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

The magnetic properties of both, the monopnictides and the monochalcogenide s, of uranium show some systematic features on going from the light to the heavy cations. There is, however, an essential difference in their systemat ics 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 exper iments were mostly measurements of high-temperature susceptibilities from w hich we extracted the paramagnetic Curie temperatures theta (p), the effect ive moments mu (eff) and a value chi (0) for the temperature-independent pa ramagnetic contribution of the modified Curie-Weiss law, which was valid fo r all cases. We changed systematically the chemical environment, i.e. the n umber of unbound electrons, by forming pseudobinary mixed crystals of the f ollowing classes: dilution with non-magnetic trivalent ions, mixtures of ch alcogens with pnictogens and dilution with tetravalent non-magnetic thorium ions. Our results show that the number of hybridized electrons is proporti onal to the number of unbound electrons. Hybridization is enhanced by dilut ion. chi (0) depends directly on the number of hybridized unbound electrons . (C) 2001 Elsevier Science B.V. All rights reserved.