(中山大学物理系，广州510275)
摘 要: 采用惰性气体保护蒸发凝聚技术制备出粒径为4~15nm的稀土金属Gd微粉(nm-Gd)。经振动样品磁强计测试，表明nm-Gd微粉在某一特征粒径dc时磁化率χ取得最小值。利用小角X射线散射方法分析了nm-Gd微粉的三维生长分形特征，表明nm-Gd微粒聚集体系呈质量分形，制备气压越小则分维系数Df越小。微粒生长模型是扩散限制聚集(DLA)与扩散限制团聚聚集(DLCA)模型共存，相应这两个模型阶段的分维系数Df存在一特征粒径df。根据纳米微粒理论对nm-Gd微粉体系的量子尺寸效应的特征尺dq进行了估算，并就三种特征粒径dc、df和dq进行了分析和比较。
关键字: 稀土金属 纳米材料 磁性 生长分形
GROWTH FRACTAL CHARACTERISTICS OF
NANOMETER GADOLINIUM POWDER
（Department ofPhysics, Zhongshan University, Guangzhou 510275）
Abstract:Nanometer gadolinium powders (nm-Gd) sized 4~15 nm have been prepared by means of condensation of evaporating Gd atoms in the atmosphere of inert gas argon. The magnetic susceptibility of nm-Gd powders, measured by vibrating samples magnetometer, demonstrates a minimum when the size of nm-Gd powder approaches a special value dc. The analysis, based on the measurement of small angle X-rays scattering, shows that the as-prepared nm-Gd powders have a characteristic of mass fractal growth, and that a lower pressure of inert gas results in a small fractal dimensionDf. There are two stages corresponding to DLA (Diffusion Limited Aggregation) and DLCA(Diffusion Limited Cluster Aggregation) models in the growing process of nm-Gd powders. There exists a special sizedfof nm-Gd powder about fractal dimension between the two stages mentioned above also. According to the theory of nanometer materials, a calculation evaluating the critical sizedqof quantum-size effect of metal Gd has been carried out in order to clarify the influence of three special sizesdf,dqanddcon the magnetic susceptibility of nm-Gd powders.
Key words: rare-earth metal nanometer materials magnetic property growth fractal
