Ferromagnetic resonance studies of anisotropy in PtCo multilayers

Abstract

We report on K-band ferromagnetic resonance studies made on a sequence of PtCo multilayer films. Two principal results emerge: (a) the angular dependence of the resonance fields can be fitted only by a combination of second and fourth order anisotropy: E = Keff sin2 θ+ K4 sin4 θ, and (b) an additional resonance was observed at fields below the major resonance position in some of the specimens. Although these latter spectra were observed about the surface normal only over a restricted angular range, we were able to fit these lines as well with a combination of second- and fourth-order anisotropy. In each case the integrated absorption intensity of the secondary spectrum, when present, was comparable to that of the primary resonance. The physical origin of these additional spectra is not yet entirely clear.