The theoretical description of the thermodynamic properties of ferromagnetic/superconductor/ferromagnetic (F/S/F) systems of nanoscopic scale is proposed. Their superconducting characteristics strongly depend on the mutual orientation of the ferromagnetic layers. In addition, depending on the transparency of S/F interfaces, the superconducting critical temperature can exhibit four different types of dependences on the thickness of the F-layer. The obtained results permit to give some practical recommendations for the spin-valve effect experimental observation. In this spin-valve sandwich, we also expect a spontaneous transition from parallel to anti-parallel ferromagnetic moment orientation, due to the gain in the superconducting condensation energy.

20 pages, 5 figures, submitted to PRB