Heusler Alloys Research Articles

Investigation of the structural, mechanical, anisotropic, thermal conductivity, electronic, and phonon properties of RhTiZ(Z: As, sb) half heusler compounds under high pressure: A DFT study

This investigation delves into the effects of pressure on the structural, elastic, thermal conductivity, anisotropy, electronic, and phonon properties of the RhTiZ (Z: As, Sb) compound, characterized by a half-Heusler structure, employing the first-principles method. Parameters such as lattice constant, volume, density, bulk modulus, the first derivative of the bulk modulus, and energy were meticulously scrutinized at zero pressure, drawing comparisons with theoretical and experimental data and existing literature. Throughout all pressure values, RhTiZ (Z: As, Sb) compounds exhibit robust structural stability, meeting the stringent criteria outlined by Born, with no discernible signs of instability even under heightened pressure conditions. The compound showcases ductile characteristics based on the Pugh ratio (G/B), Cauchy pressure (C12–C44, C″), and Poisson ratio (λ) criteria. Employing the VESTA program, anisotropic properties were comprehensively assessed in three dimensions, considering the influence of pressure. In terms of electronic properties, the compound maintains its semiconducting nature, resiliently preserving this trait amidst variations in pressure. The absence of negative frequencies in the phonon distribution curve serves as a testament to the dynamic stability inherent in the compound. Finally, a comprehensive evaluation was conducted to delineate the repercussions of pressure on both the physical and electronic attributes of the RhTiZ (Z: As, Sb) compound, which holds promise for applications in thermal insulation materials.

First Principles Study of Structural, Electronic, Mechanical and Density of State Properties of the Half - heusler Alloy NaCrGe

In this study, the investigated structural parameters revealed that NaCrGe is stable at beta phase. We obtained that the material is a narrow bandgap semiconductor half-Heusler alloys with measured gap of 1.050 eV. The structure NaCrGe conduction band minimum (CBM) position at gamma(Γ) and the valence band maximum (VBM) located at X-point of the Brillouin zone. This indicates that the alloy NaCrGe has indirect bandgap semiconductors. The material NaCrGe is considered hybrids between metals and semiconductors. Hence, NaCrGe is Half-metallic heusler alloy. The calculated mechanical properties indicate that NaCrGe possesses good mechanical stability, making it suitable for structural applications. B/G ratio for NaCrGe is 2.40. This implies that NaCrGe is “ductile” in nature at ambient condition. Also NaCrGe is confirmed “ductile” in nature at positive value of C11 – C44 (+48.07). PDOS shows that Na-4p, Cr-4p and Ge- 2p has the highest orbital contribution for Na, Cr and Ge atoms respectively. At fermi energy both spin up and spin down is at zero point in the plot of projected density of state (PDOS) against energy. This revealed that NaCrGe is a half metallic heusler alloy.

First-principles calculations of structural, magneto-electronic, mechanical, optical and thermoelectric properties of novel quaternary Heusler alloys type ZrCoYAs (Y= Fe and Mn)

