Isotropic magnetoelastic interaction and the pressure-induced first-order magnetic phase transition in CoS2

Abstract

The change in the order of the magnetic phase transition in ferromagnetic CoS2 under pressure recently revealed by Goto et al. [Phys. Rev. B56, 14019 (1997)] is explained in terms of an exchange-magnetostriction model that takes into account the magnetoelastic interactions (MEI) of the first and second order with respect to volume deformations. Using numerical values of MEI constants determined from experimental data, the equilibrium and nonequilibrium magnetic phase diagrams have been calculated for CoS2 in the space of variables T (temperature), P (pressure), and H (magnetic field). The temperature dependence of magnetization at various pressures and the magnetization isotherms have been calculated. The results of the calculations show satisfactory agreement with experiment. Analytical expressions for the critical magnetic field and temperature of the first-order magnetic phase transition (FOMPT) and for the FOMPT curve in a magnetic field at a constant pressure have been obtained. The effect of an applied magnetic field on the characteristics of the FOMPT are analyzed.