Observation of a current-induced force on Bloch lines in Ni-Fe thin films

Finite displacements of Bloch lines, induced by current pulses directly traversing the sample, have been observed by the ferrofluid technique in Ni81Fe19 films of thickness 33–68 nm containing cross-tie domain walls. The pulses of duration ≤ 1 μs are normal to the wall. Bloch lines move along the wall whenever the current density exceeds a critical value ≊1×1012 A/m2. It is possible to partly control the sense of the central spin of Bloch lines by applying a field μ0H≊100 μT normal to the film during Bloch-line creation. The sense of the current-induced force on Bloch lines is found to depend on the sense of the central spin of Bloch lines, and agrees with the sense of the theoretically predicted s-d gyroscopic force which arises from s-d exchange. However, the average value of the force is about four times smaller than the predicted value for a one-band model.