Influence of silica coating process on fine structure and magnetic properties of iron oxide nanoparticles

We present influences of silica coating process on the nanostructure and magnetic properties of superparamagnetic iron-oxide (SPIO) nanoparticles (NPs). The silica coating on SPIO NPs is done to render the composite particles suitable for biomedical applications. SPIO NPs synthesized using iron oleate in the present study are composed of an antiferromagnetic FeO core and a ferromagnetic Fe3O4 shell except NPs of 7 nm in diameter, which are a single crystal of Fe3O4. The conversion of FeO phase to Fe3O4 phase at their interface resulting from silica coating is confirmed using X-ray diffraction and magnetic measurements. The magnetic properties of SPIO NPs change with the increase in volume fraction of Fe3O4 due to the conversion from FeO by the silica coating. In addition, a temperature-dependent magnetization reveals that the magnetic interaction between the antiferromagnetic FeO and the ferromagnetic Fe3O4 influences the magnetic properties. These results suggest the strategy to obtain optimum magnetic properties of iron oxide/silica composite particles for biomedical applications.