Investigation Of The Microstructure And Texture Evolution Mechanism Of Magnetic Recording Thin Films

With the explosive growth of information storage,magnetic recording is developing towards high density and ultrahigh density recording.In order to improve the magnetic recording storge density,it can be improved from two apsects On one hand,the giant magnetoresistive heads,and the thin films should be satisfied with the high magnetoresistance,high magnetic sensitivity,low saturation field and good thermal stability.On the other hand,the magnetic recording media which is hard magnetic thin film with high magnetic anisotropy.For instance,the L10-FePt thin films should be content with the fine grain,{001}preferred orientation and low ordered transformation temperature.Different preparation parameters and buffer materials would influence on the growth model,microstructure and texture of the multilayers.Roughness and interlayer structure would affect the interlayer coupling phenomenon and spin dependent scattering.Considering the anisotropy of various properties in thin films,texture evolution would affect the giant magnetoresistance effect.Reducing the ordered transformation temperature,increasing the {001}oriented texture component and controlling the grain size have been one of difficult and attractive field in L10-FePt thin films.Additionally,in order to shed light on the growth mechanism of multilayers,it is necessary to study the growth mechanism of monolayer thin film.Therefore,in this study,we investigate the influence of buffer layer,sputtering power,thickness and annealing temperature on microstructure and texture evolution of Cu thin film,Cu/Co multilayers and FePt thin films.The results are shown as follows:First,the effect of buffer layer on microstructure and texture evolution of Cu thin film was studied.Through comparing the SiO2/Cu,Fe/Cu,Ti/Cu,Ta/Cu and TiVCrZrHf/Cu thin films,it was found that the larger average grain size and amounts of twins exsit in the SiO2/Cu thin film.The surface morphology was rough and random texture was formed.While,inserting the buffer layer Fe,Ti,Ta and high entropy alloys TiVCrZrHf would lower the large surface energy differences between Cu thin film and SiO2,improve the wettability of interface.The nucleation rate increased significantly,while,the average grain size and the quantity of twins decreased.The growth of{111}oriented grains were preferred due to its minimum surface energy,then sharp{111}fiber texture formed.The TiVCrZrHf buffer layer showed amorphous structure and did not provide rapid diffusion paths such as grain boundaries which could resist diffusion and have excellent thermal stability.Secondly,the effect of sputtering power and thickness on microstructure and texture transformation of Fe/Cu thin films was studied.When the sputtering power was 100 W,the average grain size was 1.6μm and a strong{111}fiber texture was presented in the Cu thin film.As the sputtering power increased to 200 W,the grain size was 1.2μm and the quantity of twins increased,the texture transformed to random texture.The grain size decreased to 0.7μm and the preferential growth of{100} oriented grains with lowest elastic strain energy.The strain state changed in Fe50nm/Cu1000nm thin film as the thickness of Cu thin film increased.The {100}fiber texture tansformed to {110}fiber texture and the grain size was 1.1μm.With the increase of sputtering power,nucleation density increased rapidly and the grain size decreased.As the thickness of Cu thin film increasing,the temperature of the substrate was also rising and grains began to grow up.Additionally,we dicussed the influence of surface energy,elastic strain energy and plastic strain energy on texture evolution of thin films.According to the first principle,a supercell model with periodic boundary was constructed to simulate the surface.The results show that the lowest surface energies of Cu,Fe,Ti and Ta are Es-cu{111}=1.269 J/m2,Es-Fe{110}=2.561 J/m2,Es-Ta{110}=2.601 J/m2 and Es-Ti{100}=1.322 J/m2,respectively.The elastic strain energy coefficients of several typical low index planes {111},{110} and {100} are 261.0,233.0 and 114.8,respectively.Therefore,the {100} orientation with smallest elastic strain energy coefficient can be prefered under the elastic strain state.When strain state change,grain growth depends on the average orientation factor.The orientation factors of{100},{110} and {111} oriented grains are 0.408,0.408 and 0.272,respectively.While the number of equivalent slip system is different,which are 8,4 and 6,respectively.Only considering the influence of the orientation factor and ignoring the influence of elastic anisotropy,preferential growth of{110} oriented grain due to the large orientation factor and less equivalent slip system.Finally,the effects of Ta and Ti buffer layer on microstructure and texture evolution of Cu-Co GMR multilayer,as well as the influences of sputtering power and Cu intercalation film on ordered transformation of L10-FePt thin film and the formation of{001}fiber texture were studied.Results show that the wettability of SiO2 and Cu-Co is poor and the texture was weak.Adding Ta and Ti buffer layer could effectively improve the wettability,reduce the roughness,and form a strong{111} fiber texture.When the roughness decreased,the spin dependent scattering decreased and the GMR effect significantly increased.When the sputtering power was 25 W,the ordering transformation of FePt thin film began at 400 ℃.And the ordered transition temperature raised with the increase of sputtering power.WhenCu thin film was added,the ordered degree of Llo-FePt thin film was significantly increased,a strong {001} fiber texture was formed,and the surface roughness reduced.