Maghemite and Zn2+ substituted maghemite (γ-Fe2−y Zn3y/2O3, y=0.0, 0.11, 0.24, 0.36, 0.50 and 0.66) nanoparticles were prepared by coprecipitation method. The effect of Zn2+ substitution on the structural, morphological and magnetic properties of the nanoparitcles were studied by different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), magnetometry, magnetic thermogravimetry and Mössbauer spectroscopy. The results of XRD showed that all samples have spinel structure with an increase in lattice parameter by increasing the content of Zn2+. FTIR spectra were proved the synthesis of maghemite and Zn2+ substituted maghemite with appearance of the related absorption bands and band shift upon Zn2+ substitution. Morphological studies by FESEM demonstrated that the nanoparticles were uniform and spherical with average particle size in range of 20–24 nm. Room temperature magnetic measurements showed that as Zn2+ content increases, saturation magnetization initially increase up to 75.34 emu/g for y=0.11 and then decrease to 3.65 emu/g for y=0.66, due to substitution of magnetic Fe3+ by non-magnetic Zn2+. Decrease in Curie temperature of the samples, from 510 for maghemite to 250 °C for y=0.36, by increasing the Zn2+ substitution was a result of reduction of superexchange interactions between different sites. Then, the Curie temperature increased up to 680 °C for y=0.66 which was due to migration of some Zn2+ ions from A to B sites in the structure of spinel. Room temperature Mössbauer spectra exhibited that the sample with y=0.0 was superparamagnetic, while by increasing the content of Zn2+, relaxation effect increased by weakening of A–B exchange interaction.
