Effective approach for the synthesis of monodisperse magnetic nanocrystals and M-Fe3O4 (M = Ag, Au, Pt, Pd) heterostructures

Monodisperse and size-tunable magnetic iron oxide nanoparticles (NPs) have been synthesized by thermal decomposition of an iron oleate complex at 310 °C in the presence of oleylamine and oleic acid. The diameters of the as-synthesized iron oxide NPs decrease with increasing concentrations of iron oleate complex and oleic acid/oleylamine. In addition, the size-dependent crystallinity and magnetic properties of iron oxide NPs are presented. It is found that larger iron oxide NPs have a higher degree of crystallinity and saturation magnetization. More importantly, various M-iron oxide heterostructures (M = Au, Ag, Pt, Pd) have been successfully fabricated by using the same synthesis procedure. The iron oxide NPs are grown over the pre-made metal seeds through a seed-mediated growth process. The physicochemical properties of Au-Fe3O4 heterostructures have been characterized by X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry and UV-vis spectroscopy. The as-synthesized Au-Fe3O4 heterostructures show a red-shift in surface plasmon resonance peak compared with Au NPs and similar magnetic properties to Fe3O4 NPs. The heterojunction effects present in such nanostructures offer the opportunity to tune the irphysicochemical properties. Therefore, this synthesis process can be regarded as an efficient way to fabricate a series of heterostructures for a variety of applications.