Magnetic stripe domain pinning and reduction of in-plane magnet order due to periodic defects in thin magnetic films

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 vacancies. We find that the defects produce two effects. At low temperatures the vacancies can take the place of a high energy spin and lower the energy of a domain boundary. This results in pinning of the domain boundaries, which stabilizes parallel orientation of stripes against thermal fluctuations. At higher temperatures, when spins are canted, we find that vacancies produce a dilution effect arising from the reduced demagnetizing field. The 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.