Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles

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

Nanoscale

RSC

Año: 2020 vol. 12 p. 13626 - 13626

2040-3364

Magnetite (Fe3O4) nanoparticles are one of the most studied nanomaterials for different nanotechnological and biomedical applications. However, Fe3O4nanomaterials gradually oxidize to maghemite (γ-Fe2O3)under conventional environmental conditions leading to changes in their functional properties that determine their performance in many applications. Here we propose a novel strategy to control the surfacechemistry of monodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferrite epitaxialcoating in core/shell nanostructures. We have carried out a combined Mössbauer spectroscopy, dcmagnetometry, X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4core/shell nanoparticles aged under ambient conditions for 6 months. Our results reveal that while the aged iron oxide nanoparticles consist of a mixtureofγ-Fe2O3and Fe3O4, the Zn-ferrite-coating preserves a highly stoichiometric Fe3O4core. Therefore, theaged core/shell nanoparticles present a sharp Verwey transition, an increased saturation magnetizationand the possibility of tuning the effective anisotropy through exchange-coupling at the core/shell interface. The inhibition of the oxidation of the Fe3O4cores can be accounted for in terms of the chemicalnature of the shell layer and an epitaxial crystal symmetry matching between the core and the shell