Interface transparency of superconductor/ferromagnetic multilayers

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 mu(F) of the F-layer atoms. The system studied consists of superconducting V and ferromagnetic V1-xFex alloys with x such that mu(F) on the Fe atom is varied between 2 and 0.25 mu(B). We determined the superconducting coherence length in the F layer xi(F), which is found to be inversely proportional to 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 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.