Angular dependence of auto-oscillations in YIG

Abstract

High-power, perpendicular, ferromagnetic resonance (FMR) in thin yttrium-iron-garnet (YIG) disks produces fingerlike regions of auto-oscillation as a function of static field and excitation power. These fingers are associated with the magnetostatic modes found in the low-power FMR spectra and are characterized by their onset frequency (1–10 MHz) and excitation power (2–15 dBm). Using a 9.22 GHz excitation source, the characteristics of the first finger have been examined as the static field is rotated away from the perpendicular orientation. This has been done at room temperature for four samples of varying characteristics. Very little sensitivity exists in the onset frequency within 4° of perpendicular, while in the same range a slight variation in onset power has been observed. In general, the onset frequency has been found to decrease as the static field rotates away from perpendicular. Results for the onset attenuation are inconclusive. Numerical results based upon a microscopic Hamiltonian derived for the perpendicular orientation have been examined for two of the samples to provide a first approximation of the observed spin-wave dynamics. The experimentally observed trend in onset frequency has been reproduced. A region in which the nature of the observed auto-oscillations changes dramatically has been found in three of the samples at roughly 15° off perpendicular. This region may be the result of the increased coupling of the magnetostatic modes to an increasing number of short-wavelength spin waves as the static field is rotated and the system rises above the bottom of the spin-wave band.