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

Abstract

Polycrystalline 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.

In situ Raman investigation of the phase transition of NaVO2F2 under variable temperature conditions

“…Numerous scholars have used the in situ Raman method to investigate the phase transition process of ceramics, crystals and methane hydrates under different environmental conditions. [16][17][18][19] Investigating the phase transition of NaVO 2 F 2 monocrystalline-monocrystalline transformation is of great signicance to further study the relationship between the structure and properties of this crystal. NaVO 2 F 2 is a single crystal with very special properties and the report of the phase transition is scarce.…”

Intriguing spin–lattice interactions in EuTiO3

“…The origin of this enhancement stems from strong spin–lattice coupling which on the one hand modifies the lattice dynamics, on the other hand the spin activity 7 , 15 . The interplay between both was predicted to induce “hidden” spin order visible in the magnetic susceptibility 16 , the birefringence 17 , the Raman response 18 , the lattice constants 19 and the dielectric properties 20 . Very convincing breakthrough confirmations of these predictions have been achieved by muon spin rotation (µSR) experiments 21 – 24 , which are the most sensitive tools to detect any kind of magnetic order, even if this is not visible by bulk probing experiments.…”

Magnetic field driven phase transitions in EuTiO3

“…[ 19] Here, we present high quality Synchrotron Powder Diffraction (SXPD) data of ETO with in-situ application of small magnetic fields (up to 480mT) in the temperature range 100-300 K. Our study aims to identify magnetic field induced structural changes to clarify the kind of magnetism of the fluctuating domains. Previous micro-Raman experiments performed on the same samples with in situ application of a similar magnetic field revealed the appearance of new modes in the Raman spectrum below ~ 240 K. [20] High quality 2D synchrotron powder diffraction patterns of a polycrystalline ETO sample have been collected (λ=0.6001Å) using the 2M PILATUS detector in the temperature range 100-300K with in-situ application of a static magnetic field (up to 480 mT, Figure S1) at the XRD1 beamline of Elettra Syncrotron Trieste. Details about the sample preparation and characterization can be found in Ref.…”

“…Here, we present high quality synchrotron powder diffraction (SXPD) data of ETO with in situ application of small magnetic fields (up to 480 mT) in the temperature range 100-300 K. Previous micro-Raman experiments performed on the same samples with in situ application of a similar magnetic field revealed the appearance of new modes in the Raman spectrum below ∼240 K [20]. Our study aims to investigate any structural instabilities induced by the application of the magnetic field.…”