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Design Guide
Modern
Magnet Materials
There are four classes of modern
commercialized magnets, each based on their material composition.
Within each class is a family of grades with their own
magnetic properties. These general classes are:
Neodymium Iron
Boron
Samarium Cobalt
Ceramic
Alnico
NdFeB and SmCo are collectively known as Rare Earth
magnets because they are both composed of materials from
the Rare Earth group of elements. Neodymium Iron Boron
(general composition Nd2Fe14B, often
abbreviated to NdFeB) is the most recent commercial addition
to the family of modern magnet materials. At room temperatures,
NdFeB magnets exhibit the highest properties of all magnet
materials. Samarium Cobalt is manufactured in two compositions:
Sm1Co5 and Sm2Co17
- often referred to as the SmCo 1:5 or SmCo 2:17 types.
2:17 types, with higher Hci values, offer greater
inherent stability than the 1:5 types. Ceramic, also known
as Ferrite, magnets (general composition BaFe2O3
or SrFe2O3) have been commercialized
since the 1950s and continue to be extensively used today
due to their low cost. A special form of Ceramic magnet
is "Flexible" material, made by bonding Ceramic
powder in a flexible binder. Alnico magnets (general composition
Al-Ni-Co) were commercialized in the 1930s and are still
extensively used today.
These materials span a range of properties that accommodate
a wide variety of application requirements. The following
is intended to give a broad but practical overview of
factors that must be considered in selecting the proper
material, grade, shape, and size of magnet for a specific
application. The chart below shows typical values of the
key characteristics for selected grades of various materials
for comparison. These values will be discussed in detail
in the following sections.
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Table
2.1 Magnet Material Comparisons
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Material
|
Grade
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Br
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Hc
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Hci
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BHmax
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Tmax
(Deg C)*
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NdFeB
|
39H
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12,800
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12,300
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21,000
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40
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150
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SmCo
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26
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10,500
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9,200
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10,000
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26
|
300
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NdFeB
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B10N
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6,800
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5,780
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10,300
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10
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150
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Alnico
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5
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12,500
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640
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640
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5.5
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540
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Ceramic
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8
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3,900
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3,200
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3,250
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3.5
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300
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Flexible
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1
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1,600
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1,370
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1,380
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0.6
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100
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*
Tmax (maximum practical operating temperature)
is for reference only. The maximum practical
operating temperature of any magnet is dependent
on the circuit the magnet is operating in.
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