Mutual spin-phonon driving effect and phonon eigenvector renormalization in nickel (II) oxide

The interaction between phonon quasiparticles and electronic spin degrees of freedom has long been a subject of interest due to its influence on spin and heat transport phenomena. While spin-phonon interactions are recognized for their critical role in thermal transport, their impact on acoustic phonons, the main heat propagators, remains underexplored. We utilize inelastic neutron scattering and first-principles calculations to investigate anomalous scattering spectral intensity from acoustic phonons in the collinear antiferromagnetic nickel (II) oxide (NiO). We reveal strong spin-lattice correlations that lead to a renormalization of acoustic phonon polarization. Notably, the neutron scattering intensity from acoustic phonons shows distinct magnetic signatures, with pronounced dependence on both momentum transfer and temperature. A modified magneto-vibrational scattering cross section model successfully captures these observations, implying that spin precession is driven by phonons. Furthermore, the detection of "geometry-forbidden" scattering intensity from transverse acoustic phonons points to a renormalization of phonon eigenvectors. This effect, not attributable to magnetostriction, suggests coupling between phonons and the local magnetization of ions. Time-domain thermoreflectance measurements of the thermal conductivity vs. temperature follow T^-1.5 in the antiferromagnetic phase. This temperature dependence cannot be explained by phonon-isotope and phonon-defect scattering or phonon softening. Instead, we attribute this to magnon-phonon scattering and spin-induced dynamic symmetry breaking. These results reveal the importance of spin-phonon interactions on lattice thermal transport, shedding light on the engineering of functional antiferromagnetic spintronic and spin-caloritronic materials through these interactions.