Spin-phonon coupling in Gd(Co1/2Mn1/2)O3 perovskite

We have investigated the temperature-dependent Raman-active phonons and the magnetic properties of Gd(Co1/2Mn1/2)O3 perovskite ceramics in the temperature range from 40 K to 300 K. The samples crystallized in an orthorhombic distorted simple perovskite, whose symmetry belongs to the Pnma space group. The data reveals spin-phonon coupling near the ferromagnetic transition occurring at around 120 K. The correlation of the Raman and magnetization data suggests that the structural order influences the magnitude of the spin-phonon coupling.Comment: 3 Figures, suplementary materia

Spin-phonon coupling in the incommensurate magnetic ordered phase of orthorhombic TmMnO₃

International audienceThe search for materials with strong magnetoelectric coupling has been intense since interesting properties were discovered in the perovskite TbMnO 3. Among the manganese-based perovskite family (RMnO 3), magnetic and electric orders coexist in the orthorhombic phase of the distorted perovskite TmMnO 3. The antiferromagnetic phase induces ferroelectricity, leading to type-II multiferroic behavior. Although the temperature-dependent behavior of the Raman-active phonons of other members of the orthorhombic RMnO 3 family was already reported, little information about orthorhombic TmMnO 3 has been published. In this paper, bulk samples of orthorhombic TmMnO 3 were obtained through HPHT treatment. Structural and magnetic properties of the synthesized samples were analyzed for phase con rmation. Temperature-dependent Raman spectra of bulk orthorhombic TmMnO 3 revealed weak spin-phonon coupling in the incommensurate antiferromagnetic ordered phase around 44 K. Raman spectra are also sensitive to the magnetic transition from the incommensurate to Etype antiferromagnetic phase, where the frequency renormalization due to the spin-phonon coupling vanishes. This feature shows the existence of an orbital-spin-phonon coupling based on the magnetic ordering of the lowtemperature phase

Optical phonon features in ferroelectric Bi3Fe 1/2Nb3/2O9

We have investigated the Raman scattering and infrared active optical phonons in Bi3Fe1/2Nb3/2O9. At room temperature the phonons were assigned according to lattice dynamic calculations performed using the Wilson\u27s FG method. The infrared phonon parameters allowed us to calculate the real part of the dielectric permittivity and losses in the far infrared region, and also to estimate the quality factor (Q) of the material in the microwave region. The Raman-active phonons were investigated at high temperatures and the ferroelectric phase transition underwent by this compound was observed. The change in temperature-dependent Raman spectra suggests that the high temperature crystal structure belongs to the I4/mmm(D4h17) space group. © 2012 Elsevier B.V. All rights reserved

Temperature-dependent Raman spectra of Bi2Sn2O 7 ceramics

The Bi2Sn2O7 pyrochlore is known to undergo a sequence of structural phase transitions with an increase in temperature. Raman spectroscopy was employed in the investigation of the temperature dependence of the active phonons in the Raman spectrum. We observed 19 broad modes at room temperature, reflecting the low symmetry of the α-phase of Bi2Sn2O7. The modes were discussed in relation to the Raman spectra of other pyrochlore-based oxides. The temperature dependence of the phonons evidences the α → β structural phase transition observed near 127°C. © 2012 Elsevier B.V. All rights reserved