Study Of Magnetoelectric Coupling Effect Modulation In CoFe₂O₄-Ba_0.8Sr_0.2TiO₃ Double Dispersion Multiferroic Liquid

With the deepening of the application of big data,oil big data shows the characteristics of large data volume,multiple data types,data acquisition and processing timeliness.Therefore,petroleum big data puts forward new requirements for storage technology.Storage technology with low cost,low energy consumption,fast reading and high reliability has become the development trend of petroleum big data.Among many reading and writing technologies,the“electro-writing magnetic reading”technology based on the magnetoelectric coupling effect of multiferroic materials has attracted much attention due to its advantages of fast reading and writing speed,low power consumption and non-volatile.Compared with single-phase multiferroic materials,composite multiferroic materials are more likely to produce strong magnetoelectric coupling effect at room temperature.However,the magnetoelectric coupling mechanism of traditional composite multiferroic materials originates from the interface induced magnetic/polarization,which makes the magnetic/polarization direction difficult to change and limits the further improvement of magnetoelectric coupling effect.In this paper,the flow characteristics of liquid and composite multiferroic materials are combined to construct a multiferroic liquid with fluidity,which is expected to overcome the key problem that the coupling effect is difficult to improve.Using magnetic/electric field in multiferroic liquids can make magnetic/electric particles rotate and form chain structure with clamping effect,which makes it easier to change magnetic/polarization direction and achieve strong magnetoelectric coupling effect at room temperature.However,the coupling mechanism remains to be further studied.Therefore,CoFe₂O₄ with strong magnetism and low loss was used as the magnetic phase in this paper,and Ba_0.8Sr_0.2TiO₃ with easy polarization and relatively high dielectric constant was used as the ferroelectric phase.A CoFe₂O₄-Ba_0.8Sr_0.2TiO₃ magnetic-electric bidispersed multiferroic liquid was constructed.The effects of milling time,base fluid viscosity and volume fraction on the magnetoelectric properties and magnetoelectric coupling effect of multiferroic liquid were systematically studied,and a large magnetoelectric coupling coefficient was obtained.The main conclusions are as follows:（1）Optimization of preparation process of CFO and BST nano powders.CoFe₂O₄（CFO）nano powders were prepared by chemical coprecipitation method,and the effects of sintering temperature on the microstructure and magnetic properties of the powders were investigated.The results show that CFO powders exhibits typical cubic spinel structure at600℃～900℃ for 2 h,and the particle size and magnetic properties increase with the increase of temperature.Ba_0.8Sr_0.2TiO₃（BST）nano powders were prepared by sol-gel method.The effects of sintering temperature,holding time and pH of precursor solution on the microstructure of powders were investigated.The results show that when the sintering temperature is lower than900℃,Ti₉O₁₇ secondary phase will appear due to incomplete reaction at too low temperature.With the extension of holding time,the diffraction peak intensity gradually increases.The size of BST decreases first and then increases with the increase of pH.When pH was 5,the smallest particle size of 66.10 nm was obtained.（2）Regulation of milling time on magnetoelectric properties of CFO-BST multiferroic liquid.The effect of milling time on the magnetoelectric properties of CFO-BST multiferroic liquid was studied.The results show that with the extension of milling time,the saturation magnetization of the multiferroic liquid gradually decreases,and the dielectric constant gradually increases.The magnetic dielectric response increases first and then decreases with the increase of milling time.When the milling time is 2 h,the relative change rate of dielectric constant is the largest（3.2%）.With the extension of milling time,the polarization intensity of multiferroic liquid decreases first and then increases,and the magnetoelectric coupling effect increases first and then decreases.The milling time of 2 h has the maximum magnetoelectric response.（3）Regulation of base fluid viscosity on magnetoelectric properties of CFO-BST multiferroic liquid.The effect of base viscosity on the magnetoelectric properties of CFO-BST multiferroic liquid was studied.The results show that the greater the viscosity of base fluid,the better the settlement stability of multiferroic liquid.Due to the double effects of viscous resistance and stability,the magnetic dielectric response of multiferroic liquid increases first and then decreases,and the relative change rate of dielectric constant of 1000 mPa·s multiferroic liquid is the largest（3.9%）.It is found that multiferroic liquids have obvious“switching effect”under discontinuous magnetic field.In addition,with the increase of the viscosity of the base fluid,the polarization intensity of the multiferroic liquid increases first and then decreases,reaching the maximum at 1000 mPa·s.Due to its good stability and appropriate viscosity,the multiferroic liquid with viscosity of 1 000 mPa·s obtained the magnetoelectric coupling coefficient of 89.8V/（cm·Oe）under the external magnetic field of 91 Oe.（4）Regulation of volume fraction on magnetoelectric properties of CFO-BST multiferroic liquid.The effect of volume fraction on the magnetoelectric properties of CFO-BST multiferroic liquid was studied.The results show that with the increase of volume fraction of multiferroic liquid,more magnetoelectric particles are contained in the unit volume,resulting in the increase of dielectric constant,dielectric loss and magnetoelectric response.Under the action of discontinuous magnetic field,it is found that the dielectric constant of multiferroic liquid shows“switching effect”with the change of magnetic field.With the increase of volume fraction,the polarization intensity and leakage current of multiferroic liquid gradually increase.The ultra-large magnetoelectric coupling coefficient of 100.56 V/（cm·Oe）was obtained in the multiferroic liquid with volume fraction of 2%under the external magnetic field of 61.8 Oe.