Comparison between the magnetic and transport critical current densities in high critical current density melt-textured yttrium barium copper-oxide

Using our recently developed pulsed critical current density (J _c) measuring system, the J_c of the high J_c melt-textured YBa₂Cu₃O_7-δ (Y123) bulk samples has been determined. I-V curves with a voltage resolution of 0.5 μV were obtained, and transport J_c's along the a-b plane (J _c∥ a-b) as high as 7.2×1 0⁴ A/cm² were extracted. These results are comparable to the values obtained magnetically. On the other hand, transport J_c along the c axis (J_c∥c) were found to be two orders of magnitude smaller, even though the magnetic J_c∥c is only about five times smaller than J_c∥a-b. We suggest that for the high-temperature superconducting materials which are highly anisotropic, caution should be taken when using the nontransport magnetic methods to determine J_c.