Ferromagnetic L10 Phase Formation in the Mn–Al–C Alloys Induced by High-Pressure Spark Plasma Sintering

Structural and magnetic characterization of Mn-Al-C permanent magnets obtained by spark plasma sintering (SPS) is reported. The transformation from the parent E-phase to the ferromagnetic τ-phase occurs simultaneously with the process of sintering. The use of a tungsten carbide crucible enabled us to decrease the sintering temperature, which hampered the precipitation of secondary phases. As a result, sintered samples show higher coercivity as compared with annealed powder. However, the finely milled powder, ensuring better densification, turned out to be more prone to phase decomposition during sintering. The phase constitution of the samples was determined by X-ray diffraction, and magnetic hysteresis loops were recorded using a vibrating sample magnetometer. Scanning electron microscopy and electron backscatter diffraction were employed to study the microstructure and orientation distribution of grains after SPS. The dependence of coercivity and magnetization on the preparation conditions and sintering temperature is analyzed. To combine good magnetic properties with proper density, further optimization of the production parameters is necessary.