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Experimental Study of New Ordered Phases in Magnetic Field for Stacked Triangular Lattice and Haldane System

堆叠三角晶格和Haldane系统磁场中新有序相的实验研究

基本信息

批准号：
03452038
负责人：
AJIRO Yoshitami
金额：
$ 2.18万
依托单位：
FUKUI UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

Ordering phenomena are classified to universality classes by symmetry of order parameter and spacial dimensionality. As for the magnetic transition, the symmetry of the order parameter is usually governed just by spin symmetry. Recent theoretical studies, however, have suggested that the concept of universality should be deepened more profoundly. Under such circumstances, we perfomed various experimental studies including nuclear magnetic resonance (NMR), electron spin resonance (ESR), neutron scattering and high field magnetization.The purpose of the present research is to elusidate the new ordered phases in the frustrated triangular lattice antiferromagnets and the one-dimensional Haldane systems.1. For the triangular systems, universality classes of CsMnBr3 and CsMnI3 were studied. Two compounds have the same hexagonal structure and almost the same magnetic parameters except the anisotropy which produces an essential difference in ordering process. We provided an experimental eviden … More ce that the phase transition in CsMnBr3 with XY anisotropy belongs to a new universality class characterized by the order parameter linked to a twofold discrete chiral degeneracy inherent to the frustrated triangular antiferromagnet as well as a continuous rotational degeneracy. On the contrary, in CsMnI3 with Ising anisotropy there exist two successive transitions which correspond to independent ordering of magnetic moments parallel and perpendicular to the Ising axis, respectively. The critical exponents at these transitions remarkably differ from those for CsMnBr3 reflecting an essential role of anisotropy in agreement with a theoretical prediction. The magnetic phase transitions in closely related substances, RbMnBr3 and CsNiBr3 were also studied.2. For the Haldane systems we studied magnetic properties of NENP and the related substances which are well approximated to one-dimensional Heisenberg antiferromagnet with integer spins and proved the existence of the Haldane phase with a novel ground state. The effect of magnetic field on the ground state properties were revealed from microscopic study. Less

根据序参量的对称性和空间维数的对称性，将有序现象划分为普适性类。对于磁跃迁，序参量的对称性通常仅由自旋对称决定。然而，最近的理论研究表明，普遍性的概念应该更加深刻地深化。在这种情况下，我们进行了各种实验研究，包括核磁共振（NMR）、电子自旋共振（ESR）、中子散射和高场磁化。本研究的目的是阐明受挫三角形晶格反铁磁体和一维Haldane体系中新的有序相。对于三角系统，研究了CsMnBr3和CsMnI3的通用性类。两种化合物具有相同的六方结构和几乎相同的磁性参数，但各向异性导致了排序过程的本质差异。实验证明，具有XY各向异性的CsMnBr3的相变属于一种新的普适类，其特征是与受挫三角形反铁磁体固有的双重离散手性简并以及连续旋转简并有关的序参数。相反，在具有Ising各向异性的CsMnI3中，存在两个连续的跃迁，分别对应于平行于Ising轴和垂直于Ising轴的磁矩的独立排序。这些跃迁的临界指数与CsMnBr3的显著不同，反映了各向异性的重要作用，与理论预测一致。研究了密切相关物质RbMnBr3和CsNiBr3的磁相变。对于Haldane体系，我们研究了近似于一维整数自旋海森堡反铁磁体的NENP及其相关物质的磁性，并证明了具有新基态的Haldane相的存在。通过微观研究揭示了磁场对基态性质的影响。少