Fundamentals of Permanent Magnets

1
Fundamentals of Permanent Magnets
2
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 magnets

Property of Alliance LLC
3
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

Property of Alliance LLC
4
Main Types of Magnet Materials

• Alnico
• Ferrite
• Samarium Cobalt
• Neodymium Iron Boron
• Bonded Grades of the Above Types

Property of Alliance LLC
5
Typical Supplier Data Sheet
Property of Alliance LLC
6
Hysteresis / Demagnetization Curve
Property of Alliance LLC
7
B
I
Br, Bi
I
Hci
Hc
-H
H
-B
Property of Alliance LLC
8
Temperature Effects
Property of Alliance LLC
9
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)
25.0 22.5 20.0
17.5 15.0
12.5 10.0 7.50
5.00 2.50 H (KOe)
Property of Alliance LLC
10
Magnet Characteristics
Materials Typical Shapes Pro Con
Cast Alnico AlNiCo Rods, Bars, U shape and other cast type High Br High working T Good T coef. Very Low Hc High cost High L/D Requires Cast
Sintered Alnico AlNiCo Powder pressed to shape Complex shapes High Br, T Requires Tool High cost Low market
Ceramic/Ferrite SrFe2O3 Blocks, Rings, Arcs, Discs Most flux for High usage Low corrosion Low Br Requires tool Simple shapes
Samarium Cobalt SmCo Blocks, Rings, Discs Arcs, Segments No corrosion Very low T coef Stable, No tool Very expensive Simple shapes High Co content
Neodymium NdFeB Blocks, Rings, Discs Arcs, Segments Highest magnetic properties No tooling Corrodes Low working T Difficult to Mag
Bonded Grades All materials Difficult geometries Can be insert molded or over-molded Complex shapes Various resins High tooling Low magnetics High volumes
Property of Alliance LLC
11
Cast Alnico Magnets
Property of Alliance LLC
12
Ferrites / Ceramics (SrFe2O3)
Property of Alliance LLC
13
Neodymium, Neo, NdFeB
Property of Alliance LLC
14
Injection and Compression Molded
Property of Alliance LLC