Hexagonal close-packed (hcp) Ni particles were prepared in the nanosize range (13–25 nm) by reduction
of Ni(NO3)2
in polyethylene glycol (PEG) with various molecular weights. The reaction occurred in the
presence of an equimolecular mixture of oleic acid and oleyl amine, which plays the role of
a stabilizer and gives solubility to the nanoparticles in non-polar solvents. The crystal
structure of Ni particles seems to be controlled by the molecular weight of the PEG
molecule and subsequently the reaction temperature. The magnetic properties of the hcp
Ni nanoparticles are also studied.
Cobalt platinum polypod-like nanostructures were synthesized by thermolytic reduction of Pt(acac)2 and Co(CH3COO)2 in oleylamine at 250 degrees C. The as-made CoPt nanopolypods are ferromagnetic, are soluble in nonpolar organic solvents, and reveal a coercive field of 525 and 1200 Oe at room temperature and 5 K, respectively.
Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 4 kOe and maximum energy products greater than 20 KJ/m 3 . Consisting of Co 3 C and Co 2 C phases, the ratio of phase volume, particle size, and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature.2
CoPt nanoparticles with an average size of 3 nm and narrow distribution were synthesized by chemical reduction of Co(CH(3)COO)(2) and Pt(acac)(2) by polyethyleneglycol-200. The as-prepared nanoparticles have a disordered fcc structure which transformed after thermal treatment to an ordered fct structure, which results in coercivity up to 6 kOe at room temperature and 9 kOe at 5 K because of the high magnetocrystalline anisotropy of the tetragonal structure [Formula: see text].
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