Damping as a function of pulsed field amplitude and bias field in thin film Permalloy

We have measured the step response in thin film Permalloy as a function of both a hard-axis pulsed field amplitude and an easy-axis longitudinal magnetic bias field using a pulsed inductive microwave magnetometer. The bias field ranged from 0 to 8000 A/m (0 to 100 Oe) and the pulsed field varied from 0.32 to 320 A/m (0.004 to 4 Oe). The rotation angle of the equilibrium magnetization direction varied from 0.002° to 40° for this range of field values. Data were analyzed to extract the Gilbert damping parameter, α. The damping parameter decreased monotonically with an increase in longitudinal bias field. However, there is no observed dependence of α on the pulse amplitude, indicating that the damping is independent of the angle of rotation. We conclude that there is no significant nonlinear generation of spin waves that affects the damping in the case of free induction decay for the range of field pulses employed.