Effect of very small additions on the coercivity of Dy-free Nd-Fe-(Co)-B-sintered magnets

The effect of small substitutions on the coercivity of Nd-Fe-B and Nd-Fe-Co-B-sintered magnets has been investigated. Addition of 0.18 at% Ga was found to be the most effective for improving the coercivity in both Nd-Fe-B and Nd-Fe-Co-B without decreasing much the remanent magnetization, Scanning electron microscopy on Ga-free and Ga-added magnets did not reveal a noticeable difference in phase morphology. However, Fe and especially Co concentrations in the intergranular Nd-rich phase were found to be markedly increased after the small Ga addition. Combined addition of Co with a small amount of Cu did not increase the coercivity of the Dy-free magnets, However, none of the examined very small additives can yet be considered as an alternative to Dy for extending operating temperature range of the high-energy Nd-Fe-B magnets. (C) 2002 Elsevier Science B.V. All rights reserved.