Comparison of coercivity and squareness in hot-deformed and sintered magnets produced from a Nd-Fe-B-Cu-Ga alloy

We have fabricated a hot-deformed magnet from the Fe77.1Nd11.6Pr3.7B5.1Cu0.1Co1.0Al0.9Ga0.5 alloy composition that was developed for exchange-decoupled sintered magnet. The hot-deformed magnet showed a higher coercivity, mu 0H(c) = 1.93 T, and better squareness, H-k90/H-c = 0.96, compared to those of the sintered magnet, mu 0H(c) = 1.48 T and H-k90/H-c = 0.65. Microstructural analyses revealed the higher coercivity in the hot-deformed magnet originates from a larger contribution from the anisotropy term in the Kronmuller formula owing to fine grains, while the better squareness is primarily due to the exchange coupling of the Nd2Fe14B grains through ferromagnetic grain boundary phase, as suggested by atom probe tomography and magneto-optical Kerr effect microscopy. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.