López Ortega, Alberto
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López Ortega
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Alberto
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Ciencias
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InaMat2. Instituto de Investigación en Materiales Avanzados y Matemáticas
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Publication Open Access Elucidating individual magnetic contributions in bi-magnetic Fe3O4/Mn3O4 Core/Shell nanoparticles by polarized powder neutron diffraction(Wiley, 2023) Golosovsky, Igor V.; Kibalin, Iurii A.; Gukasov, Arsen; Gómez Roca, Alejando; López Ortega, Alberto; Estrader, Marta; Vasilakaki, Marianna; Trohidou, Kalliopi; Hansen, T. C.; Puente-Orench, I.; Lelièvre-Berna, E.; Nogués, Josep; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa, PJUPNA 2020Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3O4/Mn3O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3O4 and Mn3O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials.Publication Open Access Direct evidence of a graded magnetic interface in bimagnetic core/shell nanoparticles using electron magnetic circular dichroism (EMCD)(American Chemical Society, 2021) Pozo Bueno, Daniel del; Varela, María; Estrader, Marta; López Ortega, Alberto; Gómez Roca, Alejando; Nogués, Josep; Peiró, Francesca; Estradé, Sònia; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate PublikoaInterfaces play a crucial role in composite magnetic materials and particularly in bimagnetic core/shell nanoparticles. However, resolving the microscopic magnetic structure of these nanoparticles is rather complex. Here, we investigate the local magnetization of antiferromagnetic/ferrimagnetic FeO/Fe3O4 core/shell nanocubes by electron magnetic circular dichroism (EMCD). The electron energy-loss spectroscopy (EELS) compositional analysis of the samples shows the presence of an oxidation gradient at the interface between the FeO core and the Fe3O4 shell. The EMCD measurements show that the nanoparticles are composed of four different zones with distinct magnetic moment in a concentric, onion-type, structure. These magnetic areas correlate spatially with the oxidation and composition gradient with the magnetic moment being largest at the surface and decreasing toward the core. The results show that the combination of EELS compositional mapping and EMCD can provide very valuable information on the inner magnetic structure and its correlation to the microstructure of magnetic nanoparticles.