Magnetic and Leakage Current Characteristics of Transferred CoFe₂O₄/BiFeO₃ Thin Films

The challenge of directly depositing highly crystalline thin films onto flexible substrates because of their low thermal stability has motivated the exploration of thin-film transfer techniques. In this study, we report on the thin-film transfer process of sputter-grown BiFeO3/CoFe2O4 bilayer thin films using a sacrificial α-MoO3 layer on SrTiO3(001) substrates. A significant cation diffusion into the α-MoO3 layer leading to the formation of secondary phases in CoFe2O4 films was effectively suppressed by lowering the deposition temperature. However, the formation of secondary phases could not be avoided in crystallized BiFeO3 thin films. The large leakage current in the BiFeO3 thin film dramatically decreased upon annealing; however, a critical temperature existed where α-MoO3 reacted with SrTiO3, thereby resulting in the collapse of its two-dimensional structure. The CoFe2O4 thin films not only prevented diffusion but also significantly reduced the leakage current in the BiFeO3/CoFe2O4 bilayer. Bilayer stacks transferred onto flexible substrates by rupturing the interconnection in the α-MoO3 layer maintained their magnetic anisotropy and exhibited improved leakage current characteristics.