Foldover in YIG

We have observed distinct and repeatable FMR foldover effects in specimens of pure YIG at modest microwave power levels (1–10 dBm). Our samples were small disks (8.5 μm thick, 300 μm diameter) fabricated by photolithography from a YIG film deposited by LPE on a GGG substrate. The effect was observed at GHz frequencies using a microstrip transmission line and was also detected using X-band cavity and waveguide systems. We demonstrate that the effects that we have seen are not thermal or spin-wave-type foldover but are related to the disk shape anisotropy. In addition to observing foldover in the uniform precession mode, we have also seen foldover in the excitable magnetostatic modes associated with the disk geometry.