Magnetic properties of magnetite nanoparticles prepared by mechanochemical reaction

Nanosized magnetite (Fe3O4) powders were synthesized via a mechanochemical reaction. Ball milling of 1.2FeCl(2) +2FeCl(3) + 8.4NaOH led to a mixture of Fe3O4 and NaCl. To avoid agglomeration, the excess NaCl was added to the precursor before ball milling. To prepare different size of particles, the as-milled powders were annealed at temperatures ranging from 100 to 800 degrees C for I h in 10% H-2/Ar mixed gas. Single phase Fe3O4 powders were obtained after removing the NaCl from the as-milled or heated powders. The average crystallite size of the powders varied from 12.5 to 46 nm by changing the annealed temperatures and the corresponding saturation magnetization (sigma(S)) value ranged from 52 to 66.4 emu/g. The coercivity (H-c) first increases as the crystallite size decreases, reaches a maximum value of I 10 Oe at 22.2 nm and then decreases for any further decrease in particle size. (c) 2005 Elsevier B.V. All rights reserved.