  We have performed spatially resolved Polar Magneto-Optical Kerr Effect
Microscopy measurements on as-grown and annealed Ga0.95Mn0.05As thin films with
tensile strain. We find that the films exhibit very strong perpendicular
magnetic anisotropy which is increased upon annealing. During magnetic
reversal, the domain walls propagate along the direction of surface ripples for
the as-grown sample at low temperatures and along the [110] direction for the
annealed sample. This indicates that the magnetic domain pattern during
reversal is determined by a combination of magnetocrystalline anisotropy and a
distribution of pinning sites along the surface ripples that can be altered by
annealing. These mechanisms could lead to an effective method of controlling
domain wall propagation.
