Phase Transformation of Micrometer-Sized Mn-Al-C

Mn 54 Al 46 C 2.44 alloy as new permanent magnetic materials was produced by induction melting, and its powders were produced by low energy ball milling. The milled powders were annealed to study the effect on their phase transformation and magnetic properties. The powder undergoes massive phase transformation at an annealing temperature of 450 °C, and reaches the maximum saturation magnetization (σ s ) when annealed at 480 °C for 5 min, while its intrinsic coercivity (H ci ) continually increases with the temperature. The initial increment of the H ci is due to the phase transformation from paramagnetic ε-phase to ferromagnetic τ-phase and remaining ε-phase and formation of secondary phases, such as nonmagnetic γ 2 - and β-phases, that acts as pinning points for the domain walls. The next one is caused by the increasing percentage of the secondary phases that decreases σ s . Based on the delta M analysis, it can be verified that the increased H ci with increasing secondary phases when annealed at temperatures above 480 °C is due to the decreasing magnetization.