Magnetism and superconductivity in Sr_2YRu_(1 - u)Cu_uO_6 and magnetism in Ba_2GdRu_(1 - u)Cu_uO_6

摘要

We report magnetization, surface resistance (R_s(T,H)), and electron spin resonance (ESR) for non-superconducting Ba_2GdRu_(1 - u)Cu_uO_6, and find that all three magnetic ions (Gd, Ru, and Cu) are ordered at low temperatures. Both ESR (Gd sublattice) and weak ferromagnetic resonance (dopant Cu) are observed, while no magnetic resonance due to either paramagnetic or ordered Ru is detected. In addition, for superconducting (T_C ～ 45 K) Sr_2YRu_(1 - u)Cu_uO_6, resistivity, muon spin rotation (μ ~+SR), and ~(99)Ru Mossbauer absorption are reported. None of the O_6 materials (e.g., Sr_2YRu_(1 - u)Cu_uO_6) have cuprate planes, although Cu is employed as a dopant. In Sr_2YRu_(1-u)Cu_uO_6, the Ru moments order at a temperature (～23 K) below that for the resistive onset of superconductivity, while the Cu orders at a higher temperature, ～86 K. Therefore at low temperatures, this material exhibits magnetic order, coexisting with diamagnetism. The only non-magnetic layers in the superconducting O_6 structure, the SrO layers, carry holes and exhibit diamagnetic screening characteristic of type-II superconductivity.