Inverse Heusler Compounds Research Articles

Stability of spin-spiral magnetic structures in Mn2PtSn

The stability of a long-periodic homogeneous spin-spiral configuration in an inverse tetragonal Heusler compound, Mn2PtSn, is studied with the help of density functional theory calculations. The energetically most stable collinear magnetic state in this system is the ferrimagnetic one. However, the existence of negative phonon frequency makes this configuration dynamically unstable. The energy dispersion plots reveal that an energy minimum exists at q=0.1 along [100] and [110] propagating directions, which correspond to a stable non-collinear configuration compared to the collinear spin states. The inclusion of spin–orbit coupling further reduces the ground-state energy without changing the q-vector of the energy minima. The cycloidal spiral configuration, where the spins rotate at an angle of 36° along the propagating direction, is found to be more stable than the screw spiral configuration. The calculated density of state plots further supports the stability of the non-collinear cycloidal spin order. This stable, non-collinear spin-spiral configuration of Mn2PtSn makes this compound a prospective material for spintronics device applications.

Magnetic tunability in tetragonal Mn–Rh–Ir–Sn inverse Heusler compounds

Gaining control over magnetic structure has been an ongoing challenge in materials that form complex, nanoscale, and non-collinear magnetic configurations. Recently, it was predicted that tuning the ratio of the Dzyaloshinskii–Moriya interaction to the uniaxial magnetic anisotropy in tetragonal inverse Heuslers through changes in composition could allow a range of interesting magnetic states to be accessed, from simple ferrimagnetism, to helical and antiskyrmionic phases. Here, we show tunability of the magnetic phase behavior in the Mn–Rh–Sn system through Ir substitution on the Rh substructure. Iridium substitution correlates to an increase in the strength of ferromagnetic exchange couplings, at the expense of antiferromagnetic exchange couplings. However, we do not observe the complex non-collinear magnetic phases proposed previously, likely due to the extremely narrow composition window where these phases are predicted to form in a bulk sample. This work highlights the sensitivity of complex magnetic structures to stoichiometry, which makes them difficult to discover empirically.

Thermodynamic, mechanical stability, and magneto-electronic features of Ti2-based quaternary Heusler alloys Ti2CoGa1−xCux (x=0, 0.25, 0.5, 0.75, and 1): A DFT investigation

In this work, we have used the full-potential linearized augmented plane wave (FP-LAPW) method implemented in the WIEN2k code combined with the generalized gradient approximation (GGA) of the density functional theory (DFT) to study the structural, elastic, mechanical, electronic, magnetic, and thermodynamic properties of the parent ternary inverse Heusler compounds based on Titanium and Cobalt Ti2CoGa, Ti2CoCu in the Hg2CuTi-type structure and their quaternary alloys Ti2CoGa[Formula: see text]Cux ([Formula: see text], 0.5, 0.75) for the chosen concentrations using a supercell with 16 atoms. We have calculated the structural properties, such as the lattice parameters, bulk modulus, and its first derivative, which are in good agreement with those that have been obtained based on other published theoretical methods. Also, we calculated the elastic constants of the studied Heusler alloys, and we found that these materials are elastically stable, ductile, and anisotropic. Therefore, the electronic and magnetic properties indicate that Ti2CoGa exhibits a half-metallic (HM) ferromagnetic behavior, while Ti2CoCu shows a metal and a non-magnetic (NM) character. Their quaternary alloys are found to be nearly HM ferromagnetic materials, with a magnetic moment mainly due to the atom Ti. Furthermore, the quasi-harmonic Debye model, which incorporates the lattice vibrations, was used to estimate the thermodynamic effects on some macroproperties of the Ti2CoGa[Formula: see text]Cux alloys. Successful results were achieved for the variations of the primitive cell volume, bulk modulus, heat capacities, and Debye temperature with pressure and temperature, respectively, in the ranges of 0–30[Formula: see text]GPa and 0–1400[Formula: see text]K. To our knowledge, no analogous investigations on the mechanical and thermodynamic properties of the Ti2CoGa[Formula: see text]Cux ([Formula: see text], 0.5 and 0.75) alloys have been performed to date. As a result, it is predicted that Ti2CoGa[Formula: see text]Cux Heusler alloys will be promising candidates for actual applications in spintronic devices.

