ANGULAR-DEPENDENCE OF COERCIVITY IN SINTERED RFEB MAGNETS

The angular dependence of the coercive field H(c) (V) is discussed as a means of studying magnetization reversal in permanent magnets. We consider H(c) (V) for permanent magnets RFeB (R = Pr, Nd) for temperatures between 4.2 and 300 K. At high temperatures, it is found that H(c) may increase by a factor 1.5-2 as V increases from 0 to pi/2. At low temperatures, in the Pr magnets, H(c) decreases as V increases from 0 to pi/4 and then increases for larger angles. Different possible mechanisms for magnetization reversal are considered and the associated angular dependences of the coercive field in single crystals are calculated. The corresponding H(c) (V) are deduced for permanent magnets from the grain orientation distribution. Better agreement with experimental data is obtained in models involving domain-wall propagation and leading to a 1/cos V dependence, or close to it, than in models involving coherent rotation. The behavior of the PrFeB magnets is not explained.