Magnetic and Magnetoelastic Excitations in the Multiferroic CuBr2 determined by Raman, Infrared and Neutron Spectroscopy

Multiferroicity was recently discovered in anhydrous copper (II) bromide CuBr2 with a rather high transition temperature (TN $=$ 73.5 K). By the combination of the Raman, Infrared (IR) and inelastic neutron scattering (INS) experiments, evidences for strong magneto-elastic coupling and magneto-elastic excitations are found in CuBr2. In the Raman spectra, a range of broad peaks were observed with the indications of magnetic and phonon origin at the same time. The inelastic neutron scattering experiment reveals that those nontrivial broad peaks originate from the sites of the phonons at incommensurate Q vectors that correspond to the spiral magnetic order. These results strongly suggest the existence of hybrid excitations that involve both the spin and lattice degrees of freedom, and render CuBr2 a promising platform for studying dynamic magneto-elastic coupling.