A time-resolved ferromagnetic resonance technique was used to investigate the nonlinear magnetization dynamics of a 10 nm thin PermalloyTM film in response to a sequence of large-amplitude field pulses. The magnetic field pulse sequence was set at a repetition rate equal to the magnetic system's resonance frequency. Both inductive and optical techniques were used to observe the resultant magnetization dynamics. We compared data obtained by this technique with conventional pulsed inductive microwave magnetometery. The results for damping and frequency response obtained by these two different methods coincide in the limit of a small-angle excitation. However, when applying large amplitude field pulses, there was a substantial increase in the apparant damping. Analysis of vector-resolved magnetic second-harmonic generation data indicate the the increase in damping is correlated with a decrease in the spatial homogeneity of the magnetization dynamics. This suggests that unstable spin wave generation occurs in the limit of large-amplitude dynamics.
Physical Review B (Condensed Matter and Materials Physics)
ferromagnetic resonance, magnetization dynamics, spin waves, Suhl instability