Flux pinning in Nb-Ti based nanoscale superconducting multilayers

Nanoscale Nb-Ti/Nb/Cu-Ni-Si-Zn multilayers have been fabricated by means of a plastic deformation technique where a precipitation-hardening copper alloy was used. When the thickness dependence of the global pinning force was examined at constant magnetic fields, it increased monotonically with increasing Nb-Ti layer thickness at 5 T from 4.8 to 120 nm, but it showed a maximum at 24 nm at 1.5 T. The critical temperature (T_c) decreased with decreasing thickness when the layer thickness was smaller than 20 nm. The present experimental results suggested that the major flux pinning is attributed to the superconducting/normal interface and the proximity effect resulted in the degradation of T_c