Papers by Keyword: Magnetic Phase Transition

Abstract: Based on the spin-fluctuation theory and LSDA + U + SO-calculations of the electronic structure, the spin states arising in the region of the magnetic phase transition in the helicoidal ferromagnet MnSi are studied. Within the framework of the stated model of the electronic structure, a temperature dependence of the homogeneous magnetic susceptibility is obtained near the temperature of the magnetic phase transition, which is in good agreement with experiment. At the temperature of the transition to the paramagnetic state, the left chirality vanishes, and spin correlations arise with a radius equal to the length of the spin helix, which then decreases with temperature. The results were obtained within the framework of the assignment of the Ministry of Education and Science of the Russian Federation, contract 3.9521.2017 / 8.9

Abstract: The magnetic susceptibility dependence on temperature near phase transition point was investigated by theoretical analysis. It is shown that with decreasing of the film thickness the magnetic susceptibility shape curve becomes more rounded finite-size function, centered about the lowered temperature Tc (L). The obtained results are in good agreement with experimental data.

Abstract: The purpose of this work was the complex investigation of magnetic, magnetocaloric and magnetoelastic properties of compounds based on Gd₅Si₂Ge₂ with small In substitutions in p-sublattice. The conducted measurements revealed that both the magnetocaloric effect and the volume magnetostriction upon cooling reach the higher values than upon heating. Indium substitution leads to the appearance of the second maximum on the temperature dependence of the magnetocaloric effect resulting in the increase of the refrigerant capacity.

Abstract: The “average spin” method was developed in terms of Heisenberg model. The average magnetic moment’s depending average of the temperature, the number of the nearest neighbors and spin of the atom has been calculated. It’s shown that the Curie temperature decreases with the spin of the atom.

Abstract: Within the frame of average spin the dependence of Neel temperature of ultrathin antiferromagnetic film for FCC crystalline lattice on its thickness and the concentration of magnetic atoms has been defined. The λ values calculated by us are close to experimental values obtained for the films СoO/SiO2. The increasing of thickness leads to decreasing of the critical concentration down to the value equal to percolation threshold.

Abstract: The modeling study of magnetic phase transition with account of short-range order has been carried out in the approximation of random interaction between atomic magnetic moments of the nearest neighbours and in the frame of Ising model. Curie temperature has been calculated for different kinds of crystalline lattice.

Abstract: Within the frame of average spin model the calculation of dependence of critical phase transition temperature in antiferromagnetic ultrathin films of different crystalline structure on their thickness has been carried out. I has been shown, that relative change of Neel temperature is subject to power law with exponent close to the experimental values.

Abstract: The magnetic phase transition and magnetic entropy change of melt-spun LaFe_11.6Si_1.4B_x (x=0.0, 0.3, 0.5, 0.7) ribbons were investigated by measuring the magnetization as the function of temperature. Comparing with LaFe_11.6Si_1.4, the NaZn₁₃-type structure of LaFe_11.6Si_1.4B_x did not change after introducing B atoms, while the amount of α-Fe phase in the ribbons significantly decreased. The Curie temperature slightly changes after the addition of B. The LaFe_11.6Si_1.4B_x (x=0.3, 0.5) exhibits first-order magnetic transition and large magnetic entropy change as observed in LaFe_11.6Si_1.4 compound.

Abstract: Abstract. In this paper, we modelled the phase transition between ferromagnetic and paramagneticstates in ultrathin films of different crystal structure near the percolation transition. Properties of ultrathinfilms have been studied within the framework of Ising model and the method of random-fieldinteraction. It is shown that the critical concentration of such phase transition depends on the symmetryof crystal lattice of the material. The increase in the film thickness leads to a decrease of the criticalconcentration up to a value of the percolation threshold of a massive sample of the correspondingcrystal structure.

Abstract: Modeling study of magnetic and concentration phase transition in ultrathin films of diluted magnet has been carried out under approximation of random interaction between atomic magnetic moments of nearest neighbors and within the framework of Ising model. The dependence of Curie temperature on concentration of magnetic atoms was formed. It is shown that with increasing of thickness of ultrathin film the critical concentration of transition from unordered to ordered magnetic state decreases down to the value equal to the percolation threshold.