Magnetic Resonance Study of Spin Dynamics in Frustrated Lattices

本研究的目的是阐明在高度简并态的阻挫系统中的自旋涨落效应，并发现三角晶格反铁磁体（TAL-AF）中可能的新相变。鉴于我们期望新的序参量可能出现反映有序化过程中的阻挫效应，我们进行了各种实验，包括核磁共振（NMR）、电子自旋共振（ESR）、中子散射、光学测量、高场磁化。1.对于具有不同自旋各向异性的准一维六方ABX化合物，我们发现了由磁链之间的自旋阻挫引起的异常磁有序。对于Ising AF，CsCoCl_3，我们从微观角度研究了畴壁孤子引起的纵向自旋涨落，并得出结论，这种特殊的部分无序相位是由于传播过程中的子晶格翻转机制引起的。 ...更多信息 磁孤子的作用。对于Heisenberg +弱Ising AF，CsNiCl_3和CsMnI_3，我们阐明了在连续相变中纵向和横向自旋分量的独立排序。对于XY AF，CsMnBr_3，通过对各种临界指数的精确测量，我们首次证明了该相变是由一个新的普适类表征的，该普适类与横自旋有序的手征对称性有关.为了给理想的二维TAL-AF的研究提供突破，我们还研究了新的模型物质ABO_2和AM（XO_4）_2的磁性。通过ESR、中子散射和高场测量，我们成功地观察到了许多特征性质，例如具有经典海森堡自旋的TAL-AF的磁激发、高度发达的2D短程有序以及与亚铁磁中间态相关的特征1/3磁化平台。少

The purpose of the present research is to elucidate the spin fluctuation effects among the highly degenerated states of the frustrated systems, and to discover possible new phase transitions in the triangular lattice antiferromagnets (TAL-AF). In view of our expectation for that new order parameter may appear reflecting the frustration effects in the ordering process, we performed various experiments including nuclear magnetic resonance (NMR), electron spin resonance (ESR), neutron' scattering, optical measurement, high field magnetization. 1. For the quasi-one-dimensional (1D) hexagonal ABX compounds with various types of spin anisotropy, we found unusual magnetic orderings caused by the spin frustration among the magnetic chains. For the Ising AF, CsCoCl_3, we studied the longitudinal spin fluctuations due to domain-wall solitons from the microscopic point of view, and concluded that the peculiar partially-disordered phase is caused by the sublattice flipping mechanism due to propaga … More tion of the magnetic solitons. For the Heisenberg + weak Ising AF's, CsNiCl_3 and CsMnI_3, we elucidated the independent orderings of the longitudinal and transverse spin components in the successive phase transitions. For the XY AF, CsMnBr_3, from accurate measurements of various kinds of critical exponents, we proved, for the first time, that the phase transition is characterized by a new universality class associated with chiral symmetry originated from the transverse spin ordering.2. To provide a break-through for the study of ideal 2D TAL-AF, we also studied the magnetic properties of the new model substances, ABO_2 and AM(XO_4)_2 compounds. We succeeded in observing many characteristic properties such as magnetic excitations for the TAL-AF with classical Heisenberg spin, highly-developed 2D short-range ordering, and a characteristic 1/3 magnetization plateau associated with a ferrimagnetic intermediate state, through the ESR, neutron scattering and high field magnetization measurements. Less