Effect of Terbium addition on the coercivity of the sintered NdFeB magnets

The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction (XRD) and BH magnetometers. The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd2Fe14B (space group P42/mnm) and a trace amount of Nd-rich phase. Accordingly, addition of Tb led to a decrease of the pole density factor of (004), (006) and (008) crystal plane of the Nd2Fe14B phase calculated by Horta formula, but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition. The study of the Hc(T)/Ms(T) versus HminN/(Ms(T) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets, and the microstructural parameters of αk and Neff were obtained also. The Kronmüller-plot showed an increase of the αk responsible for an increase of the coercivity.