Neutron scattering studies of the magnetic structure of cupric oxide

In light of the recent discovery of copper oxide high-$T_c$ superconductors, we have reexamined the early neutron diffraction measurements on CuO by Brockhouse [B. N. Brockhouse, Phys. Rev. 94, A781 (1954)]. Our measurement confirmed the antiferromagnetic ordering in CuO below 225 K. The magnetic unit cell has a volume double that of the chemical unit cell. The ordered moment is 0.68${\mu }_B$ per Cu, significantly smaller than 1${\mu }_B$ expected for a spin-only ${\mathrm{Cu}}^{2+}$ ion. The diffuse scattering was also studied well above the Néel temperature, and was found to be mostly elastic, in clear contrast to that of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$.