High-Performance Finemet Alloy Thin Film with Amorphous/Nanocrystalline Structure Treated by Rapid-Thermal Process
The influence of thickness and annealing treatment on the microstructure and soft magnetic properties of Fe−Si−B−Cu−Nb alloy (Finemet) thin films prepared by magnetron sputtering was systematically investigated. As-deposited films are amorphous; coercivity decreases and saturation magnetization increases with thickness, stabilizing at 400 nm. Annealing at 773 K and 873 K precipitates nanocrystalline α-Fe within the amorphous matrix. Exchange coupling between nanocrystals and the amorphous matrix enhances soft magnetic properties. Rapid thermal processing (RTP) controls the heating rate to minimize grain size and optimize nanocrystal distribution, achieving low coercivity and high saturation magnetization without additional transition metals. The film annealed at 873 K for 30 min with a heating rate of 25 K/s exhibits a coercivity of 0.8 A/m and saturation magnetization of 1.45 T. Compared to the 773 K annealed film, the 873 K annealed film shows significantly lower coercivity due to smaller precipitated nanocrystals. RTP with controlled thermal gradient enables even smaller nanocrystals, further enhancing magnetic properties. These results demonstrate that RTP-treated Finemet films are promising for high-frequency, miniaturized, and integrated electronic devices.