Perspective and prospects for nanostructured magnets

Abstract

Permanent-magnet materials are essential for modern technologies, such as robotics, electric vehicles, and wind power generators. Over the last 100 years, the pursuit for stronger magnets mainly lies in enhancing their coercivity by alloying different elements with Fe and Co. Despite the continued endeavor, the coercivity of state-of-the-art NdFeB and SmCo magnets can only reach 20%–25% of their anisotropy field (Ha, the theoretical limit of the coercivity), known as the famous Brown's paradox. On the other hand, abnormally high coercivity was observed in the materials consisting of nanograins that reaches ∼60% of Ha at room temperature and goes beyond 100 kOe (7957 kA/m) at low temperatures. Moreover, the coercivity of nanostructured TbFe2 increases to ∼3500 Oe (278 kA/m), although it is a soft-magnetic material with a low value of only ∼30 Oe (2.4 kA/m) at room temperature for coarse-grained counterparts. However, high-energy-product bulk nanostructured magnets still remain elusive so far. In this short Perspective paper, we briefly discuss the prospects and challenges in fabricating high-performance bulk nanostructured magnets. The perspective for coercivity increase in emerging permanent magnets such as nanocomposite magnets and SmFe12-type magnets is also discussed.