钙钛矿型铋铁氧体纳米微粒的弱铁磁性

Weak Ferromagnetism in Perovskite-type Bismuth Ferrite Nanoparticles

采用溶胶-凝胶法制备了不同粒径的纯净单相钙钛矿型BiFeO3纳米微粒. X射线衍射分析表明,BiFeO3纳米微粒仍为菱方结构,但晶格畸变随颗粒尺寸的减小而增大. 磁测量显示,BiFeO3纳米微粒具有明显弱铁磁性,且弱铁磁性随温度升高显著降低. 弱铁磁性的自发磁化强度随温度升高呈线性下降,磁化强度和磁化率均随颗粒尺寸的减小而增大. 穆斯堡尔谱分析揭示,颗粒愈小,自旋倾角愈大,其分布也愈宽. 从纳米微粒小尺寸效应和表面效应入手,讨论了BiFeO3纳米微粒结构与磁结构和弱铁磁性的关系.

A series of BiFeO3 nanoparticles were prepared by the sol-gel process. X-ray diffraction analysis shows that their rhombohedral crystal symmetry remains. However, as the particle size decreases, the edge length of the unit cell increases markedly and the angle between the edges deviates increasingly from 60. Magnetic measurements show obvious weak ferromagnetism. The magnetization and magnetic susceptibility increase with decreasing particle size. The spontaneous magnetization of weak ferromagnetism decreases linearly with T instead of T2. M鰏sbauer studies reveal that the spin canting angles in the smaller particles are bigger and have a wider distribution. The magnetic structure in these particles is a complicated uncompensated antiferromagnetic spin arrangement. The relations between structure, magnetostructure, and weak ferromagnetism are discussed in terms of small size effect and surface effect.