Magnetic properties of RuSr2RECu2O8 (RE = Gd, Eu) and Ru1-xSr2GdCu2+xO8-y superconductors

Synthesis in 1% oxygen at 930 degreesC leads to non-superconducting RuSr2GdCu2O8 in which superconductivity subsequently can be induced with oxygen annealings without observable stoichiometric changes. Detailed ac susceptibility and zero-field muon-spin rotation experiments reveal that the superconducting compounds always exhibit a lower temperature of the magnetic transition and larger values of the internal magnetic field in the ordered state of the Ru sublattice. The same annealings in oxygen, however, lead to non-superconducting RuSr2EuCu2O8. The magnetic properties of a newly discovered series of Ru1-xSr2GdCu2+xO8-y superconductors (maximum T-c = 72 K for x = 0.4) are reported. Low temperature behavior of the magnetization shows a significant contribution of the paramagnetic system of Gd ions to the magnetic response below the superconducting transition. Muon-spin rotation experiments reveal the presence of the magnetic transitions at low temperatures below the superconducting transition. XANES CuK absorption edge data show an increase in Cu valence with x. (C) 2001 Elsevier Science B.V. All rights reserved.