Effect of Carbon Addition on Magnetic Order in Mn-Al-C Alloys

Obtaining 100% of metastable τ-phase (L10) in Mn-Al alloys needs addition of carbon and Mn in excess to stabilize the phase. The excess of Mn could lead to partial antiferromagnetic coupling, that would result in a reduction in magnetization, which is in agreement with the experimental results. To clarify this question, (Mn0.55Al0.45)100−xCx alloys, with x between 0 and 2, were rapidly quenched from the melt (by melt-spinning) and annealed at 550 • C. In the as-cast state, the sample is in the hexagonal paramagnetic ε-phase, and after annealing, the sample is in the tetragonal ferromagnetic τ-phase. Different routes for the addition of carbon were used. The structural properties were determined by neutron diffraction, and the magnetic properties by means of VSM measurements and neutron diffraction (ND).