Study On Fe-Ga Thin Films And Magnetoelectric Coupling Devices

The magnetoelectric(ME)composite device is a combination of piezoelectric and magnetostrictive materials,which can be used as resonator,gyrators,filter and magnetic recording read head.Based on magneto-mechanical-electric coupling effect,ME devices are also sensitive to weak magnetic field,which has a good application prospect in the field of magnetic field detection and energy recovery.Magnetostrictive materials are an important component of ME devices.Compared with rare earth magnetostrictive materials,Fe-Ga has good magnetoelastic properties under a low bias magnetic field,which shows a good application prospect in ME devices.In view of the application of Fe-Ga thin film in magnetoelectric device,Fe-Ga/PZT and Fe-Ga/AIN/Mo/Si devices were prepared by magnetron sputtering.Meanwhile the correlation between the physical properties of Fe-Ga thin film and the magnetoelectric coefficient of the device was studied.This paper aims to optimize the performance of Fe-Ga magnetostrictive film,improve the magnetoelectric coefficient and reduce the bias magnetic field of the device.This work has certain significance for the development and application of magnetoelectric devices.Firstly,in this paper,the linear correlation between the ME coefficient ?ME of the ME device and the differential magnetoelastic coefficient(db/dH)of the Fe-Ga film is confirmed by experiments.And a semi-empirical formula based on differential magnetoelastic coefficient is proposed for calculating ?mE.At the same time,the properties of Fe-Ga films deposited on different Si substrates,buffer layers and under different sputtering parameters were studied to find the optimum deposition parameters.It is found that Ti and Mo buffer layers can improve the adhesion between Fe-Ga and Si substrates without affecting the magnetoelasticity of the Fe-Ga films.The abnormal grain growth of Fe-Ga thin films during heat treatment was observed by EBSD for the first time.Secondly,Fe-Ga/A1N/Mo/Si(100)ME device is designed using AIN piezoelectric film.After magnetic field heat treatment,the device shows a good spatial angular resolution.The ME coefficient of the device in the length direction is 210 V/cm Oe at the resonant frequency.The in-plane anisotropy is the necessary condition for the spatial angular resolution of the device.Finally,(Fe-Ga/Fe-Ni)multilayer film is used to replace the single Fe-Ga layer in the device.The exchange coupling between the(Fe-Ga/Fe-Ni)magnetic layers can change the domain width of the magnetic film and reduces the hysteresis loss of the device.At the same time,piezomagnetic coefficients of(Fe-Ga/Fe-Ni)multilayer is increased,the bias magnetic field of the ME device is also effectively reducded.The exchange coupling between Fe-Ga and Fe-Ni magnetic film makes the magnetoelectric coefficient of(8 nm Fe-Ga/8 nm Fe-Ni)30/A1N/Mo/Si reach 607 V/cm Oe,and the bias magnetic field is reduced to 4 Oe.Multilayer(8 nm Fe-Ga/8 nm Fe-Ni)30 films also have good soft magnetic properties,high piezomagnetic coefficients of 8.1 ppm/Oe and high differential magnetoelastic coefficient of 0.32 MPa/Oe,which can be used as a driving element for micro-sensor and micro-electro-mechanical system(MEMS).