Spin Dynamics and Quantum Effect in Geometrically Frustrated System

几何受挫系统中的自旋动力学和量子效应

• 批准号: 12640354
• 负责人: ASANO Takayuki
• 金额: $ 2.3万
• 依托单位: KYUSHU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12640354/
• 关键词: geometrical; frustrated system; spin dynamics; quantum effect; pyrochlore; kagome lattice; triangular lattice; altenating spin

The magnetic properties of molecular clusters attract considerable interest for the new physics involved and for the potential applications. At low temperatures, these molecules act as individual quantum nanomagnets, enabling to probe, at the macroscopic scale, the crossover between quantum and classical physics. Of fundamental interest is the situation of degeneracy of two magnetic levels, where quantum mechanical phenomena such as tunneling or coherence can occur. The situation of degeneracy between levels raises fundamental problems of quantum dynamics. A crucial issue is the role played by the coupling between magnetic molecular levels and the environment such as phonons. The purpose of this project is to verify experimentally the characteristic quantum energy levels and discuss the possible interplay between the anomalous magnetic relaxation phenomena and the level-crossings.For this purpose, a variety of model substances were synthesized by group and some of them were kindly supp … More lied by chemists. The representatives are dimers (binuclear complexes) such as Cs3Cr2X9 with X = C1, Br, Trimers (trinuclear complexes) such as A3Cu3(PO4)4 with A = Ca, Sr, trimerized chain system 3CuC12・2dx, polynuclear molecular magnets such as Mn12, Fe12, V15, and so on. We applied various complementary techniques, including advanced crystal preparation, nuclear magnetic resonance, electron spin resonance, neutron scattering, muon spin relaxation, high field magnetization as well as susceptibility and specific heat measurements, in sooperation with many other research groups.A high-field magnetization technique was applied to study the field-dependent behaviors of various kind of quantum spin systems by spplying high magnetic field up to 54 T at temperature down to 0.1 K. For example, we observed successive phase transitions at three restricted field regions up to 40 T in the S = 2/3 dimerozed system Cs3Cr2C19. Also, in Fe12 molecular magnet which forms a finite chain ring consisting of 12 Fe3+(S = 5/2) ions, we observed five magnetization steps with equal field spacing, arising from energy-level crossings for the discrete quantum states in the finite spin system. In these examples, we discussed the structure of the energy levels and the relaxation phenomena due to quantum spin dynamics in the metastable states around the level-crossing fields.Also, a figh-frequency electron spin resonance (ESR) texhnique was applied for our purpose, in the wide temperature range down to 0.5 K, using high frequency sources up to 800 GHz. Examples are for the S=1/2 Heisenberg antifeiTomagnetic chain system Cu benzoate, Cu(C6H5COO)2・3H_2O and for the trimerized chain system 3CuC12・2dx, in which ferromagnetic trimers consisting of three S = 1/2 spins coupled antiferromagnetically in one dimension.These results partly have been published already. Less

分子团簇的磁性因其所涉及的新物理和潜在的应用而引起人们的极大兴趣。在低温下，这些分子充当单独的量子纳米磁体，能够在宏观尺度上探测量子和经典物理之间的交叉。最基本的兴趣是两个磁能级的简并情况，在那里可以发生量子力学现象，如隧穿或相干。能级间简并的情况提出了量子动力学的基本问题。一个关键的问题是磁性分子能级和环境（如声子）之间的耦合所起的作用。本项目的目的是通过实验验证特征量子能级，并讨论反常磁弛豫现象与能级交叉之间可能的相互作用。为此，我们分组合成了多种模型物质，并对其中的一些模型物质进行了实验验证。实验结果表明，这些模型物质具有很好的稳定性和稳定性 ...更多信息 化学家的谎言代表物为二聚体（双核配合物），如Cs3 Cr2 X9，X = Cl，Br，三聚体三核配合物如A_3Cu_3（PO_4）_4（A = Ca，Sr），三聚链状体系3CuC_1_2·2dx，多核分子磁体如Mn_（12），Fe_（12），V_（15）等。电子自旋共振、中子散射、μ子自旋弛豫、高场磁化强度以及磁化率和比热测量等方面的研究工作。例如，我们观察到连续的相变在三个限制领域的区域高达40 T的S = 2/3二聚系统Cs3 Cr2 C19。此外，在形成由12个Fe ~（3+）（S = 5/2）离子组成的有限链环的Fe ~（12）分子磁体中，我们观察到五个等场间距的磁化阶跃，这是由有限自旋系统中离散量子态的能级交叉引起的。在这些例子中，我们讨论了能级结构和在能级交叉场附近的亚稳态中由于量子自旋动力学引起的弛豫现象，同时，我们还采用了一种高频电子自旋共振（ESR）技术，在低至0.5K的宽温度范围内，使用高达800 GHz的高频源。例如，对于S=1/2的Heisenberg反铁磁链体系Cu benzoate，Cu（C6 H5 COO）2·3H_2O和三聚链体系3CuC_（1/2）·2dx，其中三个S = 1/2自旋组成的铁磁三聚体在一维反铁磁耦合，这些结果部分已经发表。少

项目成果

H.Nojiri et al.: "Submillimeter-wave ESR Study on Quantum Spin Systems"J.Phys.Soc.Jpn.(Suppl.B). 69. 83-88 (2000)

H.Nojiri 等人：“量子自旋系统的亚毫米波 ESR 研究”J.Phys.Soc.Jpn.（增刊 B）。

T.Asano et al.: "ESR Investigation on the Breather Mode and the Spinon-Breather Dynamical Crossover om Cu Benzoate"Phys.Rev.Lett.. 84. 5880-5883 (2000)

T.Asano 等人：“苯甲酸铜的呼吸模式和自旋呼吸动态交叉的 ESR 调查”Phys.Rev.Lett.. 84. 5880-5883 (2000)

Y.Ajiro et al.: "High-Field, High-Frequency ESR in the One-Dimensional Quantum Spin Systems"J.Phys.Soc.Jpn.(Suppl.A). 69. 297-302 (2000)

Y.Ajiro 等人：“一维量子自旋系统中的高场、高频 ESR”J.Phys.Soc.Jpn.（增刊 A）。

T. Asano et al.: "mSR Stusy of Cu Benzoate at Very Low Temperature -Existence or Nonexistence of Long Range Order in Coupled Chains"J. Phys. Soc. Jpn.. 71. 594-598 (2002)

T. Asano 等：“苯甲酸铜在极低温下的 mSR 研究 - 耦合链中长程有序的存在或不存在”J。

T.Sakon et al.: "Electron Spin Resonance Study of Cu Benzoate Using a 3He-4He Dilution"J. Phys. Soc. Jpn.. 70. 2259-2262 (2001)

T.Sakon 等人：“使用 3He-4He 稀释对苯甲酸铜进行电子自旋共振研究”J。