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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

具有磁阻挫的量子自旋系统在低温区的磁行为和基态在理论和实验上都是一个未解决的问题。烧绿石化合物Hg_2Cu_2FeS中Cu^2+离子的S=1/2，由共角的Gu_4四面体三维键合组成，由磁化率随温度的变化关系估算出韦斯温度θ_w为150 K，表明Cu^2+钉扎之间的相互作用是反铁磁的。因此，该系统被认为是几何阻挫量子自旋系统的一个理想例子。本文对Hg_2Cu_2F_6S多晶样品进行了磁化率、比热的测量和中子衍射研究。在低于2K的温度范围内没有观察到磁相变，表明磁阻挫在最低温度下没有释放。提取显微信息 ...更多信息我们还进行了~（19）F-NMR，在100 K以上，Knight位移大致服从居里韦斯定律。随着T从100 K开始降低，奈特位移在80 K附近具有宽的最大值，并且随着T的进一步降低，奈特位移显著降低。由于NMR谱的宽度增加，当T接近零时，我们无法区分奈特位移（磁化率的自旋分量）是否接近零。通过将观测到的自旋-晶格弛豫速率除以T_（1/T_1T）与Ganals等人的理论结果进行比较，估算了磁关联长度τ。对于烧绿石晶格上的1/2自旋系统。1/（T_1T）和1/（T_1T）的值随着T的降低而逐渐增大，随着温度的降低，1/（T_1T）的值逐渐增大，且1/（T_1T）和1/（T_1T）的值随着温度的降低而增大，1/（T_1T）的值近似等于Cu-Cu原子间距。有趣的是，这些行为似乎对应于自旋系统的几何挫折的特点。由于在低温区观察到由杂质和/或缺陷的影响引起的NMR谱的加宽，因此需要合成更高纯度的样品。然而，在没有晶格缺陷和/或杂质等外在效应干扰的情况下，不容易看到本征行为，因为对于具有大简并度的系统，仅仅一个小的扰动就会带来相当严重的影响，这与它们的几何特性有关。少