Changes of reversible permeability associated with irreversible displacements of bloch walls

Measurements of reversible permeability were made on ferromagnetic specimens, in which irreversible processes were produced either by elastic strains or by rotational magnetization. It was found that, generally, there is a temporary increase of reversible permeability when irreversible processes are produced ; that permeability increases with the amount of irreversible processes per unit time, finally, approaching a saturation value of about twice the normal reversible permeability. The continuous production of irreversible processes by this method makes the sample exhibit magnetic properties very similar to those of a material whose reversible permeability is much higher. Finally, the possibility, that these permeability increases have been ascribed either to an increased mobility of Bloch walls or to a direct contribution of irreversible processes, is discussed.