Influence of jet milling process parameters on particle size, phase formation and magnetic properties of MnBi alloy

• Effect of jet milling conditions was studied in MnBi alloy system.
• Jet milling pressure plays a critical role in controlling the decomposition of MnBi.
• As the jet pressure increases, more amount of MnBi phase decomposes.
• Moderate milling pressure has resulted in powders with good properties.
• Jet milled powders displayed high coercivity (Hc) values of about 18 kOe.

The effect of jet milling conditions on phase decomposition, particle size and magnetic properties of MnBi alloy were studied. It is observed that jet milling pressure plays a critical role in controlling the decomposition of MnBi phase, particle size and associated magnetic properties. As the jet pressure increases, more amount of MnBi phase decomposes into Bi and Mn phases. The weight fraction of MnBi phase decreases from 81%, for the starting powder, to 43% by increasing the milling pressure to a high value of 80 psi. Particle size decreases rapidly to about 1 μm on jet milling and even though the average particle size does not change noticeably with further increase of milling pressure, the particle size distribution appears to be different. Moderate milling pressure has resulted in powders with narrow particle size distribution, low decomposition of MnBi phase and smooth demagnetization curves. All the jet milled powders displayed high coercivity (Hc) values of about 18 kOe with saturation magnetization in the range of 41–51 emu/g.