  We report the fabrication of an oxide-specific type of magnetoresistive
junction, which is a ferromagnetic bilayer. Both electrodes are high
spin-polarization oxides: magnetite (Fe3O4) and manganite (La0.7Sr0.3MnO3).
Negligible magnetic coupling between both ferromagnetic electrodes is realised,
which allows to obtain parallel and antiparallel magnetic configurations of the
electrodes when sweeping the applied magnetic field. The structure exhibits
negative giant magnetoresistance (GMR) at low temperatures. This negative MR
shows that both electrodes stay spin-polarized at the interface and have
opposite spin polarizations, i.e. the Fe3O4 layer has a negative spin
polarization at low temperature. Maximum GMR (-5%) is obtained at 55K.
