full-Heusler Alloy Research Articles

Effect of magnetic entropy in the thermoelectric properties of Fe-doped Fe2VAl full-Heusler alloy

The effect of spin entropy on the transport of heat/charge carriers in the Fe-doped full-Heusler alloy Fe2+xVAl1-x with x = 0–0.1 has been studied through low-temperature magnetic and thermoelectric measurements. Magnetization (M) measurements confirm itinerant-electron weak-ferromagnetic behavior. A systematic increase of the magnetic transition temperature TC (from 40 K to 223 K) and of the saturation magnetization (from 0.13 to 0.41μB/Fe) with increasing Fe doping (from x = 0 to 0.1) is observed. Applying a magnetic field causes significant suppression of the Seebeck coefficient (S) and the entropy term (S/T) with a negative magnetoresistance near TC for all weak-ferromagnetic samples, demonstrating a clear effect of spin fluctuations. Analyzing M(T) and S(T), we rule out sizeable magnon drag contributions. A large spin fluctuations-induced enhancement in the thermoelectric power factor PF of about 18 % is achieved for x = 0.1 near TC when compared to measurements in a magnetic field of 7 T. The actual improvement in PF is even much higher, as the S shows a significant enhancement (about 34 %) compared to the estimated diffusion term of S(T) at TC. The number of point defects also increases with Fe doping, causing a significant reduction of the lattice thermal conductivity. This study demonstrates the role of spin fluctuations in enhancing the thermopower/thermoelectric performance of Fe-doped Fe2VAl and opens a vista for the strategy's applicability for various thermoelectric materials.

Impact of composition on the properties of full-Heusler Ti2FexMn1-xAl alloys in spintronics

This study explores the structural, electronic, and magnetic characteristics of full-Heusler Ti2FexMn1-xAl alloys for spintronic applications. The regular Heusler structure is identified as the most stable across all x concentrations. The inverse Heusler structure exhibits half-metallic behavior with a finite energy band gap in the spin-up states, while the regular structure shows metallic behavior for both spin directions. Dirac-like points along the M→Γ direction are observed, particularly in alloys with x = 0 and 0.25 (inverse structure) and x = 0.5, 0.75, and 1 (regular structure), indicating advanced electronic properties. Magnetic analysis reveals that Ti atoms' local magnetic moments are antiparallel to those of Mn and Fe atoms. The total magnetic moment is highest for x = 1 (Ti2MnAl) and nearly zero for x = 0 (Ti2FeAl). Additionally, the inverse Heusler structure achieves 100 % spin polarization at the Fermi energy, underscoring its suitability for spintronic applications. This study highlights the potential of Ti2FexMn1-xAl alloys for future spintronic devices.

Hysteresis behavior and magnetocaloric effect in MnNiGa[formula omitted] full-Heusler alloy

In this manuscript, we studied the magnetic, magnetocaloric, and hysteresis properties of the MnNiGa2 full-Heusler alloy using mean-field theory and first-principles calculations. Initially, we employed the GGA+U method to investigate the structural characteristics of the alloy. Our findings indicated that the ferromagnetic state, with an optimal lattice parameter of 5.88 Å, was the most stable compared to the antiferromagnetic states. Additionally, the exchange interactions, defined as the Hamiltonian parameters of the studied system, were calculated and used in the mean-field approximation. The second-order transition at a Curie temperature of Tc = 373 K, previously revealed experimentally, has been confirmed. Furthermore, the alloy exhibited a relative cooling power (RCP) of 260.43 J/kg and a magnetocaloric effect of 10.34 J/kg.K at an applied magnetic field of 1.4 T. These results suggest that MnNiGa2 is a promising candidate for magnetic refrigeration applications.

Machine-learning assistant DFT study of half-metallic full-Heusler alloy N2CaNa: Structural, electronic, mechanical, and thermodynamics properties

We studied the structural, electronic, mechanical, and thermodynamic properties of N2CaNa full Heusler alloys using density functional theory (DFT). Results for the structural analysis establish structural stability with a minimum formation energy of 29.9 eV. The compound is brittle and mechanically stable, having checked out with the Pugh criteria. The B/G ratio of bulk modulus B to shear modulus G for N2CaNa is 4.766, hence the material is ductile. N2CaNa alloy is ductile in nature. The Debye model correctly predicts the low-temperature dependence of heat capacity, which is proportional to Debye’s T3 law. Just like the Einstein model, it also recovers the Dulong–Petit law at high temperatures, suggesting the thermodynamic stability of the compounds at moderate temperatures. The results demonstrate potential N2CaNa for applications in spintronics, structural engineering, and other fields requiring materials with tailored properties.

