Magnetic properties and phase evolution of sintered Nd-Fe-B magnets with intergranular addition of Pr–Co alloy

• The improved thermal stabilities of coercivity and remanence were obtained.
• An abnormal remarkable recovery of coercivity was found.
• The evolution of Co-containing phases was clarified.

The magnetic properties, thermal stability and phase evolution of sintered Nd-Fe-B magnets with intergranular addition of Pr–Co were investigated. The thermal stabilities of coercivity and remanence were simultaneously enhanced without heavy rare earth elements, resulting from the partial substitution of Pr for Nd and Co for Fe in matrix phase, respectively. After Pr–Co addition, RE-rich phase reduced and new phases containing Pr and Co, such as (NdPr) (FeCo)2 (NdPr)3(FeCo) and (NdPr)2(FeCo)17 phases, were formed. With the increase of Pr–Co addition amount, intrinsic coercivity firstly decreased sharply which was mainly caused by the formation of soft ferromagnetic (NdPr) (FeCo)2 phase, and subsequently presented a remarkable recovery induced by the formation of non-magnetic (NdPr)3(FeCo) phase and transformation of (NdPr) (FeCo)2 phase from ferromagnetic to non-magnetic. Due to the reduction of matrix phase proportion, the remanence decreased monotonously after the addition of Pr–Co for more than 10 wt. %.