Ab Initio Study of Anisotropic Magnetism in US
Among the uranium monochalcogenides US lies closest to the itinerant regime of f-electron behavior and exhibits strong magnetic anisotropy along the < 111 > direction with magnetic moment of 1.55 ?B and a Curie temperature of 180 K. We have applied two different ab initio methods to investigate the origin in the electronic structure of the magnetic behavior. First, we have carried out full-potential Linearized Muffin-Tin Orbital (FPLMTO) polarized electronic structure calculations, with only spin-polarization (orbital polarization only via spin-orbit coupling) and also with explicit orbital polarization. While both calculations give the correct ground-state (ferromagnetic < 111 > state), only the spin-and-orbitally polarized calculation gives an ordered moment of 1.61 ?B in agreement with experiment. Second, we have carried out first-principles calculations synthesizing 1) a phenomenological theory of orbitally driven magentism which incorporates the hybridization-induced and RKKY exchange interactions on an equal footing, and 2) FPLMTO electronic structure calculations allowing a first-principles evaluation of the parameters entering the model Hamiltonian. Results for the ordered moment and ordering temperature will be presented, and the validity and limitations of the two methods will be discussed.