Raman study of the laser-induced decomposition of ZnFe2O4 nanoparticles

ZnFe2O4 (ZFO) nanostructures are widely used systems thanks to their intriguing functional properties, which can lead to several crucial applications like magnetic hyperthermia, Magnetic Resonance Imaging (MRI) and water splitting. All of these, rely on the peculiar physico-chemical response of ZFO when exposed to different atmospheres and/or to specific ambient conditions. In this frame, it is important to monitor and control the ZFO response to different external stimuli and to understand the relation with their chemical, structural and defectrelated properties to avoid performance worsening. In this work, we study the laser-induced transformations of ZnFe2O4 pure and Mg-, Ga-doped nanoparticles through microRaman spectroscopy thanks to its in-situ real-time monitoring of structural and phase changes in micrometer areas of the compounds which were subjected to laser irradiation in high (3 x10-6 mbar) and low (1.5 mbar) vacuum environments. We report the occurrence of magnetite following the in-vacuum irradiation interpreted based on the sublimation of Zn cations and the subsequent reorganization of the Fe and O ions. We also report that the presence of Mg and Ga co-doping blocks the depletion of Zn-ions therefore maintaining the spinel ferrite structure. This work provides indications for the design and the synthesis of more robust Zinc Ferrite nanostructures with low or no photoinduced degradation. Moreover, it confirms the mechanism at the basis of water splitting experiments and it extends the knowledge on the fundamental instability triggers that hinder ferrite nanostructures' applications.