Charge ordering and metal-insulator transition in mixed-valence transition metal oxcides

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Developement of NMR spectrometerIn this research, we need an NMR spectrometer with wide band width to observe the resonance in magnetically ordered states. We developed a spectrometer for 5 to 220MHz.Charge ordering in vanadatesWe studied the spin dynamics in the uniform state in a charge ordering system α'-NaV_2O_5. We observed low-dimensional behavior in the nuclear relaxation ; it agrees with our expectation from the crystal structure. The further understanding of this behavior and effects of charge fluctuation is a future problem.Ferromagnetism in vanadatesIn order to study the orbital and spin states and the magnetic excitations in insulating magnetic ordered states on frustrated lattices, we studied a vanadates with the pyrochlore structure Lu_2V_2O_7. We observed NMR spectra for Lu and V sites in the ferromagnetic state to investigate the orbital state. The experiments and the data analysis are in progress.Antiferromagnetism in f-electron systemsIn order to study magnetic ordering in metals and its relation with metal-insulator transition, we studied a metallic antiferromagnet UNiGa_5. We analyzed NMR spectra for the ligand Ga sites in the antiferromagnetic and paramagnetic phases and determined the quadrupole parameters and the internal fields at the Ga sites.We proposed a new NMR analysis of magnetic structures with magnetic space group and the representation analysis of magnetic structure and applied it to UNiGa_5 (published in Phys.Rev.B).