纳米稀土金属Gd的磁性及分形特征

MAGNETIC SUSCEPTIBILITY AND D GROWTH FRACTAL CHARACTERISTICS OF NANOMETER GADOLINIUM POWDER

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寸ｄｑ进行了估算，并就三种特征粒径ｄｃ。

Nanometer gadolinium powders (nm Gd) sized 4～15nm 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 d c . 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 dimension D f. 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 size d f of 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 size d q of quantum size effect of metal Gd has been carried out in order to clarify the influence of three special sizes d f, d q and d c on the magnetic susceptibility of nm Gd powders.