Anisotropic fully dense MnBi permanent magnet with high energy product and high coercivity at elevated temperatures

The structural and magnetic properties of a fully dense anisotropic MnBi magnet prepared by hot compaction are investigated. Arc-melting and low energy ball milling are employed to synthesize highly anisotropic MnBi powders with very high remanence ratio (Mr/Ms) of 0.97, coercivity (Hc) of 11.7 kOe and maximum energy product [(BH)max] of 9 MG Oe. The bulk magnet fabricated from these powders displays anisotropic characteristics with high Mr/Ms ratio of 0.91 and a (BH)max of 5.8 MG Oe at room temperature. The Hc of bulk magnet increases linearly from 6.5 kOe at 300 K to 28.3 kOe at 530 K with a (BH)max of 3.6 MG Oe at 530 K. Analysis of the temperature dependence of Hc suggests the nucleation of reversed domains as the dominant mechanism for the magnetization reversal.