The maximum temperature at which a magnet will be effective depends greatly on the permeance coefficient, or "Pc" of the material. The Pc is a function of the magnetic circuit in which the magnet operates. The higher the Pc (the more "closed" the circuit), the higher temperature at which the magnet can operate without becoming severely demagnetized. Shown here are approximate maximum operating temperatures for the various classes of magnet material. At temperatures, close to those listed below, special attention may be needed in order to ensure that the magnet will not become demagnetized.
Magnets function at different levels of efficiency given different circuits that they operate in. The more closed the circuit the magnet is operating in, the more stable it is, and the less effect temperature will have on it.