Spin-dependent magnetoresistance of ferromagnet/superconductor/ferromagnet La_(0.7)Ca_(0.3)MnO_(3)/YBa_(2)Cu_(3)O_(7-δ)/La_(0.7)Ca_(0.3)MnO_(3) trilayers

摘要

We report on large magnetoresistance in ferromagnet/superconductor/ferromagnet trilayer structures made of La_(0.7)Ca_(0.3)MnO_(3) and YBa_(2)Cu_(3)O_(7). We find that the shape and height of the magnetoresistance peaks are not modified when the relative orientation of current and magnetic field is changed from parallel to perpendicular. Furthermore, we find that the temperature shift of the resistance curves is independent of current and of the sweep rate of the magnetic field. These observations favor the view that the magnetoresistance phenomenon originates in the spin dependent transport of quasiparticles transmitted from the ferromagnetic electrodes into the superconductor, and rule out interpretations in terms of spontaneous vortices or anisotropic magnetoresistance of the ferromagnetic layers.