Epitaxial Growth of Co0.75Fe2.25O4/NiO Bilayer on MgO(001) Substrate

To suppress the dead layer and improve the magnetic properties at the interface between Co_xFe_3-xO₄ (CFO) with x = 0.75$ and the MgO(001) substrate, we investigated the effect of inserting a NiO layer on the magnetization of CFO films. We succeeded in growing high-quality CFO films with perpendicular magnetic anisotropy on NiO(001) buffer layers. Similar to CFO/MgO(001) films, a magnetic dead layer with a thickness of ~5$ nm was observed. We concluded that the main reason for the formation of this dead layer in CFO/MgO(001) was unlikely to be Mg diffusion but was probably the formation of anti-phase boundaries (APBs). Our results suggest that the formation of a dead layer in a CFO film requires further clarification regarding the interface structure, especially the density of the APBs.