Extraordinary power and modulation dependence of the auto-oscillation frequency in tangentially magnetized YIG films

The power dependence of auto-oscillations (AO) in yttrium-iron-garnet (YIG) film within a cavity is studied experimentally. We demonstrate that the dependence of the AO frequency on the pumping power is not always positive as commonly observed and calculated. We find DC magnetic field regions where the power dependence is negative. This behavior is extraordinary as it happens under pumping powers very close to the threshold, where the power dependence is supposed to be positive. Besides we demonstrate that the dependence of the AO frequency on the modulation amplitude of the DC magnetic field is not always negative as might be expected. At certain regions of the field we observe a positive dependence. This positive dependence on the modulation amplitude is consistent with the negative power dependence.