Theoretical Study on Spin and Orbital Moments in Actinide Magnets

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We have extended the Hartree-Fock (HF) calculation of the 5f orbital and spin moments (M_<orb> and M_<spin>, respectively) to NaCl-type ferromagnet USe and UTe in addition to US on the basis of an extended Hubbard model, where the 5f, 6d and 7s orbits of U atom and the 3s, 3p ones of S atom are included and the intraatomic multipole 5f-5f interaction is taken into account. We determined the parameters of transfer integral by using the LDA-FLAPW calculation in the paramagnetic state without spin-orbit interaction. The Slater integral except F^0 representing the 5f-5f interaction is determined by HF calculation or analyzes of high-energy spectroscopies. We determine F^0 so as to obtain an agreement between the calculation and the experiment for the total 5f moment. The obtained M_<spin> and M_<orb > are antiparallel with each other and the ratio M_<orb>/M_<2spin> is - 2.1, which is in agreement with experimental results. We determine self-consistently the expectation values of 14 number operators and 91 (= _<14>C_2) off-diagonal operators of the 5f state. The includion of the latter is found to be important to estimate the magnitude of spin dipole.We have also performed the HF calculation of M_<spin> and M_<orb> of the second-type antiferromagnets CoO and FeO with taking into account the full 3d orbits and multipole interaction and the O 2p orbits. The calculated M_<orb> of both systems is found to be - 1mu_B, which has been pointed out in a single-ion model. For CoO,we found as a HF solution a non-collinear magnetic structure in addition to a collinear structure, both of which are suggested as candidates by the neutron diffraction.