Magnetic Domain Structure,magnetic Anisotropy And High Frequency Performance Of Three Kinds Of Fe-based Magnetic Thin Films

Nowadays,magnetic thin films have been widely used in various kinds of highfrequency devices such as thin-film inductors,microwave filters,and microwave absorbers,etc.In order to ensure an operating frequency in the gigahertz range for microwave devices,the ferromagnetic resonance frequency of magnetic thin films should be well tuned to a very high value.It is well known that the ferromagnetic resonance frequency fr of magnetic films is determined by the magnetic anisotropy Hk.Conventionally,there are several methods to obtain an enhanced in-plane uniaxial magnetic anisotropy in magnetic films,such as oblique deposition,magnetic field annealing,and exchange bias.Among them,the oblique deposition can be easily handled,thus has been widely employed in practice to promote the ferromagnetic resonance frequency of magnetic films.However,the quantitative investigation,especially regarding to the magnetic anisotropy which determines the high-frequency behaviors of magnetic films,is rear.In this thesis,we fabricated magnetic thin films using sputtering and then we quantitatively studied the effect of film thickness,preparing conditions and oblique deposition on the magnetic domain structure,magnetic anisotropy and high-frequency properties.It consists of the following major aspects:Firstly,we have quantitatively studied the effect of Ni20Fe80(NiFe)magnetic films thickness,sputtering power density and Ar pressure on the magnetic domain structure,in-plane static magnetic anisotropy,in-plane rotatable magnetic anisotropy and out-ofplane magnetic anisotropy.The magnetic films with thickness beyond a critical value display a stripe domain structure as well as an in-plane rotatable magnetic anisotropy,which can be an important strategy to solve the problem of magnetic field orientation dependent performance in high-frequency devices.The cross-sectional characterizations of NiFe films indicate that the formation of columnar structure produces an out-of-plane magnetic anisotropy,giving rise to the appearance of stripe magnetic domain structures.The low Ar pressure is in favor of the formation of columnar structure in magnetic films under the high sputtering power density,which gives rise to the appearance of well aligned stripe magnetic domains.Secondly,we have fabricated amorphous Co40Fe40B20(CoFeB)magnetic thin films by oblique sputtering at room temperature and quantitatively studied the effect of film thickness,oblique angle on the magnetic domain structure,in-plane static magnetic anisotropy,in-plane rotatable magnetic anisotropy and out-of-plane magnetic anisotropy.The in-plane static magnetic anisotropy and out-of-plane magnetic anisotropy of amorphous CoFeB magnetic thin films are improved with increasing the oblique angles.The cross-sectional characterizations of amorphous CoFeB films indicate that the formation of oblique columnar structure improves an out-of-plane magnetic anisotropy and gives rise to the appearance of stripe magnetic domain structures.Our investigations provide an important reference to fabricate amorphous magnetic films by oblique sputtering and control their static and dynamic magnetic properties.Thirdly,we have investigated the effect of oblique deposition on the surface morphology and magnetic property for magnetic films grown onto a wrinkled surface.Fe60Co26Ta14(FeCoTa)alloy was selected as the magnetic layer due to its high saturation magnetization and excellent high-frequency behavior.The sinuously wrinkled topography is produced by growing a non-magnetic Ta layer on a prestretched PDMS membrane.Because of the enhanced shadowing effect by the wrinkled topography,the oblique deposition gives rise to a shift of wrinkle peaks and the FeCoTa thin films display a significantly uniaxial magnetic anisotropy.Both the enhancement of PDMS pre-strain and the increase of deposition angle could improve the uniaxial magnetic anisotropy and the ferromagnetic resonance frequency of FeCoTa films.Those works can provide the theoretical and experimental foundations of flexible wrinkled magnetic films for high-frequency applilications.