Engineering magnetic properties of Ni nanoparticles by non-magnetic cores

Abstract

This work focuses on the magnetism-control study of nickel (Ni) nanoparticles (NPs) with nonmagnetic cores of noble metals (M=Ag, Au). Monodispersed M NPs used as templates were synthesized by reducing their salt with a weak reductant;oleylamine (OA). The OA acted as surfactant and non-coordinating reagent in the preparation of Ni NPs with a narrow size distribution. Then Ni atoms were controlled to grow upon the M NPs by controlling the decomposition of nickel acetylacetonate in OA. The as-preparedMand core/shell M/Ni NPs exhibit spherical shape, as characterized by transmission electron microscopy. The systematic study indicated that the Ni shell exhibits face-centered cubic crystal structure and is relatively stable in air. The hydrophobic OA molecules on the surface could be exchanged by hydrophilic imidazole to make the samples watersoluble. Magnetic study of core/shell NPs indicated that their blocking temperatures could be tuned by modulating either core size or shell thickness. The novel magnetic properties of the core/shell structured NPs are introduced by the size effect, exchange interaction, and reduced magnetic ordering. The novel core/shell M/Ni NPs are expected to have a significant potential for biomolecule separation, magnetic imaging, and optoelectronics. © 2009 American Chemical Society.