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.

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γ-Fe2O3/CoO and reverse CoO/γ-Fe2O3 binary nanoparticles have been prepared by a facile, two-step chemical route through the thermal decomposition of Co(acac)2 and Fe(acac)3 in hot oleyl amine. The synthesis is based on heterogeneous nucleation and growth of the second component on seed nanoparticles of the first one. The binary particles have been characterized by X-ray diffraction, transmission electron microscopy, and cognate techniques. The heteroparticles are very stable in nonpolar organic solvents due the organic coating that is formed in situ. The presence of the antiferromagnetic CoO phase leads to unidirectional anisotropy, which is shown to originate from both magnetically compensated and uncompensated interfaces.