Possible Origin for Oscillatory Superconducting Transition Temperature in Superconductor/Ferromagnet Multilayers

We have studied superconducting and magnetic properties of sputtered Fe/Nb/Fe trilayers. For a fixed Nb thickness and with changing Fe thickness, {ital d}{sub Fe}, a nonmonotonic behavior of the superconducting transition temperature {ital T}{sub {ital c}} was observed with a maximum at {ital d}{sub Fe}{approx_equal}10 A. The analysis of the magnetization data revealed that for {ital d}{sub Fe}{le}7 A the Fe layer is nonmagnetic. The interpretation of the observed {ital T}{sub {ital c}} behavior is attributed to the existence of this magnetically {open_quote}{open_quote}dead{close_quote}{close_quote} layer and the change of the interaction of the Cooper pairs with this layer at the onset of ferromagnetism for {ital d}{sub Fe}{ge}7 A. {copyright} {ital 1996 The American Physical Society.}