Magnetism and Superconductivity in Ru 1- x Sr 2 RECu 2+x O 8- d (RE=Gd, Eu) and RuSr 2 Gd 1- y Ce y Cu 2 O 8 Compounds

We discuss the properties of new superconducting compositions of ruthenocuprates Ru1−x Sr2RECu2+x O8−d (RE=Gd, Eu) that were synthesized at 600 atm. of oxygen at 1080°C. By changing ratio between the Ru and Cu, the temperature of superconducting transition (TC) raises up to T C max = 72 K for x=0.3, 0.4. The hole doping achieved along the series increases with Cu→Ru substitution. For x ≠ 0, TC can be subsequently tuned between T C max and 0 K by changing oxygen content in the compounds. The magnetic characteristics of the RE=Gd and Eu based compounds are interpreted as indicative of constrained dimensionality of the superconducting phase. Muon spin rotation experiments reveal the presence of the magnetic transitions at low temperatures (T m=14-2 K for x=0.1–0.4) that can originate in the response of Ru/Cu sublattice. RuSr2Gd1−y Ce1−y Cu2O8 (0 ≤ y ≤ 0.1) compounds show the simultaneous increase of TN and decrease of TC with y. The effect should be explained by the electron doping that occurs with Ce→Gd substitution. Properties of these two series allow us to propose phase diagram for 1212-type ruthenocuprates that links their properties to the hole doping achieved in the systems. Non-superconducting single-phase RuSr2GdCu2O8 and RuSr2EuCu2O8 are reported and discussed in the context of the properties of substituted compounds.