Leakage current under high electric fields and magnetic properties in Co and Mn co-substituted BiFeO₃ polycrystalline films

Co and Mn co-substituted BiFeO₃ films were prepared on Pt/Ti/SiO₂/Si(100) substrates, and the effect of co-substitution on the structural, electric, and magnetic properties of the prepared films was systematically investigated. Cross-sectional transmission electron microscopy observations showed that the films were homogeneous; moreover, no magnetic secondary phases were observed in the films. Nano-beam energy-dispersive X-ray spectroscopy, carried out at various points in the films, revealed that Co and Mn were distributed in the films. Further, the average concentration of Bi, Co, Mn, and Fe was 59, 2, 2, and 37 at.%, respectively; these values were almost consistent with the nominal composition of the precursor solution used. X-ray diffraction profiles of the films showed that the (012)-d-spacing decreased and (104) and (110) peaks merged into a single peak with increasing co-substitution content. The leakage current in films under high electric fields drastically decreased upon co-substitution without any degradation of ferroelectricity; moreover, this effect was also observed for single Mn-substituted materials. Saturation magnetization of the films monotonically increased with the co-substitution content, and this increase was quantitatively identical to that in the case of single Co-substituted materials. These results indicate that Co and Mn play significant roles in determining the properties of co-substituted BiFeO₃ films.