Ni-ferrite (NiFe2O4) nanoparticles have been synthesized via a solid state reaction process. Ni and Fe bi-metallic nanoparticles in the form of Ni33Fe67 alloy nanopowder are first synthesized by simultaneous evaporation of the required amounts of pure Ni and Fe metals followed by rapid condensation of the evaporated metal flux into solid state by means of an inert gas, helium, using the process of inert gas condensation (IGC). In order to form the NiFe2O4 structure, as-synthesized samples (Ni33Fe67) are annealed for 12 h in ambient conditions at different annealing temperatures. Structural analyses show that NiFe2O4 starts to form at around 450 degrees C and gets progressively well defined with increasing annealing temperatures yielding particle with size ranging between 15 and 50 nm. Besides successfully forming NiFe2O4, NiO/Fe3O4 core/shell nanoparticles have also been synthesized by adjusting the annealing conditions. Three different structures, Ni33Fe67, NiO/Fe3O4, and NiFe2O4, obtained in this study are compared with respect to their structural and magnetic properties. (C) 2007 Elsevier B. V. All rights reserved.