Comparison of magnetic properties of natural mischmetal and synthetic mischmetal alloyed with cobalt, copper, and magnesium

As part of its mission, one of the objectives of the Bureau of Mines is to develop substitutes for scarce materials. Alloys containing mischmetal, lanthanum, praseodymium, neodymium, cobalt, copper, and magnesium were evaluated for use in permanent magnets in lieu of Sm-Co alloys. Magnets were fabricated by powder metallurgy techniques that consisted of arc melting the metals, crushing and grinding the resultant alloy, aligning and compacting the powder, and sintering the green compacts. A cerium-free synthetic mischmetal (M) consisting of La-Pr-Nd was developed that had substantially better magnetic properties than natural mischmetal (MM) when alloyed with cobalt, copper, and magnesium. Best magnetic properties obtained were
M
H
C
= 22.9 kOe,
B
H
C
= 6.6 kOe, B
r
= 8.1 kG, and
(BH)_{\max} = 13.2
MGOe. A synthetic mischmetal containing 20 pct La, 60 Pr, and 20 Nd was the best overall rare-earth mixture with the following magnetic properties:
M
H
C
= 13.4 kOe,
B
H
C
= 6.3 kOe, B
r
= 7.9 kG, and
(BH)_{\max} = 13.2
MGOe.