| In recent years,Llo-FePt thin films have received considerable attention as the preferred material for thermally assisted perpendicular magnetic recording technology,due to its extremely high uniaxial magnetocrystalline anisotropy,high saturation magnetization and good corrosion resistance.In order to realize the application of L10-FePt thin films in perpendicular magnetic recording technology,post deposition annealing or depositing at high temperature is required to facilitate the easy magnetization axis[001]perpendicular to the film surface,forming the L10 ordered structure and(001)fiber texture in FePt thin films.Therefore,in this paper,the ordered transformation process and the evolution of texture in FePt thin films were studied in the following aspects.Firstly,the effect of sputtering pressure on the ordered transformation of FePt thin films during the preparation of FePt thin films by magnetron sputtering was studied.The results revealed that in the as-deposited state,with the increase of sputtering pressure,the size of island in the thin films gradually increased and the degree of clusters became more serious,leading to the enhancement of surface roughness in FePt thin films.Besides,the ciystallinity of FePt phase decreased as the sputtering pressure increased,resulting in the increase of internal defects in FePt thin films.Due to evolution of film microstructure,the processes of ordered transformation and grain growth was hinded,a higher annealing temperature is required to complete the ordered transformation process.Therefore,in order to reduce the ordered transformation temperature of FePt thin films,it is necessary to prepare the as-deposited FePt thin films with less internal defects,which could be realized with low sputtering pressure.In addition,the grain growth kinetics and ordering transformation kinetics of FePt thin films have been studied,respectively.According to the experimental results,the activation energy of grain growth in FePt thin films was calculated to be Q=78 kJ/mol and the ordered transformation activation energy of FePt thin films was calculated to be E=169 kJ/mol,which was greater than the activation energy of grain growth.Therefore,during the annealing process,the grain growth would occur preferentially in comparison to the ordered transformation,as the activation energy of grain growth was less than that of the ordered transformation in FePt thin films.Secondly,the texture formation mechanism of L10-FePt thin films during ordering transforamtion was studied.The Voigt,Reuss and Hill models were used to calculate anisotropy elastic constant and effective biaxial modulus of tetragonal structured L10-FePt thin films with ideally fiber texture.On this basis,we calculated the anisotropy elastic strain energy of Llo-FePt thin films after ordered transformation,and discussed the effect of in-plane strain state of thin film before ordered transformation on the anisotropic elastic strain energy of L10-FePt thin films.The results indicated that,when the film was in non-strain or tensile in-plane strains before the ordered transformation,the(001)plane has the minimum elastic strain energy,which will promote the fonnation of(001)fiber texture?Meanwhile,the characteristic of microstructure and texture of the 100 nm annealed FePt thin films was quantitatively analyzed.It was found that there was mainly {111} fiber texture in both as-deposited and 400 ?-annealed FePt thin films.In the 550 ?-annealed L10-FePt thin film after ordered transformation,the {111} fiber texture was reduced and a(001)fiber texture was appeared.When the annealing temperature raised to 600 ?,the(001)fiber texture was enhanced,but the intensity of the(001)fiber texture was still weak.This was due to the decrease of in-plane tensile strain as the grain growth before ordered transformation,leading to the insufficient driving force of(001)fiber texture formation.In this case,the strong(001)fiber texture cannot be obtained in Llo-FePt thin films.With the increase of annealing temperature,the(001)fiber texture in 700 ?-annealed Llo-FePt thin film was significantly reduced.It was found that there were growing twins in the as-deposited films and multiple twins were formed after annealing process.The existence of high-frequency twinning was an important factor in weakening(001)fiber texture.Finally,in order to avoid the occurence of weakening(001)fiber texture factors,the preparation process of L10-FePt thin films was optimized.By changing the annealing mode from heating up within furnace to annealing in the pre-heated furnace,and adjusting the thickness of FePt thin fims,the L10-FePt thin film with strong(001)fiber texture was successfully prepared on an amorphous SiO2 substrate and the perpendicular magnetic anisotropy was realized.The results indicated that when the film thickness was 5 nm,the Llo-FePt thin film has the strongest(001)fiber texture and the interface strcture was perfect.However,when the thickness was beyond 15 nm,the twins was appeared and the strength of(001)fiber texture began to decrease.In addtion,the method of annealing in the pre-heated furnace can accelerate the heating rate and reduce the time of grain growth,so that the in-plane tensile strain was large enough before the ordered transformation,it would promote the formation of(001)fiber texture.Both the annealing mode and film thickness have strong effects on formation of(001)fiber texture.Therefore,controlling heating rate and film thickness were the most important factors in fabricating strong(001)fiber-textured L10-FePt thin film on amorphous substrate.In conclusion,we investigated the microstructure of FePt thin films in ordered transformation process and the formation mechanism of(001)fiber texture have been studied systematically.According to the above analysis,an effective method for preparing strong(001)fiber-textured Llo-FePt thin film on an amorphous SiO2 substrate was proposed,which provided a valuable reference for improving the magnetic properties of Llo-FePt thin films. |
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