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多スピン交換相互作用を含む系の理論的研究

包含多重自旋交换相互作用的系统的理论研究

基本信息

批准号：
14540362
负责人：
KUBO Ken
金额：
$ 2.18万
依托单位：
AOYAMA GAKUIN UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540362/
关键词：
multiple spin exchange scalar chirality duality relation helium3 solid layer ladder spin system magnetization plateau triangular lattice frustration 拡張ハバード模型ストライプ融解相転移希薄磁性半導体

项目摘要

We have investigated the spin systems with multiple exchange interactions as well as related spin systems without multiple exchanges theoretically, and obtained following results.1)The ground state phase diagram of the system on the triangular lattice with 2-, 3- and 4-spin exchanges were determined under external magnetic field by means of the molecular field approximations. As the result it turned out that the phase diagram is quite complex. There appear 6-sublattice as well as 12-sublattice structures with scalar and vector chiral order close to the 120 degree structure when the antiferromagnetic interactions are strong. There are also large scale spatial structures with 144 and 72 sublattices close to ferromagnetic phase. More studies are necessary to confirm the stability of these large structures.2)Effects of the 5- and 6-spin exchanges on the system on the triangular lattice were studied by means of the molecular field theory. It turned out that the 5-spin exchanges have strong effect in stabilizing the ferromagnetic phase while 6-spin exchanges do not affect the ground state too much.3)We proved that there exists a rigorous duality relation between spin orders and chirality orders in spin systems on the ladder lattice with 4-spin exchanges. As a result we could rigorously proved that some ladder spin systems have ground states with scalar chirality. This duality relation was extended to the systems of correlated electrons on the ladder.4)We have investigated a 1D spin system which cnsists of tetrahedral clusters theoretically and have shown that it will show a peculiar magnetization process with magnetization plateaus.5)We investigated the effect of spin lattice interactions on magnetic plateaus in a 2D frustrated spin system SrCu_2(BO_3)_2. We proposed a spin-lattice model which can describe the magnetic plateaus experimentally observed.

我们从理论上研究了具有多重交换相互作用的自旋系统以及相关的无多重交换的自旋系统，并得到了以下结果：1）利用分子场近似，确定了在外磁场下具有2、3和4自旋交换的三角晶格系统的基态相图。结果发现相图相当复杂。当反铁磁相互作用较强时，会出现6亚晶格和12亚晶格结构，其标量和矢量手性序接近120度结构。还存在具有接近铁磁相的144和72个亚晶格的大规模空间结构。需要更多的研究来证实这些大结构的稳定性。2)利用分子场论研究了系统的5自旋和6自旋交换对三角晶格的影响。结果表明，5次自旋交换对稳定铁磁相有很强的作用，而6次自旋交换对基态影响不大。3)我们证明了4次自旋交换梯晶格上自旋系统中的自旋级数和手性级数之间存在严格的对偶关系。因此，我们可以严格证明一些梯子自旋系统具有具有标量手性的基态。这种对偶关系被推广到梯子上相关电子的系统。4)我们从理论上研究了由四面体团簇组成的一维自旋系统，并表明它会表现出具有磁化平台的特殊磁化过程。5)我们研究了二维受挫自旋系统SrCu_2(BO_3)_2中自旋晶格相互作用对磁平台的影响。我们提出了一个自旋晶格模型，可以描述实验观察到的磁高原。