Distribution of Dy in high-coercivity (Nd,Dy)–Fe–B sintered magnet

The enhanced coercivity of Dy-substituted Nd–Fe–B-based sintered magnets is generally believed to be due to the enhanced magnetocrystalline anisotropy of the compound (Nd,Dy)2Fe14B. In this work we have analyzed the distribution of Dy in sintered (Nd,Dy)–Fe–B magnets using the three-dimensional atom probe (3DAP) technique complemented with high-resolution scanning and transmission electron microscopy. We found Dy atoms are not uniformly distributed throughout the microstructure but some Dy oxides are present. 3DAP results revealed that a nearly pure Nd layer of about 6 nm is present at some of the interfaces between the (Nd,Dy)-rich phase and the (Nd,Dy)2Fe14B phase. Like other optimally annealed sintered magnets, a thin Nd- and Cu-enriched layer was found throughout grain boundaries, in which Dy was not enriched compared with the surrounding area. Based on these newly found microstructural features, the coercivity of (Nd,Dy)–Fe–B sintered magnets is discussed.

Research highlights
► Atom probe tomography of high coercivity sintered (Nd,Dy)–Fe–B permanet magnets.
► Uniform distribution of Dy along simple grain boundaries.
► Presence of a nearly pure Nd at interface of (Nd,Dy)-rich/(Nd,Dy)2Fe14B grains.
► Presence of Dy oxides as isolated (Nd,Dy)-rich grains.