Soft magnetic Fe–Co–Si/native oxide multilayer films on flexible substrates for high-frequency applications

[Fe–Co–Si (d)/native oxide]50 multilayer films with different metallic layer thicknesses were prepared on flexible substrates by DC magnetron sputtering. The films consisted of an amorphous phase with a small amount of nanocrystallites. All the films have a very high resistivity (higher than 10 mΩ cm), which is probably caused by the effect of the plastic substrate and the mixed amorphous and nanocrystalline structure. The permeability spectra show relatively high values of complex permeability and ferromagnetic resonance frequency up to 7.9 GHz.