Processing of MnBi bulk magnets with enhanced energy product

Abstract

We report magnetic properties and microstructure of high energy-product MnBi bulk magnets fabricated by low-temperature ball-milling and warm compaction technique. A maximum energy product (BH)max of 8.4 MGOe and a coercivity of 6.2 kOe were obtained in the bulk MnBi magnet at room temperature. Magnetic characterization at elevated temperatures showed an increase in coercivity to 16.2 kOe while (BH)max value decreased to 6.8 MGOe at 400 K. Microstructure characterization revealed that the bulk magnets consist of oriented uniform nanoscale grains with average size about 50 nm.

MnBi Magnetic Material: A Critical Review

“…Despite numerous efforts spent, the past development of performance of MnBi bulk magnets is sluggish [26][27][28][29][30][31][32][33][34][35][36][37][38]. This history of development of (BH) max is summarized in Fig.…”

“…12. (a) The XRD pattern of parallel surface of in-epoxy highly aligned MnBi particles [33], (b) The XRD pattern of parallel and perpendicular surfaces of a MnBi bulk magnet [34].…”

“…The practical value of P opt depends on the mold construction and was announced, for example, equal 1800 -2000 psi in Refs. [23,33,34].…”

“…The second value is the melting temperature of Bi, over which the sintering process occurs intensively; ii) the sintering time t ma must be short, around some tens minutes to avoid any destroys of LTP content; iii) the sintering must be conducted under pressure P ma , by other word the hot compaction procedure must be dealt with. The practical values are T ma ∼ 573 K, t ma ∼ 10 -30 min., P ma ∼ 2000 psi [23,33,34].…”

Enhanced Magnetic Squareness in Manganese-Bismuth Mechanical Alloys Incorporating Magnesium Oxide

“…High energy ball milling has received a great deal of attention as a pathway to fabricate MnBi alloys. Since Mn powders are easily oxidized and reacted with water, the milling has to be carried out in either inert gas atmosphere [11 -18] or liquid nitrogen [2]. The method is also demonstrated to enhance the coercive field of MnBi synthesized by hydrogen plasma metal reaction [19].…”