Hydrothermal Synthesis of Nd–Fe–B Nanoparticles with Enhanced Magnetic Properties by Nd Content Tunning and Dy Doping

This paper reports a novel, facile and low-energy consumption chemical method to synthesise Nd–Fe–B and Dy-substituted Nd–Fe–B magnetic nanoparticles with enhanced magnetic properties. Nd x Fe 95- x B 5 (15≤ x ≤ 40) and Nd 35- y Dy y Fe 60 B 5 (0≤ y ≤8) magnetic nanoparticles were synthesised using a hydrothermal method, followed by a reduction-diffusion annealing process. We carried out a detailed experimental study of the effects of Nd content and Dy substitution on the phase assemblage and magnetic properties in the two systems. The results indicated that the coercivity of the Nd–Fe–B powders increased with increasing Nd content, and the maximum coercivity measured was 262.5 kA/m for Nd 40 Fe 45 B 5 (by weight percentage). Conversely, the saturation magnetisation decreased with increasing Nd content. When the addition of Dy was less than 8 wt%, both the coercivity and the saturation magnetisation varied monotonically with the amount of Dy added, and a coercivity of 548.9 kA/m was measured for Nd 27 Dy 8 Fe 60 B 5 . The results show that hydrothermal method followed by a reduction-diffusion process is simple and economical in preparing Dy-substituted Nd 2 Fe 14 B magnetic nanoparticles, and the controllable and enhanced magnetic properties can be realised by simply adjusting the ratio of raw materials. This is also a good complement to the preparation of Nd–Fe–B nanoparticles by chemical methods.