Effect of Rare-Earth Dopant on Coercivity of Hot-Pressed Nd–Fe–B Magnet Doped With RF3

An RF₃ (R = La, Ce, Pr, Nd, and Dy)-doped Nd_13.6Fe_73.6Co_6.6Ga_0.6B_5.6 hot-pressed magnet was prepared using melt-spun flakes. The substitution of Nd in Nd-Fe-B flakes by rare-earth dopant in the hot-pressed magnets doped with various RF₃ and its effect on coercivity were investigated. In the RF₃-doped Nd_13.6Fe_73.6Co_6.6Ga_0.6B_5.6 magnet hot pressed at the modest temperature (735 °C), the dopants Ce, Pr, Nd, and Dy actively substituted Nd in the region near the flake surface to form the thin shell in the flake. RF₃ (R = Dy, Nd, and Pr) doping achieved significant coercivity enhancement in the hot-pressed magnet, and it was attributed to the enhanced anisotropy field of the Nd₂Fe₁₄B-type grains (for Dy and Pr doping) and grain boundary restructuring (for Nd doping) in the shell. The most profound coercivity enhancement as high as 5 kOe was achieved in the DyF₃-doped magnet. Doping with the light rare-earth elements using RF₃ (R = La and Ce) led to poor coercivity enhancement with respect to the RF₃ (R = Dy, Nd, and Pr) doping.