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Alliance LLC
Fundamentals of Permanent Magnets
Magnetic Orientation
Isotropic Anisotropic (non-oriented) (oriented)
•Magnetic strength is the same in all directions
•Can be magnetized in any direction
•Almost all bonded magnets
•Magnetic strength is greatest in the oriented direction
•Can be magnetized only in the oriented direction
•Almost all sintered magnetsProperty of Alliance LLC
Main Magnetic Properties
Residual induction - Br
Coercive force - Hc
Intrinsic coercive force - Hci
Maximum Energy Density – (BH)max
Maximum Working Temperature - Tw Reversible Temperature Coefficient - -%Br/C Curie Temperature - Tc
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Main Types of Magnet Materials
Alnico Ferrite Samarium Cobalt Neodymium Iron Boron Bonded Grades of the Above Types
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Typical Supplier Data Sheet
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Hysteresis / Demagnetization Curve
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I
I
Hci
Br, Bi
Hc-H
-B
+H
+B
(BiH)max
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Temperature Effects
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25.0 22.5 20.0 17.5 15.0 12.5 10.0 7.50 5.00 2.50 H (KOe)
15.0
13.5
12.0
10.5
9.00
7.50
6.00
4.50
3.00
1.50
B (Kg)
Alnico Ferrite SmCo NdFeB(SH)
Surface Flux at 0" Gap of 1" dia. Disc
0
1000
2000
3000
4000
5000
6000
0.25 0.5 1 2 4 8
Length of Magnet in inches
Ga
us
s
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Magnet CharacteristicsMaterials Typical Shapes Pro Con
Cast AlnicoAlNiCo
Rods, Bars, U shapeand other cast type
High BrHigh working TGood T coef.
Very Low HcHigh costHigh L/D
Requires Cast
Sintered AlnicoAlNiCo
Powder pressed to shapeComplex shapes
High Br, T
Requires Tool High cost Low market
Ceramic/FerriteSrFe2O3
Blocks, Rings, Arcs, DiscsMost flux for $
High usageLow corrosion
Low BrRequires tool
Simple shapes
SamariumCobaltSmCo
Blocks, Rings, DiscsArcs, Segments
No corrosionVery low T coefStable, No tool
Very expensiveSimple shapes
High Co content
NeodymiumNdFeB
Blocks, Rings, DiscsArcs, Segments
Highest magnetic properties
No tooling
CorrodesLow working TDifficult to Mag
Bonded GradesAll materials
Difficult geometriesCan be insert molded
or over-molded
Complex shapesVarious resins
High toolingLow magneticsHigh volumes
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Cast Alnico Magnets
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Ferrites / Ceramics (SrFe2O3)
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Neodymium, Neo, NdFeB
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Injection and Compression Molded
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