通过拉曼光谱揭示二维铁磁体 AgVP$_2$Se$_6$ 中的晶格动力学与隐藏结构相变
Unveiling Lattice Dynamics and a Hidden Structural Transition in the 2D Ferromagnet AgVP$_2$Se$_6$ via Raman Spectroscopy
浏览论文内容
中文总结 AI 辅助
通过偏振分辨、温度依赖拉曼光谱和DFT计算，研究了二维铁磁体AgVP$_2$Se$_6$的晶格动力学，发现约100 K处存在隐藏结构相变，并解释了输运与光学带隙差异及磁性差异。
中文摘要 AI 辅助
过渡金属硫代磷酸盐（TMCs）是二维（2D）范德华材料，支持广泛的电子和磁性特性。在四元 TMCs 中，AgVP$_2$Se$_6$ 是一种罕见的铁磁体（FM），具有三角 V 亚晶格，与硫化物 AgVP$_2$S$_6$ 的反铁磁（AFM）之字形链形成对比。先前对 AgVP$_2$Se$_6$ 的拉曼研究是在远高于居里温度（$T_C$）的条件下进行的，阻碍了对自旋-声子耦合的研究。在这里，我们报告了通过化学气相输运（CVT）和助熔剂方法生长的 AgVP$_2$Se$_6$ 单晶在跨越 FM 转变时的偏振分辨、温度依赖拉曼和磁拉曼光谱，并辅以密度泛函理论（DFT）计算声子、光学和磁性特性。低温拉曼光谱解析出多达三十个峰，而角度分辨测量使其对称性分配成为可能。CVT 和助熔剂生长晶体之间的光谱差异归因于这些样品中存在不同的层间堆叠域。温度和场依赖的拉曼光谱在 $T_C$ 附近基本保持不变，表明自旋-声子耦合较弱。然而，在约 100 K 附近显著的光谱变化表明可能存在结构相变。我们的 DFT 计算进一步调和了输运激活隙（约 0.325 eV）和光学吸收边（约 2.14 eV）之间的巨大差异，将前者归因于向 V-d 上 Hubbard 带的跃迁，该带在光学上是暗的但热学上可及。我们还提出了对硫化物和硒化物磁性特性之间定性差异（由 DFT 计算再现）的理论解释。这些结果为 AgVP$_2$Se$_6$ 的晶格动力学提供了关键信息，并将指导未来在自旋电子学中的应用。
英文摘要
Transition-metal chalcophosphates (TMCs) are two-dimensional (2D) van der Waals materials supporting a broad range of electronic and magnetic properties. Among quaternary TMCs, AgVP$_2$Se$_6$ is a rare ferromagnet (FM) with a triangular V sublattice, in contrast to the antiferromagnetic (AFM) zigzag chains of the sulfide AgVP$_2$S$_6$. Prior Raman studies of AgVP$_2$Se$_6$ have been performed far above the Curie temperature ($T_C$), preventing studies of spin-phonon coupling. Here, we report polarization-resolved, temperature-dependent Raman and magneto-Raman spectroscopy of AgVP$_2$Se$_6$ single crystals grown by chemical vapor transport (CVT) and flux methods, across the FM transition, complemented by density functional theory (DFT) calculations of phonon, optical and magnetic properties. Cryogenic Raman spectra resolve up to thirty peaks, while angle-resolved measurements enable their symmetry assignment. Spectral differences between CVT- and flux-grown crystals are traced back to the presence of different interlayer stacking domains in these samples. Temperature- and field-dependent Raman spectra remain largely unchanged across $T_C$, suggesting weak spin-phonon coupling. However, pronounced spectral alterations near 100 K suggest a potential structural phase transition. Our DFT calculations further reconcile the large discrepancy between the transport activation gap ($\approx$ 0.325 eV) and optical absorption edge ($\approx$ 2.14 eV), attributing the former to a transition to the V-d upper Hubbard band that is optically dark but thermally accessible. We also suggest a theoretical explanation of the qualitative difference (reproduced by DFT calculations) between the magnetic properties of the sulfide and selenide. These results provide key information regarding the lattice dynamics of AgVP$_2$Se$_6$ and will guide future applications in spin-based electronics.
发表机构
- George Mason University（乔治梅森大学）
- The Pennsylvania State University（宾夕法尼亚州立大学）
- NIST（美国国家标准与技术研究院）
机构由 AI 辅助整理，请以论文原文为准。
