  We study how impurities influence the current-induced dynamics of magnetic
Skyrmions moving in a racetrack geometry. For this, we solve numerically the
generalized Landau-Lifshitz-Gilbert equation extended by the current-induced
spin transfer torque. In particular, we investigate two classes of impurities,
non-conducting and magnetic impurities. The former are magnetically rigid
objects and yield to an inhomogeneous current density over the racetrack which
we determine separately by solving the fundamental electrostatic equations. In
contrast, magnetic impurities leave the applied current density homogeneous
throughout the stripe. Depending on parameters, we observe four different
scenarios of Skyrmion motions in the presence of disorder, the Skyrmion decay,
the pinning, the creation of additional Skyrmions, and ordinary Skyrmion
passage. We calculate and discuss phase diagrams in dependence of the impurity
concentration and radii of the impurities.
