What happens to a magnet at high temperatures?
Short answer: a standard neodymium magnet (grade N) can withstand up to approx. 80 °C without permanent loss of strength; N50 and N52 often only up to 60 – 70 °C. Up to that limit the loss of strength is temporary: about 0.11 to 0.12% per degree, and it returns when the magnet cools down. Above the limit the magnet permanently loses strength. At the Curie point, for neodymium 310 to 400 °C, it is fully demagnetised. For hot applications there are special grades (H, SH, UH, EH) up to 200 °C and beyond.
Maximum operating temperature per grade
| Grade | Max. operating temperature (indicative) | Example |
|---|---|---|
| N (standard) | 80 °C (N50/N52: 60 – 70 °C) | N35, N42, N48 |
| M | 100 °C | N45M |
| H | 120 °C | N42H |
| SH | 150 °C | N42SH |
| UH | 180 °C | N35UH |
| EH | 200 °C | N35EH |
| AH | 220 – 230 °C | N33AH |
For comparison: samarium cobalt magnets (SmCo) can withstand 250 – 350 °C and ferrite magnets up to approx. 250 °C, but at room temperature they are weaker than neodymium.
Temporary or permanent loss of strength?
- Temporary (reversible): below the maximum operating temperature, the force drops by about 0.11 – 0.12% per °C. A magnet that holds 10 kg at 20 °C holds about 9.5 kg at 60 °C. After cooling it is just as strong again.
- Permanent (irreversible): above the maximum operating temperature, part of the magnetisation is lost. After cooling the magnet remains weaker. Only remagnetising restores it.
- Complete: above the Curie point the material loses all its magnetism. See what is the Curie point?
Why is a flat magnet more sensitive to heat?
The temperature limit applies to a magnet with a favourable shape. A thin disc or plate (for example Ø20 x 2 mm) has a stronger internal opposing field than a thick one (Ø10 x 10 mm) and therefore permanently loses strength at a lower temperature. A magnet hanging freely in the air, without steel against it, is also more sensitive than a magnet on steel or in a steel pot. For hot applications, choose a thicker magnet or a pot magnet, or a higher temperature class.
Where does it get too hot in practice?
- in or next to electric motors and machines
- behind lamps and spotlights, or in a light fitting
- on radiators and heating pipes (usually 40 – 70 °C, so within the limit of N35 to N48)
- in a car behind the windscreen in summer (can reach 70 – 90 °C)
- during welding, soldering, powder coating or in an oven
Gluing magnets? Do not cure the glue with a heat gun above 80 °C. Read more about fixing in how do you mount a magnet?
And in the cold?
Cold is not a problem: a neodymium magnet even gets slightly stronger at lower temperatures (about 0.1% per degree). Only at extremely low temperatures, below approx. −140 °C, does the behaviour of ordinary NdFeB change. For outdoor use in winter that is not relevant.
Frequently asked questions
Can I use a neodymium magnet on a radiator?
Yes. A radiator usually does not get hotter than 70 °C, which a standard N35 to N48 magnet can handle. See also attaching radiator foil with magnets.
Is a magnet that has been too hot broken?
It is not broken, but it is weaker. How much depends on how hot and for how long. Remagnetising is only possible with special equipment.
Can a magnet go in the dishwasher or boiling water?
Boiling water (100 °C) is too hot for standard neodymium and the moisture attacks the coating. See why do neodymium magnets rust?
Read also
- What is the Curie point?
- Why do magnets lose their strength?
- What do N35, N42, N48 and N52 mean?
- What is coercivity (Hc)?
Need help choosing? Use the Magnet Advisor or contact us.
