Enhanced spontaneous polarization in double perovskite Bi2FeCrO6 films

We report the pulsed-laser deposition of epitaxial double-perovskite Bi2FeCrO6 (BFCO) films on the (001)-, (110), and (111)-oriented single-crystal SrTiO3 substrates. All of the BFCO films with various orientations show the 1/21/21/2 and 3/23/23/2 superlattice-diffraction peaks. The intensity ratios between the 1/21/21/2-superlattice and the main 111-diffraction peak can be tailored by simply adjusting the laser repetition rate and substrate temperature, reaching up to 4.4%. However, both optical absorption spectra and magnetic measurements evidence that the strong superlattice peaks are not correlated with the B-site Fe3+/Cr3+ cation ordering. Instead, the epitaxial (111)-oriented Bi2FeCrO6 films show an enhanced remanent polarization of 92 mu C/cm(2) at 10K, much larger than the predicted values by density-functional theory calculations. Positive-up-negative-down (PUND) measurements with a time interval of 10 mu s further support these observations. Therefore, our experimental results reveal that the strong superlattice peaks may come from A- or B-site cation shifts along the pseudo-cubic [111] direction, which further enhance the ferroelectric polarization of the BFCO thin films.