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The magnetic properties of ZnO:Mn(2at%) nanocrystals synthesized by ultrasonic aerosol pyrolysis were studied. It has been established that short-term thermal treatment in hydrogen does not affect the magnetization of the synthesized sample, which had ferromagnetic and paramagnetic components. The sample, which underwent heat treatment in air at T = 850°C and acquired paramagnetic properties, after heat treatment in hydrogen again became ferromagnetic without a paramagnetic phase. It has been established by the EPR method that the structure of defects in the synthesized ZnO:Mn(2%) NCs is inhomogeneous. It changes after heat treatment in hydrogen. It is shown that the controlled thermal treatment of the samples, first in air and then in hydrogen, makes it possible to predictably change their magnetic properties. The results obtained are explained using the model of coupled magnetic polarons. During thermal treatment in hydrogen, the ratio of the number of oxygen vacancies Vo and interstitial Mn2+ ions changes in the samples.

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Samples of ZnO:Mn nanocrystals with Mn concentrations of 2 and 4 at.% were synthesized by ultrasonic aerosol pyrolysis. The synthesis was carried out at 550°C using aqueous solutions of zinc and manganese nitrates. The samples obtained were subjected to heat treatment at 550°C and 850°C in air for 1 hour. The study of the samples by XRD and EPR methods shows that during the synthesis the process of doping ZnO nanocrystals with manganese occurs only partially, on the surface, in the near-surface layer. Residues of the Mn impurity are located on the surface of nanocrystals and appear during annealing at 550°С in the form of manganese oxides (Mn2O3). During heat treatment at 850°C, decomposition of Mn2O3 and bulk doping of ZnO:Mn nanocrystals occur.

Samples of ZnO and ZnO:Mn nanocrystals with Mn 2 and 4 at.% impurity concentrations obtained by ultrasonic spray pyrolysis were studied by X-ray diffraction. It was determined that the reflexes of the X-ray diffractions of the samples had a shift relative to the standard position towards large diffraction angles. This indicated the nonequilibrium state of the crystal lattice, which caused the appearance of strain stresses. Debye–Scherrer and Williamson–Hall methods were used to calculate the parameters of the crystal lattice, the size of nanocrystals, and strain stresses with different concentrations of Mn. When the concentration of Mn increased to 4 at.%, there was an increase in strain stresses in nanocrystals by 10 times in comparison with undoped ZnO. The unit cell volume of ZnO:Mn nanocrystals was significantly smaller in comparison with single-crystal ZnO, which indicated that they had their intrinsic defects.