Hartree-Fock study on the 5f orbital magnetic moment of US

The U if spin (M-spin) and orbital (M-orb) magnetic moments in the ferromag netic compound US are calculated on the basis of the Hartree-Fock approxima tion for an extended Hubbard model. Our tight-binding model includes the U 6p,5f,6d, and 7s orbitals and the S 3s,3p, and 3d ones, and the intra-atomi c 5f-5f multipole interaction and the spin-orbit interaction in the 5f stat e are taken into account. Most of the parameters involved in the model are determined by fitting with the energy of Bloch electrons in the paramagneti c state obtained by a first-principles calculation based on the local densi ty approximation (LDA). The calculated ratio of the moments M-orb/M-spin of -2.1 and M-orb of - 3.2 mu(B) are in good agreement with available experim ental results. The calculated magnetic circular dichroism spectrum at the U 3d-->5f x-ray absorption also agrees with the recent experiment. An inclus ion of the expectation values of the spin-off-diagonal operators in additio n to the number operators in the 5f state is found to be crucially importan t in describing its proper magnetic state and problems of LDA in the estima tion of M-orb are discussed in this context. [S0163-1829(99)04509-9].