Net anisotropy and ferromagnetic resonance frequency of an amorphous ferromagnet

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 H/sub A/ near H/sub A/ H/sub E/ = 1.5, where H/sub A/ and H/sub E/ are the local anisotropy and exchange fields, and at H/sub A//H/sub E/ = 10 it is less than its value for H/sub A//H/sub E/ → 0, corresponding to uniform magnetization. The FMR resonance frequency ω would contain a term of the order of H2/sub A//H/sub E/, which can be comparable to the net anisotropy field (H/sub A/), 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 (H/sub A/)