Mikhail A. Zagrebin

New Heusler alloys with a metamagnetostructural phase transition

Investigations of new ferromagnetic shape-memory Ni-Mn-Z Heusler alloys (Z = In, Sn, Sb) are reviewed. Experimental data are described and explained on the assumption that these alloys undergo a phase transition from the ferromagnetic to the antiferromagnetic state (metamagnetic transition). The results of theoretical studies of the phase diagrams of these alloys are considered with regard to the possible change in the character of magnetic ordering (from ferromagnetic to antiferromagnetic) and interaction of the structural martensitic transformation with the metamagnetic transition.

Electronic and magnetic properties of the Co2-based Heusler compounds under pressure: first-principles and Monte Carlo studies

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.

First principles investigation of structural and magnetic properties of Ni–Co–Mn–In Heusler alloys

The structural and magnetic properties of Co-doped Ni–Mn–In Heusler alloys are investigated in the framework of density functional theory and the Monte-Carlo method. The first principles calculations of the equilibrium properties (crystalline structure and magnetic ordering) indicate that the ferromagnetic state is favorable in the austenite structure, whereas the ferrimagnetic order is stable in the martensite structure. The strong competition of ferro- and antiferromagnetic exchange interactions arise from the austenite-martensite crossover. The temperature dependences of total magnetization are calculated by means of the proposed Hamiltonian model with the ab initio magnetic exchange couplings and magnetostructural interrelation. The calculated properties are in good agreement with the experimental ones.

First Principles Investigations of Structural and Magnetic Properties of Fe-Ni-Mn-Al Heusler Alloys

In this work the magnetic and structural properties of quaternary Fe-Ni-Mn-Al Heusler alloys are studied. We use first principles calculations to investigate crystal lattice relaxation of alloys and their coupling to the magnetic order, with a particular focus on the tetragonal distortions characterized by the c/a ratio. It follows from our calculations that Fe-Ni-Mn-Al alloys have very interesting magnetic properties and can be good candidates as multifunctional magnetic materials.

Ternary Diagrams of Ni-Mn-Ga from First Principles

The composition dependences of the magnetic and elastic properties of Ni-Mn-Ga Heusleralloys are investigated by using ab initio calculations. The off-stoichiometric compositions are real-ized by the coherent-potential approximation. Two types of off-stoichiometric approaches are pro-posed. Through a series of researches, the equilibrium lattice constants, bulk modulus, magnetic mo-ments, formation energies of Ni-Mn-Ga alloys are obtained and mapped onto ternary diagrams.

Structural and Magnetic Properties of Mn2NiZ (Z = Ga, In, Sn, Sb) Heusler Alloys from Ab Initio Calculations

The structural and magnetic properties of Mn-based stoichiometric Heusler alloys have investigated by means of ab initio calculations in framework of the density functional theory. First principles electronic structure calculations have shown that Mn2NiZ (Z = Ga, In, Sn, Sb) alloys are ferrimagnets with antiparallel alignment between the Mn atoms. The martensitic transition can be realized in Mn2NiGa and Mn2NiSn alloys with tetragonal ratio of 1.27 and 1.16, respectively. Calculated properties are in a good agreement with available experimental data.

Ab Initio Study of Magnetic Properties and Phase Diagram of Ni-Mn-Ga Heusler Alloys

In this work the magnetic properties (exchange parameters, magnetic moment of non-stoichiometric Ni–Mn–Ga Heusler alloys with structural disorder by the help of ab initio calculations have been performed. Theoretical composition dependences of the total magnetic moment are in qualitative agreement in qualitative agreement with experimental data. Calculations of exchange parameters show that interactions between the Mn atoms in regular positions and Mn atoms in Ni and Ga positions are antiferromagnetic.

First-Principles Study of the Structure and Magnetic Properties of Fe 8 Rh 8 – x Z x (Z = Mn, Pt, Co; x = 1, 2, 3) Alloys

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.

Phenomenological analysis of thermal hysteresis in Ni-Mn-Ga Heusler alloys

Abstract 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 crystal lattice modulation order parameters as well as an external magnetic field. It is shown that for the assigned combination of phenomenological parameters, in the phase diagrams, the Austenite–Martensite first-order phase transition has a finite (critical) point in which the thermal hysteresis is disappeared. Moreover, this point depends on the relation between modulation and elastic constants as well as on the magnetic field. Obtained results have been compared with other theoretical end experimental data.

Ab initio study of magnetic properties of Fe 1−x Ga x alloys

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