  We study the magnetic anisotropy which arises at the interface between a thin
film ferromagnet and a 3-d Rashba material. The 3-d Rashba material is
characterized by the spin-orbit strength $\alpha$ and the direction of broken
bulk inversion symmetry $\hat n$. We find an in-plane uniaxial anisotropy in
the $\hat{z}\times\hat{n}$ direction, where $\hat z$ is the interface normal.
For realistic values of $\alpha$, the uniaxial anisotropy is of a similar order
of magnitude as the bulk magnetocrystalline anisotropy. Evaluating the uniaxial
anisotropy for a simplified model in 1-d shows that for small band filling, the
in-plane easy axis anisotropy scales as $\alpha^4$ and results from a twisted
exchange interaction between the spins in the 3-d Rashba material and the
ferromagnet. For a ferroelectric 3-d Rashba material, $\hat n$ can be
controlled with an electric field, and we propose that the interfacial magnetic
anisotropy could provide a mechanism for electrical control of the magnetic
orientation.
