Magnetic field induced dehybridization of the electromagnons in multiferroic TbMnO₃

Study of crystal-field excitations and infrared active phonons in TbMnO3

The Tb³⁺ (4f ⁸) crystal-field (CF) excitations and the infrared phonons in TbMnO₃ are studied as a function of temperature and under an applied magnetic field. The phonon energy shifts reflect local displacement of the oxygen ions that contribute to the CF energy level shifts below 120 K and under magnetic field. The CF polarized transmission spectra provide interesting information about the debated nature of the excitations at 41, 65, 130 cm^-1. We also evaluate the contribution of the charge transfer mechanism to the magnetoelectric process in TbMnO₃ under magnetic field.

A comparative Raman study between PrMnO 3, NdMnO 3, TbMnO 3 and DyMnO 3

In this paper, we present a detailed Raman study of the non-multiferroic compounds PrMnO 3 and NdMnO 3 and the multiferroic compounds TbMnO 3 and DyMnO 3 as a function of temperature and magnetic field. All studied systems show anomalous phonon shifts close to the Néel transition T N . In PrMnO 3 and NdMnO 3, the frequency softenings are partly attributed to an orbital-spin-phonon coupling whereas in TbMnO 3 and DyMnO 3, the relatively weak frequency shifts are rather attributed to an expansion of the Mn-O bond lengths. On the other hand, the frequencies of TbMnO 3 phonons are shifted as a function of magnetic field, while those of PrMnO 3 remain unaffected. These frequency shifts are interpreted in terms of local oxygen rearrangements under magnetic field that could play an important role in the multiferroicity of TbMnO 3 and DyMnO 3.

Raman scattering of magnetoelectric gallium ferrite thin films

Gallium ferrite, Ga(2-x)Fe(x)O(3) (GFO), is a promising magnetoelectric material as it exhibits both magnetic and electric orders close to room temperature. Here, we report a temperature-dependent investigation of GFO thin films with x = 1.0 and 1.4 by using Raman scattering. Our investigation suggests the absence of a structural phase transition of both films in the investigated 90-500 K temperature range, which is similar to earlier observations on bulk samples. We note, however, the occurrence of weak anomalies in the temperature-dependent band position of some phonons, which we attribute to spin-phonon coupling as the anomalies occur close to the Néel temperature of the materials.

Molecular-spin dynamics study of electromagnons in multiferroic RMn2O5

We investigate the electromagnon in magnetoferroelectrics RMn(2)O(5) using combined molecular-spin dynamics simulations. We confirm that the origin of the electromagnon modes observed in the optical spectra is due to the exchange-striction interaction between the magnons and the phonons, and the dielectric step at the magnetic phase transition is due to the appearance of the electromagnon in the low-temperature phase in these materials. The magnetic anisotropy breaks the rotational symmetry of the magnetic structures and, as a result, the electromagnon splits into three modes in RMn(2)O(5). We find that the electromagnon frequencies are very sensitive to the magnetic wavevector along the a direction q(x). Therefore, the electromagnon frequencies of TmMn(2)O(5) (q(x) ~ 0.467) are expected to be much higher than those of other materials of the family, such as R= Tb, Y, Ho, etc (q(x) ~ 0.48). We further calculate the electromagnons in the magnetic field, and find a new mode appearing in the magnetic field. Although the modes' frequencies change significantly under magnetic field, the total static dielectric constant contributed from the electromagnons does not change much in the magnetic field, suggesting that the colossal magnetodielectric effects in these materials may not be caused by the electromagnons.