Guide to Magnet Materials
When choosing a magnet material for an application you should take the following factors into consideration:
• Flux requirement of the application • Maximum operating temperature • Likely exposure to corrosive conditions • Magnetic stability • Size and weight limitations
What strength/flux of magnet do you need? This table shows the comparative magnetic strengths of the same volume of the four main magnet materials in terms of their maximum energy products (BHmax) in CGS or SI units and their typical pole face flux densities. Neodymium is the most powerful magnet material available. It is ideal for applications where high flux density is required or where space is at a premium. What temperature will the magnet be operating in? In most applications, operating temperature is not a consideration but extreme temperatures will have an effect on the magnetic performance. Each material has different temperature characteristics and these must be reviewed to ensure that the correct material is used for the application. Using the wrong material could lead to loss in magnetic performance.
Magnet Material
Max Energy Product: CGS
Max Energy Product: SI
Flux Density
Ferrite
3.3 MGOe
26 Kj/m 3
1000 Gauss
Alnico
5.2 MGOe
42 Kj/m 3
1300 Gauss
Samarium Cobalt
26 MGOe
208 Kj/m 3
3500 Gauss
Neodymium
35 MGOe
279 Kj/m 3
4500 Gauss
Max Working Temperature °C
Effects of Sub Zero Temperature °C Large irreversible losses below -60°c Permanent losses no more than 10% expected down to -269°c Minimal losses down to -269°c No irreversible losses down to -196°c
Magnet Material
Reversible Effect of Temp: 20°C - 150°C
Ferrite
250
-0.19% per °c
-0.02% per °c
Alnico
550
Samarium Cobalt
300
-0.003% per °c
Neodymium 80*
-0.12% per °c
*N35 grade. Other grades available up to 230°C
Other Factors To Consider
Corrosion Another potential cause of performance loss is a breakdown of the magnet's composition due to corrosive environmental effects. This table shows relative corrosive resistance for each material when uncoated. As neodymium's corrosive resistance is poor it is usually sold with a protective coating, normally either nickel or zinc. External Demagnetising Fields / Magnet Stability Temperature has the greatest effect on magnet stability but high external magnetic fields can influence performance. This table shows the relative demagnetising effect on each material.
Corrosion Resistance Uncoated
Resistance To Demagnetisation
Magnet Material
Ferrite
Excellent
High
Alnico
Fair
Low
Samarium Cobalt
Excellent
Very High
Neodymium
Poor
Very High
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