Suppression and enhancement of the ferromagnetic response in Fe-doped ZnO nanoparticles by calcination of organic nitrogen, phosphorus, and sulfur compounds

Abstract

The current study reports on the preparation of ~10–13 nm ZnO nanoparticles homogeneously doped with Fe2+ ions ((Zn0.97Fe0.03)O) and the manipulation of their ferromagnetic response at room temperature with an appropriate post-processing. The homogeneous spatial distribution of iron is studied at atomic column level through high-resolution transmission electron microscopy, high-angle annular dark field, and electron energy loss spectroscopy. Magnetization isotherms show a ferromagnetic feature within the low field region exhibiting temperature dependence. X-ray diffraction and analytical microscopy measurements are compatible with a homogeneous distribution of Fe2+ over the ZnO lattice, and discard the formation of iron or iron oxide clusters that could account for the low field ferromagnetic signal. From the temperature dependence of the susceptibility, it is inferred that Fe2+ cations do not order magnetically. Induced defects upon calcination of different organic molecules over the (Zn0.97Fe0.03)O nanoparticles in aerobic conditions lead to a significant modification of the magnetic properties, even suppressing the room temperature ferromagnetic signal originally observed. More specifically, when the heat treatment is carried out in the presence of dodecylamine, the original room temperature ferromagnetic signal is canceled, whereas an enhancement on the same ferromagnetic contribution is observed when using trioctylphosphine oxide. No significant differences have been found after calcinating 1-dodecanethiol-doped ZnO nanoparticles.