Synthesis of nickel nanoparticles. Influence of aggregation induced by modification of poly(vinylpyrrolidone) chain length on their magnetic properties

The reaction of Ni(COD)(2) with Hz (3 bar) in CH2-Cl-2 in the presence of poly(vinylpyrrolidone) (PVP) K 30 leads to air-stable agglomerates of approximate to 30 nm, composed of individual 3-4 nm fee Ni particles and displaying a ferromagnetic behavior whereas the same reaction in the presence of PVP K 90 leads to 4 nm, well-dispersed fee Ni particles displaying a superparamagnetic behavior. In both cases the magnetic moment per atom is similar to the value found for bulk nickel, hence demonstrating the absence of oxidation of the surface of the particles.