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Thermal transport in the magnetic MoSr2YCu2O8 materials

The physical properties of sintered MoSr2YCu2O8 (Mo-1212) are found to strongly depend on the oxygen concentration. The as prepared sample is an antiferromagnet with TN=16 K, where the magnetic features are related to the Mo5+ sublattice. Annealing in oxygen atmosphere induces superconductivity in the Cu O planes, and TC depends strongly on the oxygen concentration. The annealing of as prepared sample at 1030 0C under ambient oxygen atmosphere yields TC of 18 K, whereas further annealing at 650 0C under 92 atm. of oxygen shifts TC to 32 K. The antiferromagnetic ordering, which coexists with superconductivity state through effectively decoupled subsystems, is not affected by the presence or absence of the superconductivity state (1). This behaviour resembles most of the magneto superconductors, but is in contrast to the isostructural RuSr2GdCu2O8 system (Ru-1212), in which case a TC is at lower temperatures than TN. Thermal conductivity of Mo-1212 has a temperature behaviour peculiar for the crystalline material. Small enhancement of thermal conductivity with decreasing temperature is observed at TC, attributed to enlargement of phonon mean free path due to decrease of the number of normal electrons which act as phonon scatterers. At TN, broader enhancement was observed . On the other hand, the Ru-1212 shows a temperature behaviour peculiar to the highly disordered materials. The surface morfology of Ru-1212 and Mo-1212 as detected by SEM, shows that they both have a granular structure. However, the grains are not well defined and separated in Mo-1212 system, and that might be the reason why the thermal conductivity of Mo-1212 system behaves so differently than the thermal conductivity of the Ru-1212 system. (1) I. Felner and E. Galstyan, Phys. Rev. B 69 (2004) 024512.

Coexistence of superconductivity and magnetism; Magnetism; Transport properties; Mo-2122 compounds

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