What is the Curie point?
Short answer: the Curie point (or Curie temperature, Tc) is the temperature at which a magnetic material loses all its permanent magnetism. For neodymium magnets (NdFeB) the Curie point is between approx. 310 and 400 °C. In use, the Curie point is not the limit that matters: a standard neodymium magnet already permanently loses part of its strength above approx. 80 °C.
Curie point per magnet material
| Material | Curie point (approx.) | Max. operating temperature (approx.) |
|---|---|---|
| Neodymium (NdFeB), standard | 310 – 340 °C | 80 °C |
| Neodymium, high temperature class (UH, EH, AH) | 340 – 400 °C | 180 – 230 °C |
| Ferrite | 450 °C | 250 °C |
| Samarium cobalt (SmCo) | 700 – 850 °C | 250 – 350 °C |
| AlNiCo | 800 – 860 °C | 450 – 550 °C |
| Iron (pure) | 770 °C | n/a |
| Nickel | 358 °C | n/a |
Higher temperature classes of neodymium get a higher Curie point because cobalt is added; dysprosium or terbium mainly increase the coercivity.
What happens at the Curie point?
In a magnet, the magnetic moments of the atoms point in the same direction. Heat makes the atoms vibrate and disturbs that order. At the Curie point the heat wins completely: the order disappears and the material is no longer a magnet. After cooling it can be magnetised again, but the magnetism does not return by itself. For that, the magnet has to be remagnetised in a very strong field.
The Curie point is also the reason why a magnet no longer attracts a heated nail: iron above 770 °C is not magnetic. That is a well-known experiment in physics class.
Curie point or maximum operating temperature?
- Maximum operating temperature: up to this point the magnet may get warm without permanent loss of strength. This is the value to choose by.
- Curie point: here all magnetism is gone. Permanent damage is already possible far below it.
An overview of the operating temperature per grade (N, M, H, SH, UH, EH) is in what happens to a magnet at high temperatures?
Frequently asked questions
Who discovered the Curie point?
The French physicist Pierre Curie described the phenomenon in 1895.
Can I demagnetise a magnet by heating it?
Yes, above the Curie point. Do not do this at home: the coating burns, harmful fumes are released and neodymium can oxidise at high temperature or ignite as powder.
Is a magnet in the sun or in the car affected by the Curie point?
No, those temperatures are far too low. However, in a car in summer it can get above 80 °C, the operating limit of standard neodymium.
Read also
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