Tripling in coercivity (Hc) for the thermal and structural highly stabilized MnAlBi-C rare earth free permanent magnet via Bi doping

Abstract

The limited coercivity (Hc) and metastability of the ferromagnetic τ phase MnAl-C magnet have constrained its magnetic performance and application potential. Bi was doped into the Mn54Al44-xBixC2 alloy system in this study. The doped Bi could effectively stabilize the metastable τ phase and inhibit the non-magnetic Al-rich phase formation. The ferromagnetic τ phase ratio increased dramatically as the doped Bi increase, with a peak Ms of 81 emu/g was achieved for the post-annealed Mn54Al43.6Bi0.4C2 alloy at 19 kOe. High Hc ferromagnetic LTP MnBi phase forms within the Mn54Al44-xBixC2 (x = 0.2, 0.4, 0.6) alloys when it been annealed at 300℃ for 24 h, the samples tripled or even quadrupled in Hc compared with the initial synthesized alloy. The doped Bi dissolved within lattice caused the τ phase thermally stability, structural stability improves substantially; 0.4 Bi doped Mn54Al43.6Bi0.4C2 alloy exhibited a combination of high Ms and Hc even after been ball milled for a long period of 15 and 20 h. The (Ms, Hc) achieved a value of (59.6 emu/g, 3526 Oe) for the 15 h milled sample and (51.5 emu/g, 4546 Oe) for the 20 h milled sample at 19 kOe, respectively; which is desirable for its application as a high-performance rare earth free permanent magnet.

Keywords

• Permanent magnet
• Coercivity
• MnAl
• LTP MnBi
• Metastable