• Publisher-DOI

Mn–Al–C is intended to be one of the ‘‘gap magnets’’ with magnetic performance in-between ferrites and Nd-Fe-B. These magnets are based on the metastable ferromagnetic τ-phase with L1₀ structure, which requires well controlled synthesis to prevent the formation of secondary phases, detrimental for magnetic properties. Here, we investigate the formation of τ-phase in Mn–Al–C using Spark Plasma Sintering (SPS) and compare with conventional annealing. The effect of SPS parameters (pressure and electric current) on the phase formation is also studied. Single τ-phase is obtained for annealing 5 min at 500°C with SPS. In addition, we show that the initial grain size of the τ-phase is influencing the τ-phase transformation and fraction at a given annealing condition, independently of the annealing method used. A faster transformation was observed for smaller initial ϵ-grains. The samples obtained by SPS showed comparable magnetic properties with the conventional annealed ones, reaching coercivity of 0.18 T and saturation magnetization of 114 Am ²/kg in the optimized samples. The similarity in coercivity is related to the microstructure, as we reveal the presence of structure defects like twin boundaries and dislocations in both materials.

This work was funded by the Deutsche Forschungsgemeinschaft DFG (German Research Foundation) under the Priority Programme SPP1959-Fields Matter and European Union’s Horizon 2020 research and innovation programme under grant agreement No 101003914 (PASSENGER).