Revealing Nanoscale Disorder in W / Co - Fe - B / MgO Ultrathin Films Using Domain-Wall Motion

Disorder in ultrathinmagnetic films can significantly hinder domain-wall motion. One of the main issues on the path toward efficient domain-wall-based devices remains the characterization of the pinning landscape at the nanoscale. In this paper, we study domain-wall motion in W/Co-Fe-B/MgO thin films with perpendicular magnetic anisotropy crystallized by annealing at 400 degrees C and a process based on He+ irradiation combined with moderated temperatures. The magnetic properties are similar for the whole series of samples, while the magnetic domain-wall mobility is critically improved in the irradiated samples. By using an analytical model to extract the nanoscale pinning parameters, we reveal important variations in the disorder of the crystallized samples. This work offers an opportunity to selectively analyze the effects of disorder on the domain-wall dynamics, without the contribution of changes in the magnetic properties. Our results highlight the importance of evaluating the nanoscale pinning parameters of the material when designing devices based on domain-wall motion, which in return can be a powerful tool to probe the disorder in ultrathin magnetic films.