Superconductivity and magnetism in Sr2Y(Ru1-uCuu)O6 and in Ba2Gd(Ru1-uCuu)O6

[[abstract]]Muon spin rotation and electron spin resonance data on sintered samples of superconducting Sr2Y(Ru1−uCuu)O6 and non-superconducting Ba2Gd(Ru1−uCuu)O6 are reported, both for u=0.1. In the case of Sr2Y(Ru1−uCuu)O6, the SrO layers are found to be p-type and to exhibit an onset for superconductivity at ≈45 K – a temperature considerably lower than the spin-ordering temperature of the Cu ions (≈86 K), indicating that the Cu ions themselves do not play a significant role in the superconductivity. Below Tc, the fluctuating Ru moments begin to slow down and freeze, so that at about ≈29.3 K a spin-glass state is observed, which gives way to ferromagnetic ordering of the Ru ions in the Y(Ru1−uCuu)O4 planes, with the magnetization alternating direction in the a–b plane from one magnetic layer to the next. These data confirm our earlier discovery that fluctuating moments (in this case, Ru moments) interfere with pairing. Ba2Gd(Ru1−uCuu)O6 shows no evidence of superconductivity, which we interpret as due to pair breaking by the L=0 magnetic Gd ions, which are not crystal-field split.[[journaltype]]國外[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]NL