Tm-Substituted 2:17-type magnets: balancing room-temperature magnetic properties and temperature stability

Abstract

Precision instruments demand permanent magnets with exceptional thermal stability and high room-temperature performance—requirements that traditional temperature-compensated magnets struggle to meet simultaneously. We develop a Tm-substituted (Sm,Tm)₂Co₁₇ magnet that achieves an outstanding remanence temperature coefficient (α_20–150°C = −0.008%/°C), while simultaneously maintaining a high maximum energy product [(BH)_max = 19.26 MGOe], remanence (B_r = 9.25 kG), and coercivity (H_cj = 9.94 kOe) at room temperature. First-principles calculations indicate that Tm stabilizes the 2:17H phase, suppressing phase decomposition. Microstructural analysis confirms that Tm substitution retains the 2:17H phase in the final magnet, impeding the formation of a complete cellular structure and consequently weakening pinning strength and coercivity. Excessive Tm substitution also induces micron-scale Tm–Zr-rich precipitates that truncate the Zr-rich lamellae, thereby hindering Cu enrichment in the cell walls and further diminishing the pinning effect. Guided by these insights, we introduce a high-temperature processing strategy that refines the cellular structure, enhances Cu partitioning into the cell walls, and reduces residual stress. This optimization boosts coercivity to 25.03 kOe, a 152% increase. The resulting (Sm,Tm)₂Co₁₇ magnet combines outstanding magnetic performance and stability from 20 °C to 150 °C with superior room-temperature properties, offering a robust design paradigm for high-performance, temperature-compensated permanent magnets in aerospace, military, and precision-instrument applications.