Spin Dynamics in Low Dimensional Quantum Spin System

低维量子自旋系统中的自旋动力学

• 批准号: 04640334
• 负责人: CHIBA Meiro
• 金额: $ 1.34万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1992
• 资助国家: 日本
• 起止时间: 1992 至 1993
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04640334/
• 关键词: Low Dimensional Magnetism; Quantum Spin Effect; Nuclear Magnetic Resonance; 低係元礒性体

The quantum spin effect is one of the most interesting phenomena in the physics of the low dimensional magnetium. The study is focussed on the S=1 and S=1/2 quantum spin effects of the1D magnets through the experiments of NMR in high magnetic fields up to 15T.1. S=1 Quantum Effect (Haldane Effect)Haldane has predicted that in 1D Heisenberg antiferromagnet with integer spin the ground state is singlet. The prediction has given an impetus to experiments on S=1, quasi-1D antiferromagnets. Among several S=1 antiferromagnets, NENP [Ni(C_2H_8N_2)_2NO_2(CIO_4)] has been reported to be one of the best candidates to study the Haldane gap.In NENP we have observed, even below the critical field (9.8T), a large transverse moment through the proton NMR experiment. We have attributed the transverse moment to the staggered moment induced by the cooperation of the field induced staggered field and the large staggered susceptibility. The appearance of the transverse staggered moment is not a property o … More f the Haldane state, but is peculiar to NENP where the local symmetry axis at the site of Ni^<2+> tilts from the crystalline axis. Thus, under the magnetic field the special attention must be paid to treat the spin states of NENP.Nevertheless, we found that the proton spin-lattice relaxation rate was still consistent with the Haldane gap.2. S=1/2 Quantum EffectIn CsCuCl_3, one of the ABX_3-type triangular-lattice magnets, an anomalous jump of the magnetization has been reported in the ordered phase at the magnetic field around 12 T.The material is quasi-1D Heisenberg ferromagnet with S = 1/2. In the classical spin model such a magnetization jump can not be expected. A theoretical model has been proposed that the magnetization jump will appear through the transition of the spin structure caused by the quantum spin fluctuation.We have observed through the NMR experiment a discontinuity in the spectrum of^<133>Cs at the magunetic field corresponding to the magnetization jump. The critical field was clear-cut and no hysteresis was observed for the sweep direction of the magnetic field. The discontinuity of the spectum can be analyzed as due to the abrupt change in the spin structure. The spectra above and below the critical field are compatible with the spin structure of the theoretical model. Less

量子自旋效应是低维磁物理中最有趣的现象之一。本文通过15T.1强磁场下的核磁共振实验，研究了一维磁体的S=1和S=1/2量子自旋效应。S=1量子效应（Halfton效应）Halfton预言了整数自旋的一维海森堡反铁磁体的基态是单态。这一预言推动了S=1、准一维反铁磁体的实验研究。在几种S=1的反铁磁体中，NENP [Ni（C_2H_8N_2）_2NO_2（ClO_4）]被认为是研究Half带隙的最佳候选者之一，我们通过质子NMR实验观察到，即使在临界场（9.8T）以下，NENP也有很大的横动量。我们把横向磁矩归结为场致交错场和大的交错磁化率共同作用所产生的交错磁矩。横向错列弯矩的出现并不是一种特性， ...更多信息 但这是NENP所特有的，在NENP中Ni^<2+>位置的局部对称轴从晶轴倾斜。因此，在磁场作用下，必须特别注意对NENP自旋态的处理，但我们发现质子自旋-晶格弛豫速率仍然与Haldom带隙一致.在CsCuCl_3（ABX_3型三角晶格磁体之一）中，在12 T左右的磁场下，有序相的磁化强度出现了反常的跳跃，该材料为准一维海森堡铁磁体，S = 12。在经典自旋模型中，这种磁化跳变是不可能的。本文提出了一个理论模型，认为磁化强度跃变是通过量子自旋涨落引起的自旋结构的跃迁而出现的，并通过核磁共振实验观察到在<133>磁化强度跃变所对应的磁场处~（13）Cs谱的不连续性。临界场是明确的，没有观察到的磁场的扫描方向的滞后。光谱的不连续性可以被分析为由于自旋结构的突变。临界场以上和以下的谱与理论模型的自旋结构是一致的。少

项目成果

千葉明朗: "NMR Study on the Quntum Spin Effect of the 1D Magnet in High Magnetic Fields" Physica B. (印刷中). (1994)

Akira Chiba：“高磁场中一维磁体的量子自旋效应的核磁共振研究”Physica B.（出版中）。

M.Chiba, Y.Ajiro and T.Morimoto: ""NMR Study on the Quantum Spin Effect of the 1D Magnet in High Magnetic Fields"" Physica B. (in press). (1994)

M.Chiba、Y.Ajiro 和 T.Morimoto：“高磁场中一维磁体的量子自旋效应的核磁共振研究”Physica B.（出版中）。

千葉明朗: "Anomalous Spectrum of ^<133>Cs NMR in CsCu Cl_3 around the Applied Field 11T" Journal of the Physical Society of Japan. 62. 4186-4189 (1993)

Akira Chiba：“应用场 11T 周围 CsCu Cl_3 中 ^<133>Cs NMR 的异常谱”日本物理学会杂志 62. 4186-4189 (1993)。

M.Chiba, K.Ohara, Y.Ajiro and T.Morimoto: ""Anomalous Spectrum of ^<133>Cs NMR in CsCuCl_3 around the Applied Field 11 T"" J.Phys.Soc.Jpn.62. 4186-4189 (1993)

M.Chiba、K.Ohara、Y.Ajiro 和 T.Morimoto：“应用场 11 T 周围 CsCuCl_3 中 ^ 133 Cs NMR 的异常光谱”J.Phys.Soc.Jpn.62。

千葉明朗: "Successive Phase Transitions in CsNiBr_3 Observed by ^<133>Cs NMR Including Critical Examination of the Local Field" Journal of the Physical Society of Japan. 61. 1758-1771 (1992)

Akira Chiba：“通过 ^<133>Cs NMR 观察到的 CsNiBr_3 中的连续相变，包括对局部场的严格检查”，日本物理学会杂志 61。1758-1771 (1992)。