Sun X C, Dong X, Toledo J A
Prog. Molecular Simulation, Instituto Mexicano del Petróleo, Lázaro Cárdenas 152, 07730, D.F. México City, México.
J Nanosci Nanotechnol. 2001 Sep;1(3):291-4. doi: 10.1166/jnn.2001.036.
Carbon-encapsulated Ni nanoparticles [Ni(C)] were synthesized using a modified arc-discharge reactor under methane atmosphere. The average particle size was revealed to be typically 10.5 nm with a spherical shape. The intimate and contiguous carbon fringe around these Ni nanoparticles is good evidence for complete encapsulation by carbon shell layers. Superparamagnetic property studies indicate that the blocking temperature (TB) is around 115 K at 1000 Oe applied field. Below TB, the temperature dependence of the coercivity is given by Hc = Hci[1 -(T/TB)1/2], with Hci approximately 500 Oe. Above TB, the magnetization M(H, T) can be described by the classical Langevin function L using the relationship M/Ms(T = 0) = coth(microH/kT)-kT/microH. The particle size can be inferred from the Langevin fit (particle moment mu) and the blocking temperature theory (TB), with values slightly larger than the high-resolution transmission electron microscopy observations. It is suggested that these assemblies of carbon-encapsulated Ni nanoparticles have typical single-domain, field-dependent superparamagnetic relaxation properties.
在甲烷气氛下，使用改进的电弧放电反应器合成了碳包覆镍纳米颗粒[Ni(C)]。结果表明，其平均粒径通常为10.5 nm，呈球形。这些镍纳米颗粒周围紧密相连的碳边缘是其被碳壳层完全包覆的有力证据。超顺磁性研究表明，在1000 Oe的外加磁场下，阻塞温度（TB）约为115 K。在TB以下，矫顽力的温度依赖性由Hc = Hci[1 - (T/TB)1/2]给出，其中Hci约为500 Oe。在TB以上，磁化强度M(H, T)可以用经典的朗之万函数L来描述，其关系为M/Ms(T = 0) = coth(μH/kT) - kT/μH。粒径可以从朗之万拟合（颗粒磁矩μ）和阻塞温度理论（TB）推断得出，其值略大于高分辨率透射电子显微镜的观察结果。研究表明，这些碳包覆镍纳米颗粒的组装体具有典型的单畴、场依赖超顺磁弛豫特性。
