Nonequilibrium Three-magnon Scattering of Ferromagnetic Resonance in YIG Thin Films

In thin films, large ferromagnetic resonance (FMR) amplitudes excite the first order Suhl instability, a nonlinear regime where FMR undergoes three-magnon scattering to two modes of half the frequency and wavevectors ±k. Despite its applicability to magnon BECs, magnonics, and other fields, a comprehensive study and formal model of the nonequilibrium behavior is lacking. We have developed an experimental technique for sensitive detection of the time-evolution of the FMR amplitude over five orders of magnitude in power, which provides a highly comprehensive view of the three-magnon scattering process. Applying this technique to 3μm thick YIG thin films, we observe strong agreement with results from micromagnetic simulations. We also developed a semianalytical model to describe the nonequilibrium three-magnon scattering process. This model shows quantitative agreement with the experiment and simulations, including the timescales of the instability (~100ns-1us), a new secondary nonlinear regime with MHz-frequency oscillatory behavior, and the scaling of this oscillation frequency with power. At high powers, we find broadening of the oscillation spectra correlated to the simulations’ onset of higher-order scattering processes. Additional findings will also be discussed.