Crystal structure and the effect of oxygen on the superconductivity and weak magnetism in RE1.5Ce0.5RuSr2Cu2O10 (RE = Eu, Gd)

The superconducting tetragonal RE1.5Ce0.5RuSr2Cu2O10 (RE = Eu, Gd) system i s the first known Cu-O based material in which superconductivity (SC) and w eak-ferromagnetism (W-FM) coexists at T-M > T-c (T-c = 32, 42 K, and T-M = 122, 180 K for RE = Eu and Gd respectively). Superconductivity is confined to the CuO2 planes, and the magnetic ordering is due to the Ru sublattice. The as-prepared sample (ASP), is an under-doped SC compound. The hole dopin g in the CuO2 planes can be controlled with appropriate variation of oxygen concentrations, obtained by annealing the ASP sample under various oxygen pressures. Oxygen treatment (for RE = Gd) shifts both T-c and T-M (T-c = 52 K for RE = Gd at 600 atm). On the other hand, quenching the ASP sample to ambient temperature, suppresses SC and enhances the W-FM properties of the Ru sublattice. X-ray diffraction studies performed at various low temperatu res. indicate that the tetragonal structure is preserved (down to 10 K), an d no anomalies in the a and c lattice parameters are observed at T-c and T- M. (C) 2001 Elsevier Science B.V. All rights reserved.