Ab initio study of anisotropic magnetism in uranium compounds

We have applied two methods to investigate the origin in the electronic str ucture of the unusual magnetic behavior of the uranium monochalcogenides an d monopnictides. First, we have carried out spin-polarized electronic struc ture calculations based on the full-potential linearized muffin-tin orbital (FPLMTO) method with only spin-polarization (orbital polarization only via spin-orbit coupling) and also with orbital polarization correction. Second , we have carried out first-principles calculations synthesizing (1) a phen omenological theory of orbitally driven magnetism using a model Hamiltonian which incorporates explicitly the hybridization-induced and Coulomb exchan ge interactions on an equal footing, and (2) FPLMTO electronic structure ca lculations allowing a first-principles evaluation of the parameters enterin g the model Hamiltonian. Within the purely band calculation greater success is obtained for the zero-temperature ordered moments for the more itineran t compounds (US and UP), while the synthesis of phenomenology and electroni c structure method gives better agreement with experiment for the more loca lized pnictides (UBi, USb). Results for the ordered moments and ordering te mperatures are presented, and the validity and limitations of the two metho ds are discussed. (C) 1999 American Institute of Physics. [S0021-8979(99)73 308-6].