How Does Heat Affect Neodymium Magnets?   
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How Does Heat Affect Neodymium Magnets?

Posted on July 17, 2017

A key property for stable magnet materials is to keep all of its domain atoms rotate in the same direction. When the magnets are exposed to heat, the balance between temperature and magnet atoms are disturbed affecting their magnetic properties. In other words, the tiny magnetic atoms act like tiny magnets themselves and together to form a large magnetic force field. When they are oriented randomly in different directions, the total magnetism is zero. The higher the temperature, the magnet domains move faster and become more disordered. Depending on the degree of elevated temperature, a magnet can be temporarily decrease its strength or permanently damaged. On the contrary, cooling the magnet can cause the magnet to have a stronger magnetic field with the magnet atoms having less vibration and the magnetic field becoming more steadily concentrated in a given direction. Bringing the magnet sudden to hot environment, however, it can experience thermal shock and become more physically vulnerable.

Neodymium Magnet Domains

Figure: Magnet domains aligned at room temperature (left) and at high temperature (right).

Neodymium magnets have a range of grades with different maximum working temperature and Curie temperature. See below for guidance.
Neodymium Magnet Grades Max. Working Temp (oC) Curie Temp (oC)
N 80 310
M 100 340
H 120 340
SH 150 340
UH 180 350
EH 200 350
AH 230 350

Curie temperature, named after a French physicist Pierre Curie, is the temperature at which the magnetic atoms can no longer be aligned in their spin direction and angle permanently, and the ferromagnetic (having magnetic attraction) property of the magnet material becomes paramagnetic (having magnetic attraction only when there are external magnetic fields). This paramagnetic conversion or demagnetization is irreversible even when the neodymium magnets have been cooled. Neodymium magnets have relatively lower Curie temperatures (~310-340 oC) as compared to other kinds of magnet materials (~800 oC for Sm2Co17, ~450 oC for ceramic magnets). Keep this magnetic property in mind when you design and select materials for your high temperature applications.