Superconductor/Ferromagnet Hybrids: Bilayers and Spin Switching

In research on superconductor (S)/ferromagnet (F) multilayers, a number of issues are at play simultaneously. In phenomena such as interlayer coupling in S/F/S systems or superconducting spin valve effects in F/S/F systems, questions about the interface transparency, the effect of magnetic domains on the F-side of the interface, or the stray fields produced by the F-layer arise all the time. Investigating bilayers of S/F combinations is useful and necessary to discern the effects which can be produced by the bare interface and one F-layer from those which occur when coupling between S- or F-layers also plays a role. In this chapter, we review insights gained from bilayer studies, using both weak and strong ferromagnets, with particular attention to the interface transparency and the issue of inhomogeneous exchange fields; we also review some of the questions pertaining to the superconducting spin valve effect, again for both weak and strong ferromagnets.