Ferromagentic resonance foldover in single crystal YIG films--Sample heating or suhl instability

Foldover and linebroadening effects have been observed in 500 µm diameter, 7.9 µm thick yttrium iron garnet single crystal films at 9.18 GHz and room temperature. The distortions in lineshape and field shifts of the prominent FMR curve features were a strong function of the microwave power level and duty cycle. At high duty cycles, distortions and shifts were quite similar to those reported by previous authors and attributed to sample heating. As the duty cycle is reduced, however, the characteristic foldover profiles evolve into a simple line broadening without appreciable foldover. This linebroadening occurs at power levels which are on the order of the expected Suhl threshold.