Published online by Cambridge University Press: 18 March 2011
We report on the new superconducting materials with the formula Ru1−xSr2GdCu2+xO8-z that have been synthesized under high-pressure oxygen conditions. By changing the ratio between Ru and Cu in the compound we were able to increase the temperature of the superconducting transition up to 72 K for x=0.3 and 0.4. Reentrant dependencies of the magnetization found at low temperatures are qualitatively explained assuming a quasi two-dimensional character of the superconducting regions. The magnetic characteristics of these compounds are discussed and compared to the existing data on RuSr2GdCu2O8 magnetic superconductor (Tcon=45K, TN=132 K).