Nanostructured bulk MnBi magnets fabricated by hot compaction of cryomilled powders

Cryomilling was employed for Mn50+xBi50-x (x = 0,5) alloys to synthesize nanocrystalline powders with particle size of 400-500 nm without much increase of the unwanted secondary Bi phase. At room temperature, the cryomilled powders showed large coercivity (H-c) values of 18.5 kOe and 20.7 kOe for Mn50Bi50 and Mn55Bi45, respectively. Cryomilled powders were hot compacted to form a bulk nanostructured MnBi magnet. The Mn50Bi50 hot compacted magnet exhibits H-c of 12.9 kOe with remanence value of 26 emu g(-1) at room temperature. The microstructure of hot compacted magnet illustrates uniform grains with an average size of 40 nm. Furthermore, the magnet shows a large positive temperature coefficient of H-c which reaches a value of more than 30 kOe above 450 K.