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In the search for new magnetic functional materials, non-stoichiometric compounds remain a relatively unexplored territory. While experimentalists create new compositions looking for improved functional properties, their work is not guided by systematic theoretical predictions. Being designed for perfect periodic crystals, the majority of first-principles approaches struggle with the concept of a non-stoichiometric system. In this work, we attempt a systematic computational study of magnetic and structural properties of Ni–Mn–Ga, mapped onto ternary composition diagrams. Compositional stability was examined using the convex hull analysis. We show that the cubic austenite has its stability region close to the stoichiometric Ni2MnGa, in agreement with experimental data, while the tetragonal martensite spreads its stability over a wider range of Mn and Ni contents. The unstable compositions in both austenite and martensite states are located in the Ga-rich corner of the ternary diagram. We note that simultaneous stability of the austenite and martensite should be considered for potentially stable compounds suitable for synthesis. The majority of compounds are predicted to be ferrimagnetically ordered in both austenitic and martensitic states. The methodology used in this work is computationally tractable, yet it delivers some predictive power. For experimentalists who plan to synthesize stable Ni–Mn–Ga compounds with ferromagnetic order, we narrow the target compositional range substantially.

In this work, based on structural and magnetic phase transition temperatures estimated theoretically from the first principles, the concentration phase diagram for Fe100−xAlx (15.625≤x≤31.2...

The influence of partial Mn and Co content on magnetic properties and martensitic transformation in full Heusler compounds Ni-Co-Mn-Sn with the regular and inverse structure is studied theoretically by first-principles calculations within density functional theory. The optimized lattice parameters, magnetic moments and bulk moduli are calculated. It is shown that the substitution of Sn for Mn atom in the regular structure and of Sn for Ni atom in the inverse structure leads to an appearance of stable martensitic phase. For both considered systems with excess Ni and Mn content, the magnetic reference state of austenite and martensite is found to be the ferrimagnetic one except for Ni 1.75 Co 0.25 Mn 1.75 Sn 0.25 . For the latter, martensitic and austenitic phases are ordered ferri- and ferromagnetically that results in a large change in magnetization.

In this article we present the theoretical study of structural and magnetic properties in a series of compositions Fe1−xMnxRh (x = 0.125, 0.25, 0.375). The properties of alloys were studied by first principles calculations. It is shown that the equilibrium lattice parameter change with increasing Mn concentration. For all systems the checkerboard-like antiferromagnetic configuration was found to be more energetically favorable. For Fe0.875Mn0.125Rh composition the cubic phase is more energetically favorable. For alloys Fe0.75Mn0.25Rh and Fe0.625Mn0.375Rh the martensitic phase transformation is observed.

Using density functional theory, the ground state properties, magnetocrystalline energy, and tetragonal magnetostriction λ 001 for Fe-Ga alloys with A2, D 0 3 and L12 structures were calculated. It was found that the equilibrium lattice parameters for every structure increase with increasing Ga content. The magnetocrystalline anisotropy energy (MAE) was projected into the tetragonal distortion – Ga concentration diagram, according to which the MAE reveals an alternating character. For Fe 78.125 Ga 21.875 , the largest value of tetragonal magnetostriction λ 001 was found.

We present density functional theory calculations to study the interplay between magnetic and structural properties in Ni-Co-Mn-Sn. The relative stability of austenite (cubic) and martensite (tetragonal) phases depends critically on the magnetic interactions between Mn atoms. While the standard generalized gradient approximation (GGA) stabilizes the latter phase, correlation effects beyond GGA tend to suppress this effect. Mn atoms treated as magnetic impurities can explain our results, where a delicate balance between magnetic interactions mediated by Ni d and Sn p orbitals determines the equilibrium structure of the crystal. Finally, we discuss the role of Co doping in stabilizing ferromagnetic austenite phases.

This work presents a theoretical investigation of the Heusler compound Ni 2 MnGa with PHONON and VASP software. In particular, in the focus of this study is the role of the atomic disorder in the phonon instabilities that are characteristic for some Heusler alloys.