Investigations on full-Heusler alloys Mn2TaAl and Mn2WAl for spintronic and thermoelectric applications

Investigations on full-Heusler alloys Mn2TaAl and Mn2WAl for spintronic and thermoelectric applications

Semiconducting Heusler Compounds beyond the Slater-Pauling Rule

Heusler compounds with semiconducting properties represent an important class of functional materials. Usually, research on these systems is guided by simple electron-counting rules, such as the Slater-Pauling principle. Here, we report on the discovery of Heusler-type semiconductors, significantly deviating from the Slater-Pauling rule. We theoretically predict the occurrence of nonmagnetic semiconducting ground states in various highly off-stoichiometric full-Heusler alloys, where self-substitution leads to a band-gap opening. This unexpected trend is confirmed experimentally by thermoelectric transport measurements on a multitude of Fe2−2xV1−xAl1+3x samples with up to 20% substitution of Fe and V atoms. The band-gap opening leads to an exceptionally large Seebeck coefficient in p-type Fe2VAl thermoelectrics, previously limited by bipolar conduction and low-density-of-states effective mass. Consequently, our work presents a paradigm to tune the band gap of Heusler compounds by self-substitution and introduces a hitherto unexplored class of semiconductors with exceptional thermoelectric properties, offering significant potential for advancements in energy science and sustainable-energy technologies. Published by the American Physical Society 2024

Investigation on the structural, elastic, electronic, thermodynamic, and vibrational properties of the full heusler Sc2XAl (X =Cd and Zn): An ab initio study

The structural, mechanical, electronic, thermodynamic, and phonon characteristics of Sc2CdAl and Sc2ZnAl in L21 phase were the main focuses on this investigation. The density of states (DOS) and electronic band spectra signify the metallic behavior of the L21 phase of both materials. The impact of atomic arrangement with respect to the Wyckoff sites on the mechanical stability were additionally studied. The elastic constants of Sc2CdAl and Sc2ZnAl alloys indicated that these alloys convened Born mechanical stability criteria. Using the density functional perturbation theory's first-principle linear response method, complete phonon spectra have been acquired. Moreover, the quasi-harmonic approximation, specific heat capacity at constant volume, the internal free energy, entropy, and vibrational free energy variations of Sc2CdAl and Sc2ZnAl as full Heusler alloys have been utilized in examination the change over the temperature between 0 and 800 K. Both alloys might find application in real industrial applications.

First-principles Study on Structural and Electronic Properties: The Li Based of Full-Hesulter Alloys LiGa2Ir

Abstract: Due to their excellent electronic properties, full-Heusler compounds have become one of the most interesting families of alloys in superconductivity. More recently, computational methods have been actively employed to support the rapid discovery of new complete Heusler alloys by identifying stable compositions with desired properties. Therefore, we investigated the stability, structure, and electronic properties of the lithium-based Heusler compound LiGa2Ir using first-principles calculations. We explored the effects of exchange-correlation, namely Perdew-Burke-Ernzerhof (PBE), PBE+U, and Tran-Blaha modified Becke-Johnson potentials, as well as the effect of heavy metal spin-orbit coupling on these Heusler compounds. The results show that LiGa2Ir is energetically stable, and the obtained lattice parameter value (a = 6.0927 Å) agrees with the experimental results. LiGa2Ir exhibits metallic behavior under all three exchange-correlation estimates. A much stronger spin-orbit coupling effect is observed for electronic states with energies below the Fermi level EF, especially in the Tran-Blaha modified Becke-Johnson approximation. Significant spin-orbit coupling effects are evident from the total and partial density of states figures, especially in the energy range from -4.5 eV to -2 eV. The contributions from Ir-d and Ga-p orbitals are the largest, while the contribution from the Li atom is small. Our findings will benefit future theoretical and practical work on lithium-based full-Heusler alloys. Keywords: Full-Heusler, DFT, Spin-orbit coupling, Electronic properties, Density of states.

