Coercivity Mechanism in Nd-Fe-B Nanoparticles Synthesized by Reduction-Diffusion Process

Abstract

Nd-Fe-B gel was prepared by employing the precursors of chloride-based metal salts including NdCl3⋅6H2O, FeCl3⋅6H2O, H3BO3, citric acid, and ethylene glycol. Mixed oxide powders were fabricated by subsequent annealing. The oxide powders were reduced at 800 °C in Ar + H2 atmosphere for different times (2, 5, 10, 15, and 24 h) to prepare Nd2Fe14B nanoparticles. The role of reduction time in phase, morphologies, microstructure, and magnetic properties of the final powders was investigated by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM) techniques, respectively. The results show that the Nd2Fe14B phase was formed successfully at higher reduction times (15 and 24 h), and the average size of reduction-treated products was less than 220 nm. The magnetic properties were fluctuated with an increase in reduction time at a reduction temperature of 800 °C. The samples reduced for 15 h had a maximum coercivity of 1873 Oe, and the samples reduced for 24 h had a maximum saturation magnetization of 118.52 emu/g. A maximum squareness ratio of 0.64 was obtained by reduction for 24 h. The results show that the reduction-diffusion process at 800 °C was done successfully in higher reduction times.