Transmission Electron Microscopy Study on the Grain Boundaries and Magnetic Domains in Nd–Fe–B Based Magnets

Abstract

The effect of post-sintering heat treatment on the coercivity of Nd–Fe–B based permanent magnets was studied by observing their crystallographic and magnetic microstructures. High-resolution transmission electron microscopy revealed meandering grain boundaries in the as-sintered state, and the smoothness of the boundaries was improved by the post-sintering heat treatment. Electron holography demonstrated that magnetization reversal occurred in a stepwise manner in individual grains in the specimen subjected to the post-sintering heat treatment, whereas reversal was occurred simultaneously in different grains in the as-sintered specimen.