Superconductivity of a Composite of Fine Niobium Wires in Copper

Abstract

Composites consisting of fine Nb filaments in a copper matrix were fabricated, and the following superconducting properties measured: the critical temperature, critical transverse magnetic field as a function of temperature, critical current density at 4.2°K as a function of transverse magnetic field, and magnetization at 4.2°K. The reduction in Nb filament size was checked by optical and electron micrography. Filament diameters ranged down to 100 Å. As the diameter decreased, T_c, H_c(T), and J_c all decreased. This behavior was attributed to the proximity effects of the copper matrix on the Nb. The results are closely comparable to those of investigations of superimposed thin films. It is therefore not expected that high critical fields can be attained by composites involving a type II superconductor in a matrix of a nonsuperconductor.