Epitaxial Bi2FeCrO6 multiferroic thin films

Abstract

We present experimental results on Bi2FeCrO6 (BFCO) epitaxial films deposited by laser ablation directly on SrTiO3 substrates. It has been theoretically predicted by Baettig and Spaldin [Appl. Phys. Lett. 86 012505 (2005)], using first-principles density functional theory, that BFCO is ferrimagnetic (with a magnetic moment of 2 µB per formula unit) and ferroelectric (with a polarization of ∼80 µC/cm2 at 0 K). The crystal structure has been investigated using X-ray diffraction, which shows that the films are epitaxial with a high crystallinity and have a degree of orientation depending on deposition conditions determined by the substrate crystal structure. Chemical analysis, carried out by X-ray microanalysis and X-ray photoelectron spectroscopy (XPS), indicates the correct cationic stoichiometry in the BFCO layer, namely (Bi:Fe:Cr = 2:1:1). XPS depth-profiling revealed that the oxidation state of Fe and Cr ions in the film remains 3+ throughout the film thickness and that both Fe and Cr ions are homogeneously distributed throughout the depth. Cross-section high-resolution transmission electron microscopy images plus selected area electron diffraction confirm the crystalline quality of the epitaxial BFCO films with no identifiable foreign phase or inclusion. The multiferroic character of BFCO is demonstrated by ferroelectric and magnetic measurements showing that the films exhibit ferroelectric and magnetic hysteresis at room temperature. In addition, local piezoelectric measurements carried out using piezoresponse force microscopy (PFM) show the presence of ferroelectric domains and their switching at the sub-micron scale.