Internal sublattice fields of antiferromagnetic ${\mathrm{O}}_2$ as determined by the nuclear heat capacity of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$

Below 23 °K, solid oxygen becomes antiferromagnetic. Interaction between the sublattice magnetic fields and the magnetic moments of the isotope ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ gives rise to a nuclear heat capacity. This paper describes the results of measurements of the specific heat of solid oxygen with 40% enriched ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ from 0.05 to 0.20 °K. The effective field seen by the nuclei is measured to be 4.97 ± 0.2 T.