Structural, mechanical, electronic, thermal, and optical properties of the inverse-Heusler compounds X2RuPb(X = La, Sc): A first-principles investigation

Topological insulators are novel quantum material states with insulating bulk band gaps and topologically protected metallic surface states that have been extensively studied owing to their intriguing properties for spintronic and quantum-computing applications. The structural, mechanical, electronic, thermal, and optical properties of inverse Heusler compounds La2RuPb and, Sc2 RuPb in two Hg2CuTi, Cu2 MnAltype structures were calculated using the full potential linear muffin-tin orbital simulation methodology as implemented in the computer code,which is based on density functional theory.We employed the local-density approximation for the exchange and correlation potential (XC) terms. Consequently, the optical characteristics of La2 RuPb, Sc2 RuPb and elastic constants Cij and their corresponding elastic moduli were computed for the first time. According to our structural calculations, La2 RuPb is more stable in its Hg2 CuTi-type structure than Sc2 RuPb in its Cu2 MnAl-type structure. However, the mechanical characteristics demonstrate their stability in the final stages of elastic deformation.

Theoretical pursuit of structural, mechanical, magneto-electronic, and thermoelectric features of new inverse full Heusler compounds Rb2ZrZ (Z = C, Si, Ge, and Sn). A first-principles investigation

Theoretical pursuit of structural, mechanical, magneto-electronic, and thermoelectric features of new inverse full Heusler compounds Rb2ZrZ (Z = C, Si, Ge, and Sn). A first-principles investigation

Stoichiometry and spin-orbit coupling in Mn–Pt–Sn Heusler compound

This study uses density functional theory implemented in the Vienna ab initio simulation package (VASP) software to examine the impact of spin-orbit coupling (SOC) on the electronic and magnetic properties of the inverse tetragonal Heusler compound Mn1.5PtSn with various spin orientations. Regardless of the presence or absence of SOC, it has been found that the ferrimagnetic configuration is more stable at the ground state than the ferromagnetic and antiferromagnetic one. The SOC influences the ground state energy of the compounds. The exchange coupling parameters, density of states, bandstructure plots, charge density distribution, and Bader charge analysis help in understanding the magnetic and electronic properties of the system. The high spin-polarization in the vicinity of the Fermi level and the low magnetocrystalline anisotropy energy obtained for the stable ferrimagnetic configuration opens up the possibility of tuning the system for spin-transfer-torque based device applications, like magnetic recording heads.

Experimental studies of Cr2NiAl half-metallic inverse Heusler compound for spintronic applications

Experimental studies of Cr2NiAl half-metallic inverse Heusler compound for spintronic applications

Antisite disorder and Berry curvature driven anomalous Hall effect in the spin gapless semiconducting Mn2CoAl Heusler compound

Spin gapless semiconductors exhibit a finite band gap for one spin channel and a closed gap for another spin channel, and they have emerged as a new state of magnetic materials with a great potential for spintronic applications. The first experimental evidence for spin gapless semiconducting behavior was observed in an inverse Heusler compound ${\mathrm{Mn}}_{2}\mathrm{CoAl}$. Here, we report a detailed investigation of the crystal structure and anomalous Hall effect in ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ using experimental and theoretical studies. The analysis of the high-resolution synchrotron x-ray diffraction data shows antisite disorder between Mn and Al atoms within the inverse Heusler structure. The temperature-dependent resistivity shows semiconducting behavior and follows Mooij's criteria for disordered metal. The scaling behavior of the anomalous Hall resistivity suggests that the anomalous Hall effect in ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ is primarily governed by an intrinsic mechanism due to the Berry curvature in momentum space. The experimental intrinsic anomalous Hall conductivity (AHC) is found to be $\ensuremath{\sim}35$ S/cm, which is considerably larger than the theoretically predicted value for ordered ${\mathrm{Mn}}_{2}\mathrm{CoAl}$. Our first-principles calculations conclude that the antisite disorder between Mn and Al atoms enhances the Berry curvature and hence the value of intrinsic AHC, which is in very good agreement with the experiment.

