Zn-doped nickel ferrite nanoparticles (Zn0.6Ni0.4Fe2O4) have been prepared via a surfactant, polyethylene glycol assisted hydrothermal route. X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and vibrating scanning magnetometry (VSM) were used for the structural, morphological, and magnetic characterizations of the product, respectively. TEM analysis revealed that the nanoparticles have a narrow size distribution, with average particle size of 15 +/- 1 nm, which agrees well with the XRD based estimate of 14 +/- 2 nm. The absence of saturation and remanent magnetization, and coercivity in the high temperature region of the M-H curve and non-zero magnetic moments indicate superparamagnetism of the nanoparticles with a canted spin structure. The appearance of a peak on the temperature-dependent zero-field cooling magnetization curve at similar to 190 K indicates the blocking temperature of the sample. (C) 2008 Elsevier B.V. All rights reserved.