Superconductor/ferromagnet proximity effect in Fe/Pb/Fe trilayers

We report on measurements of structural, superconducting, and magnetic prop erties of trilayer and bilayer systems combined of superconducting Pb and f erromagnetic Fe. The Pb/Fe layers can be grown on Al2O3 with reasonably fla t interfaces, there is no alloying of the components at the interface and F e is found to be ferromagnetic down to the monolayer range. This is a favor able situation for an SIF proximity system, since it corresponds closely to the situation treated in theoretical models. We find an oscillation of the superconducting transition temperature when plotted versus the thickness o f the ferromagnetic layer, which we regard as a clear indication of an unco nventional, propagating superconducting pair wave function in the Pb/Fe sys tem. We fit our results using recent theoretical model calculations and fin d evidence for a strongly reduced transparency of the Pb/Fe interface. We r egard this as an essential feature of the proximity effect in Pb/Fe and dis cuss its physical origin.