Rare-earth/transition-metal magnets at finite temperature: Self-interaction-corrected relativistic density functional theory in the disordered local moment picture

TL;DR

This paper develops a new computational approach combining disordered local moment theory and self-interaction-corrected density functional theory to accurately model the magnetic properties of rare-earth transition-metal magnets at finite temperatures.

Contribution

It introduces a novel framework that effectively captures thermally induced magnetic disorder and localized 4f electron effects in rare-earth magnets, improving predictive accuracy.

Findings

Reproduces experimental trends in magnetic moments and Curie temperatures across RECo5 series.

Identifies SmCo5 as having the strongest high-temperature magnetic properties among studied compounds.

Highlights the significant influence of rare-earth elements on Co--Co magnetic interactions.

Abstract

Atomic-scale computational modeling of technologically relevant permanent magnetic materials faces two key challenges. First, a material's magnetic properties depend sensitively on temperature, so the calculations must account for thermally induced magnetic disorder. Second, the most widely-used permanent magnets are based on rare-earth elements, whose highly localized 4$f$ electrons are poorly described by standard electronic structure methods. Here, we take two established theories, the disordered local moment picture of thermally induced magnetic disorder and self-interaction-corrected density functional theory, and devise a computational framework to overcome these challenges. Using the new approach, we calculate magnetic moments and Curie temperatures of the rare-earth cobalt (RECo$_5$) family for RE=Y--Lu. The calculations correctly reproduce the experimentally measured trends across the series and confirm that, apart from the hypothetical compound EuCo$_5$, SmCo$_5$ has the strongest magnetic properties at high temperature. An order-parameter analysis demonstrates that varying the RE has a surprisingly strong effect on the Co--Co magnetic interactions determining the Curie temperature, even when the lattice parameters are kept fixed. We propose the origin of this behavior is a small contribution to the density from $f$-character electrons located close to the Fermi level.