  We study clean ferromagnet-superconductor-ferromagnet (FSF) nanostructures in
which the magnetization of the F layers can be parallel (P) or antiparallel
(AP). We consider the case where the thickness of the S layer is of order of
the coherence length, with thinner F layers. We find that reversing the
direction of the magnetization in one of the F layers leads in general to
drastic changes in the superconductor's state. Under a wide variety of
conditions, the AP geometry favors superconductivity. Magnetization reversal in
one of the F layers can lead to the superconductivity turning on and off, or to
switching between different states. Our results are obtained via self
consistent solution of the Bogoliubov-de Gennes equations and evaluation of the
condensation energies of the system.
