General aspects of the physical behavior of polycrystalline BiFeO3/VO2 bilayers grown on sapphire substrates.

Heterostructures composed of bismuth ferrite, BiFeO₃, and vanadium dioxide, VO₂, films were successfully grown by means of the radio-frequency and DC sputtering on sapphire substrates. The X-ray diffraction (XRD) patterns showed that both films were polycrystalline in nature. The XRD data revealed the formation of the monoclinic VO₂(M) phase. The bottom VO₂ exhibited a sharp metal–insulator transition (MIT) at ~ 327 K with a variation in the value of the resistance of two orders of magnitude. Measurements of the electric polarization (P) versus the electric field (E) of the top BiFeO₃ showed closed loops, although visually distinct from those of a true ferroelectric. In spite of the well-defined MIT of VO₂, the effect of the structural change associated with the transition on the ferroelectric properties of BiFeO₃ was masked by the large leakage currents. The probably perturbation of the ferroelectric order in the BiFeO₃, associated with the structural changes through the MIT of VO₂ was investigated by measuring the P-E dependence at temperatures below and above the MIT of VO₂. Although round-shaped hysteresis were obtained, a small but sizeable difference in the values of the apparent remnant P at the temperatures of interest was observed. By the same token, the transition of VO₂ seemed to influence the possible magneto-electric coupling in the BiFeO₃ layer. [ABSTRACT FROM AUTHOR]