Highly (111)-oriented rhombohedral BiFeO3 (BFO) thin films were grown on (111) SrTiO3 substrates by pulsed laser deposition. Polarized Raman-scattering study of the (111)-oriented epitaxial BFO thin film with rhombohedral R3c symmetry was carried out by employing two distinct backscattering geometries. The A1-symmetry transverse-optical [A1(TO)] phonons were selectively isolated from the E-symmetry transverse-optical [E(TO)] phonons by employing Y′(ZZ)Y′ polarization configuration in a novel side-view backscattering. By comparing the Y′(ZZ)Y′ spectrum with the Z(X′X′)Z polarization spectrum in a normal backscattering, we were able to assign most of A1 and E-symmetry normal modes of R3c BFO. In addition, we found that there was a negligible LO-TO splitting in the A1-symmetry normal modes.

Magnetic properties of $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_3$ (BFO) single crystals with rhombohedral symmetry $\left(R3c\right)$ were measured in the temperature range of $4.2–350\mathrm{K}$. Zero field cooled (ZFC) and field cooled magnetization curves split below $250\mathrm{K}$ with a sharp cusp around $50\mathrm{K}$ in the ZFC curves revealing spin-glass behavior in BFO single crystals. The observed coercive field increases with decreasing temperature, suggesting week ferromagnetism below $\sim 10\mathrm{K}$ and spin glass behavior below $\sim 120\mathrm{K}$. The cusps around the freezing temperature $\left[T_f\left(\omega \right)\right]$ which are frequency dependent confirm the spin-glass behavior in BFO single crystals with spin freezing temperature $(T_{\mathit{SG}}=29.4\pm 0.2\mathrm{K})$. The critical exponent $z\nu =1.38$ agrees rather well with experimental values in $\mathrm{La}{\mathrm{Mn}}_{0.5}{\mathrm{Fe}}_{0.5}{\mathrm{O}}_3$ $(z\nu =1.0)$ [K. De et al., J. Appl. Phys. 99, 13908 (2006)] and the mean field theory $(z\nu =2.0)$ of Kirkpatrick and Sherrington [Phys. Rev. B 17, 4384 (1970)].

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 $\mathrm{BFO}$.

Low-temperature magnetic properties of epitaxial BiFeO(3) (BFO) thin films grown on (111) SrTiO(3) substrates have been studied. Zero-field-cooled and field-cooled magnetization curves show a large discrepancy beginning at a characteristic temperature T(f) that is dependent on the magnetic field strength. T(f)(H) varies according to the well known de Almeida-Thouless line [Formula: see text] suggesting an acentric long-range spin-glass behavior and mean field system.