| The magnetoelectric effect is a combination of ferroelectric and ferromagnetic properties and is the basis of a memory device..BiFeO3 exhibiting both ferroelectric and ferromagnetic properties, therefore it is a material having magnetoelectric effect and is worthy of studying. BiFeO3 has been proved to possess a rhombohedrally distorted perovskite structure at room temperature. The ferroelectricity is caused by the shift of Bi3+ and Fe3+ off the equilibrium position compared with O2-, and the BiFeO3 has a spiral and antiferromagnetic spin structure.Single-phase BiFeO3,Bi1-xBaxFeO3 and (BiFeO3)1-x(BaMnO3)x were prepared using Bi(NO3)3 and Fe(NO3)3 as precursors and Ba(NO3)2 and Mn(CH3COO)2 as additives. The phase transition characteristics, sturucture, surface morphology, micromagnetism and macromagnetism are investigated by TG/DTA,XRD,SEM,Mossbauer spectra and VSM respectively. The main results are:1. BiFeO3 gel is prepared by sol-gel method. Then the single phase magnetoelectrical BiFeO3 is produced by rapid annealing the dry gel. This method is a new, simple and easy way for preparation of single phase BiFeo3 and is very convenient for investigating and improving of the properties of BiFeO3.2. For Bi(1-x)BaxFeO3, when x is smaller than 0.2, it has a rhombohedrally perovskite structure, when x is over 0.3, it has a Orthorhombic sturucture. With Ba doping the structure of BiFeO3 should be distorted, then the bond angle of Fe3+- O-Fe3+ and Fe4+-O-Fe3+ may be changed, this change in the bond angle results in the magnetization of Bi1-xBaxFeO3. the increase of Fe4+ makes the Neel temperature (TN) increase.3. For (BiFeO3)1-x(BaMnO3)x, when x is smaller than 0.2, it has a rhombohedrally perovskite structure. When x is over 0.3, it has a cubic structure. With the increase of sintering time, the Bi and Fe riched region and Ba and Mn riched region are observed in the sample. In the Bi and Fe riched region, the tilt of the spin decreases, the Fe3+-O-Fe3+ exhibits weak ferromagnetic. In the Ba and Mn riched region, the Mn4+-O-Mn4+ also exhibits weak ferromagnetic.4. The soft magnetic sodium ferrite is synthesized by the sol-gel method in the end of this work. The Na0.5Fe2.5O4-γ-Fe2O3 solid solutions are prepared by varing Fe/Na ratio. The Mossbauer spectra results show that the occupation of the iron of the solid solution is different from that of the iron of Na0.5Fe2.5O4.These results provide basic experimental data for improving the properties ofmegnetoelectrical BiFeO3 further.
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