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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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