Calculating the Magnetic Anisotropy of Rare-Earth-Transition-Metal Ferrimagnets

TL;DR

This paper introduces a first-principles method to accurately calculate the temperature-dependent magnetocrystalline anisotropy of rare-earth-transition-metal ferrimagnets, validated by experiments on GdCo$_5$.

Contribution

It presents a novel first-principles approach to determine temperature-dependent anisotropy in RE-TM ferrimagnets, improving upon naive calculations and aligning well with experimental data.

Findings

Naive calculations overestimate anisotropy at 0 K

New approach accurately predicts temperature dependence

Excellent agreement with experimental measurements

Abstract

Magnetocrystalline anisotropy, the microscopic origin of permanent magnetism, is often explained in terms of ferromagnets. However, the best performing permanent magnets based on rare earths and transition metals (RE-TM) are in fact ferrimagnets, consisting of a number of magnetic sublattices. Here we show how a naive calculation of the magnetocrystalline anisotropy of the classic RE-TM ferrimagnet GdCo$_5$ gives numbers which are too large at 0 K and exhibit the wrong temperature dependence. We solve this problem by introducing a first-principles approach to calculate temperature-dependent magnetization vs. field (FPMVB) curves, mirroring the experiments actually used to determine the anisotropy. We pair our calculations with measurements on a recently-grown single crystal of GdCo$_5$, and find excellent agreement. The FPMVB approach demonstrates a new level of sophistication in the use of first-principles calculations to understand RE-TM magnets.