We report on the properties of new ruthenocuprates ${\mathrm{Ru}}_{1-x}{\mathrm{Sr}}_2{\mathrm{GdCu}}_{2+x}{\mathrm{O}}_{8-y}$ $(x=0,$ 0.1, 0.2, 0.3, 0.4, and 0.75) that extend the superconductivity found previously in ${\mathrm{RuSr}}_2{\mathrm{GdCu}}_2{\mathrm{O}}_8{(T}_c=45\mathrm{}\mathrm{K})$ to the solid solution with varied Ru/Cu ratios. The compounds have been synthesized in a high-pressure oxygen atmosphere. The maximum temperature of the superconducting transition is 72 K for the $x=0.3\mathrm{}$ and 0.4 compositions. The reported behavior of magnetization at low temperatures can be qualitatively explained assuming a quasi-two-dimensional character of the superconducting regions in the compounds studied.

• Received 13 November 2000

DOI:https://doi.org/10.1103/PhysRevB.63.224512