The structural and magnetic properties of Mn- and Pt-doped Fe-Rh alloys are investigated by first principles calculations. The 16-atom supercell (Fe8 Rh 8 - x Z x ) with different initial spin configurations including ferromagnetic and two types of antiferromagnetic orders are considered. It is shown that in a case of Fe8 Rh 8 - x Mn x , the ferromagnetic spin configuration in a cubic cell is energetically favorable compared to other magnetic configurations. The addition of Mn content stimulates the martensitic transformation from ferromagnetic cubic phase to antiferromagnetic tetragonal one. Moreover, an increase in Mn content leads to increase in the energy difference between cubic and tetragonal phases which is equivalent of increase in a temperature of structural transformation. Contrary, for Fe8 Rh 8 - x Pt x , an increase in Pt content results to appearance of stable tetragonal state with the checkerboard-like antiferromagnetic configuration.

By using first-principles calculations in combination with supercell approach a series of Ni8Mn2 Cr 2 Z 4 (Z = Ga, Ge, In, Sn) are studied with partial replacing of Mn by Cr to investigate the effect of such substitution on their structural and magnetic properties. Two 16-atom supercells with different distribution of Cr in the Mn sublattice and magnetic ordering are considered. Crystal structure optimization shows that the magnetic ground state of Ni8Mn2 Cr 2 Z 4 (Z = Ga, In) alloys is the state with pairwise antiparallel magnetic moments of Cr atoms. While for Ni8Mn2 Cr 2 Z 4 (Z = Ge, Sn) alloys is it ferromagnetic state with parallel magnetic moments of Cr and Mn atoms. Based on ground state energies it is shown that martensitic phase can be realized only in Ni8Mn2 Cr 2 Z 4 (Z = Ga, Ge) alloys. For the stable crystal structures with associated magnetic order magnetic exchange constants are calculated, to estimate Curie temperatures with the help of mean-field approximation. Obtained results are in qualitative agreement with experimental and theoretical data.

The structural, electronic and magnetic properties of Fe100−xGax alloys are studied computationally in the composition range up to x≤ 31.25 at.% and experimentally about 27 at.%. Ga content. Using ...

We propose a ferromagnetic Heusler alloy that can switch between a metal and a half-metal. Thiseffect can provide tunable spintronics properties. Using the density functional theory (DFT) withreliable implementations of the electron correlation effects, we find Mn2ScSi total energy curvesconsisting of distinct branches with a very small energy difference. The phase at low lattice crystalvolume is a low magnetic half-metallic state while the phase at high lattice crystal volume is a highmagnetic metallic state. We suggest that the transition between half-metallic and metallic statescan be triggered by a triaxial contraction/expansion of the crystal lattice or by an external magneticfield if we assume that the lattice is cubic and remains cubic under expansion/contraction. However,the phase at high volume can also undergo an austenite-martensite phase transition because of thepresence of Jahn-Teller active3delectrons on the Mn atoms., Comment: Supplementary materials is located on https://journals.aps.org/prb/supplemental/10.1103/PhysRevB.103.054414

A significant difference in properties and structure of Fe-Ga alloys in their equilibrium and metastable states limits their application. This necessitates an immediate understanding of the importance of cooling rate in the formation of alloy metastable and equilibrium structures. In this paper, we experimentally studied the structure of the Fe-(23−24) Ga alloys after both (i) cooling with different cooling rates and (ii) isothermal annealing between 300 and 575 °C up to 1800 h to report the alloy structure and present the Time-Temperature-Transformation (TTT) diagrams for the metastable to equilibrium transition in these alloys. The critical cooling rates were defined with respect to the formation of the equilibrium state. A theoretical model along with corresponding Monte Carlo simulations for modeling phase transitions and construction of TTT diagram for the same alloys were developed: simulated phase diagrams were analyzed with respect to our the experimental findings.

