Magnetically ordered Cu and Ru in Ba2GdRu1-uCuuO6 and in Sr2YRu1-uCuuO6 -: art. no. 214412

Magnetic orderings of the Cu, Gd, and Ru moments in nonsuperconducting Ba2GdRu1-uCuuO6 and of the Cu and Ru moments in superconducting Sr2YRu1-uCuuO6 (whose superconducting onset temperature is similar to 45 K) have been studied using dc susceptibility, microwave magnetic resonance, and neutron diffraction ton Sr2YRu0.85Cu0.15O6 only). In both homologues, Cu exhibits antiferromagnetism with an ordering temperature of similar to 86 K (much greater than the resistive superconductivity onset transition of similar to 45 K), and a magnon energy gap h omega (magnon)(q = 0) that exceeds the microwave photon frequency of omega /2 pi =13 GHz. The Cu moment extracted from neutron data for Sr2YRu1-uCuuO6 is similar to1.7 mu (B) at low temperature. Gd, in Ba2GdRu1-uCuuO6 is paramagnetic and displays a g = 2 electron spin resonance at temperatures above similar to 48 K, which also persists well below similar to 48 K (but with a very much broadened line), and orders antiferromagnetically at similar to 12 K. Ru in Ba2GdRu1-uCuuO6 orders at similar to 48 K,but in Sr2YRu1-uCuuO6 orders at similar to 23 K and has a moment of similar to1.6 mu (B) extracted from neutron scattering data. In both Sr2YRu1-uCuuO6 and Ba2GdRu1-uCuuO6 the Ru orders ferromagnetically in the a-b 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 Sr2YRu1-uCuuO6 the magnetic moments of the Ru and the Cu are ordered at low temperatures, its superconductivity is inconsistent with a spin-fluctuation pairing model.