发表机构
TU Dortmund University; Sejong University; National Institute of Chemical Physics and Biophysics; Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences; HFML-FELIX; University of Cologne; Helmholtz-Zentrum Dresden-Rossendorf（多特蒙德工业大学; 世宗大学; 化学物理与生物物理学国立研究所; 中国科学院福建物质结构研究所; 高磁场综合设施-费利克斯实验室; 科隆大学; 德累斯顿-罗斯多夫亥姆霍兹中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过太赫兹和拉曼光谱及高场磁化测量，揭示了准二维量子磁体Cu$_2$(OH)$_3$Br中场致相变中磁化过程与自旋动力学的演化，阐明了磁场对耦合铁磁与反铁磁子系统的重组机制。
AI 中文摘要
我们展示了准二维自旋-1/2磁体$\mathrm{Cu_2(OH)_3Br}$中磁化强度和自旋动力学随磁场演化的行为，该材料由交替耦合的铁磁Cu1链和反铁磁Cu2自旋链组成。太赫兹光谱揭示了低能磁激发谱对磁场方向具有显著的依赖性。对于垂直于自旋链方向施加的磁场，即$B\parallel a$和$B\parallel c^*$，光谱在自旋翻转转变处发生突变重构，该转变由高场磁化测量独立确认。相比之下，对于$B\parallel b$方向，没有发生自旋翻转；相反，激发谱随磁场连续演化，并且随着铁磁Cu1子系统逐渐极化，表现出强烈的太赫兹辐射偏振依赖性。在更高磁场下，复杂的低场谱被一组简化的宽激发所取代，这与铁磁和反铁磁链子系统之间耦合的减弱一致。互补的拉曼光谱解析了磁振子和自旋子激发以及若干声子模式，并追踪了磁激发随温度和磁场变化的特征演化。结合光谱和磁化测量结果，描绘了磁场如何通过场致相变重组$\mathrm{Cu_2(OH)_3Br}$中耦合的铁磁和反铁磁子系统。
英文摘要
We present magnetic-field-dependent evolution of magnetization and spin dynamics in the quasi-two-dimensional spin-$1/2$ magnet $\mathrm{Cu_2(OH)_3Br}$, consisting of alternately coupled ferromagnetic Cu1 and antiferromagnetic Cu2 spin chains. Terahertz spectroscopy reveals a pronounced field-direction dependence of the low-energy magnetic excitation spectrum. For magnetic fields applied perpendicular to the spin chains, $B\parallel a$ and $B\parallel c^*$, the spectra undergo abrupt reconstructions at the spin-flop transitions identified independently by high-field magnetization measurements. For $B\parallel b$, by contrast, no spin-flop occurs; instead, the excitation spectrum evolves continuously with field and exhibits a strong terahertz radiation polarization dependence as the ferromagnetic Cu1 subsystem becomes progressively polarized. At higher fields, the complex low-field spectrum is replaced by a reduced set of broad excitations, consistent with a weakening of the coupling between the ferromagnetic and antiferromagnetic chain subsystems. Complementary Raman spectroscopy resolves magnon and spinon excitations alongside several phonon modes and traces the characteristic temperature- and magnetic-field-dependent evolution of the magnetic excitations. The combined spectroscopic and magnetization results map out how a magnetic field reorganizes the coupled ferromagnetic and antiferromagnetic subsystems in $\mathrm{Cu_2(OH)_3Br}$ across field-induced phase transitions.
Comments12 pages, 11 figures
