中文摘要：

采用金属有机物分解法在Si衬底上制备了不同厚度的BiFeO3薄膜,利用X射线衍射、原子力显微镜以及超导量子干涉仪对薄膜材料的微结构、铁电以及磁学性能进行了研究.结果表明,即使在厚度低至30nm的情况下,BiFeO3多晶薄膜也能够呈现出清晰的铁电畴结构及良好的铁电开关效应.随膜厚增加,平均颗粒尺寸和铁电畴尺寸迅速增加,但在膜厚超过120nm以后颗粒和畴尺寸的增加幅度明显降低.相应地,饱和磁化强度MS随着膜厚的增加先快速减小,后变化趋缓,分析认为其与颗粒比表面积的变化有关.

英文摘要：

Room temperature multiferroic BiFeO3 material has recently become the focus of research for its potential applications in multifunctional devices.It is meaningful to systematically investigate the thickness-dependent properties of BiFeO3 films since the polarization of ferroelectrics have been reported to be size-dependent and the special cycloidal spin structure with a period of 62 nm could bring about additional complexity to BiFeO3.BiFeO3 films with various thicknesses are prepared on Si substrates by metal organic decomposition method.The microstructure,ferroelectricity and magnetism of the films are investigated by X-ray diffraction,the piezoresponse force microscope,and superconducting quantum interference device,respectively.It is found that the polycrystalline films exhibit ferroelectric properties even with thickness as low as 30 nm.The grain size increases rapidly first with the film thickness increasing from 30 nm to 120 nm,and then increases slowly.Similarly,the ferroelectric domain size also increases with increasing film thickness,which implies the probable enhancement of the ferroelectric polarization.The single-domain state is predominant for the grains with size about 47-104 nm,while multi-domain state can be found for larger grains.Moreover,the ferroelectric domain can be switched by voltages applied through the probe of piezoresponse force microscope.The magnetism of BiFeO3 also shows thickness dependence.The saturation magnetization MS decreases abruptly with the film thickness increasing up to 120 nm,and then it decreases much slower,which could be attributed to the variation of surface-to-volume ratio.