Thickness dependent size effect of BiFeO₃ films grown on LaNiO₃-buffered Si substrates

BiFeO₃ films of different thicknesses were grown on the LaNiO₃-buffered Si (100) substrate via a sol-gel spin-coating processing. X-ray diffraction and Raman spectra studies revealed a thickness dependent structural and strain state evolution. The thickness dependent size effect on ferroelectric behavior was reflected in the polarization versus electric field hysteresis loops and domain structures. Enhancement in magnetization of the thin BiFeO₃ films resulted from the strain-induced canting antiferromagnetic structure, and remarkable anisotropy was observed in the 40 nm BiFeO₃ film as well due to the magnetoelastic effect induced by strain. With the increase in the film thickness, the magnetic moment of BiFeO₃ films decreased back to the ordinary canted antiferromagnetic state.