Staff directory Marta Estrader Bofarull

Marta Estrader Bofarull

Visiting Postdoctoral Researcher
Magnetic Nanostructures



  • Combining X-Ray Whole Powder Pattern Modeling, Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study

    Ichikawa R.U., Roca A.G., López-Ortega A., Estrader M., Peral I., Turrillas X., Nogués J. Small; 14 (30, 1800804) 2018. 10.1002/smll.201800804.

    Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk-approach based on the combined analysis of synchrotron X-ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe3O4 core/shell nanocubes is studied at different time intervals. The results indicate that a two-phase approach (FeO and Fe3O4) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe3O4) are needed to obtain satisfactory fits, i.e., an onion-type structure. The analysis shows that the Fe3O4 phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe3O4 nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles

    Roca A.G., Golosovsky I.V., Winkler E., López-Ortega A., Estrader M., Zysler R.D., Baró M.D., Nogués J. Small; 14 (15, 1703963) 2018. 10.1002/smll.201703963.

    Although cubic rock salt-CoO has been extensively studied, the magnetic properties of the main nanoscale CoO polymorphs (hexagonal wurtzite and cubic zinc blende structures) are rather poorly understood. Here, a detailed magnetic and neutron diffraction study on zinc blende and wurtzite CoO nanoparticles is presented. The zinc blende-CoO phase is antiferromagnetic with a 3rd type structure in a face-centered cubic lattice and a Néel temperature of TN (zinc-blende) ≈225 K. Wurtzite-CoO also presents an antiferromagnetic order, TN (wurtzite) ≈109 K, although much more complex, with a 2nd type order along the c-axis but an incommensurate order along the y-axis. Importantly, the overall magnetic properties are overwhelmed by the uncompensated spins, which confer the system a ferromagnetic-like behavior even at room temperature. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


  • 3D Visualization of the Iron Oxidation State in FeO/Fe3O4 Core-Shell Nanocubes from Electron Energy Loss Tomography

    Torruella P., Arenal R., De La Peña F., Saghi Z., Yedra L., Eljarrat A., López-Conesa L., Estrader M., López-Ortega A., Salazar-Alvarez G., Nogués J., Ducati C., Midgley P.A., Peiró F., Estradé S. Nano Letters; 16 (8): 5068 - 5073. 2016. 10.1021/acs.nanolett.6b01922. IF: 13.779

    The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe2+ and Fe3+ ions in a FeO/Fe3O4 core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample. © 2016 American Chemical Society.


  • Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

    López-Ortega A., Estrader M., Salazar-Alvarez G., Roca A.G., Nogués J. Physics Reports; 553: 1 - 32. 2015. 10.1016/j.physrep.2014.09.007. IF: 20.033

    The applications of exchange coupled bi-magnetic hard/soft and soft/hard ferromagnetic core/shell nanoparticles are reviewed. After a brief description of the main synthesis approaches and the core/shell structural-morphological characterization, the basic static and dynamic magnetic properties are presented. Five different types of prospective applications, based on diverse patents and research articles, are described: permanent magnets, recording media, microwave absorption, biomedical applications and other applications. Both the advantages of the core/shell morphology and some of the remaining challenges are discussed. © 2014 Elsevier B.V.

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

    Estrader M., Lopez-Ortega A., Golosovsky I.V., Estrade S., Roca A.G., Salazar-Alvarez G., Lopez-Conesa L., Tobia D., Winkler E., Ardisson J.D., Macedo W.A.A., Morphis A., Vasilakaki M., Trohidou K.N., Gukasov A., Mirebeau I., Makarova O.L., Zysler R.D., Peiro F., Baro M.D., Bergstrom L., Nogues J. Nanoscale; 7 (7): 3002 - 3015. 2015. 10.1039/c4nr06351a. IF: 7.394

    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. © 2015 The Royal Society of Chemistry.


  • Direct evidence for an interdiffused intermediate layer in bi-magnetic core-shell nanoparticles

    Juhin A.; Lopez-Ortega A.; Sikora M.; Carvallo C.; Estrader M.; Estrade S.; Peiro F.; Baro M.D.; Sainctavit P.; Glatzel P.; Nogues J. Nanoscale; 6 (20): 11911 - 11920. 2014. . IF: 6.739

  • Oxide wizard: An EELS application to characterize the white lines of transition metal edges

    Yedra L.; Xuriguera E.; Estrader M.; Lopez-Ortega A.; Baro M.D.; Nogues J.; Roldan M.; Varela M.; Estrade S.; Peiro F. Microscopy and Microanalysis; 20 (3): 698 - 705. 2014. 10.1017/S1431927614000440. IF: 2.161