Creep in magnetic films, a phenomenological theory

A phenomenological theory of creep is proposed which relates the threshold for creep and the creep distance per cycle of applied transverse field to film material parameters. The model accommodates both quasi-static and dynamic effects. Key parameters in the theory relate to wall energy, material inhomogeneity, and the variation of wall contour, shape, and width with the application of transverse fields. The model assumes an abrupt creep threshold, a creep distance per cycle of transverse field which is typically a fraction of the wall width, and a creep distance per cycle of transverse field which is linear in the magnitude of the transverse field in the neighborhood of the threshold fields. A mechanical analog of the simple linearized theory has been constructed to demonstrate creep properties. In the model energetic binding of a wall to film inhomogeneities is replaced by mechanical friction, the energy storage properties of the walls by elastic bodies, and the driving fields by mechanical forces. The mechanical analog clearly demonstrates many of the aspects of creep.