Coercivity enhancement in Dy-free Nd–Fe–B sintered magnets by using Pr-Cu alloy

The grain boundary phase of Dy-free sintered Nd-Fe-B magnets is modified by using Pr68Cu32 eutectic alloy. The coercivity of the modified magnets reaches 21 kOe, which is the highest value in Dy-free Nd-Fe-B sintered magnets. Microstructural investigations show that a smooth and thick grain boundary layer is formed, and the content of the ferromagnetic elements in the grain boundary layer decreases from 65 at. % to 9 at. %. In addition, the mean grain size (4.5 μm) in the doped sintered magnets is smaller than that (6.5 μm) in the original sintered magnets. The modification in grain boundary and grain size reduces the magnetic interactions among grains and hinders nucleation of reversed magnetic domains, resulting in a coercivity enhancement.