Erbium: key to simultaneously achieving superior temperature-stability and high magnetic properties in 2 : 17-type permanent magnets

Abstract

To address the demands of rapidly advancing precision instruments requiring higher efficiency and miniaturization, permanent magnets must exhibit exceptional energy density, temperature stability, high magnetic energy product [(BH)_max], and adequate coercivity (H_cj). Herein, we design rare earth Er-based magnets (2 : 17-type Er-magnets) with a composition of (Er, Sm)(Co, Fe, Cu, Zr)_7.6. Erbium-based compounds (Er₂Co₁₇) offer a unique combination of temperature compensation and high saturation magnetization compared to other heavy rare earth elements, resulting in 2 : 17-type Er-magnets with superior temperature stability in B_r and (BH)_max. Partially substituting Sm reduces the energy barrier for the 2 : 17H-to-2 : 17R phase transition, promoting the development of a complete cellular structure and achieving enhanced coercivity. Notably, the optimal performance is obtained with Er constituting 60% of the total rare earth content, delivering a near-zero temperature-coefficient for B_r and (BH)_max within 20–150 °C while maintaining B_r at 8.92 kG, H_cj at 29.83 kOe, and (BH)_max at 18.5 MGOe. These 2 : 17-type Er-magnets provide valuable insights for developing permanent magnets with exceptional comprehensive properties.