Superconducting and Magnetic Properties of Nb/Pd_1-xFe_x/Nb Triple Layers

The superconducting and magnetic properties of Nb/Pd_1-xFe_x/Nb triple layers with constant Nb layer thickness d_Nb=200 A and different interlayer thicknesses are investigated. The thickness dependence of the magnetization and of the superconducting transition temperature shows that for small iron concentration x the Pd_1-xFe_x layer is likely to be in the paramagnetic state for very thin films whereas ferromagnetic order is established for x>=0.13. The parallel critical field B_c2II(T) exhibits a crossover from two-dimensional (2D) behavior where the Nb films are coupled across the interlayer, towards a 2D behavior of coupled Nb films with increasing d_PdFe or x. This 2D-2D crossover allows a determination of the penetration depth xi_F of Cooper pairs into the Pd_1-xFe_x layer as a function of x. For samples with a ferromagnetic interlayer xi_ is found to be independent of x.