Magnetization and remagnetization of anisotrophic magnetically hard ferrites

Magnetization curves and hysteresis loops of anisotropic hard ferrites were analyzed after the specimens had been demagnetized either thermally or by an ac field parallel or perpendicular to the preferred axis (PA) between -196°C and Curie temperature, or by a dc field. Each demagnetization yields a specific magnetization curve; below saturation fields, asymmetrically positioned and noncentrosymmetrical loops develop, except after ac demagnetization at 20°C (=measuring temperature) parallel to PA. This is due to domain configurations differently arranged and of different stability. The asymmetry is caused by "frozen" unstable configurations, which undergo an irreversible change due to the action of the field. Therefore, with reversed field not all of the previous possibilities for remagnetization are still available.