A first-principles study on the effect of Cr, Mn, and Co substitution on Fe-based normal- and inverse-Heusler compounds: Fe3−xYxZ (x=0, 1, 2, 3; Y= Cr, Mn, Co; Z=Al, Ga, Si)

First-principles calculation has become one of the most reliable approaches in predicting structural, electronic, and magnetic properties for material applications. Alloys in Heusler structures have also attracted much attention recently since they can be easily synthesized and provide interesting properties for future spintronic applications. In this work, we investigate a series of Fe-based Heusler compounds Fe3−xYxZ (x = 0, 1, 2, 3; Y= Cr, Mn, Co; Z= Al, Ga, Si) with L21- and XA-type structures using first-principles calculations based on density functional theory. According to formation energy calculations and mechanical property analysis, most of the studied Heusler compounds are thermodynamically stable and could be synthesized experimentally. The Co substitution leads Fe3−xCoxZ to a ferromagnetic ground state like Fe3Z with a strong magnetization ranging from 4 to 6 μB/f. u. While replacing Fe with Cr or Mn, the exchange coupling between Cr (Mn) and its neighboring atoms generally tend to be anti-parallel. Among the antiferromagnetic compounds, Mn3Al and Mn3Ga are antiferromagnetic half metal while Mn3Si is ferrimagnetic half metal. These rarely found type of half metals with low magnetic moment and high spin polarization at the Fermi level are important for low energy consumption spintronic applications. The estimated Curie temperatures for Mn3Al, and Mn3Si and Co2FeSi (XA) are in good agreement with previously theoretical values, while for Fe3Al and Fe3Si, they are in good agreement with previous experimental results. The good consistency in Curie temperature demonstrates high reliability of our predictions based on first-principles calculations. As for the topological property aspect, we predict Fe2CrAl and Fe2MnAl as the 3-dimensional Weyl semimetal. Furthermore, Fe2CrSi is predicted to be the magnetic nodal-line semimetal. Interestingly, our mechanical property analysis demonstrates that Co3Si and Fe2CoSi (L21) exhibit ultraelastic metal behavior, which is of high potential in advanced mechanical industry. This work suggests that Heusler compounds are excellent candidates for future spintronics as well as for high-performance ultraelastic metals.

Collinear magnetism and spin-orbit coupling in Mn2PtSn

The materials having high magnetic anisotropy energy are prospective materials for application in non-volatile memory technologies. In this report, the effect of spin–orbit coupling (SOC) on electronic and collinear magnetic properties of the inverse tetragonal Heusler compound Mn2PtSn with different spin orders has been studied with the help of density functional theory calculations using the Vienna ab initio simulation package. We have found that the ferrimagnetic (FiM) spin order is more stable at the ground state than the ferro- and antiferromagnetic order, irrespective of the inclusion of SOC. All the results are explained by examining the density of states, and bandstructure plots, supported by the charge density distribution of the atoms and Bader charge analysis. A significant value of magnetocrystalline anisotropy (MCA) energy of around 58.48 Merg cm−3 is obtained for the FiM spin order. The small total magnetic moment and high MCA energy make this magnetic ordering suitable for spin-transfer-torque based devices.

Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound.

