An aerosol-mediated magnetic colloid: Study of nickel nanoparticles

A method is presented for the synthesis of high-quality nickel nanoparticles. Laser-driven decomposition of nickel carbonyl vapors is used to produce particles in the form of an aerosol, followed by exposure to a solvent containing an appropriate surfactant to yield a stable dispersion of particles. This method is scalable and yields a substantially monodisperse distribution of particles at a relatively high rate of production. The particles produced by this method are subjected to a detailed characterization using transmission electron microscopy, atomic force microscopy, energy dispersive spectroscopy, and dc magnetization. They have an average diameter of 5 nm, and the observed magnetization curves show no hysteresis above 200 K. The normalized magnetization curves follow a scaling law proportional to the quotient of the applied field over temperature. This data indicates the presence of randomly oriented superparamagnetic particles. The measured magnetization is significantly smaller than that of the bulk, probably due to an effective surface anisotropy and spin canting. The coercivity is the same in either direction of the applied field which indicates that there is negligible exchange coupling between the nickel particles and any possible antiferromagnetic oxide layer on their surfaces. © 2005 American Institute of Physics. DOI: 10.1063/1.2033145