Polarization and ordering of conduction bands in highly concentrated f-electron systems

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Variety of ordering phenomena and dynamics of f-electron systems were theoretically investigated paying special attention to the role of the spin degree of freedom of the conduction electrons, and following results were obtained.1.CeRh3B2 has the highest Curie temperature (120 K) as Ce compounds, and shows various anomalies such as the reverse-polarization of conduction electrons, strong anisotropy, and a small moment. We proposed a model which respects mixture between 4d molecular orbitals of Rh and 4f electron of flanking Ce ions, and explained this ferromagnetism in terms of a flat band mechanism.2.We have identified the order parameter of the phase IV of Cel-xLaxB6 as magnetic octupoles, which has been a longstanding mystery. Our model explains recent X-ray scattering results consistently. Our paper became an Editors' Choice in J.Phys.Soc.Jpn, and was reported by the press.3.The band calculation by dynamical mean-field theory was formulated, and the program code was developed. Previous theories could not take account of important spin-orbit interaction and the crystalline electric field effects. Quantitative calculations were performed by extending the NCA method, and incorporating this in the LMTO band calculation.4.Ternary Np compounds NpTGa5(T=Co, Ni, Rh) have been actively studied by neutron scattering. We have proposed a unified model that can explain a variety of magnetic orders of these compounds, and explained naturally complex ordered states. The Np orbital degrees of freedom are identified as the source of various magnetic orders, and a crystal deformation was predicted associated with the order.5.We have proposed the order parameters of Pr skutterudites as the scalar-type that keeps the cubic symmetry of the crystal. Our model naturally explains the NMR characteristics such as dependence on magnetic field direction, the anisotropy of the magnetization, and isotropic susceptibility.