Control Of The Growth Of Ferromagnetic Pure Metal Fe,Ni,Co Nanocrystalline Thin Films By High Magnetic Fields

Ferromagnetic nanocrystalline thin films have unique magnetic phenomena such as giant conductance,giant magnetoresistance and giant hall effect,which play an irreplaceable role in the fields of high density storage,magnetic resistance sensor,high frequency sensor,micro electro mechanical system,micro transformer,anti-electromagnetic interference and microwave absorption medium.In order to realize the application of the ferromagnetic nanocrystalline thin films,controlling the microstructure of the films is essential.The microstructure of the films depends on the growth process.Therefore,it is important to control the growth process of the films.High magnetic field(HMF)exhibits the characters of non-contact operation,enhanced Lorentz force,magnetization force,magnetization energy and magnetic dipole interaction.It has become one of the essential means to discover new phenomena,create new structure and reveal the nature of physical phenomena.During the growth of films,the nucleation,particle diffusion,crystal growth and orientation of films can be affected by HMF.This provides the conditions to control the growth of the ferromagnetic nanocrystalline films by HMF.In addition,revealing the effect mechanism of HMF is helpful to control the growth of ferromagnetic nanocrystalline films.The effect of HMF on different elements of alloy and multilayer films is complicated.And it is difficult to reaveal the control mechanism of HMF.In this paper,HMF was applied in the preparation process of Fe,Ni and Co pure metal ferromagnetic nanocrystalline thin films.The effect of HMF on the growth of the films was investigated.And the soft magnetic and electrical properties induced by structure evolution were also explored.Furthermore,the control mechanism of HMF on the film growth was also revealed.The research content and achievements are given in details as follows:(1)The microstructure evolution of Fe films was investigated when HMF was applied in different formation stages of films.Then we analyzed the effects of HMF on the microstructure,magnetic and electrical properties of Fe films preprared at different substrate temperatures and growth rates,respectively.The results show that HMF could effectively improve the microstructure of Fe films when it was applied in the growth stage of film.Columnar growth along the HMF direction in Fe films was induced by HMF at low substrate temperature(room temperature and 200?).However,the HMF failed to induce the columnar growth of Fe film at high substrate temperature(400?).The grain and particle(composed of grains)size were obviously improved by HMF.However,the surface roughness of Fe films was decreased by HMF.The HMF could increase the saturation magnetization and decrease the resistivity of Fe films.The coercivity of Fe film was decreased by HMF when the substrate temperature is room temperature.However,HMF increased the coercivity of Fe film fabricated at the substrate temperature of 200?.The effects of HMF on the surface morphology and soft magnetic properties of Fe films were weakened at high substrate temperature.(2)The effects of HMF on the microstructure,soft magnetic and electrical properties of Ni films with different growth rates and acting time were studied.The results show that HMF changed the growth mode of Ni films:from disorderly stack of uiaxial grains(OT)to the columnar growth along the direction of HMF.And the columnar growth was more obvious at high growth rate of film and long acting time of HMF.HMF effectively increased the average grain size of Ni films.However,the particle size and surface roughness of Ni films were decreased by HMF.Furthermore,HMF could remarkablely increase the saturation magnetization,but decrease the resistivity and coercivity of Ni films.The remanence ratio of Ni films could be controlled by HMF.(3)The effects of HMF on the microstructure,magnetic and electrical properties of Co films prepared under different growth rates,acting time and magnetic flux densities were investigated.At the same time,the competitive influences of HMF and substrate temperature on the structure and magnetic properties of Co films were also analyzed.The results show that magnetic field changed the microstructure of Co films at different magnetic flux densites:from disorderly stack of uiaxial grains(OT)to columnar growth along the direction of magnetic field.In addition,with the increase of growth rate,the nano columnar crystal was changed to columnar stacking of nano uiaxial grains gradually.HMF remarkably increased the grain size,but decreased the particle size and surface roughness of Co films.HMF could decrease the coercivity and resistivity,and change the magnetic anisotropy of Co films.Furthermore,Co films with nano-columnar crystal prepared under HMF had the highest saturation magnetization.HMF changed the microstructure and magnetic anisotropy,and improved the coercivity of Co films under substrate thermal disturbance.(4)The control mechanism of HMF on the growth of pure metal ferromagnetic nanocrystalline thin films was revealed.The columnar growth of the films was induced by HMF due to the magnetic dipolar interaction.The magnetic dipolar interaction and magnetization energy led to the change of grain shape in the films prepared at different growth rates.Zeeman energy(magnetization energy),which was induced by HMF,improved the formation energy of the films.This increased grain sizes and decreased the surface roughnesses of the films prepared under HMF.The particle size of Co and Ni films was refined by HMF because of the magnetic dipole interaction.However,the low cohesive energy and the atomic binding energy of the Fe films resulted in the increase of particle size under HMF.