Relevance of $4f$-$3d$ exchange to finite-temperature magnetism of rare-earth permanent magnets: an ab-initio-based spin model approach for NdFe$_{12}$N

TL;DR

This paper develops an ab initio-derived classical spin model for NdFe$_{12}$N, revealing insights into its finite-temperature magnetism and suggesting engineering strategies to improve its magnetic properties for practical applications.

Contribution

It introduces a realistic spin model for NdFe$_{12}$N$ derived from first principles, advancing understanding of its magnetic behavior and potential enhancement methods.

Findings

Temperature-dependent magnetization matches experimental data.

Anisotropy field behavior aligns with observations.

Proposed $5d$-electron-mediated exchange as a key to improvement.

Abstract

A classical spin model derived ab initio for rare-earth-based permanent magnet compounds is presented. Our target compound, NdFe$_{12}$N, is a material that goes beyond today's champion magnet compound Nd$_{2}$Fe$_{14}$B in its intrinsic magnetic properties with a simpler crystal structure. Calculated temperature dependence of the magnetization and the anisotropy field agree with the latest experimental results in the leading order. Having put the realistic observables under our numerical control, we propose that engineering $5d$-electron-mediated indirect exchange coupling between $4f$-electrons in Nd and $3d$-electrons from Fe would most critically help to enhance the material's utility over the operation-temperature range.