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=trans ition metal, X=p electron metal). These compounds are formed in severa l structure types and the occurrence and stability of particular struc tures with respect to the transition metal content suggests reasonable systematics. We have also investigated the magnetic structures of sel ected UTX compounds and it is revealing to relate the crystallographic and magnetic structures, because of the relationship between the magn etic symmetry and that of the U atom environment produced by the 5f-li gand 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 con fined to the b-c plane (perpendicular to the uranium chains) and the s tructures 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 p erpendicular to the nearest-neighbour uranium spacing.