Microstructure and magnetic properties of Mn–Al–C alloy powders prepared by ball milling

• Magnetically anisotropic flake-shaped Mn–Al–C powders were prepared by ball milling.
• Magnetization decreased due to the defects introduced during the milling process.
• Annealing the as-milled powders could recover the crystal structure of τ-phase MnAl.
• The easy axis lies in the planar direction of the flakes.

Magnetically anisotropic Mn–Al–C powders have been prepared by ball milling the τ-phase Mn53.3Al45C1.7 alloy. Flake-shaped powders were obtained after milling for 2 h and the thickness decreased continuously with extended milling time. No sign of decomposition was observed in the as-milled state, however, magnetization decreased and coercivity increased continuously with milling time because of the defects introduced in the milling process. μ0iHc of 0.52 T was obtained in powders milled for 12 h. By annealing the as-milled powders at 773 K for 30 min, the magnetization increased significantly because of the recovered crystal structure of τ-phase. A degree of texture ranging from 17.8% to 37.1% has been obtained and the magnetically easy axis lies within the plane of the flakes. Optimized magnetic properties, with Mr of 54.8 Am2 kg−1 and μ0iHc of 0.28 T, was obtained in Mn53.3Al45C1.7 powders milled for 5 h followed by heat treatment at 773 K.