Papers by Author: V. Spasojević

Abstract: Phase transformations and magnetic properties of multiphase Nd4.3Fe76.2B19.5 alloy were investigated in the temperature range of heat treatment 600-700°C. The influence of different heat treatment regimes was observed by correlation of phase composition and measured magnetic properties. The heat treatment regime, which provided the microstructure that improves exchange interactions between grains of soft and hard magnetic phases and consequently enhances magnetic properties, was defined and discussed. For optimized magnetic alloy grain size of the present phases Fe3B, Nd2Fe14B and α-Fe was calculated by size-strain analysis of X-ray powder diffraction data. Calculated mean grain size was on a nanoscale, below 30 nm.

Abstract: Zn-Mn-O semiconductor crystallites with nominal manganese concentration x = 0.01, 0.02, 0.04 and 0.10 were synthesized by a solid state reaction route using oxalate precursors. Thermal treatment procedure was carried out in air at different temperatures in the range 400 - 900°C. The samples were investigated by X-ray diffraction, magnetization measurements and electron paramagnetic resonance. X-ray analysis reveals that dominant crystal phase in the Zn-Mn-O system corresponds to the wurtzite structure of ZnO. Room temperature ferromagnetism is observed in the Zn-Mn-O samples with lower manganese concentration, x ≤ 0.04, thermally treated at low temperature (500°C). Saturation magnetization in the sample with x = 0.01 is found to be 0.05 μB/Mn. The ferromagnetic phase seems to be developed by Zn diffusion into Mn-oxide grains.

Abstract: In this paper the influence of tribophysical activation on non-isothermal sintering of barium titanate has been investigated. BaTiO3 powders were tribophysically activated in a planetary ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380oC. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380oC with heating rates of 10, 20 and 30oC/min. The samples were analyzed by the X-ray powder diffraction method. Investigation of the morphology of microstructure constituents was performed using the scanning electron microsocopy method. With the purpose of optimizing technological parameters the results obtained by microstructure analysis were correlated with the results of quantitative dilatometric analysis.