What does the term maximum operating temperature (Tmax) mean?
The maximum operating temperature is exactly what it sounds like: it is the maximum temperature at which a given type of magnet can operate before it becomes permanently demagnetized.
All permanent magnets weaken in proportion to their temperature coefficient, but as long as the maximum operating temperature is not exceeded, this loss is fully recoverable on cooling. If the maximum operating temperature is exceeded, the losses are not fully recovered on cooling. Repeatedly heating a magnet above its maximum operating temperature and cooling it again will demagnetize the magnet considerably.
Neodymium magnets work best at cold temperatures down to about -130C. Standard neodymium magnets retain their magnetism at operating temperatures up to 80C, while various grades of neodymium magnets can operate at temperatures up to 230C.
