Interface coupling in a ferromagnet/antiferromagnet bilayer

A micromagnetic model accounting for exchange, dipolar interactions, and magnetocrystalline anisotropy has been applied to simulate the magnetic structure of a low anisotropy antiferromagnetic thin film on a ferromagnetic substrate. In particular, the influence that interface uncompensated moments have on the type of magnetic coupling between the antiferromagnetic and ferromagnetic layers has been evaluated. The long-range magnetic dipole-dipole interactions force the antiferromagnetic film to have in-plane anisotropy. For the fully magnetically compensated interface, the model gives an antiferromagnetic uniaxial anisotropy perpendicular to the magnetization of the ferromagnetic film. There is a rapid transition from perpendicular to parallel anisotropy as the amount of uncompensated moments is increased. The density of uncompensated moments necessary to induce such transition decreases as the interface exchange coupling is reduced. These predictions are compared to the experimentally observed behavior of NiO in various types of interfaces with ferromagnetic materials.