Distinct stochasticities between ferromagnetic domain-wall motions driven by magnetic field and electric current

We report the experimental observation of distinct stochasticities between domain-wall motions driven by either a magnetic field or an electric current. In Pt/Co/Ta trilayer films, the arrival time of the current-induced domain-wall motion has a much broader dispersion compared to that of the field-induced motion. Images of the magneto-optical Kerr effect microscope reveal that the current-induced motion experiences significantly stronger domain-wall pinning, contrary to the field-induced domain-wall motion, even though both types of motion take place in the same area of the film. Consequently, the former exhibits stepwise propagation in time, whereas the behavior of the latter is smooth and monotonic. A simple analytic model based on depinning statistics is proposed to explain the relationship between the wide dispersion and the strong pinning mechanisms in current-induced domain-wall motion.