Dependence of the composition, morphology and magnetic properties with the water and air exposure during the Fe1-yO/Fe3O4 core–shell nanoparticles synthesis

The thermal decomposition of organometallic precursors in the presence of surfactants and a long-chain alcohol is a valuable method to synthesize magnetic nanoparticles (MNPs) because it provides good control of the final morphology and crystallinity of the magnetic material. These parameters, and consequently the magnetic properties, depend on several details of the experimental procedure of chemical synthesis. We have studied the role of the pre-decomposition step, heating the system to 373–393 K in inert gas flux, on the final composition and morphology of the system. By adding this intermediate step, we were able to produce MNPs with a Fe1-yO/Fe3O4 core–shell structure and sizes of 20–25 nm. When the same synthesis protocol was used skipping the pre-decomposition stage, monophasic MNPs of 11 nm with ferrite structure were obtained. These differences in the composition have a major effect on the resulting magnetic properties of MNPs, and are related to some by-reactions in the synthesis solution during the preparation procedure.The authors acknowledge the financial support of the Argentinian Agencia Nacional de Promoción de Ciencia y Tecnológica (ANPCyT) through the project nos. PICT-2016–0288 and PICT-2018–02565. The authors also thank the Universidad Nacional de Cuyo (UNCuyo) by the financial support through the project nos. 06/C527 and 06/C528. The authors also acknowledge the support of the EU commission under the grant H2020-MSCA-RISE-2016, SPICOLOST project no. 734187. GFG thanks the Spanish Ministerio de Ciencia, Innovación y Universidades by the partial financial support through project PID2019-106947RB-C21.Peer reviewe