The binary compound V$_3$Ga can exhibit two near-equilibrium phases, consisting of the A15 structure that is superconducting, and the Heusler D0$_3$ structure that is semiconducting and antiferromagnetic. Density functional theory calculations show that the two phases are closely degenerate, being separated by only ~10 meV/atom. Magnetization measurements on bulk-grown samples show superconducting behavior below 14 K. These results indicate the possibility of using V$_3$Ga for quantum technology devices utilizing both superconductivity and antiferromagnetism at the same temperature., Comment: submitted to Applied Physics Letters

We discuss the interplay between magnetic and structural degrees of freedom in elemental Mn. The equilibrium volume is shown to be sensitive to magnetic interactions between the Mn atoms. While the standard generalized gradient approximation underestimates the equilibrium volume, a more accurate treatment of the effects of electronic localization and magnetism is found to solve this longstanding problem. Our calculations also reveal the presence of a magnetic phase in strained $\ensuremath{\alpha}$-Mn that has been reported previously in experiments. This new phase of strained $\ensuremath{\alpha}$-Mn exhibits a noncollinear spin structure with large magnetic moments.

The stability of the nonmodulated martensitic phase, the austenitic Fermi surface, and the phonon dispersion relations for ferromagnetic ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ are studied using density functional theory. Exchange-correlation effects are considered with various degrees of precision, starting from the simplest local spin density approximation (LSDA), then adding corrections within the generalized gradient approximation (GGA), and finally, including the meta-GGA corrections within the strongly constrained and appropriately normed (SCAN) functional. We discuss a simple procedure to reduce a possible overestimation of magnetization and underestimation of nesting vector in SCAN by parametrically decreasing self-interaction corrections.

In this work, the magnetic, structural and thermodynamic properties in a series of Mn 3 -X-C (X = Ga, Sn) have been studied by means of first-principles based on the density-functional theory and quasi-harmonic approximations based on the Debye model. To evaluate the magnetic effects, first-principles calculations have been carried out for different magnetic spin configurations including ferro- and ferrimagnetic configurations as well as different non-colinear ones. It has been shown that for both compounds the non-colinear spin orderings with a lower magnetic moment are favorable configurations at zero-temperature as compared with the ferromagnetic one. The magnetic exchange coupling constants showing an oscillation behavior becomes weaker along the sequence of Mn 3 -Ga-C → Mn 3 -Sn-C. Using the thermodynamic approach, the magnetic phase transition between ferromagnetic and non-colinear states in Mn 3 -Ga-C is found. While for Mn 3 -Sn-C, this transition does not occur in a studied temperature range. The pressure effect on the thermodynamic properties has been estimated. The calculated results are in a good agreement with available experimental data.

In this work we study the magnetic states of ternary Ni 2 Cr Z ( Z = Al, As, Bi, Ga, Ge, In, P, Pb, Sb, Si, Sn, Tl) Heusler alloys in comparison with Ni 2 Mn Z ones by ab initio methods. It is shown that the Ni-Mn based alloys are ferromagnetic. Contrary, the Ni-Cr based alloys with Z = Ga, In, Tl, Si, Ge, Sn, Pb are compensated aniferromagnets and with Z = Al, P, As, Sb, Bi are ferromagnets. The formation energy of alloys studied is calculated and stable compounds are predicted. The possible martensitic transitions in Ni-Mn and Ni-Cr based Heusler alloys are estimated. Within the Heisenberg model and Monte Carlo technique, the Curie temperatures are obtained. Theoretical results are compared with other theoretical end experimental results.

The crystal structure, magnetic and magnetocaloric properties of Co-doped Ni-Mn-(Sn, Al) Heusler alloys were calculated using ab initio zero-temperature calculations combined with Monte Carlo finite-temperature simulations. To find the stable magnetic ground state for austenite and martensite, the calculations for ferromagnetic and ferrimagnetic orderings were carried out. Once accurate lattice constants were calculated, magnetic moments, exchange coupling constants, bulk moduli, Debye temperatures for the alloys studied were determined. Using the thermodynamic approach jointly with Monte Carlo simulations, martensitic phase transition temperatures were obtained from intersection of the Free energy curves. Finally, the temperature dependences of magnetic and magnetocaloric properties for the studied systems were simulated by the effective Potts-Blume-Emmery-Griffiths Hamiltonian. The obtained results are in a good agreement with available experimental data.

