Synthesis and characterizations of Ni–Fe@spinel oxide core–shell nanoparticles

Core–shell Ni–Fe@ferrite nanoparticles with an average diameter of 14 nm and shell thickness of 3 nm were synthesized through a redox-transmetalation process. The alloy core and spinel oxide shell were verified by X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy. The hydrophobic oleylamine molecules on the surface were replaced by hydrophilic meso-2,3-Dimercaptosuccinic acid to make the nanoparticles to be water-soluble. X-ray diffraction study of the as-prepared core–shell nanoparticles indicates that they remained face centered cubic alloy core and spinel shell form in air. Magnetic measurements indicate that the core–shell nanoparticles exhibit superparamagnetic and exchange bias characteristics at 300 K and 5 K, respectively.