Data-driven design of high-curie temperature full-heusler alloys for spintronic applications

In this study, we employ density functional theory (DFT) and subgroup discovery (SGD) to explore the structural and magnetic properties of full cubic Heusler compounds, with a particular emphasis on their Curie temperatures (Tc) and magnetic stability. Our comprehensive examination of 2903 structures across both L21 and Xa phases identifies configurations that exhibit both structural stability and superior magnetic properties. Notable among these, compounds such as Co2MnSi, Co2CrGe, and Cr2VGe exhibit remarkable magnetic stability, maintaining their ferromagnetic properties well above room temperature. Co2MnSi displays a substantial magnetic moment of 5.00 μB and maintains its ferromagnetic properties up to a Curie temperature of 937 K, underscoring its suitability for high-temperature applications. Similarly, Co2CrGe, with a magnetic moment of 4.00 μB, transitions to a paramagnetic state at a higher temperature of 952 K, demonstrating enhanced thermal durability. Moreover, Cr2VGe, notable for its robust magnetic moment of 2.81 μB, retains its ferromagnetic characteristics until an exceptional 2412 K, making it extremely valuable for thermally intensive environments. These findings underscore the potential of these materials in developing durable and efficient spintronic devices that operate under extreme thermal conditions. By mapping the interplay between electronic structure and magnetic properties, our study provides a predictive framework for optimizing the performance of spintronic materials.

Unraveling the negative charge-to-spin conversion in the Heusler alloy Co2FeSi

Recent discoveries of Heusler alloy achieve a strong advantage of the chemically disordered sample in the charge-to-spin conversion and attracted interests for spintronics applications. Here, we observe the negative charge-to-spin conversion in single magnetic layer of Co2FeSi/MgO and prove generations of σy and σx by spin-torque ferromagnetic resonance (ST-FMR). We also report that the change in charge-to-spin conversion efficiency could be controlled by chemical disordering. Furthermore, the thickness dependents of Co2FeSi demonstrated bulk effect is responsible for the generation of spin current. This study contributes to understanding the mechanisms of spin current generation from magnetic full Heusler alloy and also paves the way for the applications of magnetic memory and nonvolatile spin logic technologies.

Excellent thermoelectric performance of Fe2NbAl alloy induced by strong crystal anharmonicity and high band degeneracy

Full-Heusler alloys with earth-abundant elements exhibit high mechanical strength and favorable electrical transport behavior, but their high intrinsic lattice thermal conductivity limits potential thermoelectric application. Here, the thermoelectric transport properties of Fe-based Full-Heusler Fe2MAl (M = V, Nb, Ta) alloys are comprehensively investigated utilizing density functional theory. The results suggest that Fe2NbAl exhibits exceptionally low lattice thermal conductivity due to low phonon velocities and weakly bound Nb atoms. In Fe2NbAl, the underbonding of the Nb atoms leads large Grüneisen parameters and high anharmonic scattering rates of low-frequency acoustic phonon. Meanwhile, the high band degeneracy and large electrical conductivity lead to a maximum p-type power factor of 255.6 μW·K−2·cm−1 at 900 K. The combination of low lattice thermal conductivity and favorable electrical transport properties leads a maximum p-type dimensionless figure of merit of 1.7. Our work indicates Fe2NbAl, as a low-cost, environmentally friendly, is a potential high-performance p-type thermoelectric material.

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.

Ab-initio prédiction of the structural ,electro-magnetic and thermodynamic properties of Co-based Full Heusler alloy

The structural, thermodynamic, electronic, magnetic and elasticproperties of the Full-Heusler Co2MnTi compoundon the cobalt (Co) are determined byusing first-principles calculations based on density functional theory (DFT). We have used the linear Muffin-Tin Orbitals method (FP-LMTO) combined with the generalized gradient approximation (GGA) with spin. The obtained results demonstrate that our material is ferromagnetic and exhibits metallic behavior around the Fermi level .The study of the elastic properties show that Co2MnTi is mechanically stable and is also classified as a ductile material. The GIBBS program is used to comput the thermodynamic properties such as the modulus of compressibility, the heat capacity volume and pressur, the thermal expansion, the Debye temperature and the volume variation at constants. This type of material is considered as promising for spintronic applications.

Theoretical Calculation of the Structural, Electronic, and Magnetic Properties of a New Rare-Earth Based Full Heusler Alloys Pr2CoZ (Z = Al, Ga, In)

Theoretical Calculation of the Structural, Electronic, and Magnetic Properties of a New Rare-Earth Based Full Heusler Alloys Pr2CoZ (Z = Al, Ga, In)

Crystal structure, stability, and transport properties of Li2BeAl and Li2BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li2BeAl and Li2BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange–correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li2BeAl and Li2BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and − 0.22 eV for Li2BeAl and Li2BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li2BeAl increased to 0.26 eV, and for Li2BeGa, it decreased to − 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li2BeAl and Li2BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li2BeAl and 0.39 at 1000 K for Li2BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.

