Raman Scattering from Magnons and Phonons in FeBO3and FeF3

Scattering from all the $k=0\mathrm{}$ first-order Raman-active phonons in FeB${\mathrm{O}}_3$ and Fe${\mathrm{F}}_3$ has been observed. Underlying the $A_{1g}$ phonon in FeB${\mathrm{O}}_3$ is a broad second-order phonon-scattering peak which accounts for the peculiar temperature behavior of the $A_{1g}$ band when viewed with low resolution. Scattering from magnon-pair states has been observed at 538 ${\mathrm{cm}}^{-1\mathrm{}}$ in FeB${\mathrm{O}}_3$ and at 564 ${\mathrm{cm}}^{-1\mathrm{}}$ in Fe${\mathrm{F}}_3$. The nearest-neighbor-exchange parameters $J$ are 19.2 and 20.1 ${\mathrm{cm}}^{-1\mathrm{}}$, respectively. Estimates are given for various processes by which exchange striction may contribute to first-order phonon scattering. There are no observable effects due to a strong magnon-phonon interaction as previously reported for FeB${\mathrm{O}}_3$.