The influence of alloying or interdiffusion on the superconducting properties of ferromagnet/superconductor layered systems

We present the theoretical investigation of alloying or interdiffusion at the interface on the superconducting properties of ferromagnet/superconductor (S/F) layered films. The intermixed layer is modeled by the nonsuperconducting alloy (A) layer, which is characterized by strong scattering on paramagnetic impurities. The linearized Usadel equations are derived, which take into account the exchange scattering of excitations on the paramagnetic impurities in the alloyed layer. The superconducting transition temperature of the S/A/F trilayer is calculated as a function of spin-dependent scattering strength and thickness of A-layer. The nonmonotonic behavior of superconducting T c at the onset of ferromagnetism in F-layer is discussed in the framework of the presented theory. The oscillations of T c due to ferromagnetic layer thickness variation, and additional influence introduced by an alloy layer, are investigated.