Antidot density dependence of magnetization reversal dynamics in ultrathin epitaxial Fe/GaAs(001

Easy axis dynamic magneto-optic Kerr effect loops have been measured from ultrathin (2 nm) epitaxial Fe/GaAs(001) films patterned with arrays of 1 mum square antidots of different densities (antidot spacings 10-50 mum). The applied field was sinusoidal with frequency f = 0.01 Hz-2.3 kHz. A study of dynamic coercivity H-c* as a function of f reveals an intermediate dynamic regime (20 Hz < f < 1000 Hz) characterized by a dip in H-c* that is suppressed at high antidot density. The dip is attributed to timescale matching of the sweeping applied field with the domain wall propagation in the film. Suppression of the dip is explained by an increase of domain nucleation in the higher antidot density films in the intermediate dynamic regime.