τ-MnAl with high coercivity and saturation magnetization

In this paper, high purity tau-Mn54Al46 and Mn54-xAl46Cx alloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD), powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm(-1), coercivity of 0.5 T, and a maximum energy product of (BH)(max) = 24.7 kJm(-3) were achieved for the pure Mn54Al46 powders without carbon doping. The carbon substituted Mn54-xAl46Cx, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 mu(B) which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 mu(B) at a volume expansion rate of Delta V/V approximate to 20%. (C) 2014 Author(s).