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

Synthesis in 1% oxygen at 930 degreesC leads to non-superconducting RuSr2Gd Cu2O8 in which superconductivity subsequently can be induced with oxygen an nealings without observable stoichiometric changes. Detailed ac susceptibil ity and zero-field muon-spin rotation experiments reveal that the supercond ucting compounds always exhibit a lower temperature of the magnetic transit ion and larger values of the internal magnetic field in the ordered state o f the Ru sublattice. The same annealings in oxygen, however, lead to non-su perconducting 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 tempera ture behavior of the magnetization shows a significant contribution of the paramagnetic system of Gd ions to the magnetic response below the supercond ucting transition. Muon-spin rotation experiments reveal the presence of th e magnetic transitions at low temperatures below the superconducting transi tion. XANES CuK absorption edge data show an increase in Cu valence with x. (C) 2001 Elsevier Science B.V. All rights reserved.