Magnetic Softness, Dynamic Magnetic Properties, And Thermal Stability Of FeCoAIN Films

With the rapid development of electronic information technology,the magnetic induction devises are becoming more and more miniaturized and integrated and desired for high frequency applications.Meanwhile,we need more advanced microwave absorption materials to elimate the increasing interference and pollution of electromagnetic wave.Therefore,the soft magnetic films with high saturation magnetization and good dynamic characteristics in high frequency range have attracted more attentions.Systematical studies of the soft magnetic films for high frequency applications are of significance for the practical applications mentioned above.FeCo alloys are important materials for their high saturation magnetization. But it is difficult for FeCo alloys to achieve low coercivity and in-plane uniaxial anisotropy due to its high magnetocrystalline anisotropy and magnetostriction. The recent studies have indicated that Fe₇₀Co₃₀N,Fe₆₀Co₄₀N,and Fe₈₁Co₁₉N films have good soft magnetic properties.But these films do not show soft magnetic properties after annealing at higher than 200℃.Addition of proper elements into the FeCoN films can improve thermal stability of the films.In our work of this thesis,a series of FeCoAlN films with Fe:Co ratio of 64.8:35.2 are prepared by the reactive radio frequency magnetron sputtering.The structure, static and dynamic magnetic properties,and thermal stabilities are studied.The results show that the FeCoAlN films can achieve good soft magnetic properties and dynamic characteristics in high frequency.The thermal stability of (Fe_64.8Co_35.2)AlN films is evidently improved with increase of Al content.The main results are shown as follows:(1) The as-deposited(Fe_64.8Co_35.2)_96.3Al_3.7N films show good soft magnetic properties and in-plane uniaxial anisotropy when N₂/(Ar+N₂) flow rate ratio(R) is in 9%.These films show high resonance frequency above 2 GHz and the real part of permeability larger than 400 before rolloff.(2) The as-deposited(Fe_64.8Co_35.2)AlN films with R of 9%show good soft magnetic properties and the uniaxial anisotropy when Al content is lower than 6.2%.The dynamic characteristics exhibit the uniform resonance mode.The resonance frequencies are higher than 2 GHz.With the further increase of Al content,the coercivity become larger and the uniaxial anisotropy become lower. The dynamic characteristics are deteriorated.The reason may be the increase of stresses in the films with the increase of Al content.(3) Thermal stability of the films is evidently improved with increase of Al content.The magnetic properties of the films with different Al content transform from soft magnetic and uniaxial anisotropic properties to hard magnetic and isotropic properties when they are annealed at the temperature higher than an optimal temperature(T_opt).T_opt clearly increases with the increase of Al content in the films.The Fe_64.8Co_35.2N film without Al become hard magnetic and isotropic properties after annealed at 200℃.No resonance show in the permeability spectrum.The(Fe_64.8Co_35.2)_86.5Al_13.5N film annealed at 400℃for 60 min still remain the good soft magnetic properties,uniaxial anisotropy and uniform resonance mode of permeability spectrum.The resonance frequency is about 1.89 GHz and the real part of permeability is higher than 380 before rolloff.(4) Saturation magnetization of the as-deposited(Fe_64.8Co_35.2)_93.8Al_6.2N films does not change with the variation of film thickness.This may be due to the saturation magnetization has nothing to do with the film thickness and structure. The coercivity increase as the film thickness is gradually reduced,which may be due to the increase with the thickness,internal stress gradually decreased,the coercivity also decreases.