Ferromagnetic thickness dependence of superconducting transition temperature in a superconductor/ferromagnet bilayer system with an inhomogeneous exchange field

摘要

The superconducting transition temperature of superconductor/ferromagnet bilayer with an inhomogeneous exchange field within the framework of the Usadel equations is studied. With the geometry of superconductor/ferromagnet junction on z-axis, the exchange field rotates with constant angle ? respect to the z-axis and with the angle θ, θ = Qy, varying in xy-plane along the direction y that Q is a spiral wave vector. The boundary condition parameter (W_0) and corresponding eigenvalues and eigenvectors are shown in analytic forms for two small angle case as measured from the xy-plane and measured from z-axis. The behavior of superconducting transition temperature versus thickness of ferromagnetic layer with varying Qξ_s, the transparency parameters (γ_b) an the proximity effect parameter (γ) are considered in our calculations. We can find monotonic, non-monotonic, and reentrant behavior of superconducting transition temperature in our calculation depending on parameters. The non-monotonic behavior is found with low γ_b, Qξ_s and the reentrant behavior is found with large γ.