CRITICAL-CURRENT DENSITIES AND IRREVERSIBILITY LINES OF NEW OXYCARBONATE SUPERCONDUCTORS (CU0.5C0.5)BA2CAN-1CUNO2N+3 (N=3, 4)

From the hystereses in DC magnetization curves, we estimated critical current densities J(c) and irreversibility fields B(irr) of (Cu0.5C0.5)Ba2Ca2Cu3O9+/-delta((Cu, C)-1223) and (Cu0.5C0.5)Ba2Ca3Cu4O11+/-delta((Cu, C)-1234) new superconductors, and the data were compared with those values reported for other high-T(c) oxide superconductors. The temperature dependence of J(c) in a magnetic field for the (Cu, C)-based oxides is much smaller than that of HgBa2Ca2Cu3O8+delta(Hg-1223). At 77 K, B(irr) of (Cu, C)-1234 is 3.8 T which is higher than that of Hg-1223 in spite of a lower critical temperature of (Cu, C)-1234. The slopes of the irreversibility lines for (Cu, C)-1223 and (Cu, C)-1234 are steeper than that of Hg-1223. The results suggest that the anisotropy in the (Cu, C)-based oxides seems to be smaller than that of Hg-based oxide although the crystal structure is almost the same for both systems.