We report the results of a numerical test of the coherent-anisotropy-field approximation (CAFA) for characterizing the high-field limit of the magnon spectrum for a lattice model of a ferromagnet with random anisotropy axes. The CAFA reproduces the downward shift in the ferromagnetic resonance frequency and accounts for the modification of the density of states induced by the disorder. The agreement confirms the analogy between the random-axis model in the high-field limit and the potential fluctuation model for the random-alloy problem.

• Received 10 May 1989

DOI:https://doi.org/10.1103/PhysRevB.40.2578