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Abstract: Zinc ferrites, ZnFe2O4 and zinc ferrite nanoparticles substituted with indium and yttrium, Zn1−x In x Fe2O4 and ZnY x Fe2−x O4 (0≤x≤0.3), were synthesized by co-precipitation method. We have investigated the effect of composition on the cation distribution in the spinel structure, and on the magnetic properties with a view to obtain magnetic ceramics with improved properties compared to their bulk counter parts. The results of X–ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the nanoscale dimensions and spinel structure of the samples. The estimated crystallite size lies within the range 4–10nm. Additional experiments had been conducted using a scanning mobility particle sizer spectrometer (SMPS) in order to measure the number size distribution of the nanoparticles. Mössbauer spectroscopy was used to investigate the cation distribution between the tetrahedral and octahedral sites and the formation of the partially inverse spinel. The study of the magnetic properties showed that the hysteresis loops do not saturate even in the presence of high magnetic fields, confirming the superparamagnetic single domain nature of the samples. The particle size and composition variations (e.g. addition of yttrium and indium) cause significant structural rearrangements which affect the magnetic behavior of these materials. [Copyright &y& Elsevier]