The results of examination of the structural, magnetic, electronic, and thermodynamic properties of Pd2MnZ (Z = Ga, Ge, As) Heusler alloys obtained in ab initio and Monte Carlo modeling are presented. It is demonstrated that a stable martensitic state is possible for Pd2MnGa and Pd2MnAs alloys. The equilibrium lattice parameter increases in the considered series of alloys with the number of valence electrons per atom (e/a). The Curie temperature of Pd2MnZ (Z = Ga, Ge, As) alloys is determined using the calculated parameters of exchange interaction and total magnetic moments.

The results of first-principles studies of the structure and magnetic properties of Fe–Rh–Z alloys conducted using the VASP package are reported. The magnetic moments and lattice parameters are determined, and the possibility of existence of stable tetragonal distortions in Fe–Rh–Z alloys with various magnetic configurations set by the level of doping with Mn, Pt, and Co is examined. It is demonstrated that the equilibrium lattice parameter and the type of magnetic ordering change with the concentration of the third element.

The manipulation of thermal hysteresis in Ni-Mn-Ga Heusler alloys with coupled magnetostructural phase transition is studied theoretically using the Landau theory, including magnetic, elastic and c...

In order to discuss the difference between the available theoretical and experimental values of the total magnetic moment of Co2CrAl Heusler alloy, in this paper we studied the effects of a structural disorder on the magnetic and electronic ground state properties of the alloy studied by means of ab initio and Monte Carlo methods. On the one hand, it is shown that a calculated magnetic ground state of the austenite L21 structure is ferromagnetic, and the alloy demonstrates half-metallic behavior. However, the equilibrium lattice parameter and magnetic moment calculated for ferrimagnetic state (where the Cr atoms are ordered antiferromagnetically) are in better agreement with the available experimental data than the ferromagnetic one. On the other hand, an account of a structural disorder results in a decrease in the magnetic moment to a value close to the experimental. However, systems with a structural disorder are energetically unfavorable in comparison with the ordered L21 structure at zero temperature. Using the calculated exchange coupling parameters in the Heisenberg Hamiltonian, the temperature dependences of magnetization, specific heat, magnetic part of internal energy as well as Helmholtz energy are simulated in the framework of Monte Carlo technique for both ordered and disordered cases. Eventually, it is shown that the disordered structure with smaller magnetization is more stable at higher temperatures. This indicates that the experimental compound might be disordered.

The crystal lattice parameters, tetragonality degree, magnetic moments, magnetic exchange parameters in the Ni7Co1Mn5Cr1Sn2 Heusler alloy are investigated by ab initio calculations and supercell approach. Three 16-atom supercells with different atomic configurations relative to Cr atom are considered. On the one side, if the Cr atom is surrounded by one Sn and two Mn nearest neighbors the respective supercell in austenite is found to be favorable with compared to other ones. On the other side, the supercell consisting three nearest Mn atoms against Cr atom is more stable in martensite. Total magnetic moment of all supercells is almost the same and it increases linearly with increasing lattice parameter. Exchange interactions between Cr and Mn atoms depend strongly on the atom distribution. The strong antiferromagnetic coupling between nearest Cr-Mn pairs is found.

The magnetic and structural properties of a series of nonstoichiometric Ni–Mn–Ga Heusler alloys are theoretically investigated in terms of the density functional theory. Nonstoichiometry is formed in the coherent potential approximation. Concentration dependences of the equilibrium lattice parameter, the bulk modulus, and the total magnetic moment are obtained and projected onto the ternary phase diagram of the alloys. The stable crystalline structures and the magnetic configurations of the austenitic phase are determined.

