Influence of oxygen deficiency on anisotropy and c-axis critical current densities in TmBa2Cu3Oy single crystals

The coupling between the CuO2 layers has been studied in a series of six Tm Ba2Cu3Oy (6.40 less than or equal to y less than or equal to 6.90) single c rystals, together with a YBa2Cu3O6.9 and a Bi2Sr2CaCu2O8 crystal, in terms of the magnetically measured interlayer critical current. The Ginzburg-Land au thermodynamic anisotropies Gamma have been estimated too. As oxygen is r emoved, the coupling weakens and both Gamma and the anisotropy between inte r- and intralayer critical current densities, Omega increases rapidly. The current anisotropy Omega appears to be larger than Gamma, and increases as the temperature is reduced, whereas Gamma should be temperature independent . These results are discussed in terms of Abrikosov versus Josephson vortic es, and their effective dimensionality; possible pinning mechanisms are con sidered.