Raman Spectra of Multiferroics TbMnO₃

Abstract

The dream to have multifunctional materials has triggered an intense study of multiferroicity,i.e.of materials in which magnetic and electric polarizations are simultaneously present and strongly coupled. Here we study TbMnO3, a perovskite manganite exhibiting multiferroicity. It has an incommensurate antiferromagnetic ordering transition at 41 K and a transition into a multiferroic spin spiral state at 26 K. In this study, Raman spectroscopy has been used to elucidate the nature of the excitations related to phase transitions. We show that the optical phonons in TbMnO3resemble the phonon characteristics typical for perovskite manganites, corresponding to MnO6octahedral vibrations. The appearance of a new low energy modes at 32 cm-1, 40 cm-1, and 63 cm-1observed below 41 K signifies the antiferromagentic ordering in TbMnO3. The 32 cm- 1and 63 cm-1are interpreted as spin ordering activated phonon while the 40 cm-1is interpreted as spin ordering induced splitting of Tb quasi doublet cystal field level.

Spin-phonon and magnetoelectric coupling in oxygen-isotope substituted TbMnO3 investigated by Raman scattering

“…Within these spectra, five out of seven A g modes and three out of seven B 1g modes are identified. The observed peaks in the Raman spectra are in good agreement with previously published data [43][44][45][46][47]. The two lowest energy A g modes, which appear at 111.1 cm −1 (110.6 cm −1 ) and 138.5 cm −1 (138.8 cm −1 ) for TbMn 16 O 3 and TbMn 18 O 3 (in brackets) can be attributed to vibrations of the Tb ions within the xy plane.…”