High frequency permeability of soft magnetic CoFeAlO films with high resistivity

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 Al ₂O₃ 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 (Hc) and anisotropy field (Hk) 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 Hk.