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 (M-r/M-s) of 0.97, coercivity (H-c) of 11.7 kOe and maximum energy product [(BH)(max)] of 9MGOe. The bulk magnet fabricated from these powders displays anisotropic characteristics with high M-r/M-s ratio of 0.91 and a (BH)(max) of 5.8 MG Oe at room temperature. The H-c 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 H-c suggests the nucleation of reversed domains as the dominant mechanism for the magnetization reversal.