Theory of field induced spin reorientation transition in thin Heisenberg films

TL;DR

This paper develops a generalized theoretical approach to analyze the spin reorientation transition in thin ferromagnetic Heisenberg films under arbitrary external magnetic fields, achieving excellent agreement with quantum simulations.

Contribution

It introduces a generalized Callen decoupling method applicable for any external field direction, extending previous analytical limitations.

Findings

The new theory accurately predicts field-induced reorientation at finite temperatures.

Results show strong agreement with Quantum Monte Carlo data.

The temperature dependence of the transition is thoroughly analyzed.

Abstract

We consider the spin reorientation transition in a ferromagnetic Heisenberg monolayer with a second order single ion anisotropy as a function of temperature and external field. Up to now analytical methods give satisfying results only for the special case that the external field is aligned parallel to the easy axis of the crystal. We propose a theory based on a generalization of the Callen decoupling, which can be used for arbritrary direction of the external field. Excellent agreement between our results and Quantum Monte Carlo data is found for the field induced reorientation at finite temperatures. Additionally, we discuss the temperature dependence of the transition in detail.