MAGNETIC AND CRYSTALLOGRAPHIC STRUCTURES IN UTX INTERMETALLIC COMPOUNDS

Uranium, together with other actinides and lanthanides, forms a large group of ternary intermetallic compounds of stoichiometry UTX (T=transition metal, X=p electron metal). These compounds are formed in several structure types and the occurrence and stability of particular structures with respect to the transition metal content suggests reasonable systematics. We have also investigated the magnetic structures of selected UTX compounds and it is revealing to relate the crystallographic and magnetic structures, because of the relationship between the magnetic symmetry and that of the U atom environment produced by the 5f-ligand hybridization, and the consequent anisotropic exchange. Those of ZrNiAl structure type are collinear, with moments along the hexagonal c axis. In the orthorhombic TiNiSi structure type, the moments are confined to the b-c plane (perpendicular to the uranium chains) and the structures are often incommensurate. In the hexagonal CaIn2 (or GaGeLi) structure type, the magnetic structures form in an orthorhombic cell and, at ]east in the disordered centric group, again the moments lie perpendicular to the nearest-neighbour uranium spacing.