Stabilizing magnetic order of cobalt-based anisotropic nanoparticles prepared using NaBH4 as a reducing agent

Abstract

A one-pot chemical method was used to prepare cobalt nanoparticles (Co NPs) by employing sodium borohydride (NaBH₄) as a reducing agent, as well as graphite and activated carbon as stabilizer materials. The resulting NPs were characterized by XRD, FE-SEM, EDX mapping and VSM measurements before and after annealing under a mixture of argon and hydrogen atmosphere at 600 ℃, in order to study their structural, morphological, and magnetic properties. This study focused on the shape and size of Co NPs, involving the formation of Co and Co₃O₄ phases with the effect of oxygen as the main factor that can significantly contribute to the magnetic anisotropy. Co NPs exhibited a high saturation magnetization (M_s) value after performing the annealing process, achieving M_s> 99 emu/g when using the graphite stabilizer. The results indicate that surface atoms play a significant role in the modification of magnetic characteristics of Co NPs.