Dependence of the coercive field and magnetic viscosity coefficient in NdFeB magnets on the magnetic history of the sample

The dependence of the coercive field H/sub c/ and magnetic viscosity coefficient S/sub v/ on an initial magnetizing field H/sub init/ are determined in NdFeB sintered and MQII magnets. In sintered magnets, coercivity progressively develops as H/sub init/ is increased. The variation of S/sub v/ is attributed to different values of the activation volume for different grains. The variation of the coercive field deduced from the variation of the coercive field deduced from the variation of the activation volume corresponds to the experimental one. In MQII magnets, the high field part of the first magnetization curve is shown to be determined by the same irreversible processes which govern the magnetization processes on the hysteresis loop. The field dependence of the magnetization and of the magnetic viscosity coefficient S/sub v/ are analyzed assuming that the angular dependence of the coercive field obeys a simple 1/cos Θlaw