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

低温区的磁行为和磁挫败量子自旋系统的基态在理论上和实验上仍然是一个悬而未决的问题，烧绿石化合物Hg_2Cu_2FeS具有S=1/2的Cu^2+离子，其由3维组成。共享角 Gu_4 四面体的连接，根据磁化率的温度 (T) 依赖性估算出的 Weiss 温度 θ_w 约为 150 K，表明Cu^2+针具有反铁磁性，该系统被认为是几何受挫量子自旋系统的理想例子，并且已经在多晶上进行了磁化率和比热的测量以及中子衍射研究。 Hg_2Cu_2F_6S样品在2K温度范围内没有观察到磁转变，表明磁挫败没有释放到最低温度。磁行为的微观信息；我们还进行了^19F-NMR，在~100K以上，奈特位移大致遵循以下居里维斯定律，随着T从~100K降低，奈特位移在大约100K处有一个宽的最大值。 80K，并且随着 T 进一步减小，我们无法区分奈特位移（磁化率的自旋分量）是否接近零，因为 T 接近零。核磁共振谱宽度的增加通过将观察到的自旋晶格弛豫率除以 T,1/ (T_1T) 与 Ganals 等人获得的理论结果进行比较来估计。烧绿石晶格上的自旋系统 1/ (T_1T) 的值随着 T 的减小而逐渐增大，并且随着温度的降低， xi 增大到约等于 Cu-Cu 原子的值。有趣的是，这些行为似乎与具有几何挫败性的自旋系统的特征相对应，因为在低温区域观察到由杂质和/或缺陷的影响引起的核磁共振谱的展宽，这是必需的。然而，在没有晶格缺陷和/或杂质等外在效应的干扰下观察内在行为并不容易，因为即使是一个小的扰动也会对具有大的系统带来相当严重的影响。简并性，这取决于它们的几何特征。