Mechanical alloying and theoretical studies of MnAl(C) magnets

Mn55Al45, Mn55Al44C1, Mn52.2Al45.8C2 and Mn54.2Al43.8C2 were synthesized by the mechanical alloying method. It was the first time that a high purity τ phase up to 99% of weight percentage was obtained in Mn54.2Al43.8C2, which gave the highest saturation magnetization Ms = 570 kAm−1 ever reported by mechanical alloying up to date. The crystallite size of the τ phase of MnAl(C) alloy decreased with increasing carbon doping, varying from 79 to 159 nm. Additionally, the coercivity (Hc) was found to be inversely proportional to the crystallite size of τ phase. Effect of doping carbon and its position in the τ phase of MnAl(C) alloy were also investigated for the first time by first-principle calculations. It was found that by inserting carbon at the interstitial site in the tetragonal structure, a strong stabilization effect and an expansion of unit cell were observed, which are in good agreement with the experimental results. Moreover, our results indicate that carbon doping reduces the magnetic moment of Mn.