Limits of grain boundary engineering in nanocrystalline Nd-Fe-B melt-spun ribbons

Abstract Grain boundaries in rapidly quenched Nd-Fe-B melt-spun ribbons are of major importance for achieving superior coercivity. Using the so-called grain boundary diffusion process (GBDP) initiated by the electrophoretic deposition (EPD) of DyF3, we have improved the coercivity for 8 %, while the remanence remained almost unchanged. Coercivity-improvement is attributed to higher magnetocrystalline anisotropy of Dy-rich regions, which were detected in outer parts of the Nd–Fe–B grains. Electron microscopy study revealed significant limitation hindering the diffusion efficiency; thin and dry grain-boundaries.