Ti-Al intermetallic coatings thickness of about 60–150 μm was fabricated on Al, Ti, and hypo-eutectoid steel substrates by mechanical alloying (MA) using a vibratory ball mill. The coatings was then laser treated to obtain homogenous and equilibrium structure. Phase composition and the cross-sectional microstructure of the coatings were investigated using X-ray diffraction and the Scanning electron microscopy respectively while chemical analysis of the coatings was carried out using Bruker energy-dispersive X-ray Spectrometer (EDS). Micro-hardness (HV) of the obtained coatings was observed to be increased more than twice after the deposition and subsequent laser treatment in comparison with microhardness of the initial substrates materials.. Surface roughness of the obtained coatings was also reduced significantly after laser treatment i.e. for Al substrate it reduced from 52 μm to 26 μm. The parameters of mechanical alloying and laser treatment used in this work provided a successful way to deposit nano-structured intermetallic coatings with homogenous and smooth surface finish and high value of micro-hardness.

In this work we report results of ab initio calculations of structural and magnetic properties in a series of Heusler compositions Ni2+xMn1-x(Ga, Ge) (x = 0, 0.25, 0.50 and 0.75). It was found that, in contrast to the Ni-Mn-Ga, the martensitic transformation in Ni-Mn-Ge alloys occurs only in off-stoichiometric compositions. For both types of alloys studied in this work, the energy difference between austenite and martensite, were found to increase with increasing Ni excess, x, while the martensite is lower in energy compared with the austenite. By using optimized lattice parameters for the austenite, exchange coupling constants required for estimation of the Curie temperature by means of Monte Carlo simulations have been obtained. It was shown that the Curie temperature for the austenitic phase of Ni2+xMn1-x(Ga, Ge) decrease with increasing a Ni excess. In general, these theoretical results agree well with available experimental data and other theoretical results, and reveal a clear chemical trend.

A series of Ni 2 Mn 1- x Cr x Ga (0.125 ≤ x ≤ 0.5) Heusler alloys have been theoretically investigated by density functional theory as well as finite-temperature Monte Carlo simulations to obtain Curie temperatures. By using ab initio calculations it was found that the most energetically favorable magnetic state for both austenite and martensite phases in Ni 2 Mn 1- x Cr x Ga is a ferromagnetic state. Besides, an increase in energy difference between austenite and martensite with increasing Cr content was observed. With respect to the exchange coupling constants, it was shown that Ni-Mn(Cr) pairs show the strongest ferromagnetic exchange interaction between nearest neighbor atoms in austenite of all alloys considered. It was demonstrated that the most part of total spin up and spin down density of states is caused by Ni atoms. Estimated Curie temperatures were found to be less than experimental ones approximately by 80 K, but the T C ( x ) function repeats pattern of experimental one.

The strongly constrained and appropriately normed (SCAN) semi-local functional for exchange-correlation is deployed to study the ground-state properties of ternary Heusler alloys transforming martensitically. The calculations are performed for ferromagnetic, ferrimagnetic, and antiferromagnetic phases. Comparisons between SCAN and generalized gradient approximation (GGA) are discussed. We find that SCAN yields smaller lattice parameters and higher magnetic moments compared to the GGA corresponding values for both austenite and martensite phases. Furthermore, in the case of ferromagnetic and non-magnetic Heusler compounds, GGA and SCAN display similar trends in the total energy as a function of lattice constant and tetragonal ratio. However, for some ferrimagnetic Mn-rich Heusler compounds, different magnetic ground states are found within GGA and SCAN., 12 pages, 6 figures

Hydrogen peroxide has been detected as a reaction intermediate in the electrochemical oxygen reduction reaction (ORR) on transition-metal oxides and other electrode materials. In this work, we studied the electrocatalytic and catalytic reactions of hydrogen peroxide on a set of Mn oxides, Mn2O3, MnOOH, LaMnO3, MnO2, and Mn3O4, that adopt different crystal structures to shed light on the mechanism of the ORR on these materials. We then combined experiment with kinetic modeling with the objective to correlate the differences in the ORR activity to the kinetics of the elementary reaction steps, and we uncovered the importance of structural and compositional factors in the catalytic activity of the Mn oxides. We concluded that the exceptional activity of Mn2O3 in the ORR is due to its high catalytic activity both in the reduction of oxygen to hydrogen peroxide and in the decomposition of the latter, and furthermore, we proposed a tentative link between crystal structure and reactivity.

