Wei, J.Z.; Song, Z.G.; Yang, Y.B.; Liu, S.Q.; Du, H.L.; Han, J.Z.; Zhou, D.; Wang, C.S.; Yang, Y.C.; Franz, A.; Többens, D.; Yang, J.B.: τ-MnAl with high coercivity and saturation magnetization. AIP Advances 4 (2014), p. 127113/1-11
10.1063/1.4903773

Abstract:
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 (E9, HZB) 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 μB 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 μB at a volume expansion rate of ΔV/V≈ 20%.