Influence of grain orientation of the coercive field in Fe-Nd-B permanent magnets

The nucleation field for homogeneous rotation is calculated numerically, including higher order anisotropy constants. The results are combined with a Gaussian distribution of grain orientations in order to discuss the dependence of coercivity on the degree of grain alignment. For the degree of alignment found in sintered magnets, the coercive field is seen to be reduced severely, its value being closer to the minimum nucleation field for misaligned grains than to the theoretical value for ideal orientation. An analysis of the experimental coercive field of sintered Fe-Nd-B magnets shows that the coercive field is determined by the minimum nucleation field for misaligned grains. An expression for this field is given, which for small values of K2 takes the simple form HminN =(K1 + K2)Js.