Magnetic nano-objects, namely antiskyrmions and Bloch skyrmions, have been found to coexist in single-crystalline lamellae formed from bulk crystals of inverse tetragonal Heusler compounds with D2d symmetry. Here evidence is shown for magnetic nano-objects in epitaxial thin films of Mn2 RhSn formed by magnetron sputtering. These nano-objects exhibit a wide range of sizes with stability with respect to magnetic field and temperature that is similar to single-crystalline lamellae. However, the nano-objects do not form well-defined arrays, nor is any evidence found for helical spin textures. This is speculated to likely be a consequence of the poorer homogeneity of chemical ordering in the thin films. However, evidence is found for elliptically distorted nano-objects along perpendicular crystallographic directions within the epitaxial films, which is consistent with elliptical Bloch skyrmions observed in single-crystalline lamellae. Thus, these measurements provide strong evidence for the formation of noncollinear spin textures in thin films of Mn2 RhSn. Using these films, it is shown that individual nano-objects can be deleted using a local magnetic field from a magnetic tip and collections of nano-objects can be similarly written. These observations suggest a path toward the use of these objects in thin films with D2d symmetry as magnetic memory elements.

Spin gapless semiconductor and nearly spin semimetal antiferromagnets: The case of the inverse Heusler compounds Mn2LiZ (Z = Al and Ga)

Using first-principles calculations, we report the structural, electronic, magnetic and electronic transport properties of the new Heusler compounds Mn2LiZ with Z is Al and Ga. We show that both compounds are more stable in the inverse Heusler structure than in the regular one. The band structure calculations indicate that the Mn2LiAl compound is a spin gapless semiconductor and Mn2LiGa is a nearly spin-semimetal. In agreement with the Slater-Pauling rule, the two compounds are non-conventional antiferromagnets: they show zero spin moment accompanied by the fully spin-polarized charge carriers. Strong direct interaction between the spin moments is obtained. Consequently, the mean-field approximation reveals a high Curie temperature in the two compounds. Within the Boltzmann transport theory, the electrical conductivity shows non-metallic behavior for the two compounds at elevated temperatures, and the Seebeck coefficient appears to be large. In particular, the Mn2LiAl compound has a value greater than 150µV/K in a wide temperature range.

Magnetocrystalline anisotropies in MnxPtSn thin films

The magnetic anisotropy determines the equilibrium orientation of the magnetization in a ferromagnet. In Mn-based inverse tetragonal Heusler compounds, a large uniaxial anisotropy makes these materials excellent candidates for both spin-transfer-torque and skyrmionic devices. Here, we present systematic investigations of the magnetocrystalline anisotropies in MnxPtSn films (x = 1.0–1.6). We find that the MnxPtSn films, grown by magnetron sputtering on MgO substrates, show a structural transition between x = 1.0 and 1.2 from cubic to tetragonal, where the tetragonal structure shows a twinned in-plane c-axis orientation. From ferromagnetic resonance measurements, we determine the out-of-plane and in-plane uniaxial anisotropies, taking into account the particular structural properties of the films. We find a strong dependence of the uniaxial anisotropies on the Mn concentration, as well as on structural distortions due to the lattice-matched growth. From temperature-dependent ferromagnetic resonance measurements, we infer the evolution of the in-plane uniaxial anisotropy and observe the presence of additional magnetic interactions and magnetization relaxation mechanisms around the spin reorientation transition.

Magnetic and transport properties of inverse Heusler compound Cr2CoAl

We report magnetic and electrical transport properties of polycrystalline as-cast compound Cr2CoAl having inverse Heusler like XA structure with B2 disorder. Temperature-dependent magnetization (M-T) under zero-field cooled (ZFC) and field cooled (FC) condition and field-dependent magnetization (M-H) studies suggest that this compound is a soft magnetic material below Tc ~ 20.5 K having a very low magnetic moment as it is found that magnetization at 5 K under 50 kOe applied magnetic field is ~0.11μB/f.u. Also, M-T data taken ZFC-FC condition under different applied magnetic fields and M-H data taken at 100 K and 300 K indicate that this compound may have magnetic clusters in paramagnetic matrix. Further analysis and temperature-dependent heat capacity measurement reveal paramagnetic to a short-range ordered ferromagnetic transition near Tc ≈ 20.5 K and also reveal the presence of magnetic clusters within the compound. These magnetic clusters may arise because of B2 disorder in the compound. Temperature-dependent resistivity measurement confirms that the compound Cr2CoAl is metallic as it is found increasing with temperature. Nonlinearity in temperature dependency resistivity data, observed in low- temperature region, follows T2 dependency that generally comes because of electron–electron scattering. Magneto-resistance (MR) is also found to be positive throughout the temperature region from 8 K to 390 K.

