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

Abstract

We have studied superconducting and magnetic properties of sputtered Fe/Nb/Fe trilayers. For a fixed Nb thickness and with changing Fe thickness, ${d}_{\mathrm{Fe}}$, a nonmonotonic behavior of the superconducting transition temperature ${T}_{c}$ was observed with a maximum at ${d}_{\mathrm{Fe}}\ensuremath{\approx}10$ \AA{}. The analysis of the magnetization data revealed that for ${d}_{\mathrm{Fe}}\ensuremath{\le}7$ \AA{} the Fe layer is nonmagnetic. The interpretation of the observed ${T}_{c}$ behavior is attributed to the existence of this magnetically "dead" layer and the change of the interaction of the Cooper paris with this layer at the onset of ferromagnetism for ${d}_{\mathrm{Fe}}\ensuremath{\ge}7$ \AA{}.