MAGNON PHONON COUPLING IN FE2SIO4

In a Fe2SiO4-olivine single crystal we have investigated the magnetic collective excitations by means of FIR-spectroscopy and inelastic neutron scattering. All eight magnon branches predicted by model calculations have been found and examined in the principal directions. The experimental data correspond well to a theoretical spin-wave model but they also show evidence of magnon-phonon coupling. Strong magnetic inelastic scattering intensities have been observed even in Brillouin zones with vanishing structure factors of the magnetic Bragg peaks. In those zones some magnon branches follow different dispersion relations. Further, anticrossing effects between magnons and phonons have been found in several q-directions.