Phase Composition and Magnetic Properties of Nanostructured Fe-Co-Ni Powders

Nanostructured Fe-Co-Ni powders, with crystallite sizes of 10-35nm for different compositions, are obtained in the whole range of compositions (step change in the components content is of 10wt.% and, in the case of near the phase boundaries, 3-5wt.%) by the reduction of freshly co-precipitated mixed hydroxides with hydrazine hydrate in a strongly alkaline medium. The isothermal section of the phase diagram corresponding to the synthesis temperature (363-368K) is constructed using reflection modeling based on XRD data of the samples series with different compositions. Its features are founded, characterized, and discussed: the phase diagram of the system in the nanostructured and nonequilibrium state is compared with the phase diagram of the system in the bulk state. In the region of the FCC-solid solution, the lattice parameter-composition dependence was described by the flat surface equation (three-dimensional analog of Vegard's law). Some magnetic characteristics are measured for the Fe-Co-Ni systems containing 10wt.% Ni and variable Co/Fe ratio. Some features of the superparamagnetic component are observed above the blocking temperature; they are related to the crystallite size and the phase composition of the samples.