Magnetic orderings of the Cu, Gd, and Ru moments in nonsuperconducting Ba 2 GdRu 1Ϫu Cu u O 6 and of the Cu and Ru moments in superconducting Sr 2 YRu 1Ϫu Cu u O 6 ͑whose superconducting onset temperature is ϳ45 K͒ have been studied using dc susceptibility, microwave magnetic resonance, and neutron diffraction ͑on Sr 2 YRu 0.85 Cu 0.15 O 6 only͒. In both homologues, Cu exhibits antiferromagnetism with an ordering temperature of ϳ86 K ͑much greater than the resistive superconductivity onset transition of ϳ45 K͒, and a magnon energy gap ប magnon (qϭ0) that exceeds the microwave photon frequency of /2ϭ13 GHz. The Cu moment extracted from neutron data for Sr 2 YRu 1Ϫu Cu u O 6 is ϳ1.7 B at low temperature. Gd, in Ba 2 GdRu 1Ϫu Cu u O 6 , is paramagnetic and displays a gϭ2 electron spin resonance at temperatures above ϳ48 K, which also persists well below ϳ48 K ͑but with a very much broadened line͒, and orders antiferromagnetically at ϳ12 K. Ru in Ba 2 GdRu 1Ϫu Cu u O 6 orders at ϳ48 K, but in Sr 2 YRu 1Ϫu Cu u O 6 orders at ϳ23 K and has a moment of ϳ1.6 B , extracted from neutron scattering data. In both Sr 2 YRu 1Ϫu Cu u O 6 and Ba 2 GdRu 1Ϫu Cu u O 6 the Ru orders ferromagnetically in the aϪb planes with the sheet magnetization alternating in direction as one moves along the c axis, forming a net antiferromagnetic structure. We find no evidence of a Ru signature in the magnetic resonance data anywhere in the range from 3 to 300 K, a result which is consistent with the electrons being itinerant. Attempts to detect Ru magnetic resonances in various other materials have also failed. Since in Sr 2 YRu 1Ϫu Cu u O 6 the magnetic moments of the Ru and the Cu are ordered at low temperatures, its superconductivity is inconsistent with a spin-fluctuation pairing model.
A. Cuprate-plane-based modelsCuprate-plane theories of high-temperature superconductivity, strictly speaking, have no application to this class of
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