Xu Xing-Liang, Zheng Xu-Guang, Watanabe Isao
Department of Physics, Zhejiang University of Science and Technology, Hangzhou 310023, China.
Department of Physics, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.
Materials (Basel). 2019 Jul 3;12(13):2135. doi: 10.3390/ma12132135.
The temperature-dependent dynamics of the hydrogen/deuterium atoms in geometrically frustrated magnets Co(OH)Br and its deuterated form Co(OD)Br were investigated by muon spin relaxation (SR). The deuterium atoms in Co(OD)Br were found to be rapidly fluctuating at high temperatures, which should be arising as a quantum atomic effect due to the small mass of deuterium, then they drastically slowed down toward = 250 K where a broad anomaly appeared in the dielectric response, and finally became quasi-static at around 180 K. Meanwhile, the hydrogen atoms in Co(OH)Br also exhibited a two-step slowing at ~240 K and ~180 K, respectively. The revealed properties in Co(OH)Br/Co(OD)Br are reminiscent of relaxor-type ferroelectrics. The present study suggested the effectiveness of the SR technique on revealing the hydrogen/deuterium (H/D) dynamics in Co(OH)Br/Co(OD)Br. Furthermore, magnetic coupling was found to be existing at high temperatures in this system. This work provides clear evidence to the mechanism of ferroelectric responses in the hydroxyl salts, i.e., the slowing of protons (deuterium ions) is directly related to the newly revealed ferroelectricity.
通过μ子自旋弛豫（SR）研究了几何受挫磁体Co(OH)Br及其氘代形式Co(OD)Br中氢/氘原子的温度依赖动力学。发现Co(OD)Br中的氘原子在高温下快速波动，这应归因于氘的小质量导致的量子原子效应，然后它们在温度降至250 K时急剧减慢，此时介电响应中出现了一个宽异常，最后在约180 K时变为准静态。同时，Co(OH)Br中的氢原子也分别在约240 K和约180 K时表现出两步减慢。在Co(OH)Br/Co(OD)Br中揭示的性质让人联想到弛豫型铁电体。本研究表明SR技术在揭示Co(OH)Br/Co(OD)Br中氢/氘（H/D）动力学方面的有效性。此外，发现该系统在高温下存在磁耦合。这项工作为羟基盐中铁电响应的机制提供了明确证据，即质子（氘离子）的减慢与新揭示的铁电性直接相关。
