Physic and Chemistry of Oxygen Holes : Phase Transitions and Dynamics in High-Valence Transition-Metal Oxides

·We have succeeded in synthesizing single crystalline thin films of perovskite-type oxides SrFeO_3，CaFeO_3and SrFe_&lt；0.5&gt；Co_&lt；0.5&gt；O_3containing unusually high valence Fe^&lt；4+&gt；and Co^&lt；4+&gt；ions。The films were fabricated using the laser ablation technique and subsequent oxidation using ozone。We discovered unusual anomalous Hall effect in SrFeO_3thin film·Charge disproportionation in perovsfcite-lype Fe oxides were studied using photoemission spectroscopy and Hartree-Fock band-structure calculations.It was found that electron-lattice interaction plays an important role in the charge disproportionation in CaFeO_3whereas the charge disproportionation occurs purely electronically in La_&lt；1/3&gt；Sr_&lt；2/3&gt；FeO_&lt；3-&gt；。·Moessbauer measurements of CaFeO_3Sr_&lt；2/3&gt；La_&lt；1/3&gt；FeO_&lt；3-&gt；were made under high pressure in order to study the pressure dependence of charge disproportionation and magnetic ordering。We found that under high pressure，Sr_&lt；2/3&gt；La_&lt；1/3&gt；FeO_&lt；3-&gt；becomes a ferromagnet with a high Cu…More rie temperature。·We performed Moessbauer measurements on a double-layer perovskite Sr_3Fe_2O_7，and a triple-layer perovskite LaSr_3Fe_3O_&lt；10&gt；and discovered charge disproportionatian in these compounds.We also found helical magnetic ordering in Sr_3Fe_2O_7，and a collinear one in LaSr_3Fe_3O_&lt；10-&gt；.·Inelastic nuclear resonant scattering of synchrotron radiation was made on CaFeO_3and Sr_&lt；2/3&gt；La_&lt；1/3&gt；FeO_&lt；3-&gt；Changes in the Fe local phonon density of states were observed across the charge ordering temperature.·In the measurements of the nuclear resonance scattering from CaFeO_3and Sr_&lt；2/3&gt；La_&lt；1/3&gt；FeO_3，a dramatic change in the intensity of the elastic peak across the magnetic phase transition was discovered。·Element-selective inelastic nuclear resonance scattering measurements from^&lt；161&gt；Dy and^&lt；57&gt；Fe nuclei were made on perovskite-type DyFeO_&lt；3-&gt；.The local phonon density of states of Dy and Fe thus obtained were compared with shell-model calculations，and the mode assignment was made。·By the measurements of magnetic circular dichroism in soft-x-ray absorption，the electronic and magnetic states of SrFe_&lt；1-x&gt；Co_xO_3 and their changes induced by Co substitution were identified.·Single crystals of PrNiO_3were synthesized under high pressure.It was found that across the metal-insulator transition，the symmetry is lowered from orthorhombic to monoclinic.Furthermore，charge disproportionation at the Ni sites were confirmed in the insulating monoclinic phase.·Triclinic perovskite PrNi0_3was synthesized under high pressure.The Bi atoms at the Asites were found to charge-disproportinate into Bi^&lt；3+&gt；and Bi^&lt；5+&gt；.We found that，when La^&lt；3+&gt；ions were substituted for the Bi ions，a metal-insulator transition occurred as a function of atomic composition。·On the basis of photoemission results on perovskite-type Ni oxides，we proposed that there are two kinds of metallic states within the well-known metallic phase，namely，the conventional Pauli-paramagnetic phase and the Curie-Weiss paramagnetic phase with a peudogap.Less：Less

・ We have succeeded in synthesizing single crystalline thin films of perovskite-type oxides SrFeO_3, CaFeO_3 and SrFe_<0.5>Co_<0.5>O_3 containing unusually high valence Fe^<4+> and Co^<4+> ions. The films were fabricated using the laser ablation technique and subsequent oxidation using ozone. We discovered unusual anomalous Hall effect in SrFeO_3 thin film・ Charge disproportionation in perovsfcite-lype Fe oxides were studied using photoemission spectroscopy and Hartree-Fock band-structure calculations. It was found that electron-lattice interaction plays an important role in the charge disproportionation in CaFeO_3 whereas the charge disproportionation occurs purely electronically in La_<1/3>Sr_<2/3>FeO_<3->.・ Moessbauer measurements of CaFeO_3 Sr_<2/3>La_<1/3>FeO_<3-> were made under high pressure in order to study the pressure dependence of charge disproportionation and magnetic ordering. We found that under high pressure, Sr_<2/3>La_<1/3>FeO_<3-> becomes a ferromagnet with a high Cu … More rie temperature.・ We performed Moessbauer measurements on a double-layer perovskite Sr_3Fe_2O_7, and a triple-layer perovskite LaSr_3Fe_3O_<10> and discovered charge disproportionatian in these compounds. We also found helical magnetic ordering in Sr_3Fe_2O_7, and a collinear one in LaSr_3Fe_3O_<10->.・ Inelastic nuclear resonant scattering of synchrotron radiation was made on CaFeO_3 and Sr_<2/3>La_<1/3>FeO_<3-> Changes in the Fe local phonon density of states were observed across the charge ordering temperature.・ In the measurements of the nuclear resonance scattering from CaFeO_3 and Sr_<2/3>La_<1/3>FeO_3, a dramatic change in the intensity of the elastic peak across the magnetic phase transition was discovered.・ Element-selective inelastic nuclear resonance scattering measurements from ^<161>Dy and ^<57>Fe nuclei were made on perovskite-type DyFeO_<3->. The local phonon density of states of Dy and Fe thus obtained were compared with shell-model calculations, and the mode assignment was made.・ By the measurements of magnetic circular dichroism in soft-x-ray absorption, the electronic and magnetic states of SrFe_<1-x>Co_xO_3 and their changes induced by Co substitution were identified.・ Single crystals of PrNiO_3 were synthesized under high pressure. It was found that across the metal-insulator transition, the symmetry is lowered from orthorhombic to monoclinic. Furthermore, charge disproportionation at the Ni sites were confirmed in the insulating monoclinic phase.・ Triclinic perovskite PrNi0_3 was synthesized under high pressure. The Bi atoms at the Asites were found to charge-disproportinate into Bi^<3+> and Bi^<5+>. We found that, when La^<3+> ions were substituted for the Bi ions, a metal-insulator transition occurred as a function of atomic composition.・ On the basis of photoemission results on perovskite-type Ni oxides, we proposed that there are two kinds of metallic states within the well-known metallic phase, namely, the conventional Pauli-paramagnetic phase and the Curie-Weiss paramagnetic phase with a peudogap. Less