Critical current densities and irreversibility lines of new oxycarbonate superconductors (Cu 0.5C 0.5Ba 2Ca n−1Cu nO 2n+3 (n = 3, 4)

Abstract

From the hystereses in DC magnetization curves, we estimated critical current densities J c and irreversibility fields B irr of (Cu 0.5C 0.5Ba 2Ca 2Cu 3O 9±δ((Cu, C)-1223) and (Cu 0.5C 0.5)Ba 2Ca 3Cu 4O 11±δ((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 HgBa 2Ca 2Cu 3O 8+δ(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.