Magnetic orderings of the Cu, Gd, and Ru moments in nonsuperconducting ${\mathrm{Ba}}_2{\mathrm{GdRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ and of the Cu and Ru moments in superconducting ${\mathrm{Sr}}_2{\mathrm{YRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ (whose superconducting onset temperature is ∼45 K) have been studied using dc susceptibility, microwave magnetic resonance, and neutron diffraction (on ${\mathrm{Sr}}_2{\mathrm{YRu}}_{0.85}{\mathrm{Cu}}_{0.15}{\mathrm{O}}_6$ only). In both homologues, Cu exhibits antiferromagnetism with an ordering temperature of ∼86 K (much greater than the resistive superconductivity onset transition of ∼45 K), and a magnon energy gap $ħ{\omega }_{\mathrm{magnon}}$ $\mathrm{}(q=0\mathrm{})\mathrm{}$ that exceeds the microwave photon frequency of $\omega /2\mathrm{}\pi =13\mathrm{}\mathrm{GHz}.$ The Cu moment extracted from neutron data for ${\mathrm{Sr}}_2{\mathrm{YRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ is $\sim 1.7{\mu }_B$ at low temperature. Gd, in ${\mathrm{Ba}}_2{\mathrm{GdRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6,$ is paramagnetic and displays a $g=2\mathrm{}$ electron spin resonance at temperatures above ∼48 K, which also persists well below ∼48 K (but with a very much broadened line), and orders antiferromagnetically at ∼12 K. Ru in ${\mathrm{Ba}}_2{\mathrm{GdRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ orders at ∼48 K, but in ${\mathrm{Sr}}_2{\mathrm{YRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ orders at ∼23 K and has a moment of $\sim 1.6{\mu }_B,$ extracted from neutron scattering data. In both ${\mathrm{Sr}}_2{\mathrm{YRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ and ${\mathrm{Ba}}_2{\mathrm{GdRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ 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 ${\mathrm{Sr}}_2{\mathrm{YRu}}_{1-u}{\mathrm{Cu}}_u{\mathrm{O}}_6$ the magnetic moments of the Ru and the Cu are ordered at low temperatures, its superconductivity is inconsistent with a spin-fluctuation pairing model.

• Received 13 June 2000

DOI:https://doi.org/10.1103/PhysRevB.63.214412