Role of metal-oxide interface in determining the spin polarization of magnetic tunnel junctions

The role of the metal-oxide interface in determining the spin polarization of electrons tunneling from or into ferromagnetic transition metals in magn etic tunnel junctions is reported. The spin polarization of cobalt in tunne l junctions with an alumina barrier is positive, but it is negative when th e barrier is strontium titanate or cerium lanthanite. The results are ascri bed to bonding effects at the transition metal-barrier interface. The influ ence of the electronic structure of metal-oxide interfaces on the spin pola rization raises interesting fundamental problems and opens new ways to opti mize the magnetoresistance of tunnel junctions.