Exploring RF Magnetron Sputtering Growth Composite Thin Film BiFeO₃-Bi₂Fe₄O₉ on C-Plane Al₂O₃ Substrate

Nanocomposite films of BiFeO₃-Bi₂Fe₄O₉ were fabricated on a sapphire substrate Al₂O₃ using the method of gas discharge high-frequency cathodic sputtering of a ceramic target with a stoichiometric composition in an oxygen atmosphere. The results of the film analysis using X-ray structural analysis, Raman scattering, XPS, and atomic force microscopy are presented. The lattice parameters, surface topography, chemical composition of the films, concentration, and average sizes of the crystallites for each phase were determined. It was shown that the ratio of the BiFeO₃ to Bi₂Fe₄O₉ phases in the obtained film is approximately 1:2. The sizes of the crystallites range from 15 to 17 nm. The optical and magnetic properties of the nanocomposite layers were studied, and the band gap width and magnetization hysteresis characteristic of ferromagnetic behavior were observed. The band gap width was found to be 1.9 eV for the indirect and 2.6 eV for the direct interband transitions. The magnetic properties are characterized by a hysteresis loop resembling a "wasp-waist" shape, indicating the presence of magnetic anisotropy.