Ideal spin filters: A theoretical study of electron transmission through ordered and disordered interfaces between ferromagnetic metals and semiconductors

It is predicted that certain atomically ordered interfaces between some ferromagnetic metals $\mathrm{}\left(F\right)\mathrm{}$ and semiconductors $\mathrm{}\left(S\right)\mathrm{}$ should act as ideal spin filters that transmit electrons only from the majority spin bands or only from the minority spin bands of the F to the S (and from the S only to the majority spin bands or only to the minority spin bands of the $F)$ at the Fermi energy, even for F with both majority and minority bands at the Fermi level. Criteria for determining which combinations of F, S, and interface should be ideal spin filters are formulated. The criteria depend only on the bulk band structures of the S and F and on the translational symmetries of the S, F, and interface. Several examples of systems that meet these criteria to a high degree of precision are identified. Disordered interfaces between F and S are also studied and it is found that intermixing between the S and F can result in interfaces with spin antifiltering properties, the transmitted electrons being much less spin polarized than those in the ferromagnetic metal at the Fermi energy.