Magnetic properties of the trichlorides, tribromides, and triiodides of U(III), Np(III), and Pu(III)

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Abstract
Magnetic susceptibilities of uranium, plutonium, and neptunium trichlorides, tribomides, and triiodides were measured from 2.7°K to as high as 240°K with a vibrating‐sample magnetometer at applied fields up to 12 kOe. Antiferromagnetic transitions were observed in UCl3, TN=22.0±1.0°K; in UBr3, TN=15.0±0.5°K; in UI3, TN=3.4±0.2°K; and in PuCl3, TN=4.5±0.5°K. A ferromagnetic transition at Tc=4.75±0.1°K was found for PuI3, and a slight hysteresis was measured at 2.7°K. Temperature‐independent paramagnetism was observed for NpCl3 below 50°K, for α‐NpBr3 below 30°K, and for NpI3 below 15°K. All these latter compounds, and PuBr3, exhibited Curie‐Weiss paramagnetism at higher temperatures, with effective moments near the free‐ion moments. The experimental magnetic susceptibility of PuCl3 from 10 to 100°K agrees with the susceptibility calculated from crystal field energy levels and wavefunctions.