Influence of Nb Doping on Magnetic Properties of Nanocrystalline Nd-Fe-B Alloys

The influence of Nb doping was studied on ribbons of nominal composition Nd_yFe_86-x-yB₁₄Nb_x (y = 7, 8; x = 0, 2, 4). The alloys were prepared by melt-spinning and then annealed at 973 K for 20 minutes. The magnetic characterization revealed that niobium addition improves substantially the magnetic properties of the studied alloys. The structural characterization showed that, in most alloys, the magnetically hard phase Nd₂Fe₁₄B precipitated as the main phase. This was not the case for the ternaries (x = 0) and for the Nd₇Fe₇₇B₁₄Nb₂ alloys. Furthermore, the addition of Nb inhibited the precipitation of α-Fe, independently of the Nd content. From the complete set of samples studied in this work, we found that the sample with nominal composition Nd₈Fe₇₄B₁₄Nb₄ exhibited the highest coercive field H_C = 575 kA/m while Nd₇Fe₇₅B₁₄Nb₄ showed the highest maximum energy product, (BH)_max = 73 kJ/m³.