Polarized Raman scattering of multiferroicBiFeO3thin films with pseudo-tetragonal symmetry

Abstract

Polarized Raman scattering study of (001)-oriented epitaxial ${\mathrm{BiFeO}}_3$ $\left(\mathrm{BFO}\right)$ thin films with pseudo-tetragonal symmetry (4mm) was carried out by employing two distinct backscattering geometries. The $A_1$-symmetry transverse-optical $\left[A_1\right(\mathrm{TO}\left)\right]$ phonons were isolated from the $E$-symmetry transverse-optical $\left[E\right(\mathrm{TO}\left)\right]$ phonons by using the parallel $Y\left(ZZ\right)Y^{\prime }$ polarization configuration in a side-view backscattering geometry. With the help of lattice dynamical calculation, we have successfully assigned all the $E\left(\mathrm{TO}\right)$ and $A_1\left(\mathrm{TO}\right)$ normal modes. We found that there was a negligible LO-TO splitting in the $A_1$ normal modes. This observation suggests that the short-range interatomic force dominates over the long-range coulombic (ionic) force in the pseudo-tetragonal $\mathrm{BFO}$.