Increased coercivity in sintered Nd–Fe–B magnets with NdF3 additions and the related grain boundary phase

Enhanced coercivity was achieved by adding NdF3 to both Dy-free and Dy-containing Nd–Fe–B sintered magnets with little decrease in remanence. NdF3 reacts with the Nd-rich grain boundary phase and a new rare-earth oxyfluoride (ROF) phase with ordered face-centered cubic structure is formed. Dy was detected in the ROF phase in the Dy-containing magnet. This suggests that the increase of coercivity can be related to the ordered grain boundary phase as well as to Dy segregation.