MAGNETIZATION BEHAVIOR AND CRITICAL-CURRENT DENSITY ALONG THE C-AXIS IN MELT-GROWN YBCO FIBER CRYSTAL

The magnetic-hysteresis behavior of single-crystal YBCO fibers was inv estigated below 1 T and in the temperature range 40 to 88 K. The sampl e was prepared by the laser-heated floating zone method. The magnetiza tion curves exhibited a fairly large asymmetry with respect to the fie ld axis, especially at elevated temperatures. This behavior may be att ributed to the surface Meissner current contribution. It was demonstra ted for the temperature range examined that the magnetic hysteresis wi dth, DELTAM, versus external-field curves were well described by assum ing that the critical current density in the c-axis direction J(c)c ob eys the critical-state model of the form J(c)(B) = J(c0) [1 + (B/B0)n] -1. Then, in turn, the field dependence of the critical current densit y along the c-axis at fixed temperatures was deduced using parameters obtained by fitting the DELTAM vs. field curves. It was shown that the critical current density in the direction of the c-axis in our sample was over 10(4) A/cm2 at 77.3 K below 0.3 T. The field and temperature variations of J(c)c were discussed in relation to the previous studie s on some melt-processed YBCO.