  A theoretical study of the current-driven dynamics of magnetic skyrmions in
disordered perpendicularly-magnetized ultrathin films is presented. The
disorder is simulated as a granular structure in which the local anisotropy
varies randomly from grain to grain. The skyrmion velocity is computed for
different disorder parameters and ensembles. Similar behavior is seen for
spin-torques due to in-plane currents and the spin Hall effect, where a pinning
regime can be identified at low currents with a transition towards the
disorder-free case at higher currents, similar to domain wall motion in
disordered films. Moreover, a current-dependent skyrmion Hall effect and
fluctuations in the core radius are found, which result from the interaction
with the pinning potential.
