Cluster creation and hysteresis in soft-ferromagnetic thin-film objects

The hysteresis in soft-magnetic thin-film objects, caused by the domain-wall fields induced by the magnetic charge in the wall cores is discussed. This charge is required for balancing the exchange torques here. It is shown that the domain walls arrange themselves systematically during the build-up phase of domain structures. A central part is reserved for the cluster-creation process, in which, in the incipient phase, a number of domain walls coincide with the same orthogonal trajectory of the magnetization field. These low-angle walls are of the Néel-type and it is shown that, in the domains, the fields from these cores are globally oriented in the direction of the external field, whose amplitude is gradually decreasing in the construction phase of the domain structure. The lag in the magnetization distribution due to this wall field is calculated for the so-called concertina structure in a rectangular bar. It is shown that the total Maxwell field is zero inside the domains, so that the required charge for compensating is located at the object\´s bounding surfaces. This surface-charge pattern is numerically calculated and the related hysteresis in the object\´s magnetization for the given domain structure - the concertina - is derived. A satisfactory agreement between theoretical predictions and experiments has been achieved.