gamma-Fe2O3 nanoparticles have been synthesized by chemically-induced transition in FeCl2 solution (sample(0)). Surface modification of the particles in a post-synthesis step using Fe(NO3)(3) solution (sample (1)) and during synthesis by adding ZnCl2 (sample (2)) has been attempted, and the morphologies, crystal structures, chemical compositions and magnetizations of the resultant samples have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray energy-dispersive spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The size of the particles was of the order of 10 nm. Particles in samples (1) and (2) had a gamma-Fe2O3 core while sample (1) had a Fe(NO3)(3)center dot 9H(2)O shell, and sample (2) had an external shell of ZnFe2O4, and FeCl3 center dot 6H(2)O as an outermost layer. Adsorption on the surface of the nanoparticles lowered their diffraction intensity, such that diameters of the grains of the spinel structure estimated by XRD were larger than the average particle diameter obtained by TEM for samples (0) and (2). Sample magnetization depended mainly on the content of the gamma-Fe2O3 phase. The molar and mass ratios of the phases have been estimated from the characterization results for each sample. (c) 2013 Elsevier B.V. All rights reserved.