发表机构
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University; Jiangsu Physical Science Research Center, Nanjing University（南京大学固体微结构物理国家重点实验室和物理学院; 南京大学江苏物理科学研究中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过低波数磁拉曼光谱测量赤铁矿中莫林转变附近的有限动量磁振子，提取关键材料参数，并定量解释了莫林转变的机制。
AI 中文摘要
赤铁矿（$\alpha$-Fe$_2$O$_3$）是高速自旋电子学和磁振子学的典型反铁磁平台，然而其有限动量磁振子动力学和自旋重取向机制仍未完全理解。本文利用低波数磁拉曼光谱技术，在$\alpha$-Fe$_2$O$_3$中跨越莫林转变，解析了$k=0$和有限$k$的亚太赫兹磁振子。我们发现极限群速度$v_0$几乎与磁场无关，而有限$k$群速度$v_{\mathrm g}$在莫林转变和自旋翻转转变附近被强烈调制。通过结合平行场和横向场测量与自旋波建模，我们进一步提取了温度依赖的Dzyaloshinskii--Moriya场$H_{\mathrm D}$以及单轴各向异性场$H_{\mathrm{K1}}$和$H_{\mathrm{K2}}$。我们发现$H_{\mathrm D}$在约2.0--2.3~T范围内对温度弱依赖，而$H_{\mathrm{K1}}$迅速减小，$H_{\mathrm{K2}}$变化微弱。这种对比驱动了有效各向异性场的符号反转，并定量解释了莫林转变。我们的结果确立了低波数拉曼光谱作为有限动量反铁磁磁振子的定量探测手段，并为基于赤铁矿的磁振子学提供了关键材料参数。
英文摘要
Hematite ($α$-Fe$_2$O$_3$) is a prototypical antiferromagnetic platform for high-speed spintronics and magnonics, yet its finite-momentum magnon dynamics and spin-reorientation mechanism remain incompletely understood. Here we use low-wavenumber magneto-Raman spectroscopy to resolve both $k=0$ and finite-$k$ sub-terahertz magnons in $α$-Fe$_2$O$_3$ across the Morin transition. We find that the limiting group velocity $v_0$ remains nearly field independent, whereas the finite-$k$ group velocity $v_{\mathrm g}$ is strongly modified near the Morin and spin-flop transitions. By combining parallel- and transverse-field measurements with spin-wave modeling, we further extract the temperature-dependent Dzyaloshinskii--Moriya field $H_{\mathrm D}$ and uniaxial anisotropy fields $H_{\mathrm{K1}}$ and $H_{\mathrm{K2}}$. We find that $H_{\mathrm D}$ is weakly temperature dependent at approximately 2.0--2.3~T, while $H_{\mathrm{K1}}$ decreases rapidly and $H_{\mathrm{K2}}$ changes only weakly. This contrast drives the sign reversal of the effective anisotropy field and quantitatively accounts for the Morin transition. Our results establish low-wavenumber Raman spectroscopy as a quantitative probe of finite-momentum antiferromagnetic magnons and provide key material parameters for hematite-based magnonics.
