Antiferromagnetism in Potassium Superoxide KO2

Abstract

Neutron‐diffraction measurements made on polycrystalline samples of KO₂ at several temperatures from 295° to 1.4°K have shown the existence of an antiferromagnetic transition in this compound at 7°K. These measurements have also revealed a crystal structure change slightly above the Néel temperature at about 12°K. Since the packing in the crystal structure involves close contacts between neighboring oxygen molecules, there is probably a correlation between the packing arrangements of these molecules with the onset of magnetic order, and the antiferromagnetic structure could be the result of direct exchange. Only two magnetic reflections definitely can be observed and a unique antiferromagnetic structure cannot be determined. However, the reflections suggest a structure in which there are ferromagnetic sheets of moments parallel to the (00l) planes and the moments on molecules in adjacent planes are antiparallel. The magnetic form factor determined from an analysis of the paramagnetic neutron scattering is in satisfactory agreement with that obtained from theoretical calculations based on the O₂ molecule.