Properties of Permalloy Films Having a Magnetoelastic Easy Axis Normal to the Film

Internal isotropic strain in Permalloy films having a negative magnetoelastic constant creates a magnetoelastic easy axis normal to the film. Below a critical thickness tc such films are single domain in the film plane and have a square B-H loop; above this thickness new configurations are established, characterized by a B-H loop of special form and having relaxation properties. Above tc the Bitter pattern is “mottled” and continues so even in the presence of a 10 000 oe field. A domain structure is proposed in qualitative agreement with experiment; mottling is interpreted in terms of centers of microstrain.