Phase diagram for a magnetic thin film with dipolar interactions and magnetic surface anisotropy

The phase diagram of a model thin him with long-range dipole-dipole interactions and magnetic surface anisotropy is determined as a function of temperature and the surface anisotropy. We show that the model studied here exhibits a reorientation transition in the absence of an exchange interaction. Further we show that, unexpectedly,the transition is from an in-plane phase to an out-of-plane phase with increasing temperature, which is the opposite of the ferromagnetic case. The implications of this study for the full phase diagram of a model which includes both the dipolar and exchange interactions are discussed.