Types of Temperature Losses of Magnets (= 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.
Temperature 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. Types of Temperature Losses of Magnets
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. Types of Temperature Losses of Magnets