The influence of demagnetization on the domain structure of hard magnetic materials

The remanent states after thermal and ac demagnetization (TD and ACD), dc and ac magnetization curves as well as the influence of the demagnetization temperature and magnetic field on the domain structure, were investigated on a small specimen of aluminium substituted strontium hexaferrite single crystal. It was found that the domain structure after ACD consists of a few domains only, while after TD it consists of a great number of domains with irregular Bloch walls. The TD states are very unstable and a transition to a similar ACD occurs in a field of about 50 Oe. These results were explained in terms of a simple model which takes into account the existence of magnetic inhomogeneities spread within the specimen.