FLUX-PINNING AND THE IRREVERSIBILITY LINES IN THE HGBA2CUO4+DELTA, HGBA2CACU2O6+DELTA AND HGBA2CA2CU3O8+DELTA COMPOUNDS

Using measurements of the magnetization hysteresis we determine the temperature and field dependence of the critical current density, the pinning force and the irreversibility lines of polycrystalline HgBa2CuO4+delta, HgBa2CaCu2O6+delta and HgBa2Ca2Cu3O8+delta. For all three materials we observe an exponential decay of the critical current with increasing temperature and/or field. The temperature dependence of the irreversibility fields follows a power law, H(irr) is-proportional-to (1 - T/T(c))4, and is intermediate to that of YBa2Cu3O7 and the Bi/Tl-based superconductors. These results are analyzed in a model in which the separation between the superconducting CuO2 blocks is the important parameter. At 77 K the irreversibility field of HgBa2Ca2Cu3O8+delta is 2 T and the critical current density at 77 K in a field of 1 T is about 2 x 10(3) A/cm2. The plate-like nature of the grains in the double- and triple-layer compounds offers the possibility that textured materials with good coupling between the grains can be prepared.