Shell-Mediated Control of the Surface Chemistry in Highly Stoichiometric Magnetite Nanoparticles

LAVORATO GABRIEL C.; RUBERT ALDO A; YUTAO XING; RAJA DAS; JOSHUA ROBLES; F. JOCHEN LITTERST; ELISA BAGGIO-SAITOVITCH; MANH-HUONG PHAN; HARIHARAN SRIKANTH; CAROLINA VERICAT; FONTICELLI, MARIANO H.

Nanoscale

Royal Society of Chemistry

Año: 2020

2040-3372

Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4 nanomaterials gradually oxidize to maghemite (γ-Fe2O3) under conventional environmental conditions leading to changes in their functional properties that determine their outcome in many applications. Here we propose a novel strategy to control the surface chemistry of monodisperse 12 nm magnetite nanoparticles by means of a 2.5 nm-thick Zn-ferrite epitaxial coating in core/shell nanostructures. We report a combined Mössbauer spectroscopy, dc magnetometry, x-ray photoelectron spectroscopy and spatially-resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4 core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that the aged iron oxide nanoparticles consist of a mixture of γ-Fe2O3 and Fe3O4, while the Zn-ferrite-coated Fe3O4 cores preserve a highly stoichiometric magnetite core. Aged core/shell nanoparticles maintain the magnetic properties of Fe3O4 and present a sharp Verwey transition, an increased saturation magnetization and the possibility of tuning the effective anisotropy through the exchange-coupling at the interface. The inhibition of the oxidation of the Fe3O4 cores can be accounted for in terms of the chemical nature of the shell layer and the epitaxial crystal symmetry matching between core and shell.