Enhanced magnetic and structural properties of chemically prepared Nd-Fe-B particles by reduction-diffusion method through optimization of heat treatments

ABSTRACT We prepared the Nd-Fe-B particles with enhanced magnetic properties through cost-effective and facile chemical methods including spray drying and reduction-diffusion (RD) techniques. Since the RD process has considerably affected the structural and magnetic properties of Nd-Fe-B particles so the optimization of heat treatments for RD is in high demand. Different heating rates (5, 10, 20, and 30 oC/min) to reach annealing temperature (1000 oC) of RD and keeping times for the RD process were used to prepare Nd-Fe-B particles. Among them, the sample prepared at 20 oC/min heating rate (HR) with a 5 h RD time exhibited superior magnetic properties including the remanence (MR) of 125 emu/g, saturation magnetization (MS) of 140 emu/g, coercivity (HC) of 2.4 kOe and (BH)max of 10.66 MGOe. This was ascribed to the narrow particle size distribution with the average particle size of about 1.66 μm, and phase purity as well as high crystallinity at optimized HR and RD time. Because the HR was controlling the particle nucleation and growth process and keeping time could ensure the completion of the RD process. This present modified RD process will also be useful to prepare other potential hard-magnetic particles.