Ferromagnetic resonance foldover and spin-wave instability in single-crystal YIG films

Foldover in ferromagnetic resonance (FMR) has been theoretically investigated. The objective was to calculate field shifts for the FMR shoulder associated with foldover, following the analysis of E. Schlomann (1959), and to make a detailed comparison with perpendicular FMR data recently published by Y.T. Zhang et al. (1988). The observed shifts were somewhat smaller than predicted theoretically on the basis of a single low-power FMR linewidth. However, the theory could be fitted to the data by allowing the effective resonance linewidth to increase with the microwave power level. Such an increase in the effective resonance linewidth is consistent with the increase in losses that is known to occur at high power levels