Preparation Of BiFeO₃Film By Sol-gel Process And Study On Magnetic Properties

In this dissertation, BiFeO3films were prepared by Sol-Gel method with nitrate as raw materials and citric acid as complexing agent. the phase influence about different precursor sol, heat treatment temperature and time for preparing BiFeO3films were all studied and optimized by contrast experiments. In addition, the components’ uniformity in films was also investigated. On the basis of this, the influence on BiFeO3films’ structure and magnetic properties by A site and B site substituted were researched separately. The main contents of this dissertation are as follows:1. The influences of different Sol-Gel techniques on the crystal structure of BiFeO3films were studied. BiFeO3films were synthesized by Sol-Gel method with nitrate as reactants and citric acid as complexing agent. The contrast experimental results show that the pre-sol could be synthesized if the molar ratio of citric acid to metal ions is2:1and pH value is8. Each wetting layer was heating to210℃first and holding for10minutes, then heating to390℃and holding for another10minutes, repeat this process several times until we get the required thickness. At last the films’heat treatment temperature is500℃, holding for5minutes. By this technique we will get the pure phase BiFeO3films with weak ferrimagnetism at room temperature.2. A site Nd substituted NdxBi1-xFeO3films were prepared referring to the pure BiFeO3films’preparation process. From the results obtained by XRD and AFM, we found that when the substitution amount came to10%we would get polycrystalline thin films with well crystallization degree and smaller grain diameter. This kind of films exhibits better magnetic properties, with saturation magnetization of38.1emu/cm3. The magnetism is dominated by the destruction of spiral spin structure in films which is caused by substitution. In addition, the doping of rare earth ions may enhance the thin film magnetic.3. B site Cr substituted BiFe1-xCrxO3films were prepared referring to the pure BiFeO3films’preparation process. Research shows that, just3%of the substitution amount will cause the appearing of Bi25FeO40phase. With the increasing of Cr substitution amount, the intensity of Bi25FeO4o diffraction peak was obviously enhanced. Within2%of Cr substitution amount will make the crystallization compact and decrease the grain diameter. When the substitution amount is1%, the BiFe1-xCrxO3films possess the highest saturation magnetization of39.3emu/cm3. The magnetism is dominated by the destruction of spiral spin structure and the reduction of magnetic moment in unit volume caused by the substitution.