Phase transitions in a ferromagnet with biquadratic exchange and hexagonal single-ion anisotropy

Abstract

The phase states and the spectra of elementary excitations of a ferromagnet with a biquadratic exchange interaction and a spin-2 magnetic ion are investigated. The phase diagrams of the system are constructed for different relationships among the material constants. It is shown that the phase diagram is substantially altered at large values of the single-ion anisotropy constants and biquadratic exchange constant.