Magneto-transport measurements in a superconducting Co/Nb/Co trilayer in the presence of a thick Pb ground plane

We report magneto-transport measurements in a superconducting Co/Nb/Co trilayer with rather thin Co layers in the presence of a very thick and relatively distant Pb ground plane. The trilayer is patterned in a Hall strip geometry and the magnetoresistance is measured with field applied almost parallel to the substrate. In addition to the familiar magnetoquenching near the coercive fields of the cobalt layers, a rather strong magnetoresistance signal is observed near the critical field of Pb (about 500 G at the working temperature), resembling a peak effect achieved at relatively weak applied fields. An analysis of the voltage-current curves at the relevant fields and a comparison with the magnetoresistance of a single Nb layer are given here. The behaviour is accounted for by the small out-of-plane component of the applied magnetic field amplified by the demagnetizing factor of the thick Pb ground plane. The strong and the hysteretic magnetoresistive signal achieved in such a way could be used to implement superconducting valves