Neutron Scattering Signature of Phonon Renormalization in Nickel (II) Oxide

TL;DR

This study reveals how spin-phonon interactions in nickel oxide affect acoustic phonons, showing anomalous neutron scattering signatures and phonon eigenvector renormalization due to strong spin-lattice coupling.

Contribution

It provides experimental evidence and modeling of spin-phonon coupling effects on acoustic phonons in nickel oxide using neutron scattering and first-principles calculations.

Findings

Anomalous scattering intensity from acoustic phonons observed

Magnetic scattering signature varies with momentum and temperature

Phonon eigenvector renormalization linked to spin-lattice interactions

Abstract

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. Despite its pivotal role in transport processes, the effect of spin-phonon coupling on the phonon system, especially acoustic phonon properties, has so far been elusive. By means of inelastic neutron scattering and first-principles calculations, anomalous scattering spectral intensity from acoustic phonons was identified in the exemplary collinear antiferromagnetic nickel (II) oxide, unveiling strong spin-lattice correlations that renormalize the polarization of acoustic phonon. In particular, a clear magnetic scattering signature of the measured neutron scattering intensity from acoustic phonons is demonstrated by its momentum transfer and temperature dependences. The anomalous scattering intensity is successfully modeled with a modified magneto-vibrational scattering cross section, suggesting the presence of spin precession driven by phonon. The renormalization of phonon eigenvector is indicated by the observed "geometry-forbidden" neutron scattering intensity from transverse acoustic phonon. Importantly, the eigenvector renormalization cannot be explained by magnetostriction but instead, it could result from the coupling between phonon and local magnetization of ions.