High-Performance MnBi Alloy Prepared Using Profiled Heat Treatment

• Published in: IEEE transactions on magnetics Vol. 50; no. 12; pp. 1 - 6
• Main Authors: Van Vuong Nguyen, Poudyal, Narayan, Xubo Liu, Liu, J. Ping, Kewei Sun, Kramer, Matt J., Jun Cui
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-12-2014; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers. Magnetics Group
• Subjects: Heat treatment; Magnetic field measurement; Magnetism; Manganese; MnBi; permanent magnet; PHT; Powders; profiled heat treatment; Surface treatment; permanent magnet; MnBi; profiled heat treatment (PHT)
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2014.2341659

The profiled heat treatment (PHT) method has been used to synthesize MnBi alloys with high-purity low-temperature phase (LTP). In the PHT method, the arc-melted MnBi alloy was remelted then slowly cooled by a pseudo-equilibrium solidification process to promote the formation of LTP phase. The PHT-treated MnBi alloys had an LTP phase up to 94 wt.% and a magnetization of 73 emu/g under a field of 9 T. Scanning electron microscopy showed that there exist some micrometer-sized Mn-rich inclusions in the LTP matrix of the PHT MnBi alloy. The PHT MnBi alloys were crushed into powders with an average size of ~3 μm by low-energy ball milling. These MnBi powders were aligned in an 18 kOe field and warm compacted into a bulk magnet at 300 °C for 30 min. The magnet had a density of 8.2 g/cm 3 and magnetic properties of M s = 6.7 kG, M r = 5.3 kGs, i H c = 5 kOe, and (BH) max = 6.1 MGOe.