Ferromagnetic Film − Substrate Decoupling for Sensor Applications

This study presents the decoupling of ferromagnetic properties of Fe–Co–Hf–N films with an in‐plane uniaxial anisotropy from ferromagnetic cemented carbide (WC–Co) substrates by predepositing a non‐ferromagnetic buffer layer between the substrate and the film. Due to the ferromagnetic Co content in the substrate, a magnetic coupling effect arises which suppresses the natural ferromagnetic resonance of the Fe₃₂Co₄₅Hf₁₁N₁₂ film at a frequency of 2.13 GHz. The deposition of a non‐ferromagnetic, electrically conductive TiN layer, or a non‐ferromagnetic, electrically insulating SiO₂ layer between the substrate and the soft ferromagnetic film shows decoupling regarding the static ferromagnetic properties, so that the formation of an in‐plane uniaxial anisotropy is possible. With regard to the application as a high‐frequency sensor the paper shows that with increasing the thickness of the electrically insulating SiO₂ buffer layer the full width at half maximum (FWHM) of the resonance line becomes much sharper, in contrast to the electrically conductive TiN. The explanation was attributed to the formation of eddy‐currents in the electrically conductive material causing a magnetic field which disturbs the uniform precession of the magnetic moments. The high‐frequency properties of the decoupled film system are promising for a thermal and mechanical stress sensor system on cutting tools.