  Using small-angle neutron scattering (SANS), we investigate the deformation
of the magnetic skyrmion lattice in bulk single-crystalline MnSi under electric
current flow. A significant broadening of the skyrmion-lattice-reflection peaks
was observed in the SANS pattern for current densities greater than a threshold
value j_t ~ 1 MA/m^2 (10^6 A/m^2). We show this peak broadening to originate
from a spatially inhomogeneous rotation of the skyrmion lattice, with an
inverse rotation sense observed for opposite sample edges aligned with the
direction of current flow. The peak broadening (and the corresponding skyrmion
lattice rotations) remain finite even after switching off the electric current.
These results indicate that skyrmion lattices under current flow experience
significant friction near the sample edges, and plastic deformation due to
pinning effects, these being important factors that must be considered for the
anticipated skyrmion-based applications in chiral magnets at the nanoscale.
