Large magnetoresistance in tunnel junctions with an iron oxide electrode

We report on the fabrication and properties of (cobalt/alumina/iron oxide) tunnel junctions. We observe magnetoresistance (MR) effects reaching 43% at 4.2 K and 13% at room temperature. This large MR is ascribed to the presen ce of a Fe3-xO4 (close to half-metallic magnetite) phase identified by elec tron diffraction. At low temperature, the MR drops sharply when the bias vo ltage is smaller than 10 mV, which suggests that the magnetoresistance orig inates from the activation of tunneling channels through spin polarized sta tes below and above the Fermi level in the iron oxide. (C) 1999 American In stitute of Physics. [S0003-6951(99)01026-8].