  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).
