Superconducting properties with high-field peak effect in ohmically-heated Jelly-rolled Nb/sub 3/Al wire

Jelly-rolled Nb/sub 3/Al wires with a Nb matrix have been ohmically-heated at controlled maximum temperatures ranging from 1600 to 2000/spl deg/C in vacuum, in order to investigate the properties of pinning force densities at high magnetic fields. The samples were 1.34 mm diameter and 50 mm long. To obtain the stoichiometric composition of the A15 phase, each sample was quenched in vacuum after ohmic-heating. Critical currents have been measured up to 23 T by a four probe method. The critical temperature of the sample heated at 1940/spl deg/C was 18.3 K. In longitudinal cross-sections, the samples heated at maximum temperatures less than 1940/spl deg/C have layer structures consisting of Nb-rich regions and A15 phase regions. In the sample heated up to 1940/spl deg/C, which is the melting point of Nb/sub 3/Al, these layers were not observed. This sample showed a remarkable peak effect in the critical current at high magnetic fields, over 20 T.