Two Fe–Ga alloys with 27 and 29% Ga additionally alloyed with boron (B) were studied using neutron diffraction, scanning electron microscopy with energy dispersive spectroscopy, and magnetostriction measurements. Neutron diffraction experiments demonstrated that the preponderant phase is the cubic Fe3Ga with structure D03. The lattice parameter of the Fe3Ga phase is much larger than the expected if the Ga composition of this phase is considered. The conclusion is that boron enters in the interstitial octahedral sites of the D03 lattice causing the lattice expansion, whose result is supported by ab initio calculations. Consequently, an increase on the magnetostriction is attributed to B located at the interstices that introduces local strains in the lattice. It is also suggested that the expansion of the lattice may increase Ga solubility in the D03 phase.

In this work, based on limited experimental magnetocaloric data for Ni–Co–Mn–Al Heusler alloys, we present a theoretical study to predict a composition with higher magnetocaloric properties. By analogy with Ni–Co–Mn–(In, Sn) alloys exhibiting a large magnetization change across the structural transformation, we suppose that the addition of 10 at. % Co in Ni–Mn–Al would yield a similar trend. Our approach is based on the combination of ab initio calculations and Monte Carlo simulations within the framework of the Potts–Blume–Emery–Griffiths model. It follows from ab initio calculations that Co addition modifies the exchange interactions and enhances the ferromagnetism in austenite, while for martensite, the ferromagnetism is substantially suppressed due to the strongest antiferromagnetic Mn–Mn interactions. Thermo-magnetization curves and magnetocaloric properties under magnetic fields of 0.5 and 2 T are simulated by the Monte Carlo method assuming the ab initio exchange-interaction parameters. A large change in magnetization of approximately 100 A m 2 kg − 1, leading to a giant magnetocaloric effect ( Δ T a d ≈ − 7 K) across the martensite–austenite transformation, is predicted.

Using density functional theory, the structural, magnetic and electronic properties for Fe100−xGex (x = 12.5–25 at.%) with A2, B2, D03, L12, and D019 structures were studied. Based on the total energy calculation, the phase diagram was plotted as a function of Ge concentration. In agreement with the experimental results, the following sequences of phase transitions were observed: A2→B2→D03 (12.5 ≤ x

In this work, the one-dimensional statistical model based on the phenomenological approach for the study of the magnetic and magnetocaloric properties in Heusler alloys is considered. The proposed model is approved for Ni-Co-Mn-In exhibiting both the first-order structural transformation and second-order magnetic phase transition. Temperature dependencies of magnetization and magnetic entropy change under applied magnetic field and external pressure are studied. The results of the simulations are in good agreement with the experimental data.

In this paper, structural, magnetic and electronic properties of FeRhxPd1-x (x = 0, 0.125, and 0.25) were investigated by first principles calculations. The two types of crystal structures CuAu-type and CsCl-type are considered. The lattice parameters, energy, partial and total magnetic moments, formation energy, total density of electronic states and the projected density of states for t2g and eg orbitals for Fe–Rh–Pd with different magnetic ordering are calculated.

In this work, we present a theoretical study of the thermal hysteresis that takes place across the first order martensitic transition as a function of temperature for Heusler alloys. To simulate the structural phase transitions, we propose the degenerate three-state Blume-Emery-Griffiths (BEG) Hamiltonian taking into account the temperature-dependent lattice entropy expansion in the framework of quasi-harmonic Debye model. It is shown that the hysteresis width of structural transformation between cubic austenite and tetragonal martensite depends on the difference between σ T M and σ T A variables.

