That depends on various factors:
Neodymium magnets of the type N lose part of their magnetisation permanently at a temperature of 80 °C, tapes and sheets at 85 °C, ferrite magnets only at 250 °C.
- the magnet material used (neodymium or ferrite)
- the magnet's temperature type
- the magnet's shape
- the positioning of magnets in a group
A vigorous cool-down (e.g.
in liquid nitrogen) does not harm neodymium magnets, but ferrite magnets lose part of their magnetisation at a temperature of below -40 °C; magnetic tapes and sheets already below -20°C.
If you heat up a magnet above its so-called "maximum working temperature", it loses part of its magnetisation.
Thereafter, it adheres less strongly to an iron plate, for instance, even after the magnet is cooled down again.
At a certain temperature, the so called "Curie temperature", there is no remanence left.
Types of temperature losses (= loss of magnetisation due to high temperature)
Depending on the temperature, we distinguish between three different types of losses:
Reversible temperature loss
- Temperature area: just above the maximum working temperature
- The magnet is less magnetic as long as it is hot.
- Once it is cooled down, it regains its original strength.
It makes no difference how often the magnet is heated up and cooled down.
- Temperatur area: significantly above the maximum working temperature
- The magnet is weakened permanently, even after it is cooled down.
- Repeated heating at the same temperature does not amplify irreversible losses.
- Remagnetising an irreversibly weakened magnet through a strong enough external magnetic field can give it its original strength back.
Around the Curie temperature, the structure of permanent magnets starts to change.
Remagnetising is no longer possible.
All before-mentioned types of temperature losses are covered in the following video.
The author differentiates between "warming up" (reversible), "heating up" (irreversible) and "smouldering" (permanent).
At the end, a magnet is melted.
It is hardly a surprise that therafter it does not possess any magnetisation anymore.
Duration of heating
The duration of heating has only a minimal influence on the strength of losses when it comes to irreversible losses, given that the temperature was the same everywhere on the inside of the magnet.
When heating up a thick magnet for a short time, the outside temperature may be much higher than the maximum core temperature inside the magnet.
In that case, temperature losses are dependent on the position - the magnet is therefore irregularly magnetised.
Magnet shape, direction of magnetisation and position
Whether heating leads to irreversible losses depends not only on the temperature type of a magnet but also on the following three factors.
The maximum working temperatures are therefore only reference points.
The indicated maximum temperature is only valid when the width-to-height ratio of the magnet is "ideal." The following rule
applies: A very thin or flat (flatness = diameter divided by height) magnet already suffers irreversible losses at temperatures below the maximum working temperature.
If the ratio of diameter to height is less than 4, however, the magnet can be heated up above the maximum working temperature without losing its magnetisation.
Examples of actual maximum working temperatures of stand-alone neodymium disc magnets:
Direction of magnetisation with ring magnets
magnetised ring magnets possibly have a much lower maximum working temperature.
We recommend prior tests if the magnets will be subject to higher temperatures.
Positioning of magnets
The more a magnet in a certain position is exposed to a reverse field, the lower is its actual maximum working temperature.
The smallest temperature losses occur in arrangements where a magnet is magnetically "short-circuited" in a magnetic circuit (analogue to an electric circuit), because there is no reverse field in the magnet.
In reality however, this arrangement is rare.
Features of neodymium magnets
Overview of the various temperature types (from page Physical magnet data
* The maximum working temperatures in this table are only reference points.
Magnets with the N52 magnetisation have a maximum working temperature of 65°C.
For applications with neodymium magnets at temperatures above 80°C, we have a special magnet type with higher working temperatures in our assortment:
Features of ferrite magnets
For higher temperatures, ferrite magnets are much more suitable.
An overview of our ferrite magnets (from page Physical magnet data
Features of magnetic tapes and magnetic sheets
Temperatures under -20° C and above 85° C damage the structure of magnetic tapes and sheets.
It causes the products to permanently lose part of their adhesive force.
Therefore, do not use them in places with extremely high or low temperatures.
Does immersion in liquid nitrogen damage magnets?
Immersion in liquid nitrogen at a temperature of -196°C (77 K) does not damage neodymium magnets.
They can be used without hesitation for superconductor experiments.
Ferrite magnets lose part of their magnetisation permanently at a temperature below -40 °C.
Therefore, they should not be cooled down vigorously.
Magnetic tapes and sheets lose part of their magnetisation permanently at temperatures below -20 °C.
Therefore, they should not be cooled down vigorously.