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We have studied the magnetic properties of ZnO nanocrystals doped with MnO and CoO in the wide range of magnetic dopant (from 5 to 95 wt. %), synthetized by wet chemical method. The samples were characterized by means of XRD and micro-Raman spectroscopy. The results of systematic measurements of magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. We observed different types of magnetic behavior. ZnO nanocrystals doped with CoO demonstrate Curie-Weiss behavior at higher temperatures. For samples doped with MnO, we observed the superparamagnetism above the blocking temperature.

Nanocrystalline zinc oxide doped with different concentrations of Fe2O3(from 5 to 50 wt.%) has been prepared by means of coprecipitation and calcination processes. Depending on the chemical composition, phases of hexagonal ZnO, and/or cubic ZnFe2O4 were identified. The mean crystallite size of the latter phase, determined using the Scherrer's formula, varied from 8 to 12 nm. The EPR spectra for six different concentrations of Fe2O3 were recorded. A symmetrical, very intense and broad EPR resonance line has been obtained for the all the samples where the intensity strongly depended on the ratio of ZnO/Fe2O3 in the samples. The resonance field slightly shifted in the direction of lower magnetic field and the integrated intensities increased with increasing concentration of magnetic nanoparticles of ZnFe2O4, where the linewidth showed an extraordinary behaviour. The dipole-dipole interaction depended essentially on the concentration of magnetic nanoparticles.