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Magnetic Frustration of Spin 1/2 Pyrochlore Compound

自旋 1/2 烧绿石化合物的磁阻

基本信息

批准号：
18540346
负责人：
YASUI Yukio
金额：
$ 1.94万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18540346/
关键词：
Magnetic Frustration Pytochere Lattice Quantum Spin NMR Neutron Diffraction Maenetic Correlation Length 粉末中性子回折 NMR 中性子散乱磁化率物性実験

项目摘要

The magnetic behavior in the low temperature region and the ground state of the quantum spin system with magnetically frustrated remain open problem theoretically and experimentally. Pyrochlore compound Hg_2Cu_2FeS has Cu^2+ ions with S=1/2, which consists of a 3-dimensional linkage of corner-sharing Gu_4 tetrahedra, and the Weiss temperature θ_w estimated from the temperature (T) dependence of the magnetic susceptibility is〜150 K, indicating the interaction between the Cu^2+ pins is antiferromagnetic. From these facts, this system is regarded as an ideal example of the geometrically frustrated quantum spins systems. The measurements of the magnetic susceptibility and specific heat as well as neutron diffraction studies have been carried out on the polycrystalline samples of Hg_2Cu_2F_6S. No magnetic transition has been observed in the temperature range clown to 2 K, indicating that the magnetic frustration is not released down to the lowest temperature. To extract microscopic informat … More ion of the magnetic behavior ; we have also carried out ^19F-NMR, Above〜100K the Knight shift roughly obeys the following Curie Weiss law. With decreasing T from〜100K, the Knight shift has a broad maximum at around 80K, and with further decreasing T, the Knight shift decreases significantly. We cannot distinguish if the Knight shift (spin component of the magnetic susceptibility) approaches zero or not, as Tapproaches zero, because of the increase in the width of the NMR spectra. The magnetic correlation length ξ is estimated by comparing the observed spin-lattice relaxation rate divided T,1/ (T_1T) with the theoretical result obtained by Ganals, et. al. for a 1/2 spin system on the pyrochlore lattice. The values of 1/ (T_1T) and increase gradually with decreasing T, and as the temperature is lowered, ξ increases to a value approximately equal to the Cu-Cu atomic distance. It is interesting that these behaviors seem to correspond to the characteristics of spin system with the geometrical frustration. Because the broadening of the NMR spectra induced by the effects of impurities and/or defects is observed in the low temperature region, it is required to be synthesized the higher purity sample. However, it is not easy to see the intrinsic behavior without the disturbance of the extrinsic effects such as lattice defects and/or impurities, because just a small perturbation brings about rather serious efforts on systems with large degeneracy, which steins from their geometrical characteristics. Less

具有磁性受挫的量子自旋系统的低温区磁性行为和基态在理论和实验上仍然是一个开放的问题。烧绿石化合物Hg_2Cu_2FeS具有S=1/2的Cu^2+离子，由共享角的Gu_4四面体组成三维链接，磁化率的温度(T)依赖性估计出Weiss温度θ_w为~ 150 K，表明Cu^2+引脚之间的相互作用是反铁磁性的。根据这些事实，该系统被认为是几何受挫量子自旋系统的一个理想例子。对Hg_2Cu_2F_6S多晶样品进行了磁化率、比热测量和中子衍射研究。在温度范围0 ~ 2 K内未观察到磁跃迁，表明在最低温度下，磁阻没有释放。以提取微观信息…更多离子的磁性行为；我们也进行了^19F-NMR，在~ 100K以上，奈特位移大致遵循以下居里韦斯定律。从~ 100K开始，随着T的减小，骑士位移在80K左右有一个宽的最大值，随着T的进一步减小，骑士位移显著减小。由于核磁共振波谱宽度的增加，我们无法区分奈特位移（磁化率的自旋分量）是否趋近于零。通过将观测到的自旋-晶格弛豫率除以t1 / (T_1T)与Ganals等人对焦绿石晶格上的1/2自旋体系的理论结果进行比较，估计出磁相关长度ξ。随着T的减小，1/ (T_1T)和ξ值逐渐增大，随着温度的降低，ξ值增大到近似等于Cu-Cu原子距离。有趣的是，这些行为似乎与具有几何挫折的自旋系统的特征相对应。由于在低温区观察到杂质和（或）缺陷的影响导致核磁共振谱的展宽，因此需要合成更高纯度的样品。然而，如果没有晶格缺陷和杂质等外在影响的干扰，很难看到系统的内在行为，因为很小的扰动就会对具有大简并度的系统产生相当大的扰动，这是由于系统的几何特性。少