Abstract
Time resolved Kerr microscopy has been used to investigate the magnetisation reversal dynamics in thin (50 nm) epitaxial Fe/GaAs(001). Real time measurements of the magnetic switching in a 10 μm-diameter spot on the Fe film surface have been made at selected values of sinusoidal applied field frequency f in the range 0.3–30 kHz, and distributions of coercive field H c and domain wall speed parameter have been generated in each case. The Kerr response indicates that at low-field sweep rates ( f<3 kHz) domain walls jump in a random fashion between pinning sites, whilst at higher sweep rates ( f≈3 kHz) they are driven quasi-continuously through the laser spot. As f is increased, the distribution of coercive fields becomes more sharply peaked about the mean. This is consistent with the observation of discontinuous Barkhausen-like domain wall jumps at low-field sweep rates and field-driven, quasi-continuous switching at high sweep rates. On the scale of individual domain wall movements, the probability distribution of the wall speed parameter remains strongly skewed towards lower values even at high f, indicating that stochastic behaviour persists. This emphasises that the Kerr response is dictated by probe size and can give direct information on individual reversal events only down to the spatial resolution limit.
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