Textured Nd₂Fe₁₄B flakes with enhanced coercivity

Morphology, structure, and magnetic properties of the [001] textured Nd₂Fe₁₄B nanocrystalline flakes prepared by surfactant-assisted high energy ball milling (HEBM) and subsequent annealing were studied. These flakes have a thickness of 80–200 nm, a length of 0.5–10 μm, and an average grain size of 10–14 nm. The addition of some amount of Dy, Nd₇₀Cu₃₀ alloy, and an appropriate post annealing increased the coercivity _iH_c of the Nd₂Fe₁₄B flakes. _iH_c was 3.7, 4.3, and 5.7 kOe for the Nd_15.5Fe_78.5B₆, Nd₁₄Dy_1.5Fe_78.5B₆ and 83.3 wt.% Nd₁₄Dy_1.5Fe_78.5B₆ + 16.7 wt.% Nd₇₀Cu₃₀ flakes prepared by HEBM for 5 h in heptane with 20 wt.% oleylamine, respectively. After annealing at 450 °C for 0.5 h, their _iH_c increased to 5.1, 6.2, and 7.0 kOe, respectively. Anisotropic magnetic behavior was found in all of the as-milled and annealed flakes. Both, the thickening of Nd-rich phase at grain boundaries via diffusion of Nd₇₀Cu₃₀ and the surface modification of the Nd₂Fe₁₄B flake could be the main reasons for the coercivity enhancement in the as-milled and annealed Nd₇₀Cu₃₀-added Nd₂Fe₁₄B flakes.