The Impact of Temperature on Magnet Characteristics

The Impact of Temperature on the Strength of Neodymium Magnets

Despite their immense magnetic force, neodymium magnets do not have high resistance to extreme temperatures. Therefore, it is necessary to pay close attention to this, as exceeding temperatures can change the operational characteristics or even completely destroy the magnet. Heat is particularly harmful to them - they begin to lose their magnetic properties at temperatures around 82°C. Their Curie temperature is also low, at 320°C, which is insufficient for many applications. Some manufacturers produce special neodymium magnets capable of withstanding higher temperatures. On the other hand, cold temperatures are much better for them; -138°C allows their use in various devices.

Heating neodymium magnets always results in a decrease in their strength. However, there are two types of power loss:

• constant

• state

Temporary Power Loss

If the temperature of the magnet does not exceed the maximum working temperature, the magnet will only temporarily lose some of its strength. After cooling to room temperature, its strength is fully restored. In the case of temporary loss of strength, the magnet typically loses 5-10% of its original strength at higher temperatures. The frequency of heating and cooling the magnet has no effect on the durability of power loss.

Permanent Power Loss

After exceeding the maximum working temperature, the magnet will remain weaker even after cooling. The higher the temperature the magnet reaches, the greater the permanent loss of its strength. Once the Curie temperature is reached (usually around 300°C), the magnet loses 100% of its strength. Repeated heating to the same temperature will not cause greater strength loss. It doesn't even matter how long the magnet was heated.However, even after a permanent loss of strength, the magnet is not completely lost, and its strength can still be restored by remagnetizing it if placed in a strong magnetic field.

Thermal resistance of NdFeB magnets

The heat resistance of neodymium magnets may vary depending on the specimen. The main factors affecting the maximum working temperature and Curie temperature are:

• Magnet material

• Magnet shape

• Other magnets and magnetic metals nearby

Material

The material of neodymium magnet is usually denoted by an abbreviation (e.g., N38SH):

• N indicates neodymium magnet

• XX is a two-digit number from 27 to 55, indicating the strength of the magnet. The higher the number, the stronger the magnet. (Scientifically speaking, this is the maximum energy product in MGOe units)

• At the end, there may be 1 or 2 letters (PP), indicating the magnet's temperature resistance.

Magnet shape

Even if magnets are made of the same material, different dimensions can cause different maximum operating temperatures. Thicker magnets typically have better temperature resistance than thinner ones. Similarly, magnets in the shape of a cube or a circle behave similarly. The size of the magnet itself does not matter for the thermal resistance of the magnet; only the ratio of its dimensions matters. Cylindrical magnets magnetized diametrically (poles on the sides, not on the flat sides) often have low temperature resistance. If they are to be exposed to high temperatures, we recommend testing them before use.

Around the magnet

All previous calculations assume that there are no other magnets or magnetic metals near the magnet.
If the magnet is exposed to the influence of an opposing magnetic field (repelled by another magnet), it loses its strength even at lower temperatures. If the external magnetic field has the same direction as the magnet's field (for example, it is placed on another magnet), its temperature resistance increases, quite the contrary.
If the magnet adheres to steel or another ferromagnetic material, its maximum operating temperature will be slightly reduced.

Low Temperatures

vThe lower the temperature, the stronger the magnet. This also applies to very low temperatures down to -130°C. After cooling below -130°C, the magnet begins to lose its strength. Upon heating to room temperature, the strength returns to its original value. If the temperature suddenly rises, the magnet may crack due to uneven thermal expansion. Neodymium magnets can be cooled with liquid nitrogen without damage. Reheating and cooling the magnet does not affect its strength.

Samarium-Cobalt Magnets

Samarium-cobalt magnets perform very well at extreme temperatures, both low and high ranges. Manufacturers commonly use them in designing motors in automotive and aerospace industries because their maximum operating temperature can reach up to 350°C. The Curie temperature varies depending on the type of magnet and ranges between 700°C and 800°C, making this magnet highly resistant to potential operating condition exceedances. Manufacturers specify minimum operating temperatures around -60°C, which is a good result compared to other magnets.

Magnesy ceramiczne

Ceramic magnets are relatively brittle due to the material used, hence they poorly withstand very low temperatures as they can simply crack, leading to damage. Unlike other types of magnets, they are more prone to demagnetization at low temperatures and less so at high ones. Due to these properties, they are commonly used in places where other magnets fail because it is too hot. Their maximum operating temperature is around 250°C, while the Curie temperature is about 450°C. However, the loss of magnetic properties occurs when operating conditions drop below minus 60°C.