Magnetic and microstructural modification of the Nd-Fe-B sintered magnet by mixed DyF₃/DyH_x powder doping

We investigated the magnetic and microstructural properties of Nd-Fe-B sintered magnets doped with DyF₃, DyH_x, and a mixture of DyF₃ and DyH_x powders. In the DyH_x-doped magnet, diffusion of Dy occurs predominantly via grain boundary diffusion. However, the proportion of Dy being diffused by lattice diffusion is increased in the DyF₃-doped magnet due to the different influences of F ^- and H⁺ ions. The detailed mechanism of the microstructural changes in terms of the diffusional behavior of Dy induced by the DyF₃ and DyH_x powder doping is discussed. The formation of a Dy-segregated Nd-rich oxide phase (RE-rich, Dy-Nd-O) was suppressed only in the DyF₃-doped magnet, and the (00L) alignment of Nd₂Fe₁₄B grains in the sintered magnet increased when it was doped with the DyH_x powder. We obtained the optimum microstructural and magnetic properties of the Nd-Fe-B sintered magnet through doping with a mixture of DyF₃ and DyH_x powders, which compensated for the drawbacks of using each powder alone.