In this work, we present theoretical investigations of the structural and magnetic properties Fe (Rh, Co) and Fe (Rh, Pt) alloys using the density functional theory. The energy calculations were performed for the 16-atom supercell (Fe8Rh8-xZx) with different initial spin configurations. It is shown that a small variation of Pt or Co content leads to change the type of magnetic ordering. It is shown that the ferromagnetic configuration of Fe8Rh8-xCox (x=2, 3) is more energetically favorable as compared with other configurations in austenite. The antiferromagnetic configuration is more energetically favorable for Fe8Rh7Co1 alloy. For the Fe8Rh8-xPtx system, the checkerboard-like antiferromagnetic configuration was found to be more energetically favorable. Besides, the addition of Pt into Fe-Rh system slightly changes the optimized lattice parameter and stimulates the martensitic phase transformation.

Nowadays, magnetostrictive materials are promising for use as sensors, magnetostrictive actuators, in micro electro-mechanical systems and sensor devices.

The structural and magnetic properties for a series of Fe100-xGax alloys (x = 18 – 30 at.%) are studied in the framework of first-principles calculations and Monte Carlo simulations. The both, general gradient approximation and local density approximation are considered for the exchange-correlation functional. The ground state ab initio calculations are performed for both D03 and L12 crystal structures. It is shown that for general gradient approximation, the optimized lattice parameters and total magnetic moments are found in the better agreement with experimental ones. Using the calculated exchange coupling constants for studied compositions, Curie temperatures are estimated by means of Monte Carlo simulations of Heisenberg Hamiltonian.

In this work, we report results of ab initio and Monte Carlo investigations of structural and magnetic properties in a series of Heusler compositions Pd2MnZ (Z = Ga, Ge, As). It was found that for Pd2MnGa and Pd2MnAs, the stable martensitic state is realized on the contrast with Pd2MnGe. The equilibrium lattice parameters for the series of Pd2MnZ (Z = Ga, Ge, As) compounds increase with increasing the number of valence electrons per atom (e/a ratio). Having calculated total magnetic moments and magnetic exchange parameters from ab initio methods, the Curie temperature for Pd2Mn-based alloys has been estimated in the framework of Monte Carlo simulations of Heisenberg model.

In this work we perform a wide-range systematic study of the family off-stoichiometric Ni-Mn-Ga alloys by using the supercell approach in the framework of density functional theory. Our goal is to explore the compositional variations of the structural stability and magnetic properties of Ni-Mn-Ga compositions. As a result equilibrium lattice parameters, bulk moduli, total magnetic moments, and formation energies of a wide range of Heusler alloys have been mapped on compositional ternary diagrams.

Structural, magnetic and electronic properties of stoichiometric Co2 YZ Heusler alloys (Y = Cr, Fe, Mn and Z = Al, Si, Ge) have been studied by means of ab initio calculations and Monte Carlo simulations. The investigations were performed in dependence on different levels of approximations in DFT (FP and ASA modes, as well as GGA and GGA + U schemes) and external pressure. It is shown that in the case of the GGA scheme the half-metallic behavior is clearly observed for compounds containing Cr and Mn transition metals, while Co2FeZ alloys demonstrate the pseudo half-metallic behavior. It is demonstrated that an applied pressure and an account of Coulomb repulsion (U) lead to the stabilization of the half-metallic nature for Co2 YZ alloys. The strongest ferromagnetic inter-sublattice (Co–Y) interactions together with intra-sublattice (Co–Co and Y–Y) interactions explain the high values of the Curie temperature obtained by Monte Carlo simulations using the Heisenberg model. It is observed that a decrease in valence electrons of Y atoms (i.e. Fe substitution by Mn and Cr) leads to the weakening of the exchange interactions and to the reduction of the Curie temperature. Besides, in the case of the FP mode Curie temperatures were found in a good agreement with available experimental and theoretical data, where the latter were obtained by applying the empirical relation between the Curie temperature and the total magnetic moment.