Spin dependent transport at oxide La0.7Ca0.3MnO3/YBa2Cu3O7 ferromagnet/superconductor interfaces

We have found large magnetoresistance in ferromagnet/superconductor/ferromagnet heterostructures made of La0.7Ca0.3MnO3 and YBa2Cu3O7. It originates at an increase of the width of the resistive transition when the magnetizations of the ferromagnetic layers are aligned antiparallel. We find that the shape and height of the magnetoresistance peaks are not modified when the angle between current and magnetic field is changed from parallel or perpendicular. Furthermore, we find that the temperature shift of the resistance curves is independent of the current values. This favors the view that the magnetoresistance phenomenon originates at the spin dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor, and rules out interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers.