ELECTRICAL AND MAGNETIC PROPERTIES OF NIOBIUM-THORIUM EUTECTIC COMPOSITE SUPERCONDUCTING WIRE

Resistance and magnetization measurements have been made on pieces of niobium-thorium eutectic composite superconducting wire, some in the form of long filaments of niobium in a background matrix of thorium and some in the form of lumps of niobium in a background matrix of thorium.;The niobium in the filamentary samples has transverse physical dimensions that range from greater than to less than the coherence length in the niobium. The lumps of niobium in the nonfilamentary materials have a mean size of 1500(ANGSTROM) that is much greater than the coherence length in the niobium.;We found that all the composites have transition temperatures within 1K of the transition temperature of bulk niobium contrary to current proximity effect calculations that predict a large variation in transition temperature for the range of niobium filament sizes tested.;We also found that the filamentary composites have anisotropic upper critical fields and upper critical field curves that exhibit an upward curvature near T(,c). These effects are in qualitative agreement with theories on anisotropic superconductors.;The measurements made were used to determine transition temperatures and critical field curves that are then compared to the results of proximity effect calculations and theories about anisotropic superconductors.