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The measurements were made with a high power spectrometer at a nominal frequency of 10 GHz for in-plane and perpendicular-to-plane magnetized 100 – 300 nm thick permalloy films. The data show a clear saturation of the uniform mode FMR line and, in addition, a broad subsidiary absorption peak below the FMR field. All of these effects occur for relatively low powers, small microwave field amplitudes, and small precession angles.
Measurements of the threshold field versus static field H profiles, called “butterfly curves”, in the subsidiary absorption region show a distinct structure and a characteristic high field divergence points which mark the low frequency band edge of the spin wave band at one-half the pump frequency for the film under test. A theory of spin wave instability processes in thin films has also been developed. Fits to the data give new information on the wave vector dependence of the spin wave linewidth and relaxation rate in thin films, as well as the critical modes for the instability response.
This work was supported in part by the National Science Foundation, DMR-0108797, the United States Office of Naval Research, N00014-03-1-0070, the United States Army Research Office, DAAD19-02-1-0197, and the National Institute of Standards and Technology Nanomagnetodynamics Program