A New Permanent Magnet from Powdered Manganese Bismuthide

Abstract

Permanent magnets in present use consist chiefly of alloys containing cobalt or nickel, or both. Because these elements are currently scarce, possible substitute materials were examined. The intermetallic compound manganese bismuthide was chosen for this investigation because it has the highest recorded magnetic crystal anisotropy. The new permanent magnet was prepared by hot pressing finely pulverized MnBi in the presence of a strong magnetic field to facilitate particle alignment. Some of these compacts showed a maximum energy product (BH)_max as high as 4.3×10⁶ gauss‐oersteds, a coercive force (H_c) of 3400 oersteds and a residual flux density (B_r) of 4300 gauss. This preliminary work shows that aside from its possibilities as a substitute for magnets requiring cobalt, this new magnet material has a value which exceeds present materials for special applications where a high coercive force is desirable, e.g., where one cannot use a magnet that is long compared to the air gap required. There is also theoretical possibility of further improvement in maximum energy product.