  In thin magnetic films with strong perpendicular anisotropy and strong
demagnetizing field two ordered phases are possible. At low temperatures,
perpendicularly oriented magnetic domains form a striped pattern. As
temperature is increased the system can undergo a spin reorientation transition
into a state with in-plane magnetization. Here we present Monte Carlo
simulations of such a magnetic film containing a periodic array of non-magnetic
defects. We find that the presence of defects stabilizes parallel orientation
of stripes against thermal fluctuations at low temperatures. Above the spin
reorientation temperature we find that defects favor perpendicular spin
alignment and disrupt long range ordering of spin components parallel to the
sample. This increases cone angle and reduces in plane correlations, leading to
a reduction in the spontaneous magnetization.
