Large-angle magnetization dynamics measured by time-resolved ferromagnetic resonance

A time-resolved ferromagnetic resonance technique was used to investigate the nonlinear magnetization dynamics of a thin 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 magnetometry. 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 apparent damping. Analysis of vector-resolved magnetic second-harmonic generation data indicate that 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.