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Superparamagnetic Properties of Carbon-Encapsulated Ni Nanoparticle Assemblies

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Abstract:

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 ≈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 (H/kT) − kT/H. The particle size can be inferred from the Langevin fit (particle moment ) 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.

Keywords: MAGNETIZATION; NICKEL NANOPARTICLES; SQUID; SUPERPARAMAGNETIC PROPERTIES

Document Type: Communications

DOI: http://dx.doi.org/10.1166/jnn.2001.036

Affiliations: 1: Prog. Molecular Simulation, Instituto Mexicano del Petróleo, Lázaro Cárdenas 152, 07730, D.F. México City, México 2: Shenyang Polytechnic University, Shenyang, People's Republic of China

Publication date: September 1, 2001

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  • Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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