Raman scattering in multiferroic SmFe3(BO3)4

Abstract

Raman spectrum of single-crystal SmFe3(BO3)4 was studied in the frequency range from 3 to 1500 cm−1 at temperatures 10–300 K. All the A1 and E phonon modes predicted by the group theory for a given symmetry of the crystal were observed. The magnitudes of splitting between the LO and TO components of polar E phonons were determined. It was found that under the transition to a magnetically ordered phase, the behavior of the intensity of the line corresponding to the A1 vibrational mode is anomalous. It was shown that at low temperatures the spectrum of two-magnon excitations has a complex shape and is observed with both nondiagonal and diagonal components of the scattering tensor. This complex shape reflects the features in the density of states of the magnetic branches. An estimate of the magnon energy Em at the Brillouin zone boundary gave ∼47 cm−1. The structure of the ground multiplet 6H5/2 of a Sm+3 ion in paramagnetic and antiferromagnetic states as well as the effect of the magnetic phase transition on it were studied. Electron-phonon interaction for the electronic excitation at 225 cm−1 was revealed.