To determine the structural, mechanical, electronic, magnetic, optical, and thermoelectric properties of novel quaternary Heusler alloys type ZrCoYAs (Y= Fe and Mn), we used DFT with WIEN2k. Our results showed that the ferromagnetic Y-type-III phase is more stable due to the higher negative values of their formation energy. We calculated and discussed the elastic constants Cij, which are used to calculate the mechanical properties. The Spin-polarized band structure and DOS calculations using the GGA-PBE and GGA + U approach display a metallic character. However, using the mBJ-GGA-PBE and mBJ-GGA + U approach show a half-metallic character, a semiconductor for the spin-down channel with a direct band gap of 0.61 eV with mBJ-GGA-PBE and 0.74 eV with mBJ-GGA + U for ZrCoMnAs and a direct band gap of 0.43 eV with mBJ-GGA-PBE and indirect band gap with 0.39 eV with mBJ-GGA + U for ZrCoFeAs, in contrast, the spin-up channel is metallic, with 100 % spin polarization and an integer magnetic moment of 1.00 μB for ZrCoMnAs and 2.00 μB for ZrCoFeAs, obeying the Slater-Pauling rule. The estimated Curie temperatures of ZrCoMnAs and ZrCoFeAs are 204 K using the new model, 421 K using MFA, and 385 K using the new model, 1627 K using MFA, respectively. As exchange-correlation potential, MBJ and MBJ + U provide a better description of the electronic and magnetic properties of ZrCoMnAs and ZrCoFeAs compounds. Important optical properties such as dielectric function, absorption coefficient, refractive index, optical conductivity, reflectivity, and electron energy loss function are calculated in the infrared, visible, and ultraviolet range. The static dielectric function suggests that ZrCoMnAs possesses greater polarizability. Both alloys exhibit similar behavior in the far ultraviolet region range and reach a maximum absorption in the ultraviolet range. The half-metallic character of both alloys is revealed from the reflectivity at zero frequency. The calculation of the thermoelectric properties shows positive Seebeck coefficients, indicating that these Heuslers are p-type. Furthermore, the highest power factor is observed at a temperature of 1400 K. The maximum value of ZT is ∼1.1 at 1400 K for ZrCoFeAs and ZrCoMnAs. These studies show that these alloys may have potential applications in the thermoelectric applications.

Investigation of the effect of martensitic phase transition temperature and Curie temperature difference on magnetic and magnetocaloric properties under low magnetic field on Si-doped Ni-Mn-In Heusler alloys

This study examines the impact of substituting Si for Mn on the structural, magnetic, and magnetocaloric properties of Ni43Mn46−x Si x In11 (x = 0.3 and 0.6) alloys. To this end, a range of analytical techniques are employed, including scanning electron microscopy (SEM), room temperature x-ray powder diffraction (XRD), and magnetization measurements. Above the martensitic transition temperature, the Ni43Mn46−x Si x In11 alloys exhibit cubic L2 1 (space group FM-3M). Below this temperature they adopt a tetragonal L1 0 (space group I4/mmm). The martensitic transition temperature decreased when Si is substituted for Mn. The magnetic field-induced entropy change is calculated from magnetic field-dependent magnetization measurements using Maxwell’s equations. The maximum magnetic field-induced entropy changes for Ni43.16Mn45.56Si0.29In11 and Ni43.51Mn44.82Si0.59In11 alloys are calculated 8.20 J kg−1K−1 and 3.15 J kg−1 K−1, respectively, in the vicinity of the magnetostructural phase transition for a magnetic field change of 18 kOe. It is demonstrated that the temperature differential between the high-temperature austenite phase's Curie point (T C ) and the mean martensitic transformation temperature (T M ), namely (T M -T C ), influences the martensitic transition temperatures and, consequently, on the magnetic field-induced entropy change (ΔS M ).

Pressure effect investigation of structural, electronic, elastic and magnetic properties of X2CrSb (X = Mn, Co and Cu) Heusler alloys

Using the plane-wave pseudo-potential approach and generalized-gradient approximation for the exchange–correlation effects in the framework of the density functional theory, the structural, electronic, elastic and magnetic properties of X2CrSb ( ▪ and Cu) Heusler alloys were investigated. For ▪ , a structural phase-transition from XA to L21-phase is expected at 8.933GPa. This compound exhibits half-metallic behavior before becoming a magnetic metal at 17.5GPa. The ▪ is a half-metal under expansion and nearly half-metal above 1GPa. The total magnetic moments for ▪ , ▪ and ▪ are respectively equal to 5.0μB, 1.0μB and 3.4μB, and are mainly localized on Cr except for ▪ in XA-phase where the magnetic moment is localized on Mn. The DOS analysis shows weak spin-polarizations for ▪ and a higher polarization under expansion for ▪ and ▪ . Under compression, the polarization is weakened in ▪ , it remains at a high level before it vanishes at 29.4μB in ▪ .

Enhanced Thermoelectric Performance in Vacancy-Filling Heuslers due to Kondo-Like Effect.

