Magnon-phonon coupling and two-magnon continuum in the two-dimensional triangular antiferromagnetCuCrO2

Abstract

CuCrO2 is a manifestation of a two-dimensional triangular antiferromagnet which exhibits an incommensurate noncollinear magnetic structure similar to a classical 120• ordering. Using the inelastic neutron scattering technique, direct evidence of a magnon-phonon coupling in CuCrO2 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 reproduces the observed features accurately. 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.

Lattice dynamics and thermal transport in multiferroicCuCrO2

“…8-c), consistent with IXS measurements. We note that the T -dependence of the phonon intensity of ∼13 meV peak in our DOS measurements differs from the observation by Park et al [26], who reported no change in the phonon intensity at ∼13 meV above T N along [H,H,0] for 1 3 ⩽ H ⩽ 2 3 . Figure 3-(d-i) shows χ ′′ (Q, E) at low Q zooming on magnetic excitations (12 meV data).…”

“…This unusual T -dependence of κ L in CuCrO 2 is markedly different from that in the non-magnetic analogue CuAlO 2 . Be- sides providing lattice dynamics information for a wide range of temperature, our measurements of phonon dispersions with IXS and INS also clearly distinguish between phonon and magnon intensities, which is crucial in understanding spin-phonon coupling across T N in this class of spin driven multiferrorics [25,26].…”

“…For instance, in HoMnO 3 , the shift in position of Mn ions couples with exchange coupling constants, causing a change of cur-vature of spin waves below T SR , the spin reorientation temperature [23]. Also, recent lattice dynamics studies in LiCrO 2 and CuCrO 2 report mixed magnon-phonon modes below T N [25,26]. Tóth et al [25] observed the appearance of electromagnons below 10 meV with inelastic x-ray scattering in LiCrO 2 .…”

“…Tóth et al [25] observed the appearance of electromagnons below 10 meV with inelastic x-ray scattering in LiCrO 2 . Park et al [26] focused on spin-waves in CuCrO 2 and attributed an intensity change across T N for a 12.5 meV excitation to a mixed magnon-phonon character. Furthermore, ultrasonic measurements in delafossite compounds have indicated substantial softening of elastic constants near T N [16,27].…”

Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling

“…2, there seems to be a very diffuse intensity located at around 18 meV. This may be similar to the magneto-elastic excitations observed in (Y,Lu)MnO 3 and CuCrO 2 [7,22]; (1) the relatively strong intensity near the B and D points and (2) a similar energy transfer (18 meV) above the coherent modes. Such magnetoelastic excitations originate from a hybridization of specific phonon and magnon modes in noncollinear magnets.…”