Erase/restorable asymmetric magnetization reversal in polycrystalline ferromagnetic films

Asymmetric hysteresis loops are generally found in exchange-coupled ferromagnetic/antiferromagnetic layers or composite. Once the film is deposited the magnetization reversal behaviour becomes certain due to the fixed anisotropy of the film. We report an asymmetric magnetization reversal, which is erase/restorable in polycrystalline soft magnetic film. When the film is pre-saturated at a high field in the induced uniaxial easy direction, the asymmetric hysteresis loops with one branch governed by coherent rotation and another branch with kink induced by mixed reversal mechanism of coherent rotation and rotation/180°-domain-wall-motion/rotation are obtained. If the film is presaturated in the induced hard axis, the kink disappears and normal hysteresis behaviour is observed instead. Such asymmetric magnetization curve can be restored if the film is pre-saturated in the easy axis again. The observed phenomenon is originated from an embedded second magnetically hard phase which tunes the anisotropy in the film.