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

核磁共振谱仪的研制在这项研究中，我们需要一台宽频带的核磁共振光谱仪来观察磁序状态下的共振。我们在α‘-NaV_2O_5电荷有序体系中研究了均匀状态下的自旋动力学，观察到了核弛豫过程中的低维行为，这与我们从晶体结构上的预期是一致的。进一步了解这种行为和电荷涨落的影响是一个未来的问题。钒酸盐中的铁磁性为了研究受挫晶格上绝缘磁有序状态下的轨道和自旋态以及磁激发，我们研究了具有焦绿石结构的Lu_2V_2O_7钒酸盐。我们观察了铁磁性状态下Lu和V位的核磁共振谱来研究轨道状态。为了研究金属中的磁有序及其与金属-绝缘体转变的关系，我们研究了金属反铁磁体UNiGa5。我们分析了配体Ga位在反铁磁和顺磁相中的核磁共振谱，确定了Ga位的四极参数和内场。我们提出了一种新的具有磁空间群的磁结构的核磁共振分析和磁结构的表示分析，并将其应用于UNiGa5(发表在Physs.Rev.B上)。

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).