Direct observation of ferrimagnetic ordering in inverse Heusler alloy Mn2CoAl

Compensated ferrimagnetic Heusler compounds with high spin polarization and a low net magnetic moment are strategically important materials for spin-logic and further energy-efficient spintronic applications. However, the element-resolved magnetic ordering of these compensated ferrimagnets remains an open issue. Here, we report a direct observation of the spin and orbital moments of the B2 phase Mn2CoAl thin film using the synchrotron-based x-ray magnetic circular dichroism technique. An ferrimagnetic ordering between Mn and Co elements and a compensated-ferrimagnet-like small net magnetic moment of only 0.34 μB/f.u. were observed unambiguously in B2 Mn2CoAl. Antiparallel coupling between Mn and Co is attributed to the mixture of the Mn(B) and Al occupation in the B2 phase Mn2CoAl lattice. This work demonstrates great potential of the compensated ferrimagnetic half-metallic inverse Heusler compounds Mn2CoAl for spintronic applications.

Observation of Magnetic Antiskyrmions in the Low Magnetization Ferrimagnet Mn2Rh0.95Ir0.05Sn.

Recently, magnetic antiskyrmions were discovered in Mn1.4Pt0.9Pd0.1Sn, an inverse tetragonal Heusler compound that is nominally a ferrimagnet, but which can only be formed with substantial Mn vacancies. The vacancies reduce considerably the compensation of the moments between the two expected antiferromagnetically coupled Mn sub-lattices so that the overall magnetization is very high and the compound is almost a “ferromagnet”. Here, we report the observation of antiskyrmions in a second inverse tetragonal Heusler compound, Mn2Rh0.95Ir0.05Sn, which can be formed stoichiometrically without any Mn vacancies and which thus exhibits a much smaller magnetization. Individual and lattices of antiskyrmions can be stabilized over a wide range of temperature from near room temperature to 100 K, the base temperature of the Lorentz transmission electron microscope used to image them. In low magnetic fields helical spin textures are found which evolve into antiskyrmion structures in the presence of small magnetic fields. A weaker Dzyaloshinskii-Moriya interaction (DMI), that stabilizes the antiskyrmions, is expected for the 4d element Rh as compared to the 5d element Pt, so that the observation of antiskyrmions in Mn2Rh0.95Ir0.05Sn establishes the intrinsic stability of antiskyrmions in these Heusler compounds. Moreover, the finding of antiskyrmions with substantially lower magnetization promises, via chemical tuning, even zero moment antiskyrmions with important technological import.

Half-metallic surfaces in thin-film Ti2MnAl0.5Sn0.5

Materials exhibiting a high degree of spin polarization in electron transport are in demand for applications in spintronics—an emerging technology utilizing a spin degree of freedom in electronic devices. Room-temperature half-metals are considered ideal candidates, as they behave as an insulator for one spin channel and as a conductor for the other spin channel. In addition, for nano-size devices, one has to take into account possible modification of electronic structure in thin-film geometry, due to the potential presence of surface/interface states. It has been shown that typically these states have a detrimental impact on half-metallicity, i.e. their presence results in reduced spin-polarization. Here, we employ density functional calculations to explore an inverse Heusler compound, Ti2MnAl0.5Sn0.5, which exhibits half-metallic electronic structure in bulk geometry. In particular, this material behaves as a regular metal for majority-spin, and as a semiconductor for minority-spin states. We show that in thin-film geometry, the type of termination surface has a decisive effect on half-metallicity of this material. In particular, we analyze six possible termination configurations, and show that for four of them, energy states emerge in the minority-spin band gap, significantly reducing the spin polarization of Ti2MnAl0.5Sn0.5. At the same time, our calculations indicate that two termination surfaces preserve half-metallic properties of this material. This result is somewhat unexpected, as most of the available literature reports reduction of the spin-polarization due to the presence of surface states. Thus, our results show that a judicious choice of the termination surface may be a crucial factor in nano-device applications, where highly spin-polarized current is needed.

