Time resolved Kerr microscopy: Magnetization dynamics in thin film write heads

We have used a scanning Kerr microscope set-up with picosecond time resolution and submicron spatial resolution to directly measure the flux response in magnetic recording heads. The data rate limiting factor of a write head, which is the flux rise time at the gap, has been measured for different geometries and head materials in polar Kerr mode. Flux propagation in the yoke, which is governed by a combination of wall displacement and magnetization rotation, has been studied by one dimensional and two dimensional time response measurements utilizing the longitudinal Kerr effect. The local flux time response in the head was correlated to the respective micromagnetic structure as determined by static wide-field Kerr imaging. In addition to the intrinsic magnetic properties we have also studied the flux time response by looking at the system properties of the head/write-electronic and, by using a voltage source for excitation, information about classical eddy-current effects for different pole geometries have been derived. Further, non-stationary effects in the flux reversal process are shown to produce non-linearities in the response at the write gap which are contributing to non-linear transition shift in the write process.