Influence of gadolinium on microstructure and magnetic properties of sintered NdGdFeB magnets

The effect of Gd content on microstructure and magnetic properties of sintered Nd33.03−xGdxFe65.65B1.32 (x=0–2) was studied in this paper to improve the thermal stability of NdFeB and to reduce the raw material cost. The results showed that better magnet performance could be obtained by adding Gd (0–1.5 wt.%) with partial substitution of Nd in Nd33.03−xGdxFe65.65B1.32. It was also found that the Nd33.03−xGdxFe65.65B1.32 magnets showed the best performance when Gd addition increased to 1.0 wt.%. The temperature coefficient Br (α) could be improved from −0.15%/°C to −0.063%/°C (maximum work temperature 120 °C) and the Curie temperature could be improved from 315 °C to 323 °C because the Gd2Fe14B had positive temperature coefficient Br (α) and higher Curie temperature than that of Nd2Fe14B. The coercivity could be improved from 10.2 to 11.48 kOe and the microstructure was close to ideal microstructure. The magnetic performance decreased sharply by adding Gd (above 2 wt.%) with partial substitution of Nd in Nd33.03−xGdxFe65.65B1.32 because the Gd element concentrated in the grain boundaries.