Microstructure of core-shell NdY-Fe-B sintered magnets with a high coercivity and excellent thermal stability

We developed the NdY-Fe-B sintered magnet by effective microstructure modification, which exhibits an excellent thermal stability of coercivity with 15 at.% Nd substituted by Y. The feature of microstructure and its inherent link with the magnetic configurations were comprehensively investigated by experimental and micromagnetic simulation approaches. Microstructure analysis confirmed that the novel inhomogeneous distribution of Y in the core and shell regions of the grains was obtained in the whole magnets, contributing to the magnetic hardening of the grain surface areas. TEM observation indicates the tendency of Y depletion in grain boundary (GB) phases, which permits the significantly formation of Nd6Fe13(Ga,Cu)(1) phase in the post-annealing magnet, accompanying with the optimization of intergranular GB phase distribution. The thick and Nd-riched intergranular GB phases play a significant role in magnetic isolating the adjacent grains and thus gives rise to a remarkable coercivity increase from 1.16 to 1.72 T. In addition, since the weakened temperature dependence of the magnetocrystalline anisotropy field, the substitution of Nd by Y effectively relieves the deterioration of the coercivity with temperature increasing. Relying on the combined effect of Y substitution on microstructure and intrinsic properties, a low absolute value (0.548%/degrees C) of the temperature coefficient (20-120 degrees C) of the coercivity is achieved. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.