One step preparation of pure 𝝉-MnAl phase with high magnetization using strip casting method

Abstract

Ferromagnetic phase of Mn-Al exhibits great potential in the rare-earth free permanent magnetic materials due to its high magnetocrystalline anisotropy, high magnetization, high Curie temperature and low cost. In this work, the strip casting technique was applied to prepare MnAl magnetic phase. X-ray diffraction and energy dispersive X-ray analyses indicate that the as-prepared Mn54Al46 strip sample consists of pure τ-MnAl magnetic phase. It is found that the composition of Mn54Al46 is suitable to prepare τ-MnAl phase during the strip casting process. The Mn54Al46 strip sample synthesized through the strip casting exhibits a fairly high magnetization of 114 emu/g under a field of 5 T, while the coercivity of iHc = 2.8 kOe, magnetization of M5T = 63.9 emu/g at room temperature can be obtained for Mn54Al46 powder sample. This preparation method can produce a large amount of τ-phase MnAl alloy and promote mass industrialized production.

In situ Observation of Phase Transformation in MnAl(C) Magnetic Materials

“…The room temperature M s of MnAl-based magnets prepared by the traditional two-step process, including melting and annealing steps, was reported to be ~73 Am 2 /kg at 2 T [ 22 ], ~82 Am 2 /kg at 2 T [ 10 ], 94 Am 2 /kg at 3 T [ 23 ], and 100 Am 2 /kg at 14 T [ 24 ]. The room temperature M s of samples prepared by one-step process, including one-step strip casting technique and direct drop synthesis method, has been reported recently to be 114 Am 2 /kg at 5 T [ 7 ], and 117 Am 2 /kg at 9 T [ 9 ], respectively. The magnetization of our samples prepared by the traditional two-step process is higher than most previously reported values, indicating higher fraction of the τ-phase in our samples and the effectiveness of our method in controlling the PT.…”

“…The L1 0 structured τ-phase MnAl, usually prepared by annealing the hexagonal ε-phase MnAl at moderate temperatures, is attracting increasing research interests over decades for its low cost and high performance as promising rare earth free magnets [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. The metastable nature of τ-MnAl usually results in its decomposition during prolonged annealing or high temperature processing [ 3 , 4 , 5 , 6 ].…”

“…The metastable nature of τ-MnAl usually results in its decomposition during prolonged annealing or high temperature processing [ 3 , 4 , 5 , 6 ]. The doping of C to MnAl can improve the stability of τ-MnAl for the reason that the interstitial C atoms inhibit the diffusion of Mn and Al atoms but quantitative studies on the relationship between thermal stability, carbon content, and phase transformation are still very rare [ 3 , 4 , 7 , 15 ]. The thermal-driven diffusion process has substantial effect on the ε→τ phase transformation (hereafter denoted by PT) in MnAl-based magnets.…”

High Coercivity in MnAl Disc Prepared by Severe Plastic Deformation

“…Most of the previous studies on MnAl‐based alloys were focused on achieving a higher fraction of τ ‐phase and thus a higher saturation magnetization ( M s ), understanding the ε → τ phase transformation mechanism, and enhancing the magnetic performance, particularly the coercivity, via various methods . So far high‐purity τ‐phase has been prepared and there is not much space for improving M s . Currently, the ε → τ phase transformation mechanism is also well‐known and the ε → τ process can be controlled by optimized annealing conditions .…”

Enhanced magnetic performance of bulk nanocrystalline MnAl–C prepared by high pressure compaction of gas atomized powders

“…The preparation of tetragonal ferromagnetic phase containing about 54 at.% manganese had attracted intensive research interests in the 1960-1970s [2,3]. However, the discovery of Nd-Fe-B soon interrupted the research on MnAl-based magnets, which became attractive again recently due to the low cost of MnAl alloys and its medium magnetic performance filling the gap between ferrites and Nd-Fe-B [4][5][6][7]. Unfortunately, it has been not easy to produce large coercivity (H c ) in the MnAl-based magnets.…”