Searching the weakest link: Demagnetizing fields and magnetization reversal in permanent magnets

TL;DR

This paper uses micromagnetic modeling to identify weak points in permanent magnets where magnetization reversal begins, quantifies thermal effects on coercivity, and highlights the impact of grain boundary phases and misorientation.

Contribution

It introduces a model order reduction approach to map local nucleation fields and assesses thermal activation effects on coercivity in Nd2Fe14B magnets.

Findings

Local nucleation sites can be mapped using micromagnetic models.

Thermal fluctuations reduce coercive fields quantitatively.

Grain boundary phases and misorientation significantly lower coercivity.

Abstract

Magnetization reversal in permanent magnets occurs by the nucleation and expansion of reversed domains. Micromagnetic theory offers the possibility to localize the spots within the complex structure of the magnet where magnetization reversal starts. We compute maps of the local nucleation field in a Nd2Fe14B permanent magnet using a model order reduction approach. Considering thermal fluctuations in numerical micromagnetics we can also quantify the reduction of the coercive field due to thermal activation. However, the major reduction of the coercive field is caused by the soft magnetic grain boundary phases and misorientation if there is no surface damage.