Magnetization reversal dynamics in epitaxial Fe/GaAs(001) thin films

The magnetization reversal dynamics of epitaxial Fe films grown on GaAs(001 ) (thickness range 55-250 Angstrom) has been investigated as a function of field sweep rate H in the range 0.01-160 kOe/sec using the magnetooptic Ker r effect. The hysteresis loop area A is found to follow the scaling relatio n A proportional to H-alpha, with cu in the range 0.032+/-0.003-0.049+/-0.0 03 at low sweep rates (below 6.3 kOe/sec) and 0.325+/-0.006-0.399+/-0.008 a t high sweep rates (above 16 kOe/sec). The differing values of the exponent alpha are attributed to a change of the magnetization reversal process wit h increasing field sweep rate. Domain wall motion dominates the magnetizati on reversal at low sweep rates, but becomes less significant with increasin g sweep rate. At high sweep rates, the variation of the dynamic coercivity H*(c) is attributed to domain nucleation dominating the reversal process. T he results of magnetic relaxation studies for easy-axis reversal are consis tent with the sweeping of one or more walls through the entire probed regio n (-100 mu m). Domain images obtained by scanning Kerr microscopy during th e easy cubic axis reversal process reveal large area domains separated by z igzag walls.