Inverse Heusler Alloy Research Articles

Establishing universality in entropy change and critical behavior for magnetocaloric effect in Si-substituted Mn50Ni40Sn10 inverse Heusler alloy

Magnetic refrigeration working based on the magnetocaloric effect can be the perfect replacement of the conventional gas compression-based refrigeration technology and reduces its harmful effects on the environment. The boundary between a first-order and a second-order phase transition would be where the perfect magnetocaloric material would be found. Therefore, establishing the sequence of phase transitions clearly is essential for the characterization of other phase change materials and for applied magnetocaloric research. A quantitative fingerprint of second-order thermomagnetic phase transitions is reported here in Si-substituted high content Mn-based inverse Heusler alloy systems, which are found to be crystallized in cubic structures. The second-order nature of the phase transition has been confirmed from the Arrott plot analysis and a correlation between magnetocaloric effect and local exponent is established. Using the Arrott plot, the critical exponents are evaluated employing different techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm. Their values are found to be in great agreement with each other and follow the mean-field model signifying the presence of long-range ordering in the materials. The high value of isothermal magnetic entropy change and the reversibility justifies the suitability of the reported materials in the practical application as magnetic refrigerants.

Multifaceted investigation into the impact of Ga substitution for Al in V[formula omitted]MnAl inverse Heusler alloys

This study investigates the impact of Ga substitution for Al in V2MnAl inverse Heusler alloys, focusing on lattice parameter variations. Despite similar valence electrons, Ga’s distinct size and surface energy prompt questions about its role in alloy characteristics. Experimental synthesis of V2Mn1Al1−xGax alloys (x = 0 to 0.60) reveals crystal parameter changes. Theoretical exploration using density functional theory (DFT) probes how Ga doping at the Al site influences the density of states, altering the half-metallic properties of V2MnAl. Additionally, machine learning, with a dataset of 391 entries, predicts lattice constants based on atomic properties, enhancing our ability to maneuver material characteristics. This multifaceted approach aims to deepen our understanding of Ga’s impact on Heusler alloys, bridging experimental and theoretical realms for comprehensive insights into materials design and behavior.

Unveiling the structure-property relationship in a disordered inverse Heusler alloy Ti2MnAl

Search for novel spintronic materials in family of Heusler alloys has attained significant interest in recent years. In this context, Ti2MnAl is interesting as it is predicted to host spin gapless semiconducting state and compensated ferrimagnetic ordering. Here we report a detailed experimental investigation of Ti2MnAl. Our studies reveal that Ti2MnAl crystallizes in cubic structure with strong atomic disorder along with Pauli paramagnetic behaviour. The influence of disorder manifests in form of non-interacting superparamagnetic clusters at low temperatures and negative temperature co-efficient of resistivity. The carrier concentration obtained from Hall resistivity rules out the possibility of spin gapless semiconducting state. Our studies indicate that atomic disorder plays an important role in determination of physical properties of Ti2MnAl.

Exploring half-metallicity and pressure-induced effect in inverse heusler alloys: First principle DFT investigations of Cr2XZ (X = Ni, Pd, Pt; Z = Al, Ga, Si, Ge)

In this study, we have predicted a set of inverse Heusler alloys (HA) based on transition metals, specifically Cr2XZ (X = Ni, Pd, and Pt; Z = Al, Ga, Si, and Ge), using density functional theory (DFT) calculations. The structural, electronic, magnetic, and elastic properties, of Cr2XZ HAs have been investigated in detail to evaluate their potential for spintronic applications. Our electronic structure analysis involved the examination of band structure (BS) and density of states (DOS) to elucidate the half-metallic and magnetic characteristics of the alloys. The results indicate that Cr2XZ alloys stabilize in the F 4‾ 3 m space group in the Hg2CuTi type inverse structure, displaying a ferrimagnetic (FiM) ground state. Notably, among the inverse HAs, Cr2NiAl, and Cr2PtSi exhibit intriguing half-metallic properties with 100% spin polarization at the Fermi level (EF). Furthermore, under the influence of pressure, there is evidence of a nearly half-metallic nature in Cr2PtAl and Cr2PdGe, while the nearly half-metallic traits persist up to compressive pressures of 55 GPa and 40 GPa for Cr2PtAl, and Cr2PdGe, respectively. The Born stability criteria confirm the mechanical stability of the Cr2XZ HAs, with Cr2NiZ (Z = Al, and Ga), Cr2PdZ (Z = Ga, and Ge), and Cr2PtAl exhibiting a brittle nature, and Cr2NiZ (Z = Si, and Ge), Cr2PdZ (Z = Al, and Si), and Cr2PtZ (Z = Ga, Si, and Ge) exhibiting ductility.

