Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe3O4–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe3O4 (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe3O4 NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe3O4 NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe3O4 NPs with inverse spinel phase were formed. The results of VSM imply that the Fe3O4–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe3O4 NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.