Magnetic Properties of Nanostructured Co and Ni Synthesized by Modified NaBH4 Reduction Route

Abstract

Nanomaterials based on Co and Ni are technologically important because of their potential technological applications in recording media, catalysis, drug delivery systems, and so on. Recent research interests lie on the synthesis of Co and Ni nanomaterials by chemical synthesis, characterizations and studying for their interesting magnetic properties. In this investigation, we have focused on the synthesis of cobalt and nickel nanoparticles (NPs) in aqueous medium at ambient conditions by sodium borohydride reduction route. We have successfully stabilized the nanospheres comprising of Co and Ni by using polyethylene glycol (PEG) as capping agent. The Co and Ni nanomaterials were exhaustively characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and magnetic measurements. The phase purity and crystallite sizes were ascertained by using powder XRD method. Co and Ni NPs crystallize in face centered cubic (fcc) structure with lattice parameters (a) equal to 3.54 Å and 3.52 Å, respectively. The XRD lines were broad and indicate the fine particle nature of the materials. The estimated crystallite sizes were found to be 42 and 29 nm for Co and Ni, respectively. SEM micrograph studies show the particle sizes to be 80 and 70 nm, whereas TEM studies confirm the sizes to be 47 and 65 nm for Co and Ni, respectively. The electron micrograph studies indicate the appearance of agglomerates of the nanoparticles consisting of several crystallites. The specific magnetization versus field characteristics of Co and Ni nanoparticles shows the signature of the size and surface effects. The values of saturation magnetizations are found to be 122 and 47 emu/g, whereas the coercivity values are 111 Oe and 84 Oe for Co and Ni, respectively. In summary, we have synthesized high moment Co and Ni nanostructured materials with reduced coercivities, which may be useful for soft magnetic applications.