  Polycrystalline ceramic samples and a single crystal of EuTiO3 have been
investigated by Raman spectroscopy in the temperature range 80-300 K. Although
synchrotron 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. The temperature dependence of the main mode
that is activated shows remarkable agreement with theoretical predictions. We
attribute the puzzling absence of the Raman modes to a mechanism related to
strong spin-lattice interaction that drives the cubic to tetragonal structural
phase transition and makes the Raman tensor antisymmetric. On the contrary, the
external perturbations induce a symmetric Raman tensor allowing even symmetry
modes to be present in the spectra. Previous EPR, muon scattering and magnetic
measurements indicated the presence of small magnetic interactions deep inside
the paramagnetic phase. In order to probe those magnetic interactions in our
EuTiO3 polycrystalline sample and test our hypothesis, we have performed
temperature dependant XAS/XMCD, which support the existence of magnetic
nanodomains even close to room temperature.

Materials Science;Mesoscale and Nanoscale Physics;Applied Physics