Low field AC susceptibility study of intergranular critical current density in Mg-substituted CuBa2Ca3Cu4O12-y high temperature superconductors

Measurements of the a.c.susceptibility (chi = chi' + i chi '') have been made on the Mg substituted high T-C superconducting system, CuBa2(MgxCa1-x)(3)Cu4O12-y (Cu-1234) with x = 0, 0.10 M 0.20, at different values of the a.c.field amplitude. Estimates of the intergranular critical current density(J(C)) made from the field dependent chi ''-T curves show an improvement in the Mg-substituted Cu-1234 system. Results have been analysed in the light of the crystal structure and the superconducting anisotropy factor (gamma=xi(ab)/xi(c)) of the Cu-1234 system. Lower superconducting anisotropy emanating from Mg substitution has been found to be significant, resulting in better superconducting properties. (c) 2004 Elsevier Ltd. All rights reserved.