Electrodeposited Fe2CoSn Thin Film with Enhanced Structural and Magnetic Properties

Single-phase near-stoichiometric Fe2CoSn Heusler alloy thin film of thickness 320 nm and crystallite size of 22 ± 1 nm was electrodeposited on low-cost Cu substrate. Heat-treated Fe2CoSn film exhibited an X-type inverse Heusler alloy structure along with high saturation magnetization (∼5 μ B/f.u.), high effective anisotropy constant (∼106 erg/cc), and high Curie temperature (983 K). Apart from demonstrating a procedure to obtain considerably thin electrodeposited Fe2CoSn films with high crystalline order, the electronic density of states close to the Fermi level have also been evaluated for its stable structure for the first time.

Temperature dependence of thermodynamic and mechanical properties of Fe2RhSi and Fe2RhGe: An ab-initio investigation

In this research, we conducted an exploration of the thermodynamic and mechanical properties of ferromagnetic inverse Heusler alloys Fe2RhSi and Fe2RhGe employing computational methods based on pseudopotentials, plane waves, density-functional theory and density-functional Perturbation theory. Our study indicates that the alloys are dynamically stable, as evidenced by the presence of positive phonon frequencies for all modes. Moreover, our computational results of specific heat and Debye temperature exhibited a remarkable agreement with experimental measurements, confirming to the accuracy of our approach. Both alloys displayed positive thermal expansion and demonstrated a decrease in elastic constants with increasing temperature, consistent with the Born–Huang criteria for mechanical stability. These alloys also exhibit an anisotropic and ductility behavior. The ductility is attributed to their metallic bonds.

Unveiling the magnetic structure and phase transition of Cr2CoAl using neutron diffraction

We report the detailed analysis of temperature dependent neutron diffraction pattern of the Cr2CoAl inverse Heusler alloy and unveil the magnetic structure up to the phase transition as well as its fully compensated ferrimagnetic nature. The Rietveld refinement of the diffraction pattern using the space group I4¯m2 confirms the inverse tetragonal structure over the large temperature range from 100 to 900 K. The refinement of the magnetic phase considering the wave vector k= (0, 0, 0) reveals the ferrimagnetic nature of the sample below 730±5 K. This transition temperature is obtained from empirical power law fitting of the variation in the ordered net magnetic moment variation in intensity of (110) peak as a function of temperature. The spin configuration of the microscopic magnetic structure suggests the nearly fully compensated ferrimagnetic behavior where the magnetic moments of Cr2 are antiparallel with respect to the Cr1 and Co moments. Moreover, the observed anomaly in the thermal expansion and lattice parameters at 730±5 K suggests that the distortion in the crystal structure may play an important role in the magnetic phase transition.

Giant intrinsic magnetoresistance in spin-filtered tunnel junctions with ferrimagnetic electrode

In recent years, magnetic tunnel junctions (MTJs) have attracted strong research interest due to their potential use in nonvolatile memory technologies, such as magnetoresistive random access memory and magnetic logic applications. Half-metallic materials have been proposed as ideal electrode materials for MTJs to achieve large tunnel magnetoresistance (TMR) effects. Here, we design and investigate a spin-filter MTJ (sf-MTJ) consisting of a ferrimagnetic inverse Heusler alloy, ${\mathrm{Mn}}_{2}\mathrm{CoSi}$ as the electrode and CaS as the insulating tunnel barrier using ab initio quantum transport calculations. Our results demonstrate a high zero-bias voltage TMR ratio that initially oscillated before decreasing as the bias voltage increased. Despite the oscillatory TMR under bias voltage, the spin injection remains high and stable, highlighting the potential of sf-MTJs formed by ${\mathrm{Mn}}_{2}\mathrm{CoSi}$ electrodes for practical applications.

