Origin of the large dispersion of magnetic properties in nanostructured oxides: FexO/Fe3O4 nanoparticles as a case study

M. ESTRADER; A. LÓPEZ-ORTEGA; I.V. GOLOSOVSKY; S. ESTRADÉ; A.G. ROCA; G. SALAZAR-ALVAREZ; LLUÍS LÓPEZ-CONESA; D. TOBIA; E. WINKLER; J. D. ARDISSON; W. A. A. MACEDO; A. MORPHIS; M. VASILAKAKI; K.N. TROHIDOU; A. GUKASOV; I. MIREBEAU; O.L. MAKAROVA; R.D. ZYSLER; F. PEIRÓ; M. BARÓ; L. BERGSTRÖM; J. NOGUES

Nanoscale

Royal Society of Chemistry

Año: 2015 vol. 7 p. 3002 - 3015

2040-3364

The intimate relationship between stoichiometry and physicochemical properties in transition-metal oxides makes them appealing as tunable materials. These features become exacerbated when dealing with nanostructures. However, due to the complexity of nanoscale materials, establishing a distinct relationship between structure-morphology and functionalities is often complicated. In this regard, in the FexO/Fe3O4 system a largely unexplained broad dispersion of magnetic properties has been observed. Here we show, thanks to a comprehensive multi-technique approach, a clear correlation between the magneto-structural properties in large (45 nm) and small (9 nm) FexO/Fe3O4 core/shell nanoparticles that can explain the spread of magnetic behaviors. The results reveal that while the FexO core in the large nanoparticles is antiferromagnetic and has bulk-like stoichiometry and unit-cell parameters, the FexO core in the small particles is highly non-stoichiometric and strained, displaying no significant antiferromagnetism. These results highlight the importance of ample characterization to fully understand the properties of nanostructured metal oxides.