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 Kerr effect. The hysteresis loop area A is found to follow the scaling relation A proportional to H-alpha, with cu in the range 0.032+/-0.003-0.049+/-0.003 at low sweep rates (below 6.3 kOe/sec) and 0.325+/-0.006-0.399+/-0.008 at high sweep rates (above 16 kOe/sec). The differing values of the exponent alpha are attributed to a change of the magnetization reversal process with increasing field sweep rate. Domain wall motion dominates the magnetization reversal at low sweep rates, but becomes less significant with increasing sweep rate. At high sweep rates, the variation of the dynamic coercivity H*(c) is attributed to domain nucleation dominating the reversal process. The results of magnetic relaxation studies for easy-axis reversal are consistent with the sweeping of one or more walls through the entire probed region (-100 mu m). Domain images obtained by scanning Kerr microscopy during the easy cubic axis reversal process reveal large area domains separated by zigzag walls.