Magnetic interactions and the puzzling absence of any Raman mode in EuTiO3

Abstract

AbstractPolycrystalline ceramic samples and a single crystal of EuTiO3 have been investigated by Raman spectroscopy in the temperature range 80–300 K. Although synchrotron x‐ray diffraction (XRD) data clearly indicated the cubic to tetragonal phase transition around 282 K, no mode from the symmetry allowed Raman active phonons was found in the tetragonal phase, contrary to the case of the homologous SrTiO3. In order to study the evolution of this unique characteristic, ceramics of EuxSr1‐xTiO3 (x = 0.03–1.0) characterized by synchrotron XRD for the structural phase transition have been also investigated by Raman spectroscopy, verifying the very strong influence on the Raman yield by Eu substitution. By applying an external magnetic field or alternatively hydrostatic pressure modes are activated in the Raman spectra. Temperature dependant XAS/XMCD measurements indicate the presence of magnetic interactions even close to room temperature in agreement with previous experimental results also showing the presence of small magnetic interactions deep inside the paramagnetic phase. A possible explanation for the puzzling absence of the Raman modes is proposed related to a strong spin–lattice interaction that drives the cubic to tetragonal structural phase transition and makes the Raman tensor antisymmetric. In this model, the external perturbation will induce a symmetric Raman tensor allowing modes to be present in the spectra.