Comparison of (Pr, Nd)H x grain boundary restructuring and diffusion on the magnetic properties of Nd–La–Ce–Fe–B sintered magnet

Highlights: • Effects of (Pr, Nd)H_x GBR and GBDP into LaCe-40 sintered magnets are compared. • (Pr, Nd)H_x GBR reduces the remanence drastically due to massive REFe₂ formation. • (Pr, Nd)H_x GBDP yields a threefold coercivity due to the surface magnetic isolation. • Critical role of surface magnetic isolation to enhance the coercivity is highlighted. -- Abstract: Exploiting high-performance 2:14:1-type permanent magnet at high La–Ce substitution level remains a bottleneck concern due to the severe magnetic dilution from inferior intrinsic magnetism and microstructural deterioration. In present work, to promote the La–Ce application, (Pr, Nd)H_x is introduced into LaCe-40 sintered magnet (La–Ce/TRE = 40 wt%, TRE: total rare earth) through two approaches, grain boundary restructuring (GBR) and grain boundary diffusion process (GBDP). Results show that (Pr, Nd)H_x GBR leads to a twofold coercivity by optimizing the distribution of GB phase and forming a Pr/Nd-rich magnetically hardening shell. However, the remanence is lowered drastically due to massive formation of REFe₂ phase during high-temperature sintering. Comparably, (Pr, Nd)H_x GBDP magnet with an identical average composition to GBR one yields a nearly threefold coercivity without sacrificing the remanence, ascribing to the formation of more continuous RE-rich GB layer and thicker Pr/Nd-rich shell near the surface region. Above comparative study highlights the crucial role of surface magnetic isolation in enhancing the coercivity of Nd–La–Ce–Fe–B sintered magnet, and delights the prospect of abundant La–Ce for industrial application.