Infrared reflectance spectra of an epitaxial ${\mathrm{Bi}}_2\mathrm{Fe}\mathrm{Cr}{\mathrm{O}}_6$ thin film prepared by pulsed laser deposition on $\mathrm{La}\mathrm{Al}{\mathrm{O}}_3$ substrate were recorded between 10 and $900\mathrm{K}$. No evidence for a phase transition to the paraelectric phase was observed, but some phonon anomalies were revealed near $600\mathrm{K}$. Most of the polar modes exhibit only a gradual softening, which results in a continuous increase of the static permittivity on heating. It indicates that the phase transition from ferroelectric to paraelectric phase should occur somewhere above $900\mathrm{K}$. Magnetic measurements of the partially $B$-site-ordered ${\mathrm{Bi}}_2\mathrm{Fe}\mathrm{Cr}{\mathrm{O}}_6$ thin film deposited on Nb-doped $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrate were performed up to $1000\mathrm{K}$. They revealed a possible magnetic phase transition between 600 and $800\mathrm{K}$, but the exact critical temperature cannot be determined due to a strong diamagnetic signal from the substrate. Nevertheless, our experimental data show that the $B$-site-ordered ${\mathrm{Bi}}_2\mathrm{Fe}\mathrm{Cr}{\mathrm{O}}_6$ is one of the rare high-temperature multiferroics.

• Received 6 December 2007

DOI:https://doi.org/10.1103/PhysRevB.77.104111