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

Article

关键词: RELAXATION;    ANTIFERROMAGNET;    LIQUID;    ORDER;   

DOI  :  10.1103/PhysRevB.106.224416

来源: SCIE

【 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 similar 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.

【 授权许可】

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