Proximity Effect in Gadolinium-Backed Lead Films

Measurements of the surface reactance, at a frequency of 100 MHz and at various temperatures, have been used to study some aspects of the proximity effect in lead films in contact with gadolinium. It has been found that although the normal metal in this case is magnetic an adequate explanation of the experimental results cannot be obtained by assuming that the Ginzburg-Landau order parameter vanishes at the NS interface. The microscopic theory that allows the boundary condition (del Psi)(n) = Psi/b (where n indicates the normal component of the gradient, Psi is the order parameter, and b is called the extrapolation length) does agree well with both the dependence of the transition temperature T-cNS on the thickness Of the superconducting layer and variation of the surface reactance with temperature.