Yuqing Li

A novel (Sm,Tm) ₂ Co ₁₇ -type magnet is developed with an α of −0.008%/°C from 20 to 150 °C, while maintaining a B _r of 9.25 kG and a ( BH ) _max of 19.26 MGOe, and an optimized high-temperature process further improves H _cj by 152% to 25.03 kOe.

The grain boundary diffusion (GBD) method employing heavy rare-earth (HRE) elements effectively enhances the coercivity of sintered Nd–Fe–B magnets, yet often at the expense of the squareness factor. This trade-off remains a fundamental limitation in the pursuit of high-performance permanent magnets. Here, Al micropowder mixed with TbH₃ nanopowder was used as a diffusion source to fabricate GBD Nd–Fe–B magnets. The optimized magnets exhibit superior overall performance compared with conventional Al-free counterparts: an 8.7 kOe increase in coercivity with only 0.5 wt% Tb, a squareness factor of 0.94, a coercivity temperature coefficient of −0.495%/°C, and significantly reduced irreversible flux loss at elevated temperatures. Combined first-principles calculations, micromagnetic simulations, and experimental analyses reveal that Al promotes liquid-phase diffusion by opening HRE GBD channels, deepening Tb penetration, and mitigating concentration gradients. Moreover, Al diffuses into the main phase ahead of Tb, lowering the energy barrier for Tb incorporation and facilitating the formation of core–shell structured grains. Fine control of Al content enables the simultaneous optimization of both liquid- and solid-phase diffusion, resulting in a comprehensive improvement of magnetic performance. These findings provide valuable guidance for the development of high-performance permanent magnet materials.

The utilization of Cu micropowder as an auxiliary material presents a promising strategy to enhance the efficiency of heavy rare earth elements in grain boundary diffusion (GBD) processes.

The grain boundary diffusion (GBD) process is currently the relatively effective method for utilizing heavy rare earth (HRE) elements in NdFeB magnets, especially for magnetic sheets. However, due to a highly uneven microstructure, the recovery of GBD magnets was considered difficult. In this work, our study prioritized short-loop recycling of GBD NdFeB sheet magnets to prepare block magnets. A comparative investigation was conducted between GBD-processed NdFeB magnets and the conventional sintered magnets, with particular emphasis on their recyclability characteristics. Among them, the Tb content of GBD magnets of 0.4 wt.% was significantly lower than sintered magnets of 1.73 wt.%. When two waste magnets were supplemented with the same amount of rare earth, it was found that the coercivity of the block magnets regenerated from GBD sheet magnets was higher. Microstructural analysis revealed that the core–shell grains originally located in the surface layer of GBD magnets were uniformly mixed and diffused with the ordinary particles originally located inside during the regeneration sintering process. The regenerated GBD magnets exhibited a more uniform core–shell microstructure with submicron shells of Tb elements along with reduced areas of RE-rich phase enrichment which facilitated the formation of a continuous and uniform thin-layer grain boundary, thereby enhancing the magnetic isolation effect. Apart from the significance of recycling, these block magnets regenerated from GBD magnets also provides a new approach to solving the challenge of high coercivity and low HRE elements in bulk magnets.

Correction for ‘Erbium: key to simultaneously achieving superior temperature-stability and high magnetic properties in 2 : 17-type permanent magnets’ by Zan Long et al., Mater. Horiz. , 2025, 12 , 2999–3010, https://doi.org/10.1039/D4MH01765J.

This study investigates the significant correlation between preparation techniques, calcination temperatures, and the magnetic properties of La–Ca–Co-doped strontium ferrite. By comparing typical dry mixing and wet mixing processes and investigating the effects of different calcination temperatures, this work reveals detailed insights into how to optimize the magnetic performance of these materials. Results show that dry mixing at 1260 °C produces the largest magnetic energy product (35.4 kJ/m3) when sintered at 1225 °C, with a maximum remanence of 437 mT and coercivity of 384 kA/m. Conversely, wet mixing at 1230 °C produces the optimal magnetic performance as a coercivity of 415 kA/m, remanence of 435 mT and (BH)max of 33.4 kJ m−3 at a sintering temperature of 1215 °C. Wet mixing is better for low-temperature calcination due to reduced particle size, greater specific surface area, and lower energy needs. The dry mixing technique at 1260 °C and the wet mixing process at 1230 °C yield good magnetic characteristics for La–Ca–Co doped strontium ferrite. The importance of calcination temperatures and preparation methods on the magnetic properties of doped ferrite is highlighted in this research.