The effect of oxygen on superconductivity and magnetism in Eu1.5Ce0.5RuSr2Cu2O10+δ

The Eu1.5Ce0.5RuSr2Cu2O10+δ compound is the first known Cu-O based material in which superconductivity (SC) and weak-ferromagnetism (W-FM) coexist (Tc = 32 K, TM = 122 k). SC is confined to the CuO2 planes, and the magnetic ordering is due to the Ru sublattice. For as-prepared samples (APS), the normal-state resistivity is characteristic of an under-doped SC compound. The hole doping in CuO2 planes, can be achieved with appropriate variation of the oxygen concentrations, which is obtained by annealing the APS under oxygen pressures up to 150 atm. The effect of oxygen treatment is to shift the onset of SC monotonically, up to 49 K. For 75 atm., two transition temperatures are found, indicating the existence of two SC phases. At the same time, scanning tunneling spectroscopy measurements show spatial variations of the gap with a double-peak distribution