Thermal evolution of first-order magnetization processes in the single-ion one-sublattice system with uniaxial anisotropy

Abstract

The thermal evolution of first-order magnetization processes (FOMP's) is intensively studied within a description of the anisotropy energy of a single-ion one-sublattice system with two or three anisotropy constants. By following the temperature-induced trajectories in the anisotropy-parameter plane, all possible types of thermal evolution of the FOMP are detected by an effective parameter method in the mean-field approximation. Within the two-constant approximation, three types of thermal behavior of the FOMP are found. Within the three-constant approximation, 12 types are found when the zero-temperature second-order anisotropy constant K-1(0) is positive, and 14 types when K-1(0) is negative. Phase diagrams for the existence condition of thermal behavior of the FOMP are given in the zero-temperature anisotropy space in combination with analytical and numerical calculations. For each type of variation of the FOMP, an example is selected to describe the temperature dependence of the normalized amplitude and the critical field of the magnetization jump. The relation between the type of variation of the FOMP and the spin-reorientation transition is discussed in detail.