Demagnetization Process of Nd-Fe-B Sintered and Ferrite Magnets

The magnetization reversal mechanism for Nd-Fe-B sintered and ferrite magnets was investigated using magnetic measurements and soft X-ray magnetic circular dichroism microscopy. In magnetization reversal, discrete reversals of crystal grains occurred first in the demagnetized field region, which was lower than the coercivity. In the next step, clusters of reversed grains were formed by reversals in crystal grains around the discrete reversed grains. For highly aligned magnets, the cluster sizes at the coercivity increased with decreasing temperature, and also varied with composition. The alignment and angular dependences of the coercivity varied with cluster size, which depended on the number of discrete magnetization reversal grains that occurred in the demagnetizing field that was lower than the coercivity. Hence, if the number of discrete reversal grains was large, the cluster size was small; conversely, if the number of discrete reversal grains was small, the cluster size was significant. (c) 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.