Neutron-Diffraction Investigations on USb, UBi, and U3Sb4

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Abstract
Uranium monoantimonide, cubic rock‐salt structure, has been found to order magnetically at 246°K with a magnetic structure like that found in UN, UP and UAs, i.e., ferromagnetic sheets aligned oppositely in alternating layers perpendicular to the (001) axis. At 4.2°K Fm(110) = 2.76±0.15×10−12 cm (sinθ/λ = 0.114). Using a 5f3 extrapolation to sinθ/λ = 0, an indicated magnetic moment of 2.64 Bohr magnetons per uranium atom is obtained. Values of μf as a function of sinθ/λ were obtained and indicated a maximum in the region of sinθ/λ = 0.2, implying the presence of large orbital effects. The Néel temperature of 246°K is substantially different from that reported by Polish workers1 of 213°K. In subsequent work on U3Sb4, USb occurred as an impurity, and in this case a Néel temperature of 223°K was obtained, indicating possible compositional‐dependent magnetic behavior. UBi was prepared in a tantalum bomb and heat treated at 800°C for 24 h. The diffraction pattern could be indexed in a cubic rock‐salt lattice with parameters previously reported for UBi. However, the reflections were broader than normal, indicating a possible distortion of the rock‐salt lattice. No evidence was found for magnetic ordering in this sample to 4°K. Polish workers2 earlier had reported a magnetic behavior which was dependent on heat treatment. The discrepancy between this work and other work could be resolved if there were several polymorphic forms of UBi, and the magnetic properties were dependent on structure. U3Sb4 was found to order magnetically at 149°K in agreement with values reported by Polish workers1 of 146°K. At 4.2°K all magnetic reflections were associated with nuclear reflections and could be indexed on the chemical cell of U3Sb4, indicating a ferromagnetic ordering. However, the observed magnetic intensities did not correspond to a simple ferromagnet in which the uranium atom at each of the lattice sites had the same moment. The required moment distribution is currently under investigation.

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