COERCIVITY ACQUISITION IN PERMANENT-MAGNET MATERIALS - AN EXCHANGE-CONTROLLED MECHANISM

In this work we present an experimental study on the acquisition of coercivity in REFeB (RE = rare earth) finely microstructured hard magnetic materials with grain sizes below the single-domain critical dimensions. By measuring the volume percentage of the samples that became coercive upon application of a given magnetic field, we have obtained the values of the fields required to develop coercivity in 50% of the grains of the hard phase. These fields mere clearly lower than those obtained in previous works for materials of similar composition and larger mean grain size (multidomain grains). In order to account for the experimental behavior, we have considered the results obtained from a, simple model of the evolution with the magnetic field of the moment distribution at the grain boundary regions. From this we suggest that the acquisition of coercivity in our samples is closely linked to the occurrence of exchange-driven, collective magnetization and demagnetization processes.