  In 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 configuration. This is the so-called spin
switch, which also experimentally has been found 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 = Ni_0.80Fe_0.20
(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.
