  Based on the model of F/S/F trilayer with atomic thickness [A. Buzdin and M.
Daumens, cond-mat/0305320] we discuss the relative roles of pair-breaking and
proximity effects, as a function of the exchange field, of disorder and of a
finite thickness in the superconducting layer. The exchange field can be small
(weak ferromagnets) or large (strong ferromagnets) compared to the
superconducting gap. With weak ferromagnets we show the existence of a
reentrant superconducting gap for the F/S/F trilayer with atomic thickness in
the parallel alignment (equivalent to the F/S bilayer). Qualitatively small
disorder is equivalent to reducing the value of the hopping parameters. In the
presence of a finite thickness in the superconducting layer the superconducting
gap in the antiparallel alignment is larger than in the parallel alignment,
meaning that pair breaking dominates over the proximity effect.