Structural, Elastic, Electronic, and Magnetic Properties of Full-Heusler Alloys Sc2TiAl and Sc2TiSi Using the FP-LAPW Method

In this article, the structural, elastic, electronic, and magnetic characteristics of both regular and inverse Heusler alloys, Sc2TiAl and Sc2TiSi, were investigated using a full-potential, linearized augmented plane-wave (FP-LAPW) method, within the density functional theory. The optimized structural parameters were determined from the minimization of the total energy versus the volume of the unit cell. The band structure and DOS calculations were performed within the generalized gradient approximation (GGA) and modified Becke–Johnson approaches (mBJ-GGA), employed in the Wien2K code. The density of states (DOS) and band structure (BS) indicate the metallic nature of the regular structure of the two compounds. The total spin magnetic moments for the two compounds were consistent with the previous theoretical results. We calculated the elastic properties: bulk moduli, B, Poisson’s ratio, ν, shear modulus, S, Young’s modulus (Y), and the B/s ratio. Additionally, we used Blackman’s diagram and Every’s diagram to compare the elastic properties of the studied compounds, whereas Pugh’s and Poisson’s ratios were used in the analysis of the relationship between interatomic bonding type and physical properties. Mechanically, we found that the regular and inverse full-Heusler compounds Sc2TiAl and Sc2TiSi were stable. The results agree with previous studies, providing a road map for possible uses in electronic devices.

A machine learning approach to predict the structural and magnetic properties of Heusler alloy families

Random forest (RF) regression model is used to predict the lattice constant, magnetic moment and formation energies of full Heusler alloys, half Heusler alloys, inverse Heusler alloys and quaternary Heusler alloys based on existing as well as indigenously prepared databases. Prior analysis was carried out to check the distribution of the data points of the response variables and found that in most of the cases, the data is not normally distributed. The outcome of the RF model performance is sufficiently accurate to predict the response variables on the test data and also shows its robustness against overfitting, outliers, multicollinearity and distribution of data points. The parity plots between the machine learning predicted values against the computed values using density functional theory (DFT) shows linear behavior with adjusted R2 values majorly lying in the range of 0.80 to 0.94 for all the predicted properties for different types of Heusler alloys. Feature importance analysis shows that the valence electron numbers plays an important feature role in the prediction for most of the predicted outcomes. Case studies with one full Heusler alloy and one quaternary Heusler alloy were also mentioned comparing the machine learning predicted results with our earlier theoretical calculated values and experimentally measured results, suggesting high accuracy of the model predicted results.

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 sputtering, 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 molecular beam epitaxy 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 X-ray diffraction analysis. None of them forms the XA-type structure expected for SGS Heusler alloy, although they all exhibit SGS characteristics. To validate the SGS characteristics, it is necessary to extract not only the magnetic and electric transport properties but also information about microstructures and atomic-scale structures of the films including defects such as atomic swap.

Demonstration of reconfigurable magnetic tunnel diode and giant tunnel magnetoresistance in magnetic tunnel junctions made with spin gapless semiconductor and half-metallic Heusler alloy

Here, we report fabrication of a high quality exchanged biased trilayer magnetic tunnel junction (MTJ) utilizing a magnetron sputtering system. The MTJ is composed of a type-II spin gapless semiconductor (SGS) Ti2CoSi inverse Heusler alloy (used as a lower electrode), a thin MgO layer (used as a tunnel barrier), and a half-metallic ferromagnet (HMF) Co2MnSi Heusler alloy (used as an upper electrode). Spin dependent transport properties reveal that the micro-fabricated MTJ can act as a reconfigurable magnetic tunnel diode, which lets the electric current to flow in either the forward or reverse path relying on the relative alignment of the magnetization direction of the upper and lower magnetic electrodes. A considerably high on/off current ratio (∼103) and a significantly low turn on voltage (VT) of 0.09 V have been achieved at 5 K for both parallel and antiparallel configurations. Another important characteristic shown by our fabricated MTJ is that it exhibits extremely large tunnel magnetoresistance ratios of 892% at 5 K and 197% at room temperature, which brings to light the utmost importance of using the combination of HMF and SGS materials as magnetic electrodes in a tunnel junction for potential applications in modern spintronic devices. All these exceptional features can undoubtedly nominate CMS/MgO/TCS MTJs as a promising candidate to serve as memory or logic elements in next generation ultra-high density magnetoresistive random access memories together with contemporary spin based electronic devices.

