Magnetic Properties of NaO2 and KO2

Abstract

The powder magnetic susceptibility of NaO₂ and KO₂ has been determined as a function of temperature from 63°K to around room temperature. The data for NaO₂ show anomalies at 190° and 225°K which are in good agreement with the location of λ‐anomalies reported in the specific heat and structure changes shown by x rays. A Curie‐Weiss relation χ=C/(T−θ) is obeyed above 225°K with θ=−46°K, and C gives a value for the average effective moment of 1.77_μB. The low susceptibility below 190°K and its temperature dependence suggest that the marcasite phase is antiferromagnetic. KO₂ shows no evidence of magnetic ordering down to 63°K. The reciprocal susceptibility curve is made up of two linear regions with the change in slope at 150°K. The effective moments are 1.20 and 1.03_μB with θ=−53° and −3°K for the high‐ and low‐temperature regions, respectively. Neutron‐diffraction results show a crystallographic distortion occurring at about 25°K.