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arXiv · 2610.08030

Finite-Momentum Antiferromagnetic Magnon Dynamics across the Morin Transition in Hematite

Jiaqi Gong·Yuanzhe Tian·Jun Cui·Meiye Hou·Yuxuan Mu·Di Wang·Xiangang Wan·Di Wu·Qi Zhang
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Abstract

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.

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Jiaqi Gong, Yuanzhe Tian, Jun Cui, Meiye Hou, Yuxuan Mu, Di Wang, Xiangang Wan, Di Wu, Qi Zhang. 2026-10-06. Finite-Momentum Antiferromagnetic Magnon Dynamics across the Morin Transition in Hematite. https://arxiv.org/abs/2610.08030

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