COERCIVITY MECHANISMS IN HARD MAGNETIC-MATERIALS

In permanent magnetic materials magnetization reversal does not take place by coherent and global rotation. No collective processes are involved when the energy barrier implicated in the reversal is of magnetocrystalline nature acting at the atomic level. The mechanism by which magnetization reversal occurs involves several events which are inherently linked to the presence of defects. These events, nucleation, propagation and pinning - depinning of a domain wall, are strongly linked to the microstructure. The liaison between magnetization reversal mechanisms and microstructure is still poorly understood. Four types of magnetic characterization are used (temperature dependence of the coercive 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.