Anisotropy and Inversion in Permalloy Films

Abstract

A phenomenological model of field-induced and oblique-incidence anisotropy in Permalloy films is proposed. It is assumed that the field-induced structure does not introduce any local spatial dispersion in the macroscopic magnetization M; the opposite is assumed for oblique-incidence structure. In addition it is assumed that the oblique-incidence dispersion is anisotropic, being least when M is perpendicular to the depositing beam. Support for the model comes from anisotropies, found for oblique-incidence films only, in the following measurements: resonance line width, transmission of polarized light, and resistivity. A primary success of the model is the prediction of a correlation between anisotropy and inversion (Hw/Hk>1). Inverted films can be made by crossing the field-induced and oblique-incidence anisotropies at 90°. Such films exhibit a “locked”state in which opposite rotation of M in local regions occurs; this implies centers of spatial dispersion and provides the connection with oblique-incidence anisotropy. A method of inducing anisotropy by means of a moving substrate is described. The assumption of local dispersion is shown to apply to this type of anisotropy also. Finally, a guide to understanding the interdependence of Hk and Hw is given in terms of the anisotropy model: field-induced structure does not have any effect on Hw, while oblique-incidence structure can be a primary determinant for Hw.