Size-dependent properties of single domain Fe2CoGa nanoparticles prepared by a facile template-less chemical route

Coercivity of Fe2CoGa nanoparticles is superposed on typical single domain nanoparticle pattern. Magnetic hysteresis loop depicts superparamagnetism. HRTEM images show lattice fringes from (111) and (200) planes of inverse Heusler alloy structure.

Observation of exchange-bias in the inverse Heusler alloy Mn1.5Ru1.5Si

Recently, Mn-Ru-Ga based inverse Heusler alloys have been found to be potential candidates for half-metallic fully compensated ferrimagnetic materials. In this work, we have studied another Heusler based alloy, Mn1:5Ru1:5Si, intending to design a compensated ferrimagnet. The alloy Mn1:5Ru1:5Si crystallizes in an inverse Heusler (XA) structure with a small amount of anti-site disorder. Our magnetic study indicates that the alloy orders magnetically below about TN = 50 K, which is characterized by a sharp drop in magnetization. Nevertheless, the isothermal magnetization curve shows a tendency of saturation and finite coercivity at 5 K, which rules out a pure antiferromagnetic state. Interestingly, Mn1:5Ru1:5Si shows vanishingly small magnetic moment, which also rules out possibility of a pure antiferromagnetic state. The alloy shows a significant amount of exchange-bias at low temperature. The alloy fails to obey a Curie-Weiss law between 300 and 50 K, indicating short-range correlations prior to the long-range order at TN. The exchange bias possible arises from the interfacial coupling of the short range ferromagnetic clusters with the long range antiferromagnetic state. The observation of exchange bias for such a system along with a low net magnetization value, has immense potential for magneto-electric applications and switching devices. The resistivity versus temperature data of the sample indicates a metallic character, albeit with a rather large value resistivity. The resistivity data show an upturn below 25 K that follows a logarithmic behaviour. Such upturn may be due to weak localization effect due to the presence of antisite disorder and short range magnetic clusters.

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 $\mathrm{Mn}{}_{2}XY$ 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 $\mathrm{Mn}{}_{2}({X}_{1},{X}_{2})Y$ alloys where these critical interactions may be realized and which are likely to be synthesizable in the inverse Heusler structure. We identify the $\mathrm{Mn}{}_{2}\mathrm{Pt}{}_{1\ensuremath{-}z}{X}_{z}\mathrm{Ga}$ 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.

Skyrmionics—Computing and memory technologies based on topological excitations in magnets

Solitonic magnetic excitations such as domain walls and, specifically, skyrmionics enable the possibility of compact, high density, ultrafast, all-electronic, low-energy devices, which is the basis for the emerging area of skyrmionics. The topological winding of skyrmion spins affects their overall lifetime, energetics, and dynamical behavior. In this Perspective, we discuss skyrmionics in the context of the present-day solid-state memory landscape and show how their size, stability, and mobility can be controlled by material engineering, as well as how they can be nucleated and detected. Ferrimagnets near their compensation points are promising candidates for this application, leading to a detailed exploration of amorphous CoGd as well as the study of emergent materials such as Mn4N and inverse Heusler alloys. Along with material properties, geometrical parameters such as film thickness, defect density, and notches can be used to tune skyrmion properties, such as their size and stability. Topology, however, can be a double-edged sword, especially for isolated metastable skyrmions, as it brings stability at the cost of additional damping and deflective Magnus forces compared to domain walls. Skyrmion deformation in response to forces also makes them intrinsically slower than domain walls. We explore potential analog applications of skyrmions, including temporal memory at low density—one skyrmion per racetrack—that capitalizes on their near ballistic current–velocity relation to map temporal data to spatial data and decorrelators for stochastic computing at a higher density that capitalizes on their interactions. We summarize the main challenges of achieving a skyrmionics technology, including maintaining positional stability with very high accuracy and electrical readout, especially for small ferrimagnetic skyrmions, deterministic nucleation, and annihilation and overall integration with digital circuits with the associated circuit overhead.

