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

The Eu1.5Ce0.5RuSr2Cu2O10+delta compound is the first known Cu-O based mate rial in which superconductivity (SC) and weak-ferromagnetism (W-FM) coexist (T-c = 32 K, T-M = 122 K). SC is confined to the CuO2 planes, and the magn etic ordering is due to the Ru sublattice. For as-prepared samples (APS), t he normal-state resistivity is characteristic of an under-doped SC compound . The hole doping in CuO2 planes, can be achieved with appropriate variatio n of the oxygen concentrations, which is obtained by annealing the APS unde r oxygen pressures up to 150 atm. The effect of oxygen treatment is to shif t the onset of SC monotonically, up to 49 K. For 75 atm., two transition te mperatures are found, indicating the existence of two SC phases. At the sam e time, scanning tunneling spectroscopy measurements show spatial variation s of the gap with a double-peak distribution.