中文摘要：

为了研究BiFeO3纳米颗粒体系中的交换偏置效应，采用水热合成法制备BiFeO，纳米颗粒，分别利用X线衍射仪、扫描电子显微镜、磁学测量系统和X线光电子能谱对不同尺寸的样品进行结构表征、形貌表征、磁学性能分析和元素价态分析，并基于核壳结构模型对BiFeO，纳米颗粒体系中存在的交换偏置效应进行解释．实验结果表明：适当的温度有利于制备出纯相BiFeO3纳米颗粒，颗粒尺寸约为110nm，且具有良好的分散性和均一性．随着颗粒尺寸的减小，样品的磁性增强，磁化强度在50kOe磁场下接近0．84emu／g．在BiFe03纳米颗粒体系中观测到了明显的负交换偏置效应，其交换偏置场约为600e．此外，由元素价态分析可知，样品中的Fe元素均为二价态和三价态共存．

英文摘要：

In order to study the exchange bias effect in BiFeO3 nanoparticles （Nps） system, the BiFeO3 Nps were synthesized by hydrotherrnal method. The structural characterization, morphology characterization, magnetic analysis and element valence state analysis were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, magnetic pro- perty measurement system （MPMS） and X-ray photoelectron spectroscopy （XPS）, respectively, and the exchange bias effect existing in BiFeO3 Nps system were explained based on the core-shell structure modes. The experimental results show that appropriate temperature is beneficial to synthesizing BiFeO3 Nps. The BiFeO3 Nps exhibit well dispersity and uniformity with the average diameter of 110 nm. As the particles size decreased, magnetization of the BiFeO3 Nps is enhanced to 0.84 emu/g when magnetic field intensity is 50 kOe. An obvious negative exchange bias is observed in BiFeO3 Nps system with approximate 60 Oe exchange bias field. According to the valence state analysis, the Fe element in the samples is coexisting with divalent state and trivalent state.