Phonons in the multiferroic langasite Ba$\_3$NbFe$\_3$Si$\_2$O$\_14$ : evidences for symmetry breaking

Abstract

The chiral langasite Ba$\_3$NbFe$\_3$Si$\_2$O$\_14$ is a multiferroic compound. While its magnetic order below T$\_N$=27 K is now well characterised, its polar order is still controversial. We thus looked at the phonon spectrum and its temperature dependence to unravel possible crystal symmetry breaking. We combined optical measurements (both infrared and Raman spectroscopy) with ab initio calculations and show that signatures of a polar state are clearly present in the phonon spectrum even at room temperature. An additional symmetry lowering occurs below 120~K as seen from emergence of softer phonon modes in the THz range. These results confirm the multiferroic nature of this langasite and open new routes to understand the origin of the polar state.

References in corpus (4)

• Single domain magnetic helicity and triangular chirality in structurally enantiopure Ba3NbFe3Si2O14
• Parity Broken Chiral Spin Dynamics in Ba${}_3$NbFe${}_3$Si${}_2$O${}_{14}$
• Magnetic chirality as probed by neutron scattering
• Magnetic Control of Ferroelectric Polarization in a Self-formed Single Magnetoelectric Domain of Multiferroic Ba3NbFe3Si2O14

Cited by in corpus (2)

• Helical bunching and symmetry lowering inducing multiferroicity in Fe langasites
• Crystal Symmetry Lowering in Chiral Multiferroic Ba${}_3$TaFe${}_3$Si${}_2$O${}_{14}$ observed by X-Ray Magnetic Scattering