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Nuclear magnetic resonance studies of magnetic properties of antiferromagnetic triangular spin system isolated in nano-meter region

纳米区反铁磁三角自旋系统磁特性的核磁共振研究

基本信息

批准号：
18540330
负责人：
FURUKAWA Yuji
金额：
$ 2.43万
依托单位：
Hokkaido 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-18540330/
关键词：
Spin frustrations Nuclear magnetic resonance Spin Chirality 分子磁性体

项目摘要

We have carried out nuclear magnetic resonance (NMR) measurements at very low temperatures down to 0.05K using a He^3- He^4 dilution refrigerator in order to investigate the magnetic properties of an nanoscale molecular magnet K_6[V_<15>As_6O_<42>H_2HO]・8H_2O (in short V15). The V15 cluster is know to be an typical Heisenberg triangular antifenomagnet and an ideal and simplest system to investigate the effects of spin chirality on the magnetism. The cluster is comprised of fifteen V^<4+> ions with S=1/2, which are arranged in a quasi-spherical layered structure with a triangle sandwiched between hexagons. All the exchange interactions between V^<4+> spins are antiferromagnetic. Each hexagon of the cluster consists of three pans of strongly coupled spins with J-800K, resulting in spin singlet state at low temperatures. Only threes V^<4+> spins on the triangle therefore play an important role on the magnetic properties at low temperatures. The exchange interactions between V^<4+> spins o … More n the triangle is known to be J =2.44K Followings are summary of main results.(1) Energy level structure of V15 cluster is determined by NMR and μSR measurements. (Paper No.1 and 2)(2) A spin singlet state of V^<4+> spin on the hexagons at low temperature was directly revealed by the observation of ^<51> VNMR signal from the V ions on the hexagons. (Paper No.3)(3)We have succeeded to observe on-site ^<51>V-NMR signal from magnetic ions on the triangle at very low temperatures below 0.1K. In the total spin S_T=3/2 ground state (non frustrated state), each V^<4+> spin on the triangle has been revealed to have almost full spin moment of 1μ_B and spin of three V ions on the triangle directs along to external field, resulting in total spin S_T=3/2. In the case of S_T=1/2 frustrated state, a pure chiral state expected in an s=1/2 Heisenberg triangular antiferromagnet is found to be broken down in the V15 cluster. Instead, the two S_T=1/2 states are found to be expressed by the mixed chiral states. (paper No.5) Less

为了研究纳米级分子磁体K_6[V_As_6O_H_2HO]·8H_2O（简称V15）的磁性质，我们利用He^3- He^4稀释制冷机在0.05K以下的低温下进行了核磁共振（NMR）测量<15><42>。V15团簇是一个典型的海森堡三角形反铁磁体，是研究自旋手征性对磁性影响的理想和最简单的系统。该簇由15个S=1/2的V^<4+>离子组成，它们以准球形层状结构排列，其中三角形夹在六边形之间。所有V^<4+>自旋之间的交换相互作用都是反铁磁的。团簇的每个六边形由三个强耦合自旋组成，J-800 K，在低温下导致自旋单重态。因此，三角形上只有三个V^<4+>自旋对低温下的磁性起重要作用。研究了V^<4+>自旋之间的交换相互作用， ...更多信息已知三角形为J =2.44K。(1)用NMR和μSR测量确定了V_（15）团簇的能级结构。（2）通过观察V^<4+>离子在六角体上的^ VNMR信号，直接揭示了低温下V^<4+>在六角体上的自旋单重态<51>。（3）<51>在0.1K以下的极低温度下，我们成功地观测到了三角形上磁性离子的~ 1H ~+ V-NMR信号。在总自旋S_T=3/2的基态（非阻挫态），三角形上的每个V^<4+>自旋几乎都有1μ_B的全自旋矩，三角形上的三个V离子的自旋沿着方向指向外场，导致总自旋S_T=3/2.在S_T=1/2阻挫态的情况下，发现在S=1/2海森堡三角形反铁磁体中所期望的纯手征态在V15团簇中被击穿。相反，我们发现这两个S_T=1/2态可以用混合手征态来表示。（文件5）减