Thermally Activated Ferromagnetic Domain Wall Motion

Abstract

The properties of small ferromagnetic domains are influenced strongly by thermal agitation if the energies involved in transitions between different states of magnetization (rotations and domain wall movements) are only a few times kT (k being Boltzmann's constant and T the absolute temperature). The study of such small-scale magnetic phenomena, now known as "micromagnetics" (see, for example, Brown 1959a), has developed rapidly in recent years in response to commercial interests in fine powder permanent magnets and thin film memory cores. The possibility of observing directly thermally induced domain wall movements is therefore a matter of some interest. It appears that Olmen and Mitchell (1959) have made such an observation, although they did not specifically claim to have done so. The purpose of this note is to present an elementary theory of thermally activated domain wall motion and to show that the results reported by Ohnen and Mitchell are in agreement with it.