High-coercivity hot-deformed Nd–Fe–B permanent magnets processed by Nd–Cu eutectic diffusion under expansion constraint

The application of expansion constraint during the grain-boundary diffusion process using Nd70Cu30 eutectic alloy minimizes the remanence loss for the coercivity enhancement by optimizing the volume fraction of the Nd(Cu)-rich non-ferromagnetic intergranular layer. The diffusion-processed sample exhibits μ0Hc ∼ 2 T, μ0Mr = 1.36 T and (BH)max = 358 kJ m−3 at room temperature. Because of the low-temperature coefficient of coercivity, the magnet showed (BH)max ∼ 191 kJ m−3 at 200 °C, which is superior to that of Dy-containing high-coercivity sintered magnets.

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