Second-order magneto-optic effects in anisotropic thin films (abstract)

Abstract

The signal measured in a magneto-optic Kerr effect (MOKE) experiment is normally assumed to be proportional to the component of the magnetization (M) along a certain axis. We have observed significant effects from the M2 term in the magneto-optic response (i.e., in the rotation and/or ellipticity, which can be thought of as the real and imaginary parts of the same quantity) from films with in-plane magnetization and in-plane magnetic anisotropy. These films were: epitaxial Fe(110)/Mo(110) bilayers and multilayers, thin Fe films with ion-bombardment induced anisotropy, Co(110) thin films, and NiFe films with anisotropy induced with a field during deposition. In all of these films, the in-plane anisotropy created a coherently rotating magnetization (as evidenced by measurement of the component of the magnetization perpendicular to the applied field) that contributed a large M2 term to the magneto-optic response when an external field was applied close to parallel to the hard axis of the film. The M2 term in the magneto-optic response changed sign as H was rotated through the hard axis and reached a minimum when H was applied nearly parallel (±0.5°) to the hard axis, thus providing a sensitive indication of the location of the sample’s hard axis.