We report on experiments of spin filtering through ultrathin single-crystal layers of the insulating and ferromagnetic oxide $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_3$ (BMO). The spin polarization of the electrons tunneling from a gold electrode through BMO is analyzed with a counterelectrode of the half-metallic oxide ${\mathrm{La}}_{2∕3}{\mathrm{Sr}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_3$ (LSMO). At $3\mathrm{K}$ we find a 50% change of the tunnel resistances according to whether the magnetizations of BMO and LSMO are parallel or opposite. This effect corresponds to a spin-filtering efficiency of up to 22%. Our results thus show the potential of complex ferromagnetic insulating oxides for spin filtering and injection.

• Received 19 April 2005

DOI:https://doi.org/10.1103/PhysRevB.72.020406