ルテニウム系ペロブスカイト型酸化物の異常な遍歴電子物性

近年来，钙钛矿型结构的四维过渡金属（特别是Ru）氧化物体系得到了广泛的研究。其中，在本研究工作中，我们重点研究了Sr_<1-x>Ca_xRuO_3体系，该体系具有金属导电性。本工作的目的是从自旋涨落的角度阐明该金属体系的磁性能机理。为了得到系统的和微观的认识，我们主要对Ru和氧进行了核磁共振（NMR）。原子核，前者属于磁性原子本身，后者位于Ru原子之间的化学键中。从流动磁学的角度对其比热和强磁场进行了测量和分析。首先，从高达40 T的高场磁化测量结果中，观察到流动系统的一个典型特性：即使在40 T时，该系统的所有样品的磁化也不饱和。进一步的比热实验结果揭示了强相关电子系统的特征：电子比热系数γ在交换作用下得到了极大的增强，并随x的增大而增大，在x=0.8时达到最大值约为100 mJ/K^2mol。这些伽马值及其温度变化可以用自旋涨落的自洽重整化（SCR）理论来解释。根据他们的分析，可以得到每个x的自旋涨落参数T_0和TA，其中T_0是表示自旋涨落谱能量宽度的参数，T_A是表示自旋涨落谱波数依赖关系的参数。从170核磁共振，自旋-晶格弛豫率1/T_1为x= 1。0和0.6被SCR很好地理解。然而，1/T_1不能用SCR理论解释，导致SrRuO_3处于弱流动和局部矩铁磁系统之间的中间区，这与该化合物中invar效应的发现是一致的。此外，这些结果表明，CaRuO_3失去了长程磁序，不能归类为反铁磁性化合物，而可以归类为近铁磁性化合物。因此，我们得出结论，每个结果都可以理解为流动铁磁性质，并且有证据表明存在反铁磁相互作用。钌核磁共振现在正在进行中，有望给我们提供磁性原子本身的直接信息。少

Recently, the 4d transition metal (especially, Ru) oxide systems with perovskite type structure have been extensively investigated. Among them, in this research work, we focus on the Sr_<1-x>Ca_xRuO_3 system, which shows metallic conductivity. The purpose of this work is to elucidate the mechanism of magnetic properties of this metallic system from the standing point of spin fluctuations. In order to get systematic and microscopic understandings we mainly conducted the nuclear magnetic resonances (NMR) of Ru and Oxygen. Nuclei, former of which belongs to the magnetic atom itself and the latter locates in the chemical bonds between Ru atoms. The specific heat and high-field magnetization have also been measured and analyzed from a view point of itinerant magnetism.First, from the results of the high-field magnetization measurements up to 40 T, a typical property of itinerant system was observed : the magnetization does not saturate even at 40 T for all the sample of this system. The res … More ults of the specific heat experiments revealed characteristic property of strongly correlated electron system : the electronic specific heat coefficient gamma is largely enhanced by exchange interaction and increases with increasing x from 0, and takes a maximum value of about 100 mJ/K^2mol at x=0.8. These values of gamma and their temperature variations were found to be understood by the self-consistent renormalization (SCR) theory of spin fluctuations for itinerant-electron ferromagnetic system. As a result of their analyses, the spin fluctuation parameters T_0 and TA can be obtained for every x. Here, T_0 is the parameter indicating the energy width of spin-fluctuation spectrum, and T_A the parameter which gives the wave number dependence of spin-fluctuation spectrum.From 170 NMR the spin-lattice relaxation rates 1/T_1 for x=l .0 and 0.6 were found to be well understood by the SCR.However, 1/T_1 was not explained by the SCR theory, leading to that SrRuO_3 locates in the intermediate regime between weak itinerant and localized moment ferromagnetic systems, which is consistent with the discovery of the invar effect in this compound. Furthermore, these results indicate that CaRuO_3, which loses the long-range magnetic order, can be classified not as the antiferromagnetic compound but as the nearly ferromagnetic compound. Therefore, we conclude every result can be understood as itinerant ferromagnetic properties and there is evidence for the existence of antiferromagnetic interaction. Ru NMR is now in progress and can be expected to give us a direct information of magnetic atom itself. Less