Hard magnetic nanocrystalline alloys of Fe-Fe2O3 system

The structure and magnetic properties of Fe2O3 and Fe powders as well as their mixtures, subjected to treatment in a high-energy ball mill, were studied. It was shown that the phase composition of all the starting materials (except that of the Fe powder) was changed in the milling process. The nanocrystalline composite alloys, containing FeO and alpha-Fe with an average crystallite size of 10-20nm as well as an amorphous phase, were obtained as a result of the milling. Phase content in the milled powders depended on the composition of the starting materials. Unlike the starting materials, the milled powders (except of the milled Fe powder and Fe2O3 + 90% Fe mixture) had the properties, which are characteristic for hard magnetic materials. Further improvement of the properties was achieved by low-temperature annealing of the milled powders. The annealed powders of the mixtures contained only nanocrystallites of alpha-Fe and Fe3O4. The amount of these constituents and the magnetic properties of the annealed powders depended on the composition of the starting materials. The sufficiently high properties of the produced powders may be explained by the formation of alpha-Fe and Fe3O4 single-domain particles. (c) 2004 Elsevier B.V. All rights reserved.