a b s t r a c tNanocrystalline nickel ferrite (NiFe 2 O 4 ) has been synthesized from a stoichiometric mixture of oxides NiO and ␣-Fe 2 O 3 in a high energy planetary mill. An annealing at 350 • C, after milling, was used to improve the solid state reaction. The obtained powders were investigated by X-ray diffraction, magnetic measurements, scanning electron microscopy, X-ray microanalysis and differential scanning calorimetry. The particles size distribution was analyzed using a laser particle size analyser. The nickel ferrite begins to form after 4 h of milling and continuously form up to 16 h of milling. The obtained nickel ferrite has many inhomogeneities and a distorted spinel structure. The mean crystallites size at the final time of milling is 9 ± 2 nm and the lattice parameter increases with increase the milling time. DSC measurements revealed a large exothermic peak associated with cations reordering in the crystalline structure. The magnetization of the obtained powder depends on the milling time and annealing. After the complete reaction between the starting oxides the milling reduces the magnetization of the samples. The magnetization increases after annealing, due to the reorganization of the cations into the spinel structure.

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SmCo 5 /Fe nanostructured alloys with 20 wt% Fe, obtained by high energy ball milling of SmCo 5 and Fe powders, were investigated by 57 Fe Mössbauer spectrometry, X-ray diffraction and tomographic atom probe. The Mössbauer analysis reveals that during the first stages of milling, an interdiffusion of Co and Fe occurs, leading both to the formation of α-Fe(Co) regions in α-Fe and to the introduction of Fe in SmCo 5 regions. Annealing at temperatures up to 650°C for 0.5h promotes interdiffusion further leading to the formation of an unique α-Fe(Co) phase and a Fe-richer Sm(Co,Fe) 5 phase. The Co/Fe interdiffusion is confirmed by tomographic atom probe analysis. The data are discussed and compared to the results of previous magnetic measurements.

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