Single-Crystal-like Textured Growth of CoFe2O4 Thin Film on an Amorphous Substrate: A Self-Bilayer Approach

Single crystal or textured growth with preferred orientation of transition-metal oxide thin films is highly desirable for their application in technological devices. Commercially available single-crystal substrates are the obvious base to deposit thin films with a desired orientation. However, these substrates have inherent shortcomings including limited number of crystal structures, lattice parameters and orientations, and most importantly their high costs. Herein, a universal approach was developed to grow an oxide thin film with (100) crystal orientation on an amorphous substrate. To achieve this goal, two layers of the same material called self-bilayer were deposited at different temperatures and of different thicknesses. CoFe2O4 spinel ferrite was used as a model system to realize the approach since it is difficult to grow spinel ferrites with (100) orientation even on single-crystal substrates. X-ray diffraction pattern and transmission electron microscopy confirmed the single-crystal-like growth of CoFe2O4 with (100) orientation on an amorphous SiO2/Si substrate. The deposited CoFe2O4 bilayer thin film displays unprecedentedly giant perpendicular magnetic anisotropy with a coercivity of 14.1 kOe, saturation magnetization of 475 emu/cm3, and remanent ratio of 0.92 at room temperature. This work opens up a facile and generic route to grow complex metal oxide systems with preferred orientation on an amorphous substrate via an innovative self-bilayer approach.