Neutron inelastic scattering measurements of low energy phonons in the multiferroic BiFeO3

TL;DR

This study uses neutron inelastic scattering to investigate low-energy phonons in BiFeO3, revealing coupling between magnetic and lattice dynamics near the magnetic transition temperature.

Contribution

First detailed mapping of phonon dispersions and elastic constants in BiFeO3 across a wide temperature range using neutron scattering.

Findings

Phonon dispersions of acoustic and optic modes mapped out.

Elastic constants extracted from phonon data.

Phonon linewidths broaden near magnetic transition, indicating coupling.

Abstract

We present neutron inelastic scattering measurements of the low-energy phonons in single crystal BiFeO3. The dispersions of the three acoustic phonon modes (LA along [100], TA1 along [010] and TA2 along [110]) and two low energy optic phonon modes (LO and TO1) have been mapped out between 300 K and 700 K. Elastic constants are extracted from the phonon measurements. The energy linewidths of both TA phonons at the zone boundary clearly broaden when the system is warmed toward the magnetic ordering temperature TN = 640 K. This suggests that the magnetic and low-energy lattice dynamics in this multiferroic material are coupled.