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 BiFeO 3 /CoFe 2 O 4 bilayer thin films using a sacrificial α-MoO 3 layer on SrTiO 3 (001) substrates. A significant cation diffusion into the α-MoO 3 layer leading to the formation of secondary phases in CoFe 2 O 4 films was effectively suppressed by lowering the deposition temperature. However, the formation of secondary phases could not be avoided in crystallized BiFeO 3 thin films. The large leakage current in the BiFeO 3 thin film dramatically decreased upon annealing; however, a critical temperature existed where α-MoO 3 reacted with SrTiO 3, thereby resulting in the collapse of its two-dimensional structure. The CoFe 2 O 4 thin films not only prevented diffusion but also significantly reduced the leakage current in the BiFeO 3 /CoFe 2 O 4 bilayer. Bilayer stacks transferred onto flexible substrates by rupturing the interconnection in the α-MoO 3 layer maintained their magnetic anisotropy and exhibited improved leakage current characteristics.