Preparation of colloidal metals of iron group with uncapped surface in polar aprotic medium

A novel method of preparation of the nanoscale Fe, Co and Ni metals in colloidal form and as nanopovvders is based on reduction of metal halides with sodium naphthalide in solutions of N-methyl pyrrolidone (NMPO). Room temperature reactions followed by solution annealing at 170—200 °C result in formation of uncapped nanoparticles of iron and cobalt metals and nickel carbide Ni3C. Colloidal metallic nickel was obtained in reaction of colloidal iron with NiCl2 in NMPO solutions. The surface of the obtained metallic nanoparticles is capable of chemical derivatization; their post-synthesis reaction with oleic acid resulted in hydrocarbon-soluble products

Line Narrowing in Mössbauer Spectra of Superparamagnetic Fe3O4 Nanoparticles.

Nanoparticles of magnetic crystals below a critical size are single domain and exhibit superparamagnetism. If there are N atoms or molecules with magnetic moment μ in each particle, the magnetic moment of the particle is Nν. At high temperatures the thermal fluctuations of the magnetic moments give an ensemble average moment of zero and the Mössbauer spectrum is a single line. As the temperature, T, is lowered the fluctuations slow down and the sample acquires a magnetization and the Mossbauer line broadens and eventually shows magnetic hyperfine splitting. We have observed 57Fe line broadening in nanoparticles of ferrimagnetic Fe3O4 with diameters of 5.3 and 10.6 nm. The results have been analyzed using the motional narrowing equation familiar in nuclear magnetic resonance to determine the superparamagnetic fluctuation time and magnetic anisotropy