The physics of mutual interaction of phonon quasiparticles with electronic spin degrees of freedom, leading to unusual transport phenomena of spin and heat, has been a subject of continuing interests for decades. Understanding phonon properties in the context of spin-phonon coupling is essential for engineering functional phononic and spintronic devices. By means of inelastic neutron scattering and first-principle calculations, anomalous scattering spectral intensity from acoustic phonon was identified in the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong correlations between spin and lattice degrees of freedom that renormalize the polarization of acoustic phonon. Anomalously large spectral intensity from acoustic phonons observed at small momentum transfer decays with increasing temperature and is successfully modeled with a modified magneto-vibrational scattering cross section, suggesting the presence of phonon driven of spin precession. On the other hand, TA phonon intensity that are forbidden by the scattering geometry is observed at a wide span of momentum transfer, suggesting a renormalization of phonon eigenvector.
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