Neutron-diffraction study of $\alpha$- and $\beta$-oxygen

Neutron-diffraction experiments were performed on polycrystalline samples of $\alpha -{\mathrm{O}}_2$ at 6 and 22 K and on $\beta -{\mathrm{O}}_2$ at 30 K. A large amount of preferred orientation was observed in all samples. For the first time a quantitative analysis was carried out to determine the magnetic structures with the use of the Rietveld profile refinement technique. The magnetic structure of $\alpha -{\mathrm{O}}_2$ is collinear anti-ferromagnetic with the moments directed nearly along the monoclinic $b$ axis. In $\beta$-oxygen only short-range order is present, and the local magnetic structure is described as consisting of three anti-ferromagnetically coupled (120°) sublattices.