Funct. Mater. 2020; 27 4: 687-694.

doi:https://doi.org/10.15407/fm27.04.687

The effect of heat treatment on the magnetic properties of ZnO:Mn nanocrystals obtained by ultrasonic aerosol pyrolysis

O.V.Kovalenko, V.Yu.Vorovsky, O.V.Khmelenko

O.Honchar Dnipro National University, 72 Gagarin Ave., 49010 Dnipro, Ukraine

Abstract: 

Samples of ZnO:Mn nanocrystals (impurity concentration 2 at.%) were obtained by ultrasonic aerosol pyrolysis and subjected to heat treatment in air at temperatures of 550°C and 850°C, as well as in a gas medium with hydrogen at a temperature of 550°C. The term of the heat treatment was 20 min. The nanocrystal samples were cooled in a flow of nitrogen gas for 15 min. The samples were studied by X-ray phase analysis, EPR, and the magnetic vibration method before and after annealing. The synthesized samples had ferromagnetic properties at room temperature. The specific magnetization of the sample was Ms = 0.028 emu/g. Heat treatment at T = 550°C led to a decrease in the specific magnetization of the samples (Ms = 0.01 emu/g). After heat treatment at T = 850°C, the ferromagnetic properties in the samples disappeared. Ferromagnetic properties of the samples were restored after heat treatment in a gas medium with hydrogen (Ms = 0.023 emu/g). The regularities of the influence of heat treatment regimes on the magnetic properties of ZnO:Mn nanocrystals are explained by a change in both the number and the ratio of intrinsic defects (oxygen vacancies Vo) and impurity Mn2+ ions located in the surface layer of nanocrystals.

Keywords: 
nanocrystals, zinc oxide, heat treatment in air, heat treatment in a hydrogen atmosphere, ferromagnetic properties, X-ray phase analysis, EPR spectra, intrinsic defects, impurity defects.
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