Random Walk Of Antiferromagnetic Skyrmions In Granular Films

The impressive absence of the skyrmion Hall effect of antiferromagnetic (AFM) skyrmions in clean systems has raised high expectations of AFM skyrmions as information carriers and the potential applications in data storage technology. Here, we report an undesired behavior of current-driven AFM skyrmion dynamics in granular thin films. Understanding the motion of AFM skyrmions in disordered systems is crucial because disorders are inevitable in all materials. Micromagnetic simulations show that AFM skyrmions deviate from their trajectory in the clean limit. Interestingly, the transverse (to the current direction) motion is diffusive, i.e., the mean square of transverse displacement is proportional to the traveling time. The longitudinal (along with the current direction) motion is always hindered by disorders. An effective theory based on the stochastic Thiele equation can account for the observed phenomena. At a very strong disorder above a critical value that depends on the current density, AFM skyrmions are pinned. Our findings should be important for future spintronic devices based on AFM skyrmions.