Mn-Bi Magnetic Powders With High Coercivity and Magnetization at Room Temperature

${\rm Mn}_{55}{\rm Bi}_{45}{+}{\rm x}$
at.% Mn (
${\rm x}=0$
, 7 and 11) magnetic powders were prepared by low energy ball milling technique. The x-ray diffraction pattern showed that the samples mainly contain over 90% of the low temperature Mn-Bi phase for
${\rm x}= 0$
and 7 with a very small amount of Bi phase. Microstructural analysis showed that the amount of sub-micron particles increases with milling time. The milling time dependent magnetic properties were studied for all the compositions. An intrinsic coercivity
$({\rm H}_{\rm ci})$
of 12.2 kOe, remanent magnetization
$(4 \pi {\rm M}_{\rm r})$
of 7.1 kG, and energy product
$({\rm BH})_{\max}$
of 11 MGOe have been obtained for the 8 hours milled
${\rm Mn}_{55}{\rm Bi}_{45}{+}7$
at.% Mn sample. These Mn-Bi powders have potential use as precursor for rare earth free permanent magnets.