Electrophoretic Deposition Of Ferromagnetic Films And Magnetoelectric Composite Films

BaTiO₃ nanopowder was synthesized by sol-gel method and CoFe₂O₄ nanopowder was synthesized by chemical co-precipitation method. Traditional sol-gel method was improved to prepare BaTiO₃/CoFe₂O₄ nano-composite powder. XRD analysis results showed that the size of particles was nano-scale and there was no impurity phase.The kinetic mechanism of electrophoretic deposition and suspension stability were studied. The suspensions for electrophoretic experiments were prepared by dispersing nanoparticles into solvents composed of ethanol and acetylacetone. Different additives were added into the suspensions in order to enhance the degree of dispersion and prevent cracking. The zeta potential values were measured to reflect the stabilities of suspensions. Ultrasonic dispersion time and concentration were studied on the influence factors of suspensions. The experiment results showed that the suspensions had high zeta potential and conductivity after ultrasonic dispersion. Zeta potential and conductivity of suspensions were increased with the increase of suspension concentration in a certain range. The zeta potential values of BaTiO₃/CoFe₂O₄ composite suspensions increased with increasing CoFe₂O₄ content. The suspension with low concentration was easy to reach maximum conductivity.Electrophoretic deposition was utilized for preparation of CoFe₂O₄ films and BaTiO₃/CoFe₂O₄ composite films on different substrates. Substrates spacing, deposition time, deposition voltage and other conditions were investigated on the impact of electrophoretic deposition. It was found that deposited films were obtained only when the applied electric field was larger than a certain critical value. The components and morphology of samples were analyzed by XRD and SEM. The ferroelectric and ferromagnetic properties of samples were confirmed by ferroelectric hysteresis, magnetic hysteresis and leakage current leakage curve. The magnetoelectric coupling coefficient was also studied. The results depicted that electrophoretic deposition of CoFe₂O₄ films and BaTiO₃/CoFe₂O₄ composite films was feasible, and the choice of deposition conditions was very important to the formation of good films. CoFe₂O₄ film had good ferromagnetic properties. BaTiO₃/CoFe₂O₄ composite film simultaneously exhibited ferroelectric properties and ferromagnetic properties. The ferromagnetic properties of composite films were increased with increasing CoFe₂O₄ content. When CoFe₂O₄ content exceeded 60%, the percolation effect happened and leakage current increased rapidly. The magnetoelectric coupling coefficient of BTO/CFO composite film (molar ratio of 1:1) was 3mV/cm/Oe.