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 $d_{\mathrm{Fe}}\approx 10$ Å. The analysis of the magnetization data revealed that for $d_{\mathrm{Fe}}\le 7$ Å 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 $d_{\mathrm{Fe}}\ge 7$ Å.