Tuning of the superconducting and ferromagnetic behavior by oxygen and hydrogen in Eu1.5Ce0.5RuSr2Cu2O10-delta

Eu1.5Ce0.5RuSr2Cu2O10-delta is the first known Cu-O based material in which superconductivity (SC) and ferromagnetism (FM) coexist (T-c = 32 K, T-M = 122 K). SC is confined to the CuO2 planes, and the magnetic ordering is due to the Ru sublattice. Macroscopic magnetization and resistivity measuremen ts are combined with microscopic scanning tunneling spectroscopy (STS) stud ies, For the as-prepared (ASP) sample, the normal-state resistivity is char acteristic of an under-doped SC compound. The hole doping in the CuO2 plane s can be controlled with appropriate variation of the oxygen concentrations , obtained by annealing the ASP sample under various oxygen pressures. The effect of oxygen treatment is to shift both T-c and T-M up to 49 and 225 K, respectively (when annealed under 150 atm). For a sample annealed under 75 atm, two SC transitions are found at 32 and 46 K. On the other hand, when hydrogen atoms are loaded, they occupy interstitial sites and suppress SC a nd enhance the FM properties of the Ru sublattice. This effect is reversibl e: namely, by depletion of hydrogen, SC is restored and T-M drops back to i ts original value. STS measurements show that the ASP sample exhibits a var iety of SC gaps, which tend to grow with oxygen content, while hydrogen cha rging induces phase separation into SC, normal and insulator regions, whose relative abundance depends on the hydrogen concentration. (C) 2000 Elsevie r Science B.V. All rights reserved.