Lattice dynamics and thermal transport in multiferroicCuCrO2

Abstract

Inelastic neutron and x-ray scattering measurements of phonons and spin waves were performed in the delafossite compound ${\mathrm{CuCrO}}_{2}$ over a wide range of temperature, and complemented with first-principles lattice dynamics simulations. The phonon dispersions and density of states are well reproduced by our density functional calculations, and reveal a strong anisotropy of Cu vibrations, which exhibit low-frequency modes of large amplitude parallel to the basal plane of the layered delafossite structure. The low frequency in-plane modes also show a systematic temperature dependence of neutron and x-ray scattering intensities. In addition, we find that spin fluctuations persist above 300 K, far above the N\'eel temperature for long-range antiferromagnetic order, ${T}_{N}\ensuremath{\simeq}24\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Our modeling of the thermal conductivity, based on our phonon measurements and simulations, reveals a significant anisotropy and indicates that spin fluctuations above ${T}_{N}$ constitute an important source of phonon scattering, considerably suppressing the thermal conductivity compared to that of the isostructural but nonmagnetic compound ${\mathrm{CuAlO}}_{2}$.