Synergistic grain boundary modification and magnetic hardening for coercivity enhancement in Nd-Ce-Fe-B sintered magnets with Dy[sbnd]Cu addition

Abstract

Obtaining high coercivity in bulk magnets is essential to broaden the prospects for large-scale applications of Nd-Ce-Fe-B magnets. In this work, the potential of low-cost Nd-Ce-Fe-B magnets is unlocked by improving their magnetic properties, and the coercivity enhancement mechanism is elucidated through systematic material characterization. First, by designing the substrate with RE-rich (31.2 wt%), coercivity up to 13.5 kOe was obtained in Nd-Ce-Fe-B magnets with Ce/RE = 30 wt% (RE: rare earth). Microstructural analysis revealed that the high coercivity was attributed to the formation of a continuous GB phase layer induced by the excess RE. Furthermore, by doping only 2.4 wt% DyCu, the coercivity was substantially enhanced to 19.5 kOe and the coercivity temperature coefficient (20–150 °C) achieved −0.529%/°C while the remanence was maintained at 12.0 kG. Elemental distribution analysis shows that Dy enters the matrix phase while Nd/Ce is expelled, and the additional RE further widens the GB thickness, which weakens the exchange coupling effect between adjacent grains. Moreover, Dy mainly replaces Ce rather than Nd on the grain surface, resulting in a Dy-rich shell, which greatly enhances the anisotropy field of the shell region. Magnetic domain analysis shows that GB modification and magnetic hardening effectively suppress the nucleation and cascade propagation of the reversal domains, and their synergistic enhancement of the coercivity is also verified by micromagnetic simulations.