Critical temperature of superconductor/ferromagnet bilayers

Superconductor/ferromagnet bilayers are known to exhibit nontrivial dependence of the critical temperature $T_c$ on the thickness $d_f$ of the ferromagnetic layer. We develop a general method for investigation of $T_c$ as a function of the bilayer's parameters. It is shown that interference of quasiparticles makes $T_c(d_f)$ a nonmonotonic function. The results are in good agreement with experiment. Our method also applies to multilayered structures.