Magnetic Anistropy due to the Casimir Effect

We consider the Casimir interaction between a ferromagnetic and a non-magnetic mirror, and show how the Casimir effect gives rise to a magnetic anisotropy in the ferromagnetic layer. The anisotropy is out-of-plane if the non-magnetic plate is optically isotropic. If the non-magnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magnetic anisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal and transverse contributions to the magneto-optical Kerr effect, and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of iron, and non-magnetic plates of gold (optically isotropic), quartz, calcite and barium titanate (all uniaxially birefringent).