Effect of process parameters on the phase formation, particle size and magnetic properties of MnBi nanoparticles prepared by mechanochemical synthesis

Nanoparticles of MnBi are obtained from Bi2O3 and Mn by mechanochemical synthesis. The effect of excess dispersant (CaO) in mechanochemical synthesis and the temperature of subsequent thermal treatment on phase formation, particle size and magnetic properties of MnBi nanoparticles is investigated by means of X-ray diffraction analysis, scanning electron microscopy and magnetometry. With increase of excess dispersant, the average particle size decreases and the particles are observed to be more separated. Saturation magnetization (Ms) was found to decrease with increase of excess dispersant, while the coercivity (Hc) increases with the increase of dispersant up to 40 wt.% and thereafter it decreases. The formation of MnBi phase increases as the heat-treatment temperature is increased; however, the average particle size increases from nano to micrometer (200 nm to 2 μm).