Antiferromagnetic order in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3-x}{\mathrm{Co}}_x{\mathrm{O}}_{6+y}$

We present a neutron scattering study of oxygen-deficient $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3-x}{\mathrm{Co}}_x{\mathrm{O}}_{6+y}$ where, with increasing Co concentration, long-range antiferromagnetic order develops on the chain sites. For $x=0.2\mathrm{}$, two magnetic transitions are found: Below $T_{N_2}=211\mathrm{}$ K, there is an ordered moment on both Cu sites, while for $T_{N_2}<T<\mathrm{}{T}_{N_1}=415\mathrm{}$ K only a "plane" moment is present. For $x=0.8\mathrm{}$, an ordered moment appears on both Cu sites with a single transition at 435 K. Evidence for magnetic ordering was also found by magnetic susceptibility measurements. These results imply that Co substitution enhances antiferromagnetic coupling between the "plane" and "chain" sites.