Alnico and Alcomax Permanent Magnets

A large variety of strong permanent magnets have been made from alloys of aluminum, nickel and cobalt with iron. Alnico and alcomax are two of the trade names of such alloys. Small amounts of Cu, Ti and Nb may also be used, and the number of variants is large. Even the same composition may be given different names in different countries.

Alnico IV and Alcomax I have randomly oriented grains. Alnico V has superior properties because it has directed columnar crystals which "enable better utilization of the crystalline anisotropy"(Myers).

Material
Coercivity
(T)
Remanence
(T)
(BB0/m0)max
(kJ/m3)
Alnico IV
0.07
0.6
10.3
Alnico V
0.07
1.35
55
Alcomax I
0.05
1.2
27.8
Data from Myers
Discussion of
magnet data
 Index

References
Myers
Ch 11
 
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Barium-Iron Oxide Magnets

A useful composite oxide, BaFe12O19 is ground to a fine powder and then cold-pressed in the presence of a magnetic field to achieve magnetic alignment of the particles. It is then heat-treated to stabilize the material. Because it starts from a powder, the magnets can be made in a variety of shapes.

Material
Coercivity
(T)
Remanence
(T)
(BB0/m0)max
(kJ/m3)
BaFe12O19
0.36
0.36
25
Data from Myers
Discussion of
magnet data

BaFe12O19 forms hexagonal crystals which show a high degree of magnetic anisotropy. They are difficult to magnetize in any direction other than the c axis. This anisotropy is atomic in origin and is called "magnetocrystalline" anisotropy (Myers).

 Index

References
Myers
Ch 11
 
HyperPhysics***** Condensed Matter ***** Electricity and Magnetism R Nave
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