Electronic-environment dependence of the magnetic properties of uranium monochalcogenides and monopnictides

The magnetic properties of both, the monopnictides and the monochalcogenides, of uranium show some systematic features on going from the light to the heavy cations. There is, however, an essential difference in their systematics which we attribute to the existence of one unbound electron per uranium ion in the chalcogenides, which, in turn, means that the uranium ion is in the trivalent state, or at least in a state close to trivalency. Our experiments were mostly measurements of high-temperature susceptibilities from which we extracted the paramagnetic Curie temperatures θp, the effective moments μeff and a value χ0 for the temperature-independent paramagnetic contribution of the modified Curie-Weiss law, which was valid for all cases. We changed systematically the chemical environment, i.e. the number of unbound electrons, by forming pseudobinary mixed crystals of the following classes: dilution with non-magnetic trivalent ions, mixtures of chalcogens with pnictogens and dilution with tetravalent non-magnetic thorium ions. Our results show that the number of hybridized electrons is proportional to the number of unbound electrons. Hybridization is enhanced by dilution. χ0 depends directly on the number of hybridized unbound electrons