Enhanced stochasticity of domain wall motion in magnetic racetracks due to dynamic pinning.

Understanding the details of domain wall (DW) motion along magnetic racetracks has drawn considerable interest in the past few years for their applications in non-volatile memory devices. The propagation of the DW is dictated by the interplay between its driving force, either field or current, and the complex energy landscape of the racetrack. In this study, we use spin-valve nanowires to study field-driven DW motion in real time. By varying the strength of the driving magnetic field, the propagation mode of the DW can be changed from a simple translational mode to a more complex precessional mode. Interestingly, the DW motion becomes much more stochastic at the onset of this propagation mode. We show that this unexpected result is a consequence of an unsustainable gain in Zeeman energy of the DW, as it is driven faster by the magnetic field. As a result, the DW periodically releases energy and thereby becomes more susceptible to pinning by local imperfections in the racetrack.