To improve thermoelectric efficiency, various tactics have been employed with considerable success to decouple intertwined material attributes. However, the integration of magnetism, derived from the unique spin characteristic that other methods cannot replicate, has been comparatively underexplored and presents an ongoing intellectual challenge. A previous research has shown that vacancy-filling Heuslers offer a highly adaptable framework for modulating thermoelectric properties. Here, it is demonstrated how intrinsic magnetic-electrical-thermal coupling can enhance the thermoelectric performance of vacancy-filling Heusler alloys. The materials, Nb0.75Ti0.25FeCrxSb with 0 ≤ x ≤ 0.1, feature a fraction of magnetic Cr ions that randomly occupy the vacancy sites of the Nb0.75Ti0.25FeSb half-Heusler matrix. These alloys achieve a remarkable thermoelectric figure of merit (zT) of 1.21 at 973 K, owing to increased Seebeck coefficient and decreased thermal conductivity. The mechanism is primarily due to the introduction of magnetism, which increases the density-of-states effective mass (reaching levels up to 15 times that of a free electron's mass) and simultaneously reduces the electronic thermal conductivity. Mass and strain-field fluctuations further reduce the lattice thermal conductivity. Even higher zT values can potentially be achieved by carefully balancing electron mobility and effective mass. This work underscores the substantial prospects for exploiting magnetic-electrical-thermal synergies in cutting-edge thermoelectric materials.

Enhancement of perpendicular magnetic anisotropy in NiMnSn/Co Heterostructures: Insights from PMOKE measurements

We investigated the magnetic properties of the Heusler alloy NiMnSn grown on thermally oxidized Si (100) by performing magnetic hysteresis measurements using the Polar Magneto-Optical Kerr Effect (PMOKE) technique. For a thickness of 30 nm, the NiMnSn alloy demonstrates out-of-plane magnetic anisotropy. We observed clear exchange bias, which we attribute to the exchange coupling between the spin glass and ferromagnetic phases. Our study also revealed that the growth of a 1 nm thick Heusler alloy NiMnSn layer on a cobalt layer with perpendicular anisotropy enhances the perpendicular magnetic anisotropy. However, we observed an antagonistic effect with thicker Heusler layers, resulting in a loss of perpendicular anisotropy and the appearance of an exchange bias (EB).

A first principles study of stability, electronic and thermoelectric characteristics of novel high temperature half- heusler alloys ScAgX (X=Si,Ge,Sn)

To meet the ever-increasing renewable energy demand Half- Heusler (HH) materials can be a potential candidate. Heusler materials are seeking popularity as efficient high-temperature thermoelectric materials. Here we systematically investigated the structural, electronic, mechanical and thermoelectric properties of novel HH compounds ScAgX (X = Si,Ge,Sn) in the framework of the first principles approach. These materials are found to be chemically, mechanically and dynamically stable. Born-Oppenheimer molecular dynamics simulations (BOMD) verify the thermal stability of these materials from 300 K to 1100 K. The semiconducting nature of these materials is confirmed by the electronic band structure. ScAgX (X = Si,Ge,Sn) have an indirect band gap of 0.37 eV, 0.42 eV and 0.38 eV respectively. A high value of Seebeck coefficient of 6351 μV/K, 6955 μV/K and 6558 μV/K has been obtained at room temperature. ScAgSi shows a high value of electrical conductivity (∼106 S/m) among these compounds at room temperature. The calculated value of the figure of merit (ZT) of ScAgX (X = Si,Ge,Sn) is 0.12, 0.08 and 0.16 at 1100 K respectively. Our present investigation shows that these materials can be a potential candidate for high-temperature thermoelectric power generation.

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.

Interplay between Structural, Electronic, and Magnetic Properties in the p0-d Semi-Heusler Compounds: The Case of Li-Based Compounds

Half-metallic semi-Heusler compounds (also known as half-Heusler compounds) are currently at the forefront of scientific research due to their potential applications in spintronic devices. Unlike other semi-Heuslers, the p0(d0)-d compounds do not appear to crystallize in the typical variant of the C1b structure. We investigate this phenomenon in the p0-d Heusler compounds LiYGa and LiYGe, where Y varies between Ca and Zn, using first-principles ab initio electronic band-structure calculations. We examine the electronic and magnetic properties of these compounds in relation to the three possible C1b structures. Notably, LiVGa, LiVGe, LiMnGa, and LiCrGe are half-metallic ferromagnets across all three variations of the C1b lattice structure. Our findings will serve as a foundation for future experimental studies on these compounds.

