Prospect for HRE-free high coercivity Nd-Fe-B permanent magnets

Recent state-of-the-art microstructure investigations on Nd-Fe-B sintered magnets have revealed that the Nd2Fe14B grains in conventional sintered magnets are exchange-coupled through ferromagnetic grain boundary phase and the coercivity is governed by domain wall pinning, while exchange-decoupled sintered magnets can be processed by tuning the chemical composition to a slightly Nd-rich and B-lean one with Ga-doping. The coercivity of exchange-decoupled magnets is governed by the nucleation mechanism, giving rise to higher coercivity. Based on recent studies on microstructure-coercivity relationships of various Nd-Fe-B magnets, prospect of HRE-free high coercivity and high remanence magnets is discussed. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.