Observation of phonons in multiferroic BiFeO₃single crystals by Raman scattering

Abstract

We have grown BiFeO(3) bulk single crystals by a flux method and characterized the phonon spectra in detail by Raman scattering in the temperature range 4-1100 K. All the 13 Raman-active phonon modes predicted by group theory, 4A(1)+9E, were observed at low temperature and successfully assigned by a polarized Raman measurement. Moreover, drastic spectral changes in the Raman spectra were observed at temperatures 600-700 K and 1000-1100 K. These features are discussed from the viewpoint of phonon coupling with the magnetic ordering and the structural phase transition, respectively.

Synthesis and Characterization of Mn-Doped BiFeO3Nanoparticles

“…Here, the intensity of the 2-phonon peak has been normalized to the E mode intensity at 470 cm −1 . While the intensity change is negligibly small at higher temperatures, it changes prominently at temperatures below ≈ 600 K. This temperature is close to the Néel temperature of bulk BiFeO 3 , T N = 643 K. This phenomenon has been previously reported in bulk samples and interpreted by a coupling between the phonon and spin systems [11,13]. According to Ramirez et al [13], this 2-phonon mode is sensitive to the magnetic phase transition of BiFeO 3 .…”

“…Figure 3a shows Raman spectra of the samples. In the undoped sample (bottom), seven phonon peaks were easily identified and classified to A 1 -and E-type modes with reference to a previous result for single crystals as marked in the figure [11]. With increasing Mn content from [Mn] = 0 to 10%, all peaks broadened systematically.…”

Spin and lattice excitations of aBiFeO3thin film and ceramics

“…Probing IR-active low-energy excitations is hindered by a lack of sufficiently large single crystals. Raman-active phonons of the rhombohedral R3c BiFeO 3 structure have been reported for single crystals, [6][7][8] polycrystalline ceramics, [9][10][11] and thin films, 12,13 however, there is a significant discrepancy between the claimed phonon frequencies and symmetry representations. A possible explanation for such inconsistences between the various experimental results is the presence of oblique phonon modes, which show a continuous variation of frequency along the phonon propagation vector with respect to the crystallographic axis of the probed specimen.…”

Anharmonic phonons and magnons in BiFeO3

“…To our knowledge, there are currently no reported experimental data of the full magnon and phonon spectra in BFO, however. Multiple Raman measurements have been performed, but these only probe modes at small wavevectors q → 0 [10][11][12][13][14][15][16][17][18][19][20] . Here, we report the first INS measurement of the phonon DOS in polycrystalline BiFeO 3 , as a function of T , as well as more detailed measurements of the magnon spectrum than previously reported 21 .…”