1 College of Physics, Qingdao University, Qingdao 266071, China;2 Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Natual Materials & Micro-nano Devices, Renmin University of China, Beijing 100872, China;3 Mathematics and Physics Department, North China Electric Power University, Beijing 102206, China;4 International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China>
We report combined magnetic susceptibility, dielectric constant, nuclear quadruple resonance (NQR), and zero-field nuclear magnetic resonance (NMR) measurements on single crystals of multiferroics CuBr2. High quality of the sample is demonstrated by the sharp magnetic and magnetic-driven ferroelectric transition at TN=TC≈ 74 K. The zero-field 79Br and 81Br NMR are resolved below TN. The spin-lattice relaxation rates reveal charge fluctuations when cooled below 60 K. Evidences of an increase of NMR linewidth, a reduction of dielectric constant, and an increase of magnetic susceptibility are also seen at low temperatures. These data suggest an emergent instability which competes with the spiral magnetic ordering and the ferroelectricity. Candidate mechanisms are discussed based on the quasi-one-dimensional nature of the magnetic system.
Project supported by the Ministry of Science and Technology of China (Grant No. 2016YFA0300504), the National Natural Science Foundation of China (Grant No. 11374364), the Fundamental Research Funds for the Central Universities of China, and the Research Funds of Renmin University, China (Grant No. 14XNLF08).
Rui-Qi Wang, Jia-Cheng Zheng, Tao Chen, Peng-Shuai Wang, Jin-Shan Zhang, Yi Cui, Chong Wang, Yuan Li, Sheng Xu, Feng Yuan, Wei-Qiang Yu. NMR evidence of charge fluctuations in multiferroic CuBr2[J]. Chin. Phys. B, 2018, 27(3): 037502.