Enhancing Coercivity of Sintered Nd-Fe–B Magnets by Nanoparticle Addition

In this paper, we investigated the influence of addition of Dy
₄₀
Nd
₄₀
Al
₃₀
nanoparticles on the structure and magnetic properties of sintered Nd-Fe-B magnets. The nanoparticles with a size smaller than 50 nm were prepared using high-energy ball milling method and then mixed with micrometer Nd
₂
Fe
₁₄
B powder before magnetic anisotropic pressing, vacuum sintering, and annealing. The structure of the magnets was thoroughly analyzed using X-ray diffraction and electron microscopy techniques. The magnetic properties of the magnets were investigated on a pulsed field magnetometer. The atoms of Dy were detected mainly at the grain boundaries and partly in the near-boundary area of the grains. On adding 2% of the nanoparticles, the coercivity of the magnets is enhanced by quite a large amount, from 12 kOe for the unadded magnets to 21 kOe for the added ones. The large increase of the coercivity is probably due to the diffusion of Dy to the Nd
₂
Fe
₁₄
B grains to form (Nd,Dy)
₂
Fe
₁₄
B phases with high magnetocrystalline anisotropy. The nanoparticles might make Dy distribute more homogeneously and diffuse to the Nd
₂
Fe
₁₄
B grains more efficiently.