98 CHAPTER 11. MAGNETIC ANISOTROPYobtained in this way for several permanent-magnet materials by Strnat (1988) are shown in
Fig. 11.3.
Measurements of can be helpful for obtaining an estimate of Suppose that the
spontaneous polarization of the material is held in equilibrium by a field H normal to the
preferred direction, such that is inclined at an angle and hence at an angle with
respect to H. The magnetic field H then exerts a torque that tends to increase
The torque tending to return to the preferred direction is obtained by differentiating the
expression for the anisotropy energy