Structural Stability, Electronic Structure, and Thermoelectric Properties for Half-Metallic Quaternary Heusler Compounds NdCoMnZ (Z = Al, In), PrCoMnZ (Z = Ga, In), and PrCoCrZ (Z = Al, Ga)

Structural Stability, Electronic Structure, and Thermoelectric Properties for Half-Metallic Quaternary Heusler Compounds NdCoMnZ (Z = Al, In), PrCoMnZ (Z = Ga, In), and PrCoCrZ (Z = Al, Ga)

Prediction of the structural and magnetic properties of the all-d-metal Heusler alloys Ni–Mn–Cr

In this work, all-d metal Heusler alloys Ni–Mn–Cr were predicted by first principles. Their structure, magnetism, tetragonal distortion and electronic properties were studied. The cubic groud state structures of Ni2MnCr and NiMnCr2 are XA type, and that of NiMn2Cr is L21 type. All of them have magnetism. The change of their lattice constants is closely related to the covalent radius of atoms. Ni2MnCr has a stable tetragonal phase and may undergo martensitic transition. NiMn2Cr has a lower energy tetragonal phase, but is dynamically unstable. The equilibrium volumes of the two compounds expand through tetragonal distortion. NiMnCr2 does not have a lower energy tetragonal phase. In the tetragonal distortion, the atomic magnetic moments are influnced by the interatomic distance and the magnetic moments of neighboring atoms. The origin of the tetragonal distortion and magnetic properties was discussed in terms of the electronic density of states.

Magnetocaloric effect and phase transformation of Zn-doped Ni–Mn–Ti all-d metal Heusler alloys

Ni–Mn–Ti Heusler alloys have gained a great consideration recently due to their important magnetoresistance and magnetocaloric properties. Herein, the structure, martensitic transition (MT), and magnetocaloric effect (MCE) of Ni50-xZnxMn35Ti15 (x = 0, 2, 4, and 6) Heusler alloys have been studied. XRD results show that the studied alloy with x = 0 display a monoclinic (5 M) martensite phase. Besides, the examined alloy with x = 2 presents a combination of monoclinic (5 M) martensite and cubic (B2) austenite phases, whereas the alloys with x = 4 and x = 6 exhibit only a cubic (B2) austenite phase. By increasing Zn content x up to 6, the Curie temperature of austenite decreases from 283 K to 132 K, and the MT temperatures decrease from ferromagnetic austenite to weak-magnetic martensite, which is apparently due to the exchange interaction of Mn–Mn and the low power of d-d hybridization between the A/C and B(D) sites. The best maximum magnetic entropy change (ΔSM, max) and refrigeration capacity (RC) are for the studied alloy with x = 4 (5.22 J kg−1K−1 and 217 J kg−1 at 120 kOe, respectively). The Zn addition not only facilitates the formation of B2-type Heusler phases but also offer the possibility to tune the MT and establish strong ferromagnetic coupling.

Ni2MnAl Heusler Alloy Nanoparticles for Chemoselective Hydrogenation of Nitro Compounds

AbstractDespite immense interest for years in Heusler alloys as magnetoelastic materials, their application in heterogeneous catalysis has only recently been explored. We report the development of highly active, robust and magnetically separable Ni2MnAl Heusler alloy nanoparticles as a heterogeneous catalyst for hydrogenation of aliphatic and aromatic nitro compounds to the corresponding amines. The easily synthesizable Ni2MnAl nanoparticles are thermally and chemically robust and exhibited excellent chemoselectivity in the hydrogenation of a range of aliphatic and aromatic nitroarenes, including those bearing functional groups sensitive to reduction, such as alkene, bromo, iodo, carbonyl and cyano, yielding the respective functionalized amines in good yields. Moreover, this solid catalyst is magnetically separable from the reaction mixture and could be recycled and reused at least 10 times without any loss in catalytic activity. The mechanism of the Ni2MnAl Heusler alloy nanoparticles catalyzed nitro reduction was studied by various spectroscopy, control experiments and kinetics. Our work opens a new avenue of developing heterogeneous earth‐abundant metal catalysis for economic and environment‐friendly synthesis of fine chemicals owing to straightforward synthesis and tunable composition of Heusler alloy nanoparticles from base‐metal precursors and their diverse structure and properties in conjunction with their thermal and chemical stability, excellent chemoselectivity, magnetic separability and recyclability.

