中文摘要：

在重整化Dzyaloshinskii-Moriya相互作用的基础上,利用格林函数方法对BiFeO_3（BFO）纳米颗粒的多铁性能进行了微观研究。研究发现磁化强度和电极化强度均随温度升高而逐渐减小;当温度分别升高到磁性转变温度TN和铁电转变温度TC时,磁化强度和电极化强度分别变为零;TN和TC分别随磁性自旋间的耦合常数（Jb,Js）和铁电性赝自旋间的耦合常数（Bb,Bs）增加而向高温区移动;当磁电耦合常数（g）增大时,磁化强度和电极化强度均增大。研究还发现磁化曲线在转变温度TP为40K附近处有一峰值,这是纳米量级BFO的零场冷却曲线在低温区所特有的一种奇特现象。

英文摘要：

Based on the renormalization of Dzyaloshinskii-Moriya interaction （DMI）, the multiferroic prop- erties of BiFeO3 （BFO） nanoparticles were investigated by using Green＇s function technique. It was found that the magnetization （polarization） decreased and vanished continuously at the magnetic transition tem- perature TN（ferroelectric transition temperature To） as the temperature increased. It was found that the phase-transition temperature TN （TC） shifted to higher values as the exchange coupling constants J b and J s （Bu and Bs） increased. It was also found that the magnetization and the polarization were both enhanced as the magnetoelectric coupling constant （g） increased. For this reason, the magnetic and the ferroelectric phase coexisted in this region. In addition, it was observed that there existed a cusp around 40K, which were unique to the nanosize effect of BFO.