Chemical synthesis of self-assembled Ni nanoparticles and understanding of nonmagnetic layer inside their surface

To chemically synthesize mono-dispersed and self-assembled Ni nanoparticles, it was important to find the best combination of a Ni precursor and a ligand. Our Ni nanoparticles exhibited a face-centered cubic structure and superparamagnetism at room temperature. The value of saturation magnetization for our Ni nanoparticles was largely different from that of bulk Ni. Because of the relationship between the diameter and saturation magnetization per volume, the number of atoms composing the Ni nanoparticle was correlated with magnetization. This result indicated that a magnetic core/shell structure inside a Ni nanoparticle was produced. The nonmagnetic layer, as a magnetic shell of the core/shell structure, was created due to the low crystallinity of Ni nanoparticles and was composed of amorphous Ni-O states. As a result, antiferromagnetic spins arrayed in the Ni-O states were broken. Disordered spins were generated, which eventually decreased the total magnetization of the Ni nanoparticles. (C) 2015 Elsevier Ltd. All rights reserved.