Irreversibility field analysis for Bi2Sr2Ca2Cu3Ox tapes by using axial probe

An axial probe for evaluation of J(c) = f(B, T, theta) was designed and fabricated. The probe is capable of carrying currents over 250 A in a magnetic field up to 13 T. The critical current density of 61 filament Bi2223 tape was measured by this probe in a temperature range of from 10 to 100 K for two orientations of the magnetic field. Obtained results confirm high sensitivity of the superconductor to the field, especially for B perpendicular to tape surface, Moreover, the J(c) = f(B) dependence reveals a logarithmic relationship and it is in good agreement with the scaling law proposed by Kobayashi ei al. [S. Kobayashi, T. Kaneko, T. Kato, J. Fujikami, K. Sate, Physica C 258 (1996) 336]. Derived irreversible lines show temperature dependence as B-irr proportional to [1 - T/T-c](n), with a distinct kink observed at higher temperatures. The transition from n = 1.65 to n = 3 is believed to represent crossover from the weakly to the highly correlated regime of fluxoids. (C) 1998 Elsevier Science B.V. All rights reserved.