COERCIVITY MECHANISMS IN HARD MAGNETIC-MATERIALS

In permanent magnetic materials magnetization reversal does not take p lace by coherent and global rotation. No collective processes are invo lved when the energy barrier implicated in the reversal is of magnetoc rystalline nature acting at the atomic level. The mechanism by which m agnetization reversal occurs involves several events which are inheren tly linked to the presence of defects. These events, nucleation, propa gation and pinning - depinning of a domain wall, are strongly linked t o the microstructure. The liaison between magnetization reversal mecha nisms and microstructure is still poorly understood. Four types of mag netic characterization are used (temperature dependence of the coerciv e field, angular dependence of the coercive field, magnetic viscosity and the direct evaluation of dipolar fields) where the analysis may or may not be based on a model.