The Raman scattering under structural and magnetic phase transitions in terbium ferroborate
A.V. Peschanskii, A.V. Yeremenko, V.I. Fomin
B. Verkin Institute for Low Temperature Physics and Engineering National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
L.N. Bezmaternykh, and I.A. Gudim
L.V. Kirenskiy Institute of Physics, Siberian Branch of the Russian Academy of Sciences Krasnoyarsk 660036, Russia pos Анотація:
Received August 12, 2013
The Raman scattering spectrum for the TbFe3(BO3)4 single crystal has been studied in the frequency region 3 – 500 cm–1 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–TO 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.
PACS: 63.20.–e Phonons in crystal lattice; PACS: 78.30.–j Infrared and Raman spectra and scattering.
Key words: ferroborates, magnetic phase transition, spin-phonon coupling, vibrational spectra.