Controlling of Saturation of Magnetization of Nd–Fe–B Nanoparticles Fabricated by Chemical Method

Abstract

Nd–Fe–B oxide powders with various size distributions and structures were prepared using nitrite-based metal salts including Nd2O3, Fe(NO3)3⋅9H2O, HNO3, H3BO3, citric acid (CA), and ethylene glycol (EG) by a Pechini-type sol–gel method. Mixed oxide powders were obtained by calcination and annealing the gels. These oxides by using a reduction–diffusion process under vacuum and employing CaH2 as a reducing agent at 800 ∘C were heated to prepare Nd2Fe14B nanoparticles. The role of different EG/metal salt molar ratios on phase, morphologies, microstructure, and magnetic properties of the powders were investigated by employing XRD, FE-SEM, TEM, and VSM techniques, respectively. The results show that with an increase in EG/metal salt molar ratio, the average particle size of Nd–Fe–B oxide powders increased while the coercivity of Nd–Fe–B oxide powders decreased. The presence of excess EG/CA/metal salt molar ratio, from 2:2:1 to 50:2:1, played a role of a space-filling template or capping agent and helped initial oxide particles embedded in the gel matrix to grow as sheet-like particles. Nd2Fe14B nanoparticles can successfully be synthesized by increasing the EG/CA/metal salt molar ratio from 2:2:1 to 50:2:1. The reduced samples made of nitrite-based metal salts with a EG/CA/metal salt molar ratio of 50:2:1 had a saturation magnetization of 123 emu/g and a coercivity of 315 Oe. By controlling the ratio of precursors, the hard-phase Nd2Fe14B could be successfully synthesized.