The structure, magnetism and mechanical properties of L21-type full-Heusler alloy Cr2ZrSi: A first-principles study

Heusler alloy is a widely studied spintronic material in recent years, which has played a huge role in the field of spintronic devices due to its high spin polarization and high Curie temperature. Using first-principles calculation to predict the basic properties of Heusler alloy can not only save experimental costs and time but also provide a reliable theoretical basis for experimental research. This study used a first-principles calculation to study the magnetic and mechanical properties of full-Heusler alloy Cr2ZrSi with an L21-type structure. The research results indicate that the alloy is a half-metallic ferromagnetic material with a theoretical value of 100% spin polarization. The magnetism mainly comes from the asymmetric spin contribution of d-orbital electrons of transition metal atoms and their hybridization. At the same time, this complex hybridization coupling process is also a possible reason for the half-metallic band gaps. In terms of mechanical properties, the Cr2ZrSi alloy exhibits good ductility and anisotropy, with a Debye temperature of 303.848K. Our theoretical research results provide more choices and theoretical basis for subsequent experimental research.

First-principles screening of optoelectronics and thermoelectric response of XAcTe2 (X=K, Rb) full Heusler alloys: mBJ+SOC effect

Structural geometry, Electronic, optical, and thermoelectric attributes of XAcTe2 (X=K,Rb) full Heuser alloys were investigated theoretically via density functional theory (DFT). Structural optimization yielded optimized lattice parameters along with obtained negative formation energies (Ef) revealed the thermodynamically stable cubic geometries of alloys under investigation. For both alloys, the computed electronic band dispersions exhibit semiconductor behavior with a direct band gap. The band gap value of KAcTe2 is 1.59 eV, and 1.66 eV for RbAcTe2. The analysis of optical response shows maximum absorption α (ω) in the ultraviolet (UV) region, validating their quality for photovoltaic devices. The investigation of thermoelectric characteristics showed that both alloys display higher electrical conductivities and lower thermal conductivities.

Effect of uniaxial strain on the electronic and magnetic properties of N2SrRb: a DFT study

ABSTRACT Using the first-principles density functional theory calculations, we examined the effect of uniaxial strain on the electronic and magnetic properties of full-Heusler alloy N2SrRb. Our results show that N2SrRb is a ferromagnetic full-Heusler alloy, and it exhibits half metallic properties with 100% spin polarisation when no strain is applied. The half-metallic and magnetic properties of N2SrRb were retained under the ranges of tensile and compressive strain applied. The spin flip gap was found to increase as the tensile strain increases, while it decreases as the compressive strain increases. The mechanical properties show that the full-Heusler alloy is mechanically stable and having a ductile characteristics

Influence of structural modifications on mechanical and magnetic properties of Co2FeGa full Heusler alloys: A comparative study on L21 and XA structures

In this study we are investigating the effect of pressure and tetragonal distortion of Co2FeGa full Heusler compound in L21 and XA structures on the elastic, magnetic and thermomagnetic properties. Our approach for this is by using density functional theory (DFT) and Monte Carlo (MC) simulation. Our result reveals a significant effect of pressure on the magnetization and Curie temperature on both prototypes. The elastic constants calculated here determine the stable configuration on both structures. The exchange interaction is also influenced by the pressure. The same sort of behavior of the effect of tetragonal distortion is seen on the elastic constants, magnetization, and exchange interaction. Therefore, a detailed significant effect is found in this work and compared to previous studied.

A Computational exploration of the electronic, mechanical, and magnetic properties of Co2A1−xBxAl full heusler alloys (A, B = Cr, Mn, and Fe)

An investigation of the structural, mechanical, electronic, magnetic, and thermomagnetic properties of Co2A1−xBxAl full Heusler alloys (where A, B = Cr, Mn, and Fe, and x ranges from 0 to 1.0) has been carried out using density functional theory (DFT) and Monte Carlo simulations. The investigation reveals small variations in lattice parameters and elastic modulus across the different compositions. The band gaps, calculated using modified Becke-Johnson (mBJ) potential, are found to be approximately 1.4 eV for Co2CrAl and Co2MnAl, while a lower band gap of 0.8 eV is observed for Co2FeAl, which also exhibits the highest total magnetic moment of 5 μB. The doped structures display band gaps and magnetic moments that are intermediate to the pure compounds. The Fe-Co exchange interaction is identified as the most robust, significantly contributing to the high Curie temperatures in Fe-containing compounds, reaching up to 1120 K in the Co2FeAl alloy. Furthermore, the study underscores the strategic use of atomic substitution as an effective approach to manipulating key properties of these Heusler alloys. The ability to modulate band gaps, magnetic moments, and Curie temperatures through atomic substitution offers a promising pathway for optimizing these materials for specific technological applications, aligning with the needs of advanced functional devices.