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
₃
(R = Dy, Pr, Nd, Ce, La)-doping as a source of rare-earth substituent was investigated. Commercial melt-spun flakes of Nd
_13.6
Fe
_73.6
Co
_6.6
Ga
_0.6
B
_5.6
were mixed with 1.6 wt.% RF
₃
(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
₃
(R = Dy, Pr, Nd)-doping without severely sacrificing magnetic performance. In the RF
₃
-doped magnet, active substitution between the R atoms from the added RF
₃
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
₃
(R = Dy, Pr)-doped magnet was largely attributed to the enhancement of the anisotropy field of (Nd, Dy)
₂
Fe
₁₄
B- or (Nd,Pr)
₂
Fe
₁₄
B-type grains in the R-diffused shell on the flake surface. Coercivity enhancement in the NdF
₃
-doped magnet was attributed to grain boundary restructuring in the R-diffused shell region.