Structural and magnetic properties of ZnO:Mn nanocrystals obtained by ultrasonic spray pyrolysis

Abstract

ZnO:Mn nanopowders with Mn concentrations of 2, 4, and 8 at.%, obtained by ultrasonic spray pyrolysis at different synthesis temperatures, were studied. The structure of the nanoparticles were studied with methods of X-ray diffraction. Magnetic properties were measured using a vibrating magnetometer. It was found that an increase in the Mn impurity concentration leads to a decrease in the nanocrystal size and crystalline quality of the samples. At low synthesis temperatures of T = 650°C, secondary phases are observed in samples with a Mn concentration of > 4 at.%, indicating a low solubility of Mn impurity in ZnO. It is shown that the unit cell volume in these samples is significantly smaller compared to single-crystal ZnO. This is an indication of the presence of a large number of intrinsic defects in the crystal lattice, which cause deformation stresses. When synthesizing samples at T = 750°C, the unit cell volume is larger than that of single-crystal ZnO. This is the result of a more efficient Mn doping process during synthesis and a reduction in the number of defects in the samples. At the same time, the solubility limit increases, allowing the production of single-phase samples with a Mn concentration of > 8 at.%. The resulting samples were found to possess ferromagnetic properties at room temperature. Magnetization Мs in the samples decreased with increasing Mn concentration and synthesis temperature. The maximum magnetization (Ms = 0.035 emu/g) was observed in samples with a Mn concentration of 2at.%, obtained at a temperature of T = 550°C, which corresponds to the maximum defect state of the samples