Orbital states and polarized X-ray absorption

Roles of polarized X-ray in identifying the orbital polarization other than the spin polarization in d- and f-electron systems are reviewed from a theroretical point of view. First, by choosing the ferromagnetic uranium sulfide, we address a theoretical attempt to calculate 5f atomic orbital magnetic moment and to analyze X-ray magnetic circular dichroism (XMCD) in U M-4.5 absorption on the basis of Hartree-Fock calculation. Second. we present the relation between calculated X-ray linear dichroism (XLD) in L-2.3 absorption and the 3d orbital polarization on the basis of a single-ion model including the multipole interaction between electrons, which is called orbital ordering, in perovskite-type transition-metal oxides including LaMnO3. A prospect of hard XLD in studying orbital orderings is also discussed. (C) 2004 Elsevier B.V. All rights reserved.