Abstract

Manganese-bismuth (MnBi) mechanical alloys have been under development for novel permanent magnets without rare-earth elements. The ball-milling of bismuth (III) oxide and manganese powders in this work leads to soft magnetic MnBi alloys with rod-like MnO impurity and highly unbalanced compositions. Interestingly, the introduction of magnesium (Mg) as reducing element during the milling gives rise to unique magnetic properties. The obtained MnBi alloys incorporating plate-like MgO has an enhanced magnetic squareness but minimal coercive field. The magnetic squareness remains high after the heat treatment and washing. The washing in ammonia also brings about a balanced composition between Mn and Bi.