Mixed-Valent State and Conductivity of Rare Earth-Transition Metal Chalcogenide

稀土-过渡金属硫属化物的混合价态和电导率

• 批准号: 07454186
• 负责人: YOSHIMURA Kazuyoshi
• 金额: $ 4.42万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1995
• 资助国家: 日本
• 起止时间: 1995 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07454186/
• 关键词: rare-earth chalcogenide; mixed- valent state; dense Kondo effect; strongly correlated electron; nuclear magnetic resonance; transition metal compound; itinerant-electron magnetism; 混合原子価; フェルミ液体; 核磁気共鳴; 金属化合物

Transition metal compounds, which show metallic conductivity, are generally known to be in mixed-valent states. Among copper chalcogenide system, the compounds containing the rare earth element Pr becomes semiconducting, although they have a composition in which the mixed-valent states are realized. In order to elucidate this reason, we have measured the values of valences of cations utilizing the Coulometric titration method, performed valence bond estimations from rietvert analyzes of X-ray diffraction data, done the copper antiferromagnetic nuclear resonance (AFNMR) and nuclear quadrupole resonance (NQR). As their results, it has been found that there occurs a hybridization (mixing) between Pr 4f and copper 3d and/or oxygen 2p orbitals, resulting in the localization of holes doped to the system through a kind of Fermi surface effect (Kondo effect).As a result of our investigation of compounds based on the combination of rare earth element Yb and 3d transition metal Cu, the intermeta … More llic compound system YbCu_<5-x>Ag_x with the cubic BeCu_5-type structure has been found to show a dense Kondo effect in the whole composition x-range, where the characteristic temperature (Kondo temperature) varies systematically. On the other hand, isostructural system YbCu_<5-x>In_x has been found to show a crossover from a dense Kondo system (x=0) to a fluctuating system accompanied with the valence transition (x=1). Furthermore, the Kondo insulator-like behavior was observed in the intermediate composition. Typical phenomena due to the frustration effect have also been observed in the strongly correlated electron system, R_2V_2O_7 and R_2Ru_2O_7 (R being rare earth element) compounds with the pyrochlore-type structure.As for improving the apparatus, we made a improvement of NMR apparatus by introducing the wide-band power amplifier and the digital memory system in order to be able to measure the relaxation time in the last year. In this year, we have introduced the 8T superconducting magnet with high resolution in order to measure high resolution NMR.By using this apparatus, we have performed the ^<17>O NMR in the ruthenate system and investigated the dynamical behavior of Ru spins by measuring ^<17>O nuclear spin-lattice relaxation time. As a result, it has been found that the invar-type compound SrRuO_3 does not follow the mean-field localized moment model as well as the spin fluctuation theory which is valid in the case of weak itinerant electron magnets, implying that the system is in the intermediate metallic electron state. Furthermore, although CaRuO_3 was thought to have strong antiferromagnetic correlation, its dynamical behavior indicates that this compound is a Pauli paramagnet being very close to the ferromagnetic state with a strong ferromagnetic spin correlation. Our result of the specific heat measurement on CaRuO_3 can be explained by the itinerant electron spin fluctuation theory, which is consistent with the NMR result.Furthermore, from now on, we have a plan to investigate the Yb chalcogenide compounds from the microscopic and dynamical view points. Less

显示金属导电性的过渡金属化合物通常已知为混合价态。在铜硫属化物系统中，含有稀土元素Pr的化合物变成半导体，尽管它们具有实现混合价态的组成。为了阐明这一原因，我们利用库仑滴定法测量了阳离子的价态值，通过X射线衍射数据的里特分析进行了价键估计，进行了铜反铁磁核共振（AFNMR）和核四极共振（NQR）。结果表明，Pr 4f与Cu 3d和/或氧2 p轨道之间存在杂化（混合），通过费米表面效应（Kondo效应）使空穴局域化，并对稀土Yb与3d过渡金属Cu的化合物进行了研究，发现Pr 4f与Cu 3d和/或氧2 p轨道之间存在杂化（混合），从而使空穴局域化。 ...更多信息 具有立方BeCu_5型结构的化合物YbCu_<5-x>Ag_x在整个x范围内表现出致密的Kondo效应，其特征温度（Kondo温度）呈系统变化。而YbCu_ In_x等结构系统<5-x>则表现出从致密Kondo系统（x=0）到涨落系统（x=1）的过渡，并伴有价态跃迁。此外，在中间组合物中观察到近藤绝缘体样行为。在强关联电子系统R_2V_2O_7和R_2Ru_2O_7中也观察到了典型的阻挫效应现象（R为稀土元素）具有焦绿石型结构的化合物。至于改进该装置，我们对核磁共振仪进行了改进，引进了宽谱仪，波段功率放大器和数字存储系统，以便能够测量在过去一年的弛豫时间。今年，我们引进了高分辨超导磁体8 T，并利用该装置进行了<17>钌酸盐体系的~ 1H NMR，通过测量~ 1H自旋-晶格弛豫时间研究了Ru自旋的动力学行为<17>。结果表明，Invar型化合物SrRuO_3不符合平均场局域磁矩模型和弱巡游电子磁体的自旋涨落理论，处于中间金属电子态。此外，虽然CaRuO_3被认为具有很强的反铁磁关联，但其动力学行为表明该化合物是一个Pauli顺磁体，非常接近铁磁态，具有很强的铁磁自旋关联。我们对CaRuO_3比热的测量结果可以用巡游电子自旋涨落理论来解释，这与核磁共振结果是一致的。此外，今后我们还计划从微观和动力学角度研究Yb硫族化合物。少

项目成果

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R.L.Corey：“^<63>Cu(2)核四极杆和 YBa_2Cu_4O_8 在正常和超导状态下的核磁共振研究”Phys.Rev.B。

M. Kato: "Coulometric Determination of Pr in the Ln-Ba-Cu-O System" Proceedings (ISS'95), Advances in Superconductivity. VIII. 359-362 (1996)

M. Kato：“Ln-Ba-Cu-O 系统中 Pr 的库仑测定”论文集 (ISS95)，超导进展。

K. Yoshimura: "Supercondueting Properties of the La_<1+x>Ba_<2-x>Cu_3O_y System" Advances in Superconductivity VII(Springer-Verlag). 377-380 (1995)

K. Yoshimura：“La_<1x>Ba_<2-x>Cu_3O_y 系统的超导特性”Advances in Superconductivity VII（Springer-Verlag）。

吉村一良: "化学分野" ISTEC. 9 (1). 14-15 (1996)

吉村和义：“化学” ISTEC 9 (1)。

H. Aruga-Katori: "Field-induced Valence Transition in YbIn_<1-x>Ag_xCu_4" Journal of Magnetism and Magnetic Materials. 140-144. 1245-1246 (1995)

H. Aruga-Katori：“YbIn_<1-x>Ag_xCu_4 中的场诱导价态跃迁”《磁性与磁性材料杂志》。