Interface transparency of superconductor/ferromagnetic multilayers

Abstract

We have investigated the behavior of the superconducting transition temperature ${T}_{c}$ in superconducting/ferromagnetic (S/F) multilayers, as a function of the different layer thicknesses and for varying magnetic moment ${\ensuremath{\mu}}_{F}$ of the F-layer atoms. The system studied consists of superconducting V and ferromagnetic V${}_{1\ensuremath{-}x}$Fe${}_{x}$ alloys with $x$ such that ${\ensuremath{\mu}}_{F}$ on the Fe atom is varied between 2 and 0.25${\ensuremath{\mu}}_{B}.$ We determined the superconducting coherence length in the F layer ${\ensuremath{\xi}}_{F},$ which is found to be inversely proportional to ${\ensuremath{\mu}}_{F}.$ We also determined the critical thickness of the S layer, above which superconductivity appears. This thickness is found to be strongly nonmonotonic as function of the Fe concentration in the alloys. By analyzing the data in terms of the proximity-effect theory, we show that with increasing ${\ensuremath{\mu}}_{F},$ the increasing pair breaking in the F layer by the exchange field is counteracted by a decreasing transparency of the S/F interface for Cooper pairs.