Margeat Olivier, Ciuculescu Diana, Lecante Pierre, Respaud Marc, Amiens Catherine, Chaudret Bruno
Laboratoire de Chimie de Coordination, UPR 8241-CNRS, 205, Route de Narbonne, 31077 Toulouse Cedex 04, France.
Small. 2007 Mar;3(3):451-8. doi: 10.1002/smll.200600329.
Polytetrahedral NiFe nanoparticles with diameters of (2.8+/-0.3) nm have been obtained by hydrogenation of Ni[(COD)(2)] (COD=1,5-cyclooctadiene) and Fe[{N(SiMe(3))(2)}(2)] at 150 degrees C using stearic acid and hexadecylamine as stabilizing ligands. The nanoparticles are superparamagnetic at room temperature and display a blocking temperature of 17.6 K. Their anisotropy (2.7x10(5)J m(-3)) is determined to be more than two orders of magnitude higher than that of the bulk NiFe alloy (10(3)J m(-3)) and is close to that determined for Fe nanoparticles of the same size. Still, they display a magnetization of (1.69+/-0.05) mu(B) per metallic atom, identical to that of the bulk NiFe alloy. Combining the results from X-ray absorption and Mössbauer studies, we evidence a progressive enrichment in iron atoms from the core to the surface of the nanoparticles. These results are discussed in relation to both size and chemical effects. They show the main role played by the enriched Fe surface on the magnetic properties and address the feasibility of soft magnetic materials at the nanoscale.
通过使用硬脂酸和十六烷基胺作为稳定配体，在150℃下对Ni[(COD)(2)]（COD = 1,5 - 环辛二烯）和Fe[{N(SiMe(3))(2)}(2)]进行氢化反应，已获得直径为(2.8±0.3) nm的多面体NiFe纳米颗粒。这些纳米颗粒在室温下具有超顺磁性，其阻塞温度为17.6 K。它们的各向异性（2.7×10(5) J m(-3)）被确定比块状NiFe合金（10(3) J m(-3)）高两个数量级以上，并且接近相同尺寸的Fe纳米颗粒所确定的值。尽管如此，它们每个金属原子的磁化强度为(1.69±0.05) μ(B)，与块状NiFe合金相同。结合X射线吸收和穆斯堡尔研究的结果，我们证明了纳米颗粒从核心到表面铁原子的逐渐富集。这些结果结合尺寸和化学效应进行了讨论。它们展示了富集的Fe表面对磁性的主要作用，并探讨了纳米级软磁材料的可行性。
