Demagnetisation through heat

How hot a magnet can get depends on various factors:

the magnet material used (neodymium or ferrite)
the magnet's temperature type
the magnet's shape
the positioning of magnets in a group

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. 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.

Table of Contents

Types of adhesive force loss due to heat

If you heat 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 has cooled down. At a certain temperature, the so-called 'Curie temperature', there is no remanence left.

Depending on the temperature, we distinguish between three different types of loss:

Reversible loss of adhesive force

Temperature range: just above the maximum working temperature
The magnet is less magnetic while it is hot.
Once it has cooled down, it regains its original strength.
It makes no difference how often the magnet is heated and cooled down again.

Irreversible loss of adhesive force

Temperature range: significantly higher than the maximum working temperature
The magnet is weakened permanently, even after it has cooled down.
Repeated heating at the same temperature does not amplify irreversible losses.
A sufficiently strong external magnetic field can remagnetise an irreversibly weakened magnet and restore it to its original strength.

Permanent loss of adhesive force

At temperatures around the Curie temperature, the structure of permanent magnets begins to change permanently. Remagnetisation 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 magnitude of losses when it comes to irreversible losses, provided the temperature inside the magnet is the same everywhere during the heating process. If a thick magnet is briefly subjected to intense heating, the external temperature may be much higher than the maximum core temperature inside the magnet. In this case, temperature losses are dependent on the position - the magnet is therefore irregularly magnetised.

Magnet shape, the direction of magnetisation and position

Whether irreversible losses occur when a magnet is heated depends not only on the temperature type but also on the following three factors. The maximum working temperatures of the magnets are, therefore, only reference points.

Magnet shape

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:

Magnet	Diameter/height (flatness)	Stated max. working temperature	Actual max. working temperature
S-10-01-N	10	80°C	ca. 60°C
S-20-05-N	4	80°C	ca. 80°C
S-06-06-N	1	80°C	ca. 140°C

Direction of magnetisation with ring magnets

Diametrically 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.

Working temperatures of neodymium magnets

Overview of the various temperature types for neodymium magnets (from page Physical magnet data).

Temperature type	Max. working temperature	Curie temperature
N	80 °C	310 °C
M	100 °C	340 °C
H	120 °C	340 °C
SH	150 °C	340 °C
UH	180 °C	350 °C
EH	200 °C	350 °C
AH	230 °C	350 °C

* The maximum working temperatures in this table are only reference points. Magnets with N52 magnetisation have a maximum working temperature of 65 °C.

For applications with neodymium magnets at temperatures above 80 °C, we have a few special magnet types with higher working temperatures in our assortment:

Discover high-temperature magnets

Working temperatures of ferrite magnets

For higher temperatures, ferrite magnets are much more suitable. An overview of our ferrite magnets (from page Physical magnet data).

Temperature type	Max. Working temperature	Curie temperature
Y35	250 °C	450 °C

Discover ferrite magnets

Working temperatures of magnetic tapes and magnetic sheets

Temperatures below -20° C and above 85° C damage the structure of magnetic tapes and magnetic 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. Hence, they can be used without hesitation for superconductor experiments. Please keep in mind: At first, the adhesive force of a magnet will slightly increase when the temperature is reduced. Then, at temperatures below -125 °C, the adhesive force will steadily decrease. At -196 °C, only about 85-90% of the adhesive force will remain. When the neodymium magnet is brought back up to room temperature the original adhesive force will return to normal.

Ferrite magnets lose part of their magnetisation permanently at temperatures below -40 °C. Therefore, they should not be significantly cooled.

Magnetic tapes and sheets lose part of their magnetisation permanently at temperatures below -20 °C. Therefore, they should not be significantly cooled.

Additional information about magnets

In our FAQ pages, you will find a lot more information about magnets, including:

What temperatures can magnets withstand?