The nonlinear dynamics of the main magnetoexchange branch of a circular thin (0.45 μm) film of yttrium iron garnet are investigated at perpendicular resonance. Distinct ‘‘fingers of auto-oscillation’’ arise from each magnetoexchange mode in the low-power spectrum. A set of equations of motion derived from a microscopic Hamiltonian are integrated to compare with experiment. In the first finger, the model predicts the power for onset of auto-oscillation to within 1 dB of the experiment and the frequency to within 15%.

• Received 20 October 1989

DOI:https://doi.org/10.1103/PhysRevLett.64.64