Magneto-optical observation of four-wave scattering in a 15-nm Ni₈₁Fe₁₉ film during large-angle magnetization precession

Large-angle magnetization precession induced by a short pulsed magnetic field in a 15-nm thick Ni₈₁Fe₁₉ film is observed by use of a time-resolved magneto-optical Kerr effect technique with sensitivity to all three components of the magnetization vector. A reduction of the magnitude of the magnetization vector |M| during large-angle precession is inferred and indicates incoherent dynamics due to excitation of traveling spinwaves with wavelengths smaller than the diameter of the sampling area, that is, the laser spot size for the magneto-optical measurements. The reduction in |M| depends on the magnetic bias field Hbias, which can be qualitatively understood by comparison to the theoretical threshold for observing four-magnon scattering in a small time interval t. We estimate that two-magnon scattering cannot explain the experimental results.