Long-Range Magnetic Interactions in Uranium Monopnictides and Monochalcogenides and Their Solid Solutions

Abstract

Uranium monopnictides (Uv) and monochalcogenides (Uvi) and their solid solutions have a NaCl-type structure and are good conductors of electricity. Measurements of the magnetic properties of these compounds show that the magnetic interactions between the localized 5f-electrons are of long range. Such long-range interactions are responsible for the type-I antiferromagnetic structure of Uv compounds and the ferromagnetic structure of Uvi compounds, although these magnetic structures could be explained by molecular field theory. A neutron diffraction study of the UP-US solid solutions has revealed two new long-range magnetic structures at intermediate compositions, the type-IA (2+, 2−) antiferromagnetic structure (found also in UAs at low temperatures) and the antiphase (5+, 4−) ferrimagnetic structure. These structures are due to long-range RKKY-type interactions via the conduction electrons. Analogous structures are observed in the lanthanides (e.g., thulium) and their metallic compounds. As the weight of the anions present increases, the importance of superexchange interactions increases and affects the type of magnetic ordering. This effect is more pronounced in lanthanide monopnictides and europium monochalcogenides than in the Uv and Uvi compounds.