Electron-Spin Polarization in Tunnel Junctions in Zero Applied Field with Ferromagnetic EuS Barriers

An electron-spin polarization $P$ of as much as 80% has been observed in the tunnel current in Au/EuS/Al tunnel junctions. $P$ can be explained by the different heights of the tunnel barriers for the two spin directions. The Zeeman splitting of the Al quasiparticle density of states is greatly enhanced by the exchange interaction at the EuS/Al interface. Spin polarization was even seen in zero applied field. The value of $P$ calculated from the tunneling theory using known barrier heights in EuS is consistent with the measured values.