Hc2(4.2 K) of High-Temperature Superconducting Alloys

Abstract

Previous measurements of H_c2 versus T in selected Nb₃Al_1−xGe_x and Nb₃Al alloys for dc magnetic fields to 200 kG and for 14 K ≤ T ≤ T_c have now been extended to 4.2 K by means of pulsed magnetic fields and rf measurements. Long pulse (10 msec) multipalyer coils producing fields to 450 kG were employed for the measurements. At 4.2 K, H_c2≃410 kG and H_c2≃320 kG for the highest T_c, Nb₃Al_1−xGe_x and Nb₃Al alloys, respectively. These values of H_c2 are the highest measured for any superconductor. Measurements of H_c2 in several related alloys with somewhat lower values of T_c and H_c2 will also be presented. The large values of H_c2 (4.2 K) for all of these alloys permit great latitude of engineering design for practical wire materials. A summary of the physical properties of these high‐temperature superconductors, measurement techniques, present limits of high H_c2 materials, and a current appraisal of technical possibilities will be presented. A summary of some of the measurements has appeared.¹