Application of two-sublattice bilinearly coupled Heisenberg model to the description of certain ferrimagnetic materials

TL;DR

This paper models ferrimagnetic materials using a two-sublattice Heisenberg framework, revealing phase transitions, a compensation point, and the coexistence of collinear and non-collinear phases through Landau theory.

Contribution

It introduces a phenomenological approach applying Landau energy derived from a two-sublattice Heisenberg model to describe ferrimagnetic phase diagrams and transitions.

Findings

Second-order phase transitions with a compensation point.

Presence of a metastable non-collinear phase.

Detailed temperature dependence of magnetization.

Abstract

We study phenomenologically on the basis of two bilinearly coupled Heisen- berg models the phase diagram of some ferrimagnetic substances. Calculations are performed with the help of Landau energy obtained through applying the Hubbard-Stratonovich transformation to the initial microscopic Heisenberg Hamiltonian. The phase transitions within the model are of second order with the emergence of a compensation point at lower temperatures for some values of parameters of the system. The main phase is a two-sublattice collinear ferrimagnet but also a metastable non-collinear phase is present within the exchange approximation presented here. The numerical results give a detailed description of temperature dependence of magnetization on the strength of in- tersublattice interaction and the difference between the effective exchanges of two ferromagnetically ordered sublattices.