Net anisotropy and ferromagnetic resonance frequency of an amorphous ferromagnet

Abstract

The net anisotropy constants and the ferromagnetic resonance (FMR) frequency are calculated in a model of amorphous ferromagnetism for which the axes of strong local uniaxial anisotropy are nearly randomly oriented throughout the sample, and, consequently, the equilibrium directions of local magnetization are nonuniform. A slight preferential ordering produces net anisotropy perpendicular to the plane of a thin film sample as appropriate to sputtered Gd‐Co films. The net anisotropy is a maximum for a given HA near HA/HE=1.5, where HA and HE are the local anisotropy and exchange fields, and at HA/HE=10 it is about 3 times less than its value for HA/HE→0, corresponding to uniform magnetization. The FMR resonance frequency ω would contain a term of the order of H2PdA/HE, which can be comparable to the net anisotropy field 〈HA〉, if the magnetization were uniform, but this term cancels out if proper account is taken of the nonuniformity. As a result, ω is the same as would be computed for a uniform anisotropy field 〈HA〉.