Nanostructured ceramic oxides containing ferrite nanoparticles and produced by mechanical milling

This investigation deals with the production process and the characterization of ceramic materials consisting of magnetic particles in an insulating matrix. Composites made of magnetite particles (Fe₃O ₄ or MgFe₂O₄) in a wüstite or magnesiowüstite matrix (Fe_xO or Mg_1-xFe _xO), respectively, have been produced by means of mechanical milling and spark plasma sintering. As-milled powders have a nanocrystalline structure in both systems. As a function of milling time, low energy milling gives rise to an increasingly higher volume fraction of wüstite in the Fe _xO-Fe₃O₄ system while it promotes increasing amounts of magnesiowüstite (Mg_xFe_1-xO). Sintering is performed from 673 to 1273 K in vacuum. Sintering at low temperatures allows retention of nanosized grains containing a fine dispersion of magnetic particles in a wüstite and magnesiowüstite matrix. Measurement of magnetic properties reflects the constitution of the sintered samples and the effect of grain size. It also allows determination of the transformation sequence both during mechanical milling and sintering.