Phase transformation and magnetic properties of rapidly solidified Mn-Al-C alloys modified with Zr

Mn54−xAl43C3Zrx (x = 1, 3) alloys were prepared by rapid solidification followed by heat treatment to produce the ferromagnetic τ phase. The substitution of Zr for Mn in the structure resulted in an increase of the saturation magnetization (Ms) compared to that of Mn54Al43C3. While the highest Ms (128 ± 1 emu/g) was obtained in Mn53Al43C3Zr1, the coercivity was also improved to 1.62 kOe, compared to 1.25 kOe for Mn54Al43C3. To further improve the coercivity through grain refinement, additional C (1%, 3%, 5%, and 7%) was added to Mn53Al43C3Zr1. An increase in the coercivity was observed due to a decrease of grain size and the formation of nonmagnetic phases, which reduced the magnetostatic interactions between the τ-phase grains. However, excess C reduced the saturation magnetization due to the formation of the other non-ferromagnetic phases, including e, γ2, and β phases.