Observation of spin filtering with a ferromagnetic EuO tunnel barrier

Spin polarization (P) of the electron tunnel current is observed for a ferromagnetic EuO tunnel barrier between nonferromagnetic electrodes. Spin filtering due to different barrier heights for the spin-up and spin-down electrons gives rise to P, which was measured using a superconducting Al electrode as the spin detector. A large internal exchange field is exerted by the Eu2+ ions on the Al quasiparticle density of states, evidenced by enhanced Zeeman splitting even at zero applied field. Using a ferromagnetic barrier to filter spins has potential as a means for injecting a polarized current into semiconductors. Our EuO films show structure, magnetic moment, and Curie temperature matching bulk EuO.