Modulation of the dc Josephson current in pseudo-spin-valve Josephson multilayers

The dependence of the critical Josephson current (IC) and magnetoresistance (MR) on the relative orientation of the ferromagnetic layers is investigated in current perpendicular to plane (CPP) measurements of superconductor/ferromagnetic (S/F) multilayers. Two different Cu xNi1-x alloys were chosen so that alternate F-layers reversed at different applied magnetic fields and that the ferromagnetic coherence length was of the order of several nanometres. These structures show a significant CPP high-bias MR, which enables the magnetic state of the devices to be determined directly. We found that IC is substantially larger when the adjacent F-layers are aligned antiparallel compared to the case of parallel orientation. Since in a pseudo-spin-valve structure the relative F-layer orientation is approximately parallel for zero applied magnetic field, IC can experience an enhancement when a magnetic field is applied in the plane of the junction. The maximum change of IC corresponds to the maximum change of MR.