Physics of Magnetism

106 CHAPTER 12. PERMANENT MAGNETS

12.2. SUITABILITY CRITERIA

The maximum energy product is one of the most generally used criteria for characteriz­
ing the performance of a given permanent-magnet material. The magnitude of this product
can be shown to be equal to twice the potential energy of the magnetic field outside the
magnet divided by the volume of the magnet.
The maximum energy product is not the only criterion that can be used to specify the
quality of a given permanent-magnet material. Of importance in many static applications is,
for instance, the magnitude of the intrinsic coercivity This is illustrated in Fig. 12.1.1,
which compares the J(H) and B(H) curves of two different magnet materials that have
different hysteresis loops but the same remanence It follows from Eq. (8.29) that