Tuning the superconducting state in the magnetic MoSr₂YCu ₂O_8-δ materials

The properties of MoSr₂YCu₂O_8-δ materials are found to systematically change with the oxygen concentration determined by the sintering and annealing conditions. The as-prepared (asp) sample is antiferromagnetically ordered at 16 K. The magnetic features are related to the Mo⁵⁺ sublattice. Annealing under an oxygen atmosphere induces superconductivity (SC) in the Cu-O planes, and the T_C and the shielding fraction values obtained depend strongly on the oxygen concentration. Annealing the asp material at 1030 °C under ambient oxygen atmosphere yields T_C of 18 K, whereas further annealing at 650 °C under 92 atm. of oxygen, shifts T_C to 32 K. The antiferromagnetic ordering, which coexists with SC state through effectively decoupled subsystems, is not affected by the presence or absence of the SC state. In all samples studied, T_N<T_C. This behavior resembles most of the inter-metallic magneto-superconductors, but is in sharp contrast to the isostructural RuSr₂GdCu₂O₈ system where T_N>T_C.