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，具有钙钛矿型结构的4d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，我们重点研究了具有金属导电性的Sr_(1-x)&Gt；Ca_xRuO_3体系。这项工作的目的是从自旋涨落的角度解释该金属系统的磁性机制。为了获得系统的和微观的了解，我们主要进行了Ru和氧的核磁共振(核磁共振)。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。首先，从高达40T的高场磁化强度测量结果来看，该系统具有典型的巡回磁化特性：即使在40T时，该系统的磁化强度也不饱和。The Res…更多的比热实验结果揭示了强关联电子系统的特征：电子比热系数随交换作用的增加而显著增强，并随x的增大而增大，在x=0.8时达到最大值，约为100mJ/K~(-2)。这些伽马值及其温度变化可以用巡回电子铁磁系统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T_A。其中T_0是表示自旋涨落谱能量宽度的参数，T_A是给出自旋涨落谱的波数关系的参数。从170NMR谱中可以很好地理解x=L.0和0.6时的自旋晶格驰豫速率1/T_1，但1/T_1不能用SCR理论解释，导致SrRuO_3处于弱巡游铁磁系统和局域力矩铁磁系统之间的中间区域。这与该化合物中因瓦效应的发现是一致的。此外，这些结果还表明，失去长程磁序的CaRuO_3不属于反铁磁性化合物，而属于近铁磁性化合物。因此，我们得出结论，每个结果都可以理解为巡回铁磁性质，并且有证据表明存在反铁磁相互作用。RU核磁共振目前正在进行中，有望给我们提供关于磁性原子本身的直接信息。较少

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