Zero thermal expansion permanent magnet: an innovative exploration in permanent magnet research

Abstract

Zero thermal expansion (ZTE) materials offer unparalleled dimensional stability, thermal stress resistance, and thermal shock resilience, making them indispensable in precision engineering and demanding industrial applications. Precise thermal expansion tuning was achieved using LaFe_11.2−xCo_xSi_1.8 (x = 1.0–1.3) negative thermal expansion compensators, where 20 wt% LaFe_9.9Co_1.3Si_1.8 incorporation yielded near-ZTE characteristics exhibiting low thermal expansion coefficients (2.14 vs. 0.35 × 10⁻⁶ K⁻¹, parallel to pressing direction vs. perpendicular) within 308–348 K. The dual-component strategy (10 wt% LaFe_10.2Co_1.0Si_1.8 + 10 wt% LaFe_9.9Co_1.3Si_1.8) achieved record-low thermal expansion coefficients (1.02 vs. 0.20 × 10⁻⁶ K⁻¹), representing 52.3% and 42.9% reductions over single-component, respectively. This method enables a 65 K operational window (283–348 K), surpassing previous composites (40 K) with a 62.5% broader window while maintaining 1.52 T coercivity. The presence of an amorphous intergranular phase enables ZTE in the hot-pressed Nd–Fe–B/La–Fe–Co–Si hybrid magnet, demonstrating broad temperature window operational stability. This breakthrough bridges the long-standing gap between dimensional stability and magnetic performance in permanent magnets.