Micromagnetic studies of inhomogeneous nucleation in hard magnets

Nucleation fields of reversed domains in hard magnets with magnetic planar defect are calculated based upon micromagnetism. We show that the reversal processes are classified into three types depending on the parameters characterizing the defect. In a certain region of the parameters, there exists the case where the magnetization in the defect is forced to rotate reversely by an applied field which does not yet bring about the reversal rotation in the host matrices. We suggest that this situation gives a crucial role for the angular dependence of the nucleation fields in Ne-Fe-B sintered magnets.