The structure of nanocrystalline Fe-Co-O alloys produced by high-energy ball milling and subsequent low-temperature annealing were investigated by X-ray diffraction analysis, scanning and transmission electron microscopy. The magnetic properties were measured in vibrating sample magnetometers at room temperature. The mixtures of FeO and Co powders were used as starting materials. The nanocrystalline composite alloys, obtained as a result of the milling, contained FeO and -Fe with the crystallite size of 12-18 nm as well as an amorphous phase. However, alloys subjected to subsequent annealing contained Fe3O4 and -Fe phases with crystallite size of 10-30 nm, in which Co is dissolved. Unlike the starting materials the produced powders exhibit properties typical of magnetically hard alloys. The intrinsic coercive force of the annealed powders increases with increasing (Fe,Co)3O4 phase content and reaches approximately 800 Oe.

The structure and properties of SrFe12O19 powders, which were produced by mechanical activation followed by annealing and had a nanocrystalline structure, were studied. The powders prepared exhibit a high coercive force μ0Hci=0.40-0.45 Т. The substantially higher coercive force (up to 0.75-0.82 T) was typical to SrFe12O19 powders produced by oxide-glass crystallization. Nanostructured materials comprising Fe3O4 and Fe phases with crystallite sizes of 10-30 nm are shown can be prepared from Fe2O3+Fe, Fe2O3+Fe+Co and FeO+Co powder mixtures by mechanochemical technique followed by annealing. These nanomaterials have the hard magnetic properties and their coercive force reaches μ0Hci 0. 08 T.