Coupling effects of hydrogen and Dy/Nb on magnetic properties of sintered NdFeB magnets

The magnetic-property changes in sintered NdFeB magnets with different content of Dy and Nb after electrochemical hydrogen charging (EHC) were investigated. The phases of Dy2Fe14B, NbFeB, and Fe2Nb are confirmed by energy-dispersive spectrometry (EDS) and selected area electron diffraction. The electron back-scatter diffraction (EBSD) and electrochemical test show that the amount of Nd-rich grain boundary phases as hydrogen diffusion channels and the concentration of hydrogen near the surface of the magnets increase with the addition of Dy and Nb. Before and after EHC, the surface roughness and magnetic properties were measured using a laser scanning confocal microscopy, pulsed field magnetometer and flux meter. The results revealed that the surface roughness of magnets increases, owing to the absorption of hydrogen. During EHC, the remanence (Br) remains unchanged, whereas the magnitudes of the coercivity, magnetic moment (Mt), and maximum energy density ((BH)(max)) decrease by different degrees because of the presence of Dy and Nb compounds. Hydrogen decreases the stability of the magnet in demagnetization field by reducing the critical energy required for magnetic moment rotation, nucleation of reverse domains, and expansion of domain walls, and the presence of Dy and Nb compounds exacerbates the stability. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The study showed that adding Dy and Nb increased the diffusion channels for hydrogen in the magnets, resulting in an increase in hydrogen concentration near the surface and surface roughness of the magnets. During electrochemical hydrogen charging, the magnetic properties of the magnets were affected, with coercivity, magnetic moment, and maximum energy density decreasing.