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 Ba2G dRu1-uCuuO6 and of the Cu and Ru moments in superconducting Sr2YRu1-uCuuO6 (whose superconducting onset temperature is similar to 45 K) have been stud ied using dc susceptibility, microwave magnetic resonance, and neutron diff raction ton Sr2YRu0.85Cu0.15O6 only). In both homologues, Cu exhibits antif erromagnetism 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 neut ron 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 reso nance 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 antiferr omagnetically at similar to 12 K. Ru in Ba2GdRu1-uCuuO6 orders at similar t o 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 Sr2YRu 1-uCuuO6 and Ba2GdRu1-uCuuO6 the Ru orders ferromagnetically in the a-b pla nes with the sheet magnetization alternating in direction as one moves alon g the c axis, forming a net antiferromagnetic structure. We find no evidenc e of a Ru signature in the magnetic resonance data anywhere in the range fr om 3 to 300 K, a result which is consistent with the electrons being itiner ant. Attempts to detect Ru magnetic resonances in various other materials h ave also failed. Since in Sr2YRu1-uCuuO6 the magnetic moments of the Ru and the Cu are ordered at low temperatures, its superconductivity is inconsist ent with a spin-fluctuation pairing model.