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

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

Nanoscale

Royal Society of Chemistry

Año: 2020 vol. 12 p. 13626 - 13636

2040-3364

Magnetite (Fe3O4)nanoparticles are one of the most studied nanomaterials for differentnanotechnological and biomedical applications. However, Fe3O4nanomaterials gradually oxidize to maghemite (γ-Fe2O3)under conventional environmental conditions leading to changes in theirfunctional properties that determine their performance in many applications.Here we propose a novel strategy to control the surface chemistry ofmonodisperse 12 nm magnetite nanoparticles by means of a 3 nm-thick Zn-ferriteepitaxial coating in core/shell nanostructures. We have carried out a combinedMössbauer spectroscopy, dc magnetometry, x-ray photoelectron spectroscopy andspatially-resolved electron energy loss spectroscopy study on iron oxide and Fe3O4/Zn0.6Fe2.4O4core/shell nanoparticles aged under ambient conditions for 6 months. Ourresults reveal that while the aged iron oxide nanoparticles consist of amixture of γ-Fe2O3 and Fe3O4, theZn-ferrite-coating preserves a highly stoichiometric Fe3O4core. Therefore, the aged core/shell nanoparticles present a sharp Verwey transition,an increased saturation magnetization and the possibility of tuning theeffective anisotropy through the exchange-coupling at the core/shell interface.The inhibition of the oxidation of the Fe3O4 cores can beaccounted for in terms of the chemical nature of the shell layer and anepitaxial crystal symmetry matching between the core and the shell.