Realistic finite temperature simulations of magnetic systems using quantum statistics

TL;DR

This paper introduces a method for realistic finite-temperature magnetic system simulations using quantum statistics, improving low-temperature accuracy over classical approaches and applicable to various materials.

Contribution

The paper presents a novel simulation approach incorporating quantum Bose-Einstein statistics, enhancing the modeling of magnetic properties at low temperatures.

Findings

Improved magnetization and specific heat modeling at low temperatures.

Method accurately describes various magnetic materials including alloys and ferrimagnets.

No restrictions on chemical or magnetic order in the simulations.

Abstract

We have performed realistic atomistic simulations at finite temperatures using Monte Carlo and atomistic spin dynamics simulations incorporating quantum (Bose-Einstein) statistics. The description is much improved at low temperatures compared to classical (Boltzmann) statistics normally used in these kind of simulations, while at higher temperatures the classical statistics are recovered. This corrected low-temperature description is reflected in both magnetization and the magnetic specific heat, the latter allowing for improved modeling of the magnetic contribution to free energies. A central property in the method is the magnon density of states at finite temperatures and we have compared several different implementations for obtaining it. The method has no restrictions regarding chemical and magnetic order of the considered materials. This is demonstrated by applying the method to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co random alloys and the ferrimagnetic system GdFe$_3$ .