Inverse spin switch effects in ferromagnet-superconductor-ferromagnet trilayers with strong ferromagnets

In ferromagnet-superconductor-ferromagnet (F/S/F) trilayers where the magnetization directions of the F layers can be controlled separately, it has theoretically been predicted that the antiparallel (AP) configuration can have a higher superconducting transition temperature T-c than the parallel (P) configuration. This is the so-called spin switch, which has been found experimentally for the case of weak ferromagnets. Here we show that strong ferromagnets yield the opposite effect. We study the transport properties of F/S/F trilayers with F=Ni0.80Fe0.20 (Permalloy, Py) and S=Nb, structured in strips of different sizes. Using two different thicknesses for the Py layers, we can switch, in a well-defined way, between the AP and P configurations. In the superconducting transition we find a clear increase of the resistance in the AP state. We ascribe this to enhanced reflection of spin-polarized quasiparticles at the S/F interfaces, which leads to a stronger suppression of superconductivity on the S side.