Microstructure of Sputtered CoFe2O4 Film

The growth morphology of CoFe2O4 (Co ferrite) film deposited by the sputtering method was investigated at substrate temperatures of 330–870 K. Co ferrite films were grown on (001) MgO single crystals epitaxially. Results, however, showed that the increase of substrate temperatures leads to the formation of Co precipitates in a Co ferrite matrix. Careful inspection of X-ray diffraction patterns revealed that γ-Fe2O3 formed in the films deposited at the substrate temperature of 330 K, which indicates that decomposition of Co ferrite had took place during deposition. The crystal structures of Co in the matrix were the hcp and fcc structures at the substrate temperatures of 670 and 870 K, respectively. Co was elongated in a filament-like fashion in the direction of growth in the film deposited at 670 K, but had a particle-like appearance in the film deposited at 870 K. The growth morphology of Co in the Co ferrite matrix can be understood by the interfacial energy and the anisotropic structure of hcp Co.