THE OXYGEN-CONTENT DEPENDENCE OF THE MAGNETIZATION ANISOTROPY OF HGBA2CUO4+DELTA

The anisotropy of magnetization of the HgBa2CuO4+delta superconductor has been found to depend on delta, the excess oxygen content. Nearly s ingle-phase samples of HgBa2CuO4+delta in both over-doped and under-do ped regions are successfully prepared by post-annealing the samples in different atmospheres. The magnetization for grain-aligned HgBa2CuO4delta samples are measured in magnetic fields both parallel and perpen dicular to the c-axis. In the held parallel to the c-axis, the excess oxygen in the HgBa2CuO4+delta sample has been found to work for raisin g the irreversibility line to a position higher than that for YBa2Cu3O 6.6. It is also found that the presence of excess oxygen enhances the magnitude of the magnetization and lowers its field dependence in the held parallel to the c-axis. Thus the anisotropy of magnetization is l owered by the excess oxygen. It is likely that the excess oxygen in th e HgBa2CuO4+delta phase makes the HgOdelta layer more conductive along the c-axis so that the vortices may become quasi-three-dimensional.