Magnetic Properties of Uranium Compounds with NaCl Structure

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Abstract
A model is proposed to account for the properties of uranium compounds UX, where X is either an element of the VA group (N, P, As, Sb; UV compounds) or of the VIA group (S, Se, Te; Uvi). Uv compounds are antiferromagnetic, while Uvi are ferromagnetic. All have high transition temperatures (50–220) °K and low electrical resistivities. It is assumed that uranium is in the U4+ state (3H4 configuration) both in Uv and Uvi compounds and the 5f electrons are strongly localized. The X anions are triply ionized in Uv compounds, and doubly in Uvi. The surplus electrons form a conduction band. The U ions are treated by the methods of ``crystal field'' theory. The coupling between them is via the RKKY mechanism. The coupling constant is calculated to be in the range of 12 to 22 eV Å3. In the octahedral field present the 3H4 multiplet splits, so that the ground state is a singlet. The observed saturation moment depends on the relative strength of the crystal field and the exchange interaction. The crystal-field splittings derived are in the range 500–1200 cm−1. The model accounts for the observed types of magnetic ordering. The assumptions used are justified briefly.

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