Record-High Performance 2:17-type SmCo Magnets via Fe-Driven HRE Segregation

Development of high-performance SmCo magnets, simultaneously possessing high magnetic energy product (BH)_max and low remanence temperature coefficient |α|, is critical for applications of wide-temperature precision instruments. Conventional heavy rare-earth (HRE) substitution improves temperature stability via antiferromagnetic coupling but inevitably sacrifices (BH)_max, resulting in a persistent trade-off between (BH)_max and |α|. Herein, we propose a Fe-HRE synergistic compositional-design strategy that integrates Fe enrichment and HRE segregation to break this bottleneck. First-principles calculations reveal that increasing Fe concentration provides a thermodynamic driving force for HREs segregation from the 1:5H cell boundary into the 2:17R matrix. Furthermore, molecular field simulations quantitatively demonstrate that HRE enrichment in the 2:17R phase enhances its temperature compensation effect and effectively overcomes this trade-off. Guided by these insights, a series of Sm_0.4Gd_0.6(Co_balFe_xCu_0.08Zr_0.025)_7.2 (x = 0.20-0.24) magnets are prepared. Magnetic and microstructural characterizations confirm that moderate Fe enrichment (x = 0.22) not only improves (BH)_max but also facilitates Gd segregation into 2:17R phase without microstructural degradations. These synergistic effects yield a record-high (BH)_max of 18.8 MGOe and α_20°C-300°C = -0.012%/°C. This work establishes a unified design framework integrating magnetic moment engineering with thermodynamic element distribution regulation, paving a viable path for high-temperature-stable SmCo magnets for aerospace precision instruments.