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

The intimate relationship in transition-metal oxides between stoichiometry and physiochemical properties 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 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 oxide

Depth-resolved studies of layered magnetic nanostructures using 57Fe probe layers and Mössbauer spectroscopy

AbstractAn atomic-scale quantitative analysis of the structural and magnetic properties of surfaces, interfaces and complex nanostructures is of fundamental relevance for the development of new materials for spintronics. Studies of buried magnetic interfaces and depth-resolved measurements in layered magnetic nanostructures are particularly challenging, and the combination of conversion electron Mössbauer spectroscopy and/or nuclear resonant scattering of synchrotron radiation with isotope-enriched probe layers can be a powerful tool in this field.The potential offered by the application of isotope-selective measurements for the study of Fe-based layered magnetic nanostructures is illustrated with our recent results on the investigation of depth-dependent spin structures and interfacial interdiffusion in exchange-biased ferromagnetic/antiferromagnetic bilayer systems and of an epitaxial magnetic system with perpendicular magnetic anisotropy, obtained from samples prepared with ultrathin 57Fe probe layers placed at different depths during the growth processes, via molecular beam epitaxy or sputtering deposition

Structural change and heteroepitaxy induced by rapid thermal annealing of CaF/sub 2/ films on Si(111)

In this article we show that heteroepitaxial CaF2 films can be induced on Si~111! with a rapid thermal anneal. The change from preferentially oriented polycrystals to a single crystal with type- B epitaxy is visible by different structural techniques. The x-ray photoelectron spectroscopy results indicate the presence of a reacted layer at the CaF2 /Si interface with a pronounced increase of fluorine atoms at this interface. Transmission electron microscopy results show that big structural changes occur due to the thermal pulse

Structural change and heteroepitaxy induced by rapid thermal annealing of CaF/sub 2/ films on Si(111)

In this article we show that heteroepitaxial CaF2 films can be induced on Si~111! with a rapid thermal anneal. The change from preferentially oriented polycrystals to a single crystal with type- B epitaxy is visible by different structural techniques. The x-ray photoelectron spectroscopy results indicate the presence of a reacted layer at the CaF2 /Si interface with a pronounced increase of fluorine atoms at this interface. Transmission electron microscopy results show that big structural changes occur due to the thermal pulse

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

The intimate relationship in transition-metal oxides between stoichiometry and physiochemical properties 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 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 oxide