Magnetic dipolar anisotropy in strained antiferromagnetic films

We calculate the classical dipole interaction energy in fcc collinear antiferromagnetic films. We find that the presence and the type of strain strongly conditions the dipolar anisotropy, while the finite thickness introduces an additional perturbation to the dipolar energy, similar to the well known shape anisotropy of ferromagnetic films, with sizable effects due to surface roughness. An analytic expression relating the strain and thickness contributions to the dipolar anisotropy is derived from first-order perturbation theory, showing that in films with degenerate moment directions different domains can be stabilized by different combinations of tetragonal strain and thickness. Our predictions are in good qualitative agreement with the magnetic domain structure of strained NiO(001) films recently measured by x-ray magnetic linear dichroism.