Superconducting properties and critical current density of Nb-Ti/Ti multilayers

Multilayers of Nb47Ti superconductor (S) and titanium pins (N) have been made with a critical temperature T/sub c/ and an upper critical field H/sub c2/ approaching bulk values. There is no proximity effect suppression of T/sub c/ and H/sub c2/ for layer thickness d/sub S/=d/sub N/=10 nm, in contrast to the strong suppression for comparable multilayers made with Cu, Cu-alloy, or Nb pins. This may be because the proximity length of the Ti layers, /spl sim/10 nm, is less than or equal to their thickness. The critical current density J/sub c/ exhibits, multiple peaks in J/sub c/(H), which suggests that matching effects contribute to the overall pinning. J/sub c/ for 20 nm bilayers is comparable to that of Nb47Ti tapes, which have a higher number density of pins but a lower pin volume fraction. The weak proximity coupling suggests that much higher J/sub c/ can be obtained if smaller bilayer periods can be made with good adhesion. The results are compared to other Nb-Ti/Ti multilayer experiments, and stability limitations are also discussed.