Theoretical Study on Itinerant Electron Systems Containing Transition-Metal, Rare-Earth, and Actinide Elements

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1. Electronic band structures of typical compounds containing transiton-metal, rare-earth, and actinide elements are calculated for the non-magnetic and magnetic states by a selfconsistent APW or KKR method. NiAs-type, cubic perovskite-type, Laves phase, and intercalation compounds containing 3d electrons are studied intensively. On the basis of the obtained band structures, magnetic properties of these compounds have been studied by taking account of spin fluctuations. Also a stability of the crystal structure and of the magnetic ordering is discussed by comparing the total energy of each phase. For Ce and U compounds containing 4f and 5d electrons, the effects of the spin-prbit interaction on the energy band states are investigated in detail. Band calculation of La_2CuO_4 has been performed in order to derive information about the characteristic aspects of the high-T_c oxide superconductor.2. Spin flluctuations play an essential role in the magnetism of itinerant electron systems at finite temperatures. The self-consistent renormalization theory developed by Moriya has provided a successful understanding of the observed mangetic properties of intermetallic compounds such as CrB_2 and YMn_2. Furhtermore, the unified theory of spin fluctuations is used in the study of anomalous magnetic properties of the NiAs-type compounds such as MnAs and CoAs, and of the surface magnetism of Ni.3. A strong electron correlation is extremely important in heavy-electron systems such as Ce compounds and actinide compounds and in high-T_c oxide superconductors. The Fermi liquid theory based on the perodic anderson model is extended to the case including the crystalline field and the spin-orbit interaction. Theoretical analyses of phototelectron spectroscopy in Ce and La compounds have been made by using the isngle-site impurity Anderson model.. A considerable ellort has been devoted to making clear a role of electron correlation in high-T_c oxide superconductors.