Improvement of Magnetic Performance of Nd–Fe–B-Type Die-Upset Magnet by RF3-Doping

Enhancement of magnetic performance of the Nd-Fe-B-type die-upset magnet by using RF<sub>3</sub> (R = Dy, Pr, Nd, Ce, La)-doping as a source of rare-earth substituent was investigated. Commercial melt-spun flakes of Nd<sub>13.6</sub>Fe<sub>73.6</sub>Co<sub>6.6</sub>Ga<sub>0.6</sub>B<sub>5.6</sub> were mixed with 1.6 wt.% RF<sub>3</sub> (R = Dy, Pr, Nd, Ce, La) powder. The mixture was hot pressed and then die upset. Coercivity of the die-upset magnet was enhanced by RF<sub>3</sub> (R = Dy, Pr, Nd)-doping without severely sacrificing magnetic performance. In the RF<sub>3</sub>-doped magnet, active substitution between the R atoms from the added RF<sub>3</sub> and the Nd atoms in the neighboring flakes occurred to form thin R-diffused shells near the surface of the flakes. Coercivity enhancement for the RF<sub>3</sub> (R = Dy, Pr)-doped magnet was largely attributed to the enhancement of the anisotropy field of (Nd, Dy)<sub>2</sub>Fe<sub>14</sub> B- or (Nd,Pr)<sub>2</sub> Fe<sub>14</sub> B-type grains in the R-diffused shell on the flake surface. Coercivity enhancement in the NdF<sub>3</sub>-doped magnet was attributed to grain boundary restructuring in the R-diffused shell region.

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