Development and optimisation of FeCoHfN soft magnetic thin films with high-frequency characteristics

Ferromagnetic amorphous Fe–Co–Hf–N thin films with a gradient concentration of Hf doping were fabricated by rf reactive magnetron sputtering. The evaluated magnetic properties and high-frequency characteristics were sensitive to the doping contents. In this study, a new technology was used to deposit a series of Fe–Co–Hf–N thin films on which gradient concentration of Hf was present. By this new deposited technology, the films existed residual stress, and thus the stress-induced anisotropy field was enhanced. Therefore, the as-deposited films without postannealing exhibited larger anisotropy field (Hk) of 150 Oe. In addition, coercivity (HC) of less than 5 Oe in both easy and hard axes, and electrical resistivity (ρ) of 500 μΩ cm were obtained. The permeability measurement showed a permeability of around 100 at 3 GHz and a ferromagnetic resonance frequency (fFMR) in excess of 3 GHz. It is expected that this film should be promising for practical applications as a high-frequency ferromagnetic material.