The effect of Dy addition on the microstructure and magnetic properties of the sintered NdFeB magnets was investigated. The results of the microstructure analysis showed that Dy-free and Dy-doped samples are composed of Nd 2 Fe 14 B (P42/mnm) and a trace of Nd-rich phase. Dy addition reduces significantly the pole density factor of (004), (006) and (008) crystal faces as estimated by the Horta formula. Accordingly, the coercivity of the Dy-doped sample increases from 2038 kA·m −1 up to 2288

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... −1 . The H cj (T)/M s (T) versus /M s (T) (Kronmüller-plot) behavior shows that the nucleation is the dominating mechanism for the magnetization reversal in these two kinds of magnets, and two microstructural parameters of α k and N eff are obtained. The Kronmüller-Plot gives evidence for an increase of the α k responsible for an increase of the coercivity as the result of the increase of the magnetic field as the magnetic domain reversed.