncollinear configuration of Mn moments below 135 K, which is accompanied by the emergence of a topological Hall effect. We tune the topologica…
Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the $GW$ approximation within the framework of the FLAPW method, we study the quasi-particle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the \textit{sp}-electron based semiconductors such as Si and GaAs, in these systems the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2~eV, which makes the star…
Perpendicular magnetic anisotropy (PMA) in ultrathin magnetic structures is a key ingredient for the development of electrically controlled spintronic devices. Due to their relatively large spin-polarization, high Curie temperature and low Gilbert damping the Co-based full Heusler alloys are of special importance from a scientific and applications point of view. Here, we study the mechanisms responsible for the PMA in Pt/Co-based full Heusler alloy/MgO thin films structures. We show that the ultrathin Heusler films exhibit strong PMA even in the absence of magnetic annealing. By means of ferro…
Inspired by the successful synthesis of two-dimensional (2D) V-based Janus dichloride monolayers with intrinsic ferromagnetism and high Curie temperature (T$_{c}$), the electronic structure, spin-valley splitting and magnetic anisotropy of Janus 2H-VSeS monolayers are investigated in detailed using first-principles calculations. The results show that the Janus 2H-VSeS monolayer exhibits a large valley splitting of 105meV, high T$_{c}$ of 278K and good magnetocrystalline anisotropy (0.31meV) contributed by the in-plane d$_{x^{2}-y^{2}}$/d$_{xy}$ orbitals of V atoms. The biaxial strain ($-$8%<$\…
The prediction of ultra-low magnetic damping in Co 2 MnZ Heusler half-metal thin-film magnets is explored in this study and the damping response is shown to be linked to the underlying electronic properties. By substituting the Z elements in high crystalline quality films (Co 2 MnZ with Z=Si, Ge, Sn, Al, Ga, Sb), electronic properties such as the minority spin band gap, Fermi energy position in the gap and spin polarization can be tuned and the consequence on magnetization dynamics analyzed. The experimental results allow us to directly explore the interplay of spin polarization, spin gap, Fer…
Three-dimensional topological semimetals host a range of interesting quantum phenomena related to band crossing that give rise to Dirac or Weyl fermions, and can be potentially engineered into novel quantum devices. Harvesting the full potential of these materials will depend on our ability to position the Fermi level near the symmetry-protected band crossings so that their exotic spin and charge transport properties become prominent in the devices. Recent experiments on bulk and thin films of topological half-Heuslers show that the Fermi level is far from the symmetry-protected crossings, lea…
Using Density Functional Theory and a thermodynamic model [Physical Review B 86, 134418 (2012)], in this paper, we provide an approach to systematically screen compounds of a given Heusler family to predict ones that can yield giant magnetocaloric effect driven by a first-order magneto-structural transition. We apply this approach to two Heusler series Ni$_{2-x}$Fe$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$ and Ni$_{2-x}$Co$_{x}$Mn$_{1+z-y}$Cu$_{y}$Sb$_{1-z}$, obtained by cosubstitution at Ni and Mn sites. We predict four new compounds with potentials to achieve the target properties. Our computation…
Half-Heusler compounds have emerged as promising thermoelectric materials that offer huge compositional space to tune their thermoelectric performance. A class of stable half Heusler compounds formed from elements of three specific groups in the periodic table viz. X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf, Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and 1) via various stoichiometric isoelectronic elemental substitution at the X, Y and Z sites respectively is investigated. Intelligent filters are employed at each step of our hig…
Epitaxial $\mathrm{Co_2MnSi}$ with intrinsic magnetocrystalline anisotropy as a route to bias-field-free nonlinear half-metal magnonics at the nanoscale
Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau（莱茵兰-普法尔茨技术大学凯泽斯劳滕-兰道）；Université de Lorraine（洛林大学）
To understand the effect of isoelectronic substitution on thermoelectric properties of TiCoSb based half - Heusler (HH) alloys, we have systematically studied the transport properties with substitution of Zr at Ti and Bi at Sb sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and parent TiCoSb are investigated using the full potential linearized augmented plane wave method and the thermoelectric transport properties are calculated on the basis of semiclassical Boltzmann transport theory. The band analysis of the calculated band structures reveal that TixZr1-xCoSbxBi1-…
Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. Accordi…
We present the magnetic field dependencies of transport properties for $R$PtBi ($R$ = Gd, Dy, Tm, and Lu) half-Heusler compounds. Temperature and field dependent resistivity measurements of high quality $R$PtBi single crystals reveal an unusually large, non-saturating magnetoresistance (MR) up to 300 K under a moderate magnetic field of $H$ = 140 kOe. At 300 K, the large MR effect decreases as the rare-earth is traversed from Gd to Lu and the magnetic field dependence of MR shows a deviation from the conventional $H^{2}$ behavior. The Hall coefficient ($R_{H}$) for $R$ = Gd indicates a sign ch…
Topological materials often exhibit remarkably linear, non-saturating magnetoresistance (LMR), which is both of scientific and technological importance. However, the role of topologically non-trivial states in the emergence of such a behaviour has eluded clear demonstration in experiments. Here, by reducing the coupling between the topological surface states (TSS) and the bulk carriers we controllably tune the LMR behavior in Pt1-xAuxLuSb into distinct plateaus in Hall resistance, which we show arise from a quantum Hall phase. This allowed us to reveal how smearing of the Landau levels, which …
Huge deformations of the crystal lattice can be achieved in materials with inherent structural instability by epitaxial straining. By coherent growth on seven different substrates the in-plane lattice constants of 50 nm thick Fe70Pd30 films are continuously varied. The maximum epitaxial strain reaches 8,3 % relative to the fcc lattice. The in-plane lattice strain results in a remarkable tetragonal distortion ranging from c/abct = 1.09 to 1.39, covering most of the Bain transformation path from fcc to bcc crystal structure. This has dramatic consequences for the magnetic key properties. Magneto…
Following demands for materials with peculiar transport properties, e.g. in magnetoelectronics or thermoelectrics, there is a need for materials modeling at the quantum-mechanical level. We combine density-functional with various scale-bridging tools to establish correlations between the macroscopic properties and the atomic structure of materials. For examples, magnetic memory devices exploiting the tunneling magneto-resistance (TMR) effect depend crucially on the spin polarization of the electrodes. Heusler alloys, e.g. Co2MnSi, if perfectly ordered, are ferromagnetic half-metals with (ideal…
The van der Waals class of materials offer an approach to two-dimensional magnetism as their spin fluctuations can be tuned upon exfoliation of layers. Moreover, it has recently been shown that spin-lattice coupling and long-range magnetic ordering can be modified with pressure in van der Waals materials. In this work, the magnetic properties of quasi two-dimensional CrBr3 are reported applying hydrostatic pressure. The application of pressure (0 - 0.8 GPa) shows a 72 % decrease in saturation magnetization with small decrease in the Curie temperature from 33 to 29 K. Density functional theory …
