The Raman scattering under structural and magnetic phase transitions in terbium ferro borate

The Raman scattering spectrum for the TbFe₃(BO₃)₄ single crystal has been studied in the frequency region 3 - 500 cm^- at temperatures ranged from 2 to 300 K. It is found that there exist phonon lines in high- and low-temperature phases apart from the known ones. These lines are the result of LO-O splitting of polar phonons in high-temperature phase. The existence of these additional lines in the low-temperature phase is due to a decrease in the crystal symmetry under the phase transition and an increase of the primitive cell volume. It is established that the frequencies of some phonon lines in the magneto-ordered phase are shifted towards a high-energy region with applying the external magnetic field along the third-order axis. The spectrum of a two-magnon Raman scattering is investigated. It is shown that the two-magnon band at low temperatures has a complex shape that reflects some peculiar features in the density of state of the magnon branches. The magnon energy at the Brillouin zone boundary is determined