Effect of heat treatment and ball milling on MnBi magnetic materials

MnBi alloy was prepared using arc melting, and was then heated at various temperatures and times. The alloy was ball milled for various lengths of time, following a heat treatment at 573 K for 20 h. The effects of the heat treatment and the ball milling on the magnetic performances of the material were investigated by analyzing the phases, the particle sizes, and the grain sizes. Results showed that the mass percentage of the LTP MnBi phase increased as the heat treatment time increased. The mass percentage initially increased and then decreased as the heat treatment temperature increased. The saturation magnetization increased quickly as the mass percentage of the LTP MnBi increased following the heat treatment. The value rose as high as 71.39 emu g⁻¹ at 573 K for 30 h. The magnetization decreased, due to the decomposition of MnBi phases after ball milling. The coercivity increased simultaneously, due to the grain refinement, the presence of stresses, defects, and an amorphous phase. This value was improved from 0.09 to 14.65 KOe after ball milling for 24 h. (paper)