Abstract
In this paper, high purity τ-Mn54Al46 and Mn54−xAl46Cxalloys 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 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%.
Highlights
The current generation of high performance permanent magnets is based on two of the three transition metals (Fe, Co, Mn) capable of carrying a large magnetic moment in metallic compounds
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
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
Summary
The current generation of high performance permanent magnets is based on two of the three transition metals (Fe, Co, Mn) capable of carrying a large magnetic moment in metallic compounds. Co (with a typical moment of 1.6 μB) is used as the basis of CaCu5 derived structures with Sm (1:5, 2:17, 1:7), while Fe (with about 2.0 μB) is the principal constituent in the Nd2Fe14B family of compounds.[1,2,3] the rare earth elements Nd, Sm, and Dy, etc. In order to exploit the potential of the MnAl τ-phase as a hard magnetic material, a further characterization of the crystal structure and magnetic properties is needed
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