Simultaneous measurement of surface and bulk vector magnetization dynamics in thin Ni-Fe films

The dynamics of the surface and "bulk" magnetization vectors of a Ni-Fe thin film were measured using the time-resolved second harmonic and linear magnetooptical Kerr effects. Films of 50, 250, and 400 nm thickness were measured. The magnetization dynamics of the surface and "bulk" in response to a pulsed torque field were effectively the same for all thicknesses, indicating that any induced eddy currents do not appreciably screen the interior of the film from the incident magnetic field at these thicknesses. The magnetization angle also showed both a large, fast (<1 ns) initial response to an applied field pulse, and then a slower (much greater than10-100 ns) "viscous" creep toward its dc value. Possible mechanisms for these observations are discussed.