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arXiv 2206.05409cond-mat.str-el
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Na2Co2TeO6:23 Na NMR中磁相的场演化和自旋动力学研究

Field evolution of magnetic phases and spin dynamics in the honeycomb lattice magnet Na2Co2TeO6: 23Na NMR study

Jun Kikuchi, Takayuki Kamoda, Nobuyoshi Mera, Yodai Takahashi, Kouji Okumura, Yukio Yasui

摘要:

我们报告的23 Na NMR的结果在蜂窝晶格磁体Na 2Co 2 TeO 6已被提名为Kitaev材料。磁位移和核磁共振谱线宽度随温度和磁场变化的测量结果表明,在9 T磁场下,不出现自旋无序相。在反铁磁相低于尼尔温度TN,我们发现一个温度区域延伸到~TN/2的核自旋晶格弛豫率1/T1保持增强,并进一步增加了磁场。该区域跨越到低温区域,该低温区域的特征在于场敏感性较低的1/T1迅速减小。这些观测结果表明,在中温区转换到更传统的自旋波激发在低温下的低能量与一个大的光谱权重的非相干自旋激发。低能自旋动力学的剧烈变化可能是由仅在中温区激活的自旋波的强阻尼引起的,这可能是由具有部分无序矩作为自旋波散射中心的三q磁序实现的。在TN附近的顺磁相中,观察到1/T1的剧烈场抑制。基于二维量子反铁磁体的重正化经典描述,分析了1/T1的温度依赖性,得到了与TN成比例的场依赖自旋刚度常数,它是磁场的函数.这意味着场抑制的能量标度表征两个二维的自旋相关性和三维的长程序,这可能是与一个日益增加的影响挫折磁场。

英文摘要:

We report on the results of 23Na NMR in the honeycomb lattice magnet Na2Co2TeO6 which has been nominated as a Kitaev material. Measurements of magnetic shift and width of the NMR line as functions of temperature and magnetic field show that a spin-disordered phase does not appear up to a field of 9 T. In the antiferromagnetic phase just below the Neel temperature TN, we find a temperature region extending down to ~TN/2 where the nuclear spin-lattice relaxation rate 1/T1 remains enhanced and is further increased by a magnetic field. This region crosses over to a low temperature region characterized by the rapidly decreasing 1/T1 which is less field-sensitive. These observations suggest incoherent spin excitations with a large spectral weight at low energies in the intermediate temperature region transforming to more conventional spin-wave excitations at low temperatures. The drastic change of the low-energy spin dynamics is likely caused by strong damping of spin waves activated only in the intermediate temperature region, which may be realized for triple-q magnetic order possessing partially-disordered moments as scattering centers of spin waves. In the paramagnetic phase near TN, dramatic field suppression of 1/T1 is observed. From analysis of the temperature dependence of 1/T1 based on the renormalized-classical description of a two-dimensional quantum antiferromagnet, we find the field-dependent spin stiffness constant that scales with TN as a function of magnetic field. This implies field suppression of the energy scale characterizing both two-dimensional spin correlations and three-dimensional long-range order, which may be associated with an increasing effect of frustration in magnetic fields.

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