Proximity effect in Fe/Pb/Fe trilayers

We have studied superconducting and magnetic properties of sputtered Fe/Pb/Fe-trilayers. For a fixed Pb thickness d(Pb) and with changing Fe thickness, d(Fe), a monotonic decrease of the superconducting transition temperature T-c was observed. Magnetization measurements clearly showed that Fe remains ferromagnetic down to the monolayer range. A quantitative comparison of T-c(d(Fe)) with the theory of pair breaking by the exchange field reveals that the observed T-c-suppression by the ferromagnetic Fe-layer is much weaker than expected. Possible reasons for the reduced T-c-suppression in this system are discussed.