Influence of the BiFeO₃ phase on ferromagnet properties of layered multiferroic CoFe₂O₄-BiFeO₃ films

Multiferroic layered films consisting of CoFe₂O₄-BiFeO₃(CFO-BFO) with increasing BFO constituent layers thicknesses were prepared on the LaNiO₃(LNO)-buffered Si(100) substrate via a simple spin-coating process in order to investigate the thickness effect of ferroelectric BiFeO₃ phase on the magnetic properties of the composite films. The structure and morphology were researched by XRD, SEM and TEM. Bisides, the magnetic properties were demonstrated by vibrating sample magnetometer (VSM) and the effect of different thicknesses of BFO layer on the magnetic properties of the composite films was discussed. The results reveal that magnetic CFO and ferroelectric BFO phases coexist in the heterostructured films. The buffered layer LNO and ferromagnetic layer CFO possess clear microstructure and obvious interface between them. The thickness of BiFeO₃ phase has a significant influence on the magnetic properties of the CFO-BFO films. Among the multiferroic films containing different BFO layers, the film that consisting of nine BFO constituent layers demonstrates the highest M_s value of 230 emu·cm^-3, which improves 18.6% than that of the film without BFO constituent layers. We initially conclude that it is stress that leads to the improvement of M_s with increasing the BFO thickness.