Structural, Electronic, Magnetic, Mechanic and Thermodynamic Properties of the Inverse Heusler Alloy Ti2NiIn Under Pressure

Structural, electronic, magnetic and mechanic properties of the inverse Heusler alloy Ti2NiIn under different pressure are systematically studied with density functional theory (DFT). The equilibrium lattice constant and electronic band structure at null pressure are obtained to be consistent with previous work. Under currently applied static pressure from 0 GPa to 50 GPa, it is found that the half-metallicity of the material is maintained and the total magnetic moment (Mt) is kept at 3 µB, which obeys the Slater–Pauling rule, Mt = Zt − 18, where Zt is the total number of valence electrons. Besides, the effect of the tetragonal distortion was studied and it is found that the magnetic property of Ti2NiIn is almost unchanged. Several mechanical parameters are calculated including three elastic constants, bulk modulus B, Young’s modulus E, and shear modulus S and the mechanical stability is examined accordingly. Furthermore, the thermodynamic properties, such as the heat capacity CV, the thermal expansion coefficient α, the Grüneisen constant γ and the Debye temperature ΘD, are computed by using the quasi-harmonic Debye model within the same pressure range at a series of temperature from 0 to 1500 K. This theoretical study provides detailed information about the inverse Heusler compound Ti2NiIn from different aspects and can further lead some insight on the application of this material.

Computational investigation of inverse Heusler compounds for spintronics applications

First-principles calculations of the electronic structure, magnetism and structural stability of inverse-Heusler compounds with the chemical formula \textit{X$_2$YZ} are presented and discussed with a goal of identifying compounds of interest for spintronics. Compounds for which the number of electrons per atom for \textit{Y} exceed that for \textit{X} and for which \textit{X} is one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu; \textit{Y} is one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and \textit{Z} is one of Al, Ga, In, Si, Ge, Sn, P, As or Sb were considered. The formation energy per atom of each compound was calculated. By comparing our calculated formation energies to those calculated for phases in the Inorganic Crystal Structure Database (ICSD) of observed phases, we estimate that inverse-Heuslers with formation energies within 0.052 eV/atom of the calculated convex hull are reasonably likely to be synthesizable in equilibrium. The observed trends in the formation energy and relative structural stability as the \textit{X}, \textit{Y} and \textit{Z} elements vary are described. In addition to the Slater-Pauling gap after 12 states per formula unit in one of the spin channels, inverse-Heusler phases often have gaps after 9 states or 14 states. We describe the origin and occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51 half-metals and 50 near half-metals with negative formation energy. In addition, our calculations predict 4 half-metals and 6 near half-metals to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for future spintronics applications.

Tuning the topological nontrivial nature in a family of alkali-metal-based inverse Heusler compounds: A first-principles study

Based on the first-principles calculations, the total energy and electronic structures of some new inverse Heusler-based ternary intermetallic compounds X2YZ (X = alkali metals: Li, Na, K, Rb; Y = Ag, Pd, Cu; Z = Sb, Te, As) have been investigated in detail. Our results reveal that most of them are stable in inverse Heusler structure and naturally exhibit band-inversion nature without the effect of spin–orbit coupling (SOC). That is to say, most of our studied compounds are newly designed topological semi-metals. We also study the effects of the uniform strain and the spin–orbit coupling on the band inversion. Moreover, for our predicted compounds, all of them have a negative formation energy, which makes them possible in material growth.