Thermally activated domain wall dynamics in a disordered magnetic nanostrip.

We consider the effect of disorder on the dynamics of a transverse domain wall in thin and narrow magnetic strips made of soft magnetic materials such as permalloy. Motivated by the micromagnetic description of such a domain wall, we construct a model based on two coupled flexible lines enclosing the domain wall transition region. The model captures both the finite width and the characteristic V-shape of the wall. Disorder is included via randomly distributed pinning centers interacting with the two lines, describing, e.g., thickness fluctuations of the strip. We study the thermally activated creep motion of the domain wall driven by an applied field in a disordered nanostrip, and demonstrate how such inherently stochastic motion leads to a broad distribution of the domain wall velocities, in agreement with experimental observations.