• Graham, P.J.; Rovillain, P.; Bartkowiak, M.; Pomjakushina, E.; Conder, K.; Kenzelmann, M.; Ulrich, C.: Spin-phonon and magnetoelectric coupling in oxygen-isotope substituted TbMnO3 investigated by Raman scattering. Physical Review B 105 (2022), p. 174438/1-11

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In order to investigate the effects leading to the strong magnetoelectric coupling in the type II multiferroic TbMnO3 we have studied the thermal properties and temperature dependence of the lattice vibrations of TbMn16O3 and its isotopically substituted counterpart TbMn18O3. Heat capacity measurements on powder samples revealed no significant change in the Mn3+ and Tb3+ magnetic phase transition temperatures, as well as the multiferroic ordering temperature upon isotope substitution, indicating that a change in the dynamical modulation of the MnO6 octahedral distortions and rotations altering the Mn-O-Mn bond angles has no influence on the magnetic properties of TbMnO3. Raman light scattering experiments have been performed on isotopically substituted single crystals to determine the temperature induced changes in phonon energies and linewidths at the sinusoidal and multiferroic phase transitions. A detailed modeling indicates that the spin-phonon coupling can be accounted for the pronounced anomalies in the temperature dependence of the phonon behaviors at the transition to the sinusoidal spin phase at TMnN=41 K and to the multiferroic spin-spiral phase at TFE=28 K. No further effects such as the appearance of the electric polarization or the electromagnon were required to explain the data, especially below the multiferroic phase transition.