Inelastic neutron scattering study of phonons and magnetic excitations in LaCoO$_{3}$

TL;DR

This study uses inelastic neutron scattering to explore phonons and magnetic excitations in LaCoO3, revealing phonon behavior related to structural distortion and spin-state transitions, with implications for understanding magnetic properties.

Contribution

First detailed inelastic neutron scattering analysis of phonons and magnetic excitations in LaCoO3, linking phonon softening to spin-state transitions.

Findings

Observation of phonon softening related to spin-state transition

No anomalous softening in acoustic phonons during transition

Detection of magnetic excitations consistent with low-spin to intermediate-spin states

Abstract

We have investigated the phonon and the magnetic excitations in LaCoO3 by inelastic neutron scattering measurements. The acoustic phonon dispersions show some characteristic features of the folded Brillouin zone (BZ) for the rhombohedrally distorted perovskite structure containing two chemical formula units of LaCoO3 in the unit cell. We observed two transverse optical (TO) phonon branches along (delta, delta, delta), consistent with previously reported Raman active Eg modes which show remarkable softening associated with the spin-state transition [Ishikawa et al., (Phys. Rev. Lett. 93 (2004) 136401.)]. We found that the softening takes place in the TO mode over the whole BZ. In contrast, the acoustic phonons show no anomalous softening associated with the spin-state transition. The low-energy paramagnetic scattering at 8 K is weak, increasing towards a maximum at E > 15 meV, consistent with excitation of the nonmagnetic low-spin to magnetic intermediate-spin state of Co 3+ ions.