Magnetic properties of mischmetal-(Co, Cu,Fe,Mg) alloys

To relieve the dependence for critical and strategic minerals through conservation and substitution the Bureau of Mines, U. S. Department of the Interior, investigated alloys containing mischmetal (MM), cobalt, copper, magnesium, and iron for use in permanent magnets in place of the scarce samarium-cobalt alloys. The magnetic properties of selected MM-Co-Cu-Mg and MM-Co-Cu-Fe-Mg alloys were evaluated. Magnets were fabricated by powder metallurgy that consisted of arc-melting the metals, crushing and grinding the resultant alloy, aligning and compacting the powder, and sintering the green compacts. Magnetic values of
M
H
c
= 4.7 kOe,
B
H
c
= 4,070 Oe, B
r
= 6,810 G, and (BH)
max
= 10.0 MGOe were obtained with an MM-Co alloy containing 36.0 ±.5 wt-pct mischmetal. By substituting part of the cobalt with copper and magnesium, the value for
M
H
c
was increased to 29.0 kOe and that for
B
H
c
to 5,890 Oe. The intrinsic coercivity value exceeded that of Sm-Co alloy,
M
H
c
= 27.4 kOe, which was obtained in our laboratory. The addition of iron to MM-Co-Cu-Mg alloys resulted in an increase of B
r
to 6,900 G and ((BH)
max
to 10.3 MGOe. Copper and magnesium contents of these alloys were optimized to obtain maximum value of
M
H
c
.