Magnon-phonon hybridization in ordered materials is a crucial phenomenon with significant implications for spintronics, magnonics, and quantum materials research. We present direct experimental evidence and theoretical insights into magnon-phonon coupling in ${\mathrm{Mn}}_3\mathrm{Ge}$, a kagome antiferromagnet with noncollinear spin order. Using inelastic x-ray scattering and ab initio modeling, we uncover strong hybridization between planar spin fluctuations and transverse optical phonons, resulting in a large hybridization gap of $\sim 2\mathrm{meV}$. This coupling is driven by interlayer Heisenberg exchange interactions and is enhanced by the material’s symmetry and magnetic frustration. The simplicity of the ${\mathrm{Mn}}_3\mathrm{Ge}$ structure enables clear identification of the hybridized modes, bridging theoretical predictions and experimental observations. Our findings establish ${\mathrm{Mn}}_3\mathrm{Ge}$ as a model system for exploring magnon-phonon interactions and offer a pathway for designing materials with tunable magnetoelastic properties.

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• Frustrated magnetism
• Magnetoelastic effect
• Polarons
• Kagome metal
• Noncollinear magnets
• Density functional theory
• Inelastic X-ray scattering
• Spin wave theory