STRUCTURE AND PROPERTIES OF EPITAXIAL THIN FILMS OF Bi₂FeCrO₆: A MULTIFERROIC MATERIAL POSTULATED BY AB-INITIO COMPUTATION

ABSTRACT

Experimental results on Bi₂FeCrO₆ (BFCO) epitaxial films deposited by laser ablation on SrTiO₃ substrates are presented. It has been theoretically predicted using first-principles density functional theory that BFCO is ferrimagnetic (with a magnetic moment of 2μ_B per formula unit) and ferroelectric (with a polarization of ∼ 80 μ C/cm² at 0K). The crystal structure investigated using X-ray diffraction shows that the films are epitaxial with a high degree of crystallinity. Chemical analysis carried out by X-ray Microanalysis and X-ray Photoelectron Spectroscopy indicates the correct cationic stoichiometry in the BFCO layer, namely (Bi:Fe:Cr = 2:1:1). Cross-section high-resolution transmission electron microscopy images together with 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 proven by piezoresponse force microscopy (PFM) and magnetic measurements showing that the films exhibit ferroelectric and magnetic hysteresis at room temperature. The local piezoelectric measurements show the presence of ferroelectric domains and their switching at the sub-micron scale.

Keywords:

• Multiferroics
• ferroelectricity
• epitaxial thin film
• magnetism
• piezoresponse

ACKNOWLEDGMENTS

The authors want to thank Dr. P. Plamondon ((CM)², École Polytechnique de Montréal) for XTEM and SAED analysis and related discussions, as well as F. Normandin and Prof. T. Veres for performing preliminary magnetic measurements. Part of this research was supported by INRS start-up funds, NSERC (Canada), and FQRNT (Québec).