Neutron-powder-diffraction study of nuclear and magnetic structure in $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3-x}{\mathrm{Co}}_x{\mathrm{O}}_{7+y}$ with $x=0.84\mathrm{}$ and $y=0.32\mathrm{}$

Neutron powder diffraction has been used to study the crystal structure and magnetic ordering of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_{3-x}{\mathrm{Co}}_x{\mathrm{O}}_{7+y}$ with $x=0.84\mathrm{}$ and $y=0.32\mathrm{}$. Rietveld refinement of the crystal structure was carried out at 295 K (space group $\frac{P4\mathrm{}}{\mathrm{mmm}}$, $a=3.888\mathrm{}$ Å, $c=11.636\mathrm{}$ Å) and showed in particular that Co substitutes in the Cu(1) position of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$. Long-range, three-dimensional antiferromagnetism was observed up to a Néel temperature of about 405 K. All five detected magnetic peaks could be indexed on a wave vector (½ ½ ½) with $h$, $k$, $l$ all odd, indicating a body-centered tetragonal magnetic unit cell with $a_{\mathrm{mag}}=a\sqrt{2}$, $c_{\mathrm{mag}}=2c$. At 9 K the proposed magnetic structure has moments parallel to $c$ and antiferromagnetic ordering within both Cu and Co layers. Adjacent moments in neighboring Cu layers are antiparallel whereas the small moments found in the Co layers are parallel to their adjacent moments in the neighboring Cu layers. The ordered moment was 0.87${\mathrm{\mu }}_{\mathrm{B}}$ for the Cu layers and 0.16${\mathrm{\mu }}_{\mathrm{B}}$ in the Co layers, respectively. With increased temperature the ordered moments in the Co layers decrease faster than those in the Cu layer. At room temperature the ordered moment was 0.65${\mathrm{\mu }}_{\mathrm{B}}$ for the Cu layers with no detectable ordered moment in the Co layers.