Formation Of Ag Nanoparticle/BiFeO₃ Composite Thin Film With Dielectric And Magnetic Properties

With the development of current technology and diversified devices, the need for multifunctional materials is very urgent. Multiferroic material is a typical representative of multifunctional materials due to the existence of two or more than two ferroic natures simultaneously. As a typical single-phasic multiferroic material, BiFeO3 possesses both ferroelectric and antiferromagnetic orderings in the same phase at room temperature, which has great research value. Thin film is important for the miniaturization of modern electronic devices due to its micro size. BiFeO3 thin film depicts the relative weak or unpowerful properties as it is promoted from the laboratory to that of practical applications in modern devices. As one of properties of bismuth ferrite, how to improve the dielectric constant is worth considering. It is found that the dielectric constant will increase by several times when the conductive nanoparticles are introduced and dispersed uniformly in the matrix compared with that without conductive nanoparticles. This method shows a significant effect on the improvement of dielectric constant. Therefore, if the metal nanoparticles can be introduced successfully into the BiFeO3 thin film matrix, its dielectric properties may be increased. And at the same time, if the typical ferromagnetism can be guaranteed, it will be benefit for its applications in electronic devices immensely, which has great research significance.In this paper, sol gel method was used to prepare bismuth ferrite thin films. Ag+ was introduced into the Fe-Bi solution and then Ag-Fe-Bi sol precursor was synthesized. Ag-Fe-Bi sol was coated on ITO/glass by dip coating method and Ag nanoparticle/BiFeO3 composite thin film was prepared after heat treatment. Dielectric properties and magnetic properties of bismuth ferrites at different annealing temperatures and different Ag additions were investigated.The phase structure of the Ag/BiFeO3 composite thin films were identified by XRD. Results showed that the pure perovskite phase formed in the films. Some Ag+ ions doped into the bismuth ferrite lattice to replace bismuth to form Ag doped matrix. Most of the other Ag+ ions formed Ag nanoparticles dispersed in the thin films with the size of 4-8 nm by the characterization of UV-vis and TEM. Doping Ag was benefit for not only the formation of crystalline phase of bismuth ferrite, but also the preferential growth in (012) lattice plane. Ag nanopartilces increased the dielectric constant of the BiFeO3 thin film to a value which is about 2-4 times as large as that of pure BiFeO3 thin film. Bismuth ferrite thin films in our paper all showed saturated magnetic hysteresis loops. With the increase of Ag additions, the saturation magnetization decreased due to diamagnetism of Ag naonoparticles, but the coercivity and residual magnetization didn’t show a clear change trend. It is indicated that the introduction of Ag did not influenced the ferromagnetism of bismuth ferrite. Both of the typical ferromagnetism and high permittivity appears in the composite thin film simultaneously, it is attracted to be used as a multifunctional material in electronic devices for high performance and miniaturization.