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 investigated below 1 T and in the temperature range 40 to 88 K. The sample was prepared by the laser-heated floating zone method. The magnetization curves exhibited a fairly large asymmetry with respect to the field axis, especially at elevated temperatures. This behavior may be attributed to the surface Meissner current contribution. It was demonstrated for the temperature range examined that the magnetic hysteresis width, ΔM, versus external-field curves were well described by assuming that the critical current density in the c-axis direction J^c_c obeys the critical-state model of the form J_c(B)=J_cO[1+(B/B₀)ⁿ]-1. Then, in turn, the field dependence of the critical current density along the c-axis at field temperatures was deduced using parameters obtained by fitting the ΔM vs. field curves. It was shown that the critical current density in the direction of the c-axis in our sample was over 10⁴ 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 studies on some melt-processed YBCO.