${\mathrm{CuCrO}}_2$ is a manifestation of a two-dimensional triangular antiferromagnet which exhibits an incommensurate noncollinear magnetic structure similar to a classical ${120}^{\circ }$ ordering. Using the inelastic neutron scattering technique, direct evidence of a magnon-phonon coupling in ${\mathrm{CuCrO}}_2$ is revealed via the mixed magnon-phonon character of the excitation mode at 12.5 meV as well as a minimum at the zone boundary. A simple model Hamiltonian that incorporates an exchange-striction type magnon-phonon coupling accurately reproduces the observed features. Also, continuum excitations originating from the interaction between quasiparticles are observed with strong intensity at the zone boundary. These features of the magnetic excitations are key to an understanding of the emergent excitations in noncollinear antiferromagnetic compounds.

• Received 2 May 2016
• Revised 28 July 2016

DOI:https://doi.org/10.1103/PhysRevB.94.104421