High tunneling magneto-resistance ratio in Co2FeAl Heusler alloy and WSe2 2D material tunnel barrier-based magnetic tunnel junctions

This paper presents a Magnetic Tunnel Junction (MTJ) based on Co2FeAl Heusler alloy and 2D material WSe2 with an enhanced tunnelling magneto-resistance (TMR). Our study is inspired by recent investigations of 2D materials and Heusler alloys. By employing static Density Functional Theory (DFT) simulations coupled with Non-Equilibrium Green’s Function (NEGF) transport models, we evaluate conductance properties in Co2FeAl/WSe2/Co2FeAl MTJ. The half metallicity of Co2FeAl and quantum confinement properties of WSe2 are compatible, which enhances the TMR of MTJ.

Comprehensive analysis: Exploring quaternary Heusler alloys CoFeXGe (X = Hf and Ta) through first‐principles calculations

AbstractThe research focused on the quaternary Heusler alloys CoFeXGe (with X being Hf or Ta) using a first principles approach via density functional theory and the Wien2k code. The alloys demonstrated a stable ferromagnetic ground state and exhibited negative formation energies, suggesting their experimental synthesis feasibility. Investigation of the electronic properties revealed that both materials are half‐metallic ferromagnets. The calculated indirect band gaps of CoFeHfGe and CoFeTaGe are 1.46 and 0.77 eV, respectively. The mechanical stability of the materials was confirmed through elastic constants analysis. To gain insights into the materials optical behavior and their potential applications in photonics and related fields, correlation of interband optical transitions with electronic band structure was carried out. Finally, Boltzmann transport theory was utilized to evaluate the thermoelectric potential of these alloys over a temperature range extending from 100 to 1000 K.

Evolution of structure, magnetism, and electronic/thermal-transports of Ti(Cr)-substituted Fe2CrV all-d-metal Heusler ferromagnets

All-d-metal full-Heusler alloys possess superior mechanical properties and high spin polarization, which would play an important role in spintronic applications. Despite this, their electrical and thermal transport properties have not been comprehensively investigated till now. In this work, we present an analysis on the evolution of structural, magnetic and transport properties of Cr- and Ti-substituted Fe2CrV all-d-metal Heusler alloys by combining theoretical calculations and experiments. Both series of alloys crystallize in Hg2CuTi-type structure. With increasing Ti doping, the calculated total magnetic moments of Fe50Cr25V25-xTix decrease linearly. The experimental saturation magnetization is highly consistent with theoretical calculations and Slater-Pauling rule when x < 4, indicating the highly ordered atomic occupation. The magnetization and Curie temperature can be significantly tuned by altering spin polarizations and exchange interactions. The introduction of the foreign atom, Ti, results in a linear increase in residual resistivity, while electron-phonon scattering keeps relatively constant. The maximum values for electrical and thermal transport properties are observed in the stoichiometric Fe2CrV composition.

