High frequency permeability of soft magnetic CoFeAlO films with high resistivity

Abstract As-deposited CoFeAlO films have been prepared by reactive RF magnetron sputtering at input power of 300 W. The X-ray diffraction (XRD) results exhibit a multi-phase structure, which could be consisting of major phases: α-CoFe (1 1 0) and α-CoFe(2 1 1), and minor phase CoFe-oxides with Al2O3 as the amorphous matrix were formed. Moreover, it has also been demonstrated that a nanocrystalline CoFe alloy was obtained and the evaluated sizes were below 15 nm. The thickness effects on the high-frequency characteristics of as-deposited CoFeAlO soft magnetic thin films have been studied in the range of 50 to 1200 nm. The coercivity ( H c ) and anisotropy field ( H k ) of these films increases largely with decrease in the film thickness. It is explained to be the result of the change in the film composition and surface roughness. The electrical resistivity ( ρ ) also increases with decreases in the film thickness. The effective permeability of a CoFeAlO thin film is larger than 1000 and remained constant up to 700 MHz with film thickness below 1000 nm. A CoFeAlO film exhibits excellent high-frequency characteristics, which results from softness properties, high ρ , high H k .