Field sweep rate dependence of domain-wall speed distributions in a thin Ni80Fe20 film

The magnetization reversal in a thin (100 nm) Ni80Fe20/GaAs(001) film prepared by molecular-beam epitaxy has been investigated using a focused spot Kerr magnetometer. The field was sinusoidal and applied along an in-plane easy axis, with sweep rate at the coercive point in the range ∼1 kOe/s-1 MOe/s. Real time measurements of the Kerr response enabled a study of the probability distributions P(V) of the domain-wall speed as a function of sweep rate. The shape of P(V) changes from being characteristic of stochastic domain-wall motion at low sweep rate to being characteristic of quasicontinuous domain-wall motion at high sweep rate. Increasing the diameter of the focused spot from 2 to 80 μm increases the number of domain walls participating in the reversal within the probed area, which leads to an averaging effect and dulls the transition from stochastic to quasicontinuous wall motion seen in the probability distributions