Papers by Author: V.V. Sokolovskiy

Abstract: Ab initio calculations were performed to investigate composition dependences of crystal lattice parameters, magnetic moments,bulk modulus, magnetic exchange parameters inNi_2-yCo_yMn_1.5-xCr_xSn_0.5 (y =0.2, 0.4; 0.0 ≤ x ≤ 0.4) Heusler alloys. It was shown that increasing of Cr content (x) firstly leads an increasing of lattice parameter, but then a decreasing. The strongest ferromagnetic (FM) interaction for Ni_1.6Co_0.4Mn_1.4Cr_0.1Sn_0.5 is nearest-neighbor interaction between Co and Mn₁ (on own sites). The strongest antiferromagnetic (AFM) interaction is observed between nearest-neighbor Mn₁-Cr atoms in the first coordination sphere and it is equal to-15 meV. Total magnetic moment of Ni_2-yCo_yMn_1.5-xCr_xSn_0.5 (y =0.2, 0.4; 0.0 ≤ x ≤ 0.4) takes value in region from 6.1 μ_B to 6.6 μ_B.

Abstract: In this work, we report on the theoretical calculations of the temperature dependence of magnetization in Ni₂MnGa alloy by Monte Carlo simulation. The calculations have been carried out for the single crystal and polycrystalline structures with 16, 32 and 64 magnetic domains. The theoretically calculated results are in good agreement with the experimental data.

Abstract: In our work the temperature dependencies of magnetization, entropy changes, and the Curie temperature (T_C) of La_1-xCa_xMnO₃ (x = 0.33 and 0.5) were investigated using Monte Carlo method and Heisenberg model. In our simulation, magnetic Mn³⁺ and Mn⁴⁺ ions are described by classical Heisenberg spins, while oxygen, lanthanum and calcium ions are considered as non-magnetic. The Mn magnetic ions are distributed on a simple cubic lattice according to the perovskite structure of the manganite. The theoretical Curie temperatures and magnetocaloric values are in a good agreement well with experimental data.

Abstract: The twin boundary motion in Ni-Mn-Ga Heusler alloys has been investigated using Monte Carlo simulations. The Hamiltonian of system includes magnetic and elastic parts and two magnetoelastic terms. It is shown that the twin boundary shifts in a magnetic field at the constant temperature. The spin and strain volume fractions have been obtained at different temperatures.

Abstract: The magnetocaloric effect (MCE) in theNi2+xMn1-xGa (x = 0.33, 0.36, 0.39), Ni50Mn25In25, Ni54Mn21Ga18In7, Ni53.5Mn21.5Ga16In9, Ni45Co5Mn36.5In13.5 Heusler alloys and in the La0.7BayCa0.3-yMnO3 (y = 0.12, 0.24, 0.3) manganites at the Curie points have been measured by the direct method. For the magnetic field change H = 2 T, the maximal adiabatic temperature change Tad in the Ni2+xMn1-xGa alloys is larger than 0.6 K. For the Ni50Mn25In25 alloy the maximal value of Tad = 1.51 K (for the same magnetic field change H = 2 T) is observed at the magnetic phase transition temperature.

Abstract: In this paper we present a theoretical model for calculation of the (positive and negative) magnetocaloric effects and magnetic properties of the Heusler Ni50Mn34In16 alloy by the classical Monte Carlo study. By the help of the proposed model the temperature dependences of the magnetization, tetragonal deformation, heat capacity, positive and negative isothermal magnetic entropy changes for magnetic field variation are obtained. All quantities are in good qualitative agreement with the available experimental data.

Abstract: On the basis of Monte Carlo simulations, we investigate the temperature dependence of magnetization of Ni-Mn-Sb Heusler alloys, in which the part of the Mn atoms interact antiferromagnetically. It is shown that this antiferromagnetic exchange is responsible for existence of several magnetic phase transitions in the Heusler alloys. For a certain set of parameters of the model Hamiltonian we obtain coupled martensitic and magnetic phase transitions. Results of simulations agree in an excellent way with the experimental magnetization curves.

Abstract: The three-dimensional model for the theoretical description of the phase transformations and the magnetocaloric effect in shape – memory Heusler Ni2+xMn1-xGa alloys (x=0.18 – 0.27) with a coupled magnetostructural phase transition by the classical Monte Carlo method is proposed. It is shown that the isothermal magnetic entropy change upon magnetic field variations from 0 to 5 T and other magnetic properties are in good agreement with the available experimental data.