Positive linear magnetoresistance effect in disordered L21B -type Mn2CoAl epitaxial films

The inverse Heusler alloy ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ is known as a spin gapless semiconductor (SGS). It is believed that the positive linear magnetoresistance (PLMR) effect observed at low temperatures indicates the quantum linear MR effect in the gapless electronic band structures near the Fermi level, i.e., evidence of the realization of a SGS [Ouardi et al., Phys. Rev. Lett. 110, 100401 (2013)]. For this reason, one presumes that the observation of the PLMR effect is indirect proof of the demonstration of $XA$-type ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ consisting of the inverse Heusler structure. In this paper, we observe the PLMR effect at 10 K in homogeneous and single-phase ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ epitaxial films grown by low-temperature molecular beam epitaxy at $100{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. From anomalous x-ray diffraction measurements and analyses, we clarify that the $100{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$-grown ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ epitaxial film is not composed of the $XA$-type structure but a disordered $L{2}_{1}B$-type structure including some amount of Mn(A site) $\ensuremath{\Leftrightarrow}\mathrm{Co}$(C site) swapping and Mn(B site) $\ensuremath{\Leftrightarrow}\mathrm{Al}$(D site) swapping. On the basis of first-principles density-functional theory calculations, we discuss the correlation between the PLMR effect observed at 10 K and the possible electronic band structure in the disordered $L{2}_{1}B$-type ${\mathrm{Mn}}_{2}\mathrm{CoAl}$.

First-Principles Study of Structural, Electronic, Magnetic and Elastic Properties of the Mn2XSb (X = Co, Fe) Inverse Heusler Alloys

First-Principles Study of Structural, Electronic, Magnetic and Elastic Properties of the Mn2XSb (X = Co, Fe) Inverse Heusler Alloys

Ab initio study of electronic and magnetic properties of Mn2RuZ/MgO (001) heterojunctions (Z = Al, Ge)

We studied the applicability of Heusler alloys Mn2RuZ (Z = Al, Ga, Ge, Si) to the electrode materials of MgO-based magnetic tunnel junctions. All these alloys possess Hg2CuTi-type inverse Heusler alloy structure and ferrimagnetic ground state. Our study reveals the half-metallic electronic structure with highly spin-polarized Δ1 band, which is robust against atomic disorder. Next we studied the electronic structure of Mn2RuAl/MgO and Mn2RuGe/MgO heterojunctions. We found that the MnAl- or MnGe-terminated interface is energetically more favorable compared to the MnRu-terminated interface. Interfacial states appear at the Fermi level in the minority-spin gap for the Mn2RuGe/MgO junction. We discuss the origin of these interfacial states in terms of local environment around each constituent atom. On the other hand, in the Mn2RuAl/MgO junction, high spin polarization of bulk Mn2RuAl is preserved independent of its termination.

Elastic, mechanical, anisotropic, optical and magnetic properties of V2NiSb Heusler alloy

We have addressed the several unpublished elastic, mechanical, optical, anisotropic and magnetic properties of V2NiSb inverse Heusler alloy through the density functional theory (DFT) framework. Calculated elastic constants indicate mechanical stability and ductile mechanical character of the alloy. The alloy has high elastic anisotropy. Some optical properties like dielectric function, absorption, reflectance, optical conductivity, etc were also surveyed. According to the obtained results, V2NiSb is a good absorber and high refractive index material in the ultraviolet (UV) region. The magnetic results of the alloy signify typical ferromagnetism with 0.8 μ B total magnetic moment and compares well former findings. Our results may further shed light on the possible experimental researches of V2NiSb alloys for practical applications.