Critical Currents of Superconducting Nb 25 at.% Zr in High Magnetic Fields

Measurements of critical current as a function of applied magnetic field were made on wire samples of Nb 25% at. Zr alloy at 4.22°K and 2.24°K. Curves are plotted for the cases for which the applied magnetic field is parallel to or perpendicular to the current direction. At 4.22°K, Hc(I → 0) for H perpendicular to I is found to be 70 kG, while for H parallel to I, it is found to be 82 kG. Reduction of the temperature to 2.24°K results in an increase of 13 kG in both cases. For H perpendicular to I, current densities of 4.4×104 A/cm2 are observed at 60 kG and 4.22°K, and at 73 kG and 2.24°K. The effective demagnetization factor of the current carrying elements is 0.6 π. All measurements were made in a dc magnetic field with quasidirect currents by observation of the first resistive voltage to appear across the sample.