Institut de Physique et Chimie des Matériaux (IPCMS), UMR 7504 Université de Strasbourg-CNRS, 23, rue du Loess, BP 43, 67034, Strasbourg Cedex 2, France.
Nanoscale. 2011 Jan;3(1):225-32. doi: 10.1039/c0nr00521e. Epub 2010 Nov 8.
The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3-xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x=1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.
氧化铁纳米晶的精细尺寸控制在纳米范围内（直径范围为 2.5 至 14nm），使我们能够准确地研究其结构和磁性能的尺寸依赖性。通过热分解油酸铁前体在高沸点溶剂中获得这些纳米晶的生长条件进行了研究。所用溶剂的类型和配体/前体的比例都经过了系统的改变，结果发现它们是控制生长过程的关键参数。从 X 射线衍射测量中推断出的所有纳米晶的晶格参数都与 Fe3-xO4 类型的结构一致，即介于磁铁矿和磁赤铁矿之间，对于最小尺寸（x=1/3），结构向磁赤铁矿结构演变。随着纳米颗粒尺寸的变化，磁性能的演变清楚地强调了表面的影响，特别是对饱和磁化强度 Ms 和磁晶各向异性 K 的影响。在研究纳米级磁性能的尺寸效应时，还考虑了偶极相互作用和热依赖性。
