Non-equilibrium nanostructured permanent magnets with excellent magnetic properties over an exceptionally wide temperature range

Abstract

Space exploration demands lightweight high-performance permanent magnets that are fully functional in a wide temperature range of 2∼450 K. However, Nd-Fe-B permanent magnets, which have the strongest room-temperature magnetic properties, are unsuitable for such applications because of their degraded performance at both elevated and cryogenic temperatures. It is well-established that substituting praseodymium enhances the low-temperature properties of these magnets, while cobalt substitution improves high-temperature stability. However, using conventional manufacturing techniques, it is virtually impossible to replace more than 10 % of iron with cobalt without a significant reduction in coercivity. Herein, we propose a non-equilibirum nanostructuring strategy, which is implemented by co-doping Pr and Co to attain a non-equilibrium microstructure with Co supersaturation in the matrix to overcome both the upper and lower temperature limitations. We constructed phase diagrams and operational temperature maps to determine the optimal composition and production temperature, resulting in a (Nd_0.2Pr_0.8)_13.6(Fe_0.75Co_0.25)_80.4Ga_0.5B_5.5 heavy-rare-earth-free permanent magnet with the desired properties. The operational temperature range is broadened from 135–350 K for ternary Nd-Fe-B magnets to 2–450 K for the (Nd_0.2Pr_0.8)_13.6(Fe_0.75Co_0.25)_80.4Ga_0.5B_5.5 magnet. The microstructural characterizations and micromagnetic simulations highlight the significance of non-equilibrium microstructures in this magnet, whereas the supersaturation of Co in the matrix and the suppression of unfavorable soft-magnetic phases are critical to realizing superior magnetic properties. The new non-equilibrium magnet plug the gap of high-performance magnet for space explorations, and the non-equilibrium nanostructuring strategy offers new possibilities for designing magnets with unprecedented properties.