Phase transitions in rare-earth ferrimagnets with surface anisotropy near the magnetization compensation point

TL;DR

This paper presents a theoretical model for phase diagrams of rare-earth ferrimagnets considering surface anisotropy, revealing tricritical points and phase transition modifications due to surface effects.

Contribution

It introduces a new theoretical approach to analyze surface anisotropy effects on phase transitions in ferrimagnets, including the formation of exchange springs.

Findings

Identification of tricritical points influenced by surface anisotropy.

Reduction of first order transition lines due to surface effects.

Prediction of first order transitions between collinear phases with perpendicular magnetic field.

Abstract

We report of a theoretical model for calculating the H-T phase diagrams of a rare-earth ferrimagnet, taking into account anisotropies originated by both magnetization sublattices' and by the surface. The possibility of an exchange spring formation due to surface anisotropy is considered. This situation is realized in heterostructures containing a ferrimagnet and a heavy metal. We derive the stability lose lines of the collinear phase from the free energy of the two sublattice ferrimagnet. We numerical calculate the magnetic phase diagrams for the cases when the magnetic field applied along and perpendecular to the easy axis. We demonstrate that tricritical point down at the low field range due to surface anisotropy effect. Moreover, the line of the first order phase transition between angular and collinear phases reduces due to surface anisotropy. In the case when magnetic field is applied perpendicular to the easy axis we show the possibility of the first order phase transition between two collinear phases in contrast to the phase diagram without surface anisotropy.