Nanocomposite powder and compacts of NiFe2O4/Ni3Fe type were synthesized using mechanical milling and spark plasma sintering (SPS) techniques. The samples have been investigated by X-ray diffraction (XRD), laser particles size analysis, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The nanocomposite powder was obtained by mechanical milling in a high planetary ball mill of nanocrystalline NiFe2O4 and nanocrystalline Ni3Fe powders. The nanocomposite powder consists from Ni3Fe particles covered at the surface with a layer of NiFe2O4 fine particles and NiFe2O4 particles. The nanocomposite particles have the median diameter d(50) of 1.6 mu m. The sintering in 400-600 degrees C temperature range preserve the nanocomposite phases but lead to a high porosity. The nanocomposite compacts consist in Ni3Fe clusters surrounded by NiFe2O4. A sintering temperature of 800 degrees C leads to a good density for the nanocomposite compacts and to the new phase formation. The new phase is a wustite type (Fe1-xNixO) and is formed at the metal/ceramic interface. A change in the Ni/Fe ratio, in the spinel structure, was evidenced during sintering. Sintering at a temperature of 800 degrees C, leads to the formation of a mixed iron-nickel ferrite with a very small amount of nickel, Ni1-xFexFe2O4. (C) 2013 Elsevier B. V. All rights reserved.