Reversible permeability enhanced by Barkhausen jumps in ferromagnetic samples exhibiting a strong magnetic aftereffect

Reversible permeability increases associated with irreversible displacements of Bloch walls are here studied on iron flat rings exhibiting a strong magnetic aftereffect. Measurements are taken by means of an ac bridge while irreversible processes are produced by a constant field Horotating in the plane of the sample. The increases of both real μ\´ and imaginary part μ" of complex permeability are observed, for different rotational frequencies of Ho, as a function of frequency and amplitude of the measuring field. The data obtained indicate that the complex permeability increases through reversible and irreversible contribution. The reversible contribution is caused by the occurrence of "excited" Bloch walls, the number of which is the greater the stronger the aftereffect of the sample. The irreversible contribution is due to the possibility that the measuring field will produce irreversible jumps of most "excited" walls.