| Highly functional soft magnetic materials have received a dramatically growing interest in the last two decades, along with amazing technological advances in electronics and telecommunications. Among soft magnetic materials ferrites are important and promising candidates for use at high frequencies because of their high resistivities. There has been another important development towards better soft magnetic materials, which is nanostructured materials technology. As a result of an ultrafine grain size and consequent large volume fraction of atoms occupying the interfacial regions, nanocrystalline materials show interesting properties that are often different from those of conventional bulk materials.; Nanocrystalline ferrite materials are novel candidates for high-frequency soft magnetic applications because of their higher resistivities than metallic counterparts and of grain size dependent magnetic properties. For the first time, RF plasma torch synthesis of a series of ferrite nanoparticles using metallic precursor powders was carried out in this study. Microstructural and magnetic properties of the as-synthesized powders were examined.; The viability of plasma torch synthesis for production of ferrite nanoparticles has been demonstrated over the results. Magnetite, Ni-, NiZn-, Mn-, and MnZn-ferrite have been successfully synthesized. The only oxygen source for oxide formation is the compressed air flowing through the reactor. The average grain sizes of the plasma-torched powders are in the range of 10–30 nm, with a standard deviation of ∼10 nm. Their stoichiometries are slightly off from the desired ones.; These ferrite nanoparticles had well-defined polygonal growth shapes showing (100) and (111) faceting. Most of them are truncated octahedral or truncated cubic shapes. Some theoretical calculations based on the cuboctahedron model revealed that the surface energy ratio of (100) to (111) planes, γ100/γ111, must have a value between 0.577 and 1.732 under the assumption of the same edge length.; EXAFS analysis was helpful to determine the interstitial site occupation by the metallic cations in the ferrites and to reveal that there is a surface truncation of the lattice. Mössbauer analysis of the ferrite nanoparticles showed that Zn addition to the ferrite structure decreases the hyperfine magnetic fields of both sublattices and increases in the fraction of superparamagnetic particles. |