Theoretical perspectives on the electronic, optical, mechanical, magnetic, and anisotropic behaviors of the quaternary Heusler alloys RhFeMnZ and IrMnCrZ (where Z = Si, Ge)

High-spin-polarised materials are the most promising candidates for spintronic devices. Here, the spin-polarised electronic structure, magnetism, mechanical, and optical properties of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) Quaternary Heusler alloys were calculated by first-principles calculations. The calculations show that type III for the RhFeMnSi, RhFeMnGe, and IrMnCrSi and type I for the IrMnCrGe compound configuration is the most stable crystal structure for the studied alloys. The four alloys were found to have a half-metallic ferromagnetic structure with indirect band gaps in the majority spin channels of 0.957, 0.66, 0.745, and 0.891 eV for RhFeMnSi, RhFeMnGe, IrMnCrSi, and IrMnCrGe, respectively. They exhibit an appreciable total magnetic moment of 4 μB for RhFeMnZ (Z = Si, Ge) and 2 μB for IrMnCrZ (Z = Si, Ge). The results show that RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are ferromagnetic half-metals with 100 % spin polarisation. The results of the elastic constants demonstrate the mechanical stability of RhFeMnZ and IrMnCrZ (where Z = Si, Ge) alloys. Optical properties such as dielectric function, absorption, reflectance, optical conductivity, and other optical properties were also probed. In the ultraviolet region, RhFeMnZ and IrMnCrZ (where Z = Si, Ge) are effective absorbers and have a high refractive index. Alloys are promising candidates for potential applications in spintronic devices.

Control of spin on structural stability, mechanical, magneto-optoelectronic and thermodynamic properties of RbTaX (X =P and As) materials: Emerging candidates for opto-spintronics and spin filter applications

In the present work, the density functional theory has been utilised in inspecting the ground state-structural, electronic, magnetic, optical, elastic and thermodynamic properties of new semiconductor RbTaX (X = P and As) half-Heuslers. Out of the possible three structures (α, β, γ) studied in ferromagnetic (FM) as well as non-magnetic (NM) phases, α – FM phase is found to be the most stable configuration. Both studied materials have estimated a net magnetic moment of 3μB, following the Slater-Pauling rule (Mtot=Ztot−8). With the use of modified Becke Johnson potential (mBJ) potential, the band profile reveals non-zero band gap in the spins and henceforth display spin filter property in the compounds. The predicted energy band gaps for RbTaP and RbTaAs are 3.04 and 2.87 eV for minority spin channels and 0.137 and 0.26 eV for majority spin channels, respectively. This unique feature of the Heusler compound may be advantageous for quantum information processing and spin-transport in electronic and magnetic devices. Also, a moderate exchange splitting and a Curie temperature well above the room temperature are noted. The stability of the materials under investigation was further confirmed by calculations of cohesive energy, formation energy, and second order elastic constants. The optoelectronic as well as thermodynamic properties of the studied compounds are also investigated. The estimated high value of refractive index (>4) is making them suitable for optical lenses. Moreover, photon energy absorption in the visible and ultraviolet spectrums renders them valuable for UV-VIS absorbers.

The martensitic structures, exchange bias effect and training effect in Ni-Mn-Ga ribbons

The exchange bias effect is the physical basics of spin valves and magnetic recording devices. A stable exchange bias effect would be suitable for practical application. In this work, Ni50Mn50-xGax (11≤ x ≤16) ribbons were obtained by melt spinning. The grain size and microstructure have been tuned through melt spinning, which changes the exchange interaction in ribbons and thus gets a giant and stable exchange bias effect. As the increase of x, the structure of Ni50Mn50-xGax (11≤ x ≤16) ribbons undergoes a transition from non-modulated martensite to non-modulated martensite &10 layers modulated martensite to 10 layers modulated martensite. The average grain size of all ribbons is less than 10 μm, and the martensitic plate widths are smaller than 200 nm. With the increasing x or the cooling fields, the magnetization of the ribbons has been enhanced. As a result, the competition between ferromagnetic and antiferromagnetic interactions has been changed and thus influencing spin glass behavior. Furthermore, a low degree of attenuation for the exchange bias effect after continuous cycles has been achieved which arises from the stable spin configuration with a larger contribution of frozen spin which has a slow relaxation rate. For example, the exchange bias field of 8.78 kOe in Ni50Mn38Ga12 ribbons can be achieved under the 40 kOe field cooling at 10 K, and the exchange bias field after infinite cycles can be kept at 8.58 kOe, the degree of attenuation is only 3.4 %. This work enriches the research on the exchange bias effect of Heusler alloys and provides the experimental basis and theoretical support for designing a stable exchange bias effect.