BUSCADOR RECOLECTA

[EN] NiFe-carbon magnetic nanocomposites prepared using hybrid sebacate intercalated layered double hydroxides (LDHs) as precursors are shown to be of interest as supercapacitors. Here, the low-temperature formation mechanism of these materials has been deciphered by means of a combined study using complementaryin situ(temperature-dependent) techniques. Specifically, studies involving X-ray powder diffraction, thermogravimetry coupled to mass spectrometry (TG-MS), statistical Raman spectroscopy (SRS), aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have been carried out. The experimental results confirm the early formation of FeNi(3)nanoparticles atca.200-250 degrees C, preceding the concerted collapse of the starting NiFe-LDH laminar structure over just 50 degrees C (from 350 to 400 degrees C). At the same time, the catalytic interactions between the metallic atoms and the organic molecules permit the concomitant formation of a graphitic carbon matrix leading to the formation of the final FeNi3-carbon nanocomposite. Furthermore,in situtemperature-dependent experiments in the presence of the intrinsic magnetic field of the STEM-EELS allow observing the complete metal segregation of Ni and Fe even at 400 degrees C. These results provide fundamental insights into the catalytic formation of carbon-based nanocomposites using LDHs as precursors and pave the way for the fine-tuning of their properties, with special interest in the field of energy storage and conversion, Financial support from the European Union (ERC Advanced Grant Mol-2D 788222, ERC Starting Grant 2D-PnictoChem 804110, ERC Proof of Concept Grant Hy-MAC 713704, and COST-Action on Molecular Spintronics (MOLSPIN CA15128)), the Spanish MINECO (Projects MAT2017-89993-R, MAT2015-66888-C3-3-R, RTI2018-097895-B-C43 co-financed by FEDER, and the Unit of Excellence "Maria de Maeztu" MDM-2015-0538), and the Generalitat Valenciana (Prometeo Program and iDiFEDER/2018/061 co-financed by FEDER) is gratefully acknowledged. G. A. acknowledges the support by the Deutsche Forschungsgemeinschaft DFG (FLAG-ERA AB694/2-1) and the Generalitat Valenciana (CIDEGENT/2018/001 grant). G. A. received financial support through the Postdoctoral Junior Leader Fellowship Programme from "la Caixa" Banking Foundation. J. R. thanks the Spanish MINECO for his predoctoral grant. Electron microscopy observations were carried out at the ICTS ELECMI node at Centro Nacional de Microscopia Electronica at the Universidad Complutense de Madrid. The authors thank Dr Maria Dolores Jordan Martin for her kind assistance with the XPS measurements.

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films., This work has been financially supported through the projects MAT2015-66888-C3-3-R and MAT2015-66726-R (MINECO/FEDER) of the Spanish Ministry of Economy and Competitiveness, RTI2018-097895-B-C43 of the Spanish Ministry of Science, Innovation, and Universities, and Gobierno de Aragón (Grant E10-17D) and Fondo Social Europeo. A.M.-N. is thankful for the contract from Universidad Complutense and Comunidad de Madrid “Atracción de Talento” program 2018-T1/IND-10360, and A.B. thanks MINECO for the Ph.D. grant BES-2016-076482., Peer reviewed

Epitaxial orthorhombic Hf0.5Zr0.5O2 (HZO) films on La0.67Sr0.33MnO3 (LSMO) electrodes show robust ferroelectricity, with high polarization, endurance and retention. However, no similar results have been achieved using other perovskite electrodes so far. Here, LSMO and other perovskite electrodes are compared. A small amount of orthorhombic phase and low polarization is found in HZO films grown on La-doped BaSnO3 and Nb-doped SrTiO3, while null amounts of orthorhombic phase and polarization are detected in films on LaNiO3 and SrRuO3. The critical effect of the electrode on the stabilized phases is not consequence of differences in the electrode lattice parameter. The interface is critical, and engineering the HZO bottom interface on just a few monolayers of LSMO permits the stabilization of the orthorhombic phase. Furthermore, while the specific divalent ion (Sr or Ca) in the manganite is not relevant, reducing the La content causes a severe reduction of the amount of orthorhombic phase and the ferroelectric polarization in the HZO film., Financial support from the Spanish Ministry of Science and
Innovation, through the Severo Ochoa FUNFUTURE (CEX2019-
000917-S) and the MAT2017-85232-R (AEI/FEDER, EU), and PID2019-
107727RB-I00 (AEI/FEDER, EU) projects, and from Generalitat de
Catalunya (2017 SGR 1377) is acknowledged. IF and JG acknowledge
Ramón y Cajal contracts RYC-2017-22531 and RYC-2012-11709,
respectively. IF acknowledges Beca Leonardo from Fundación BBVA.
SE acknowledges the Spanish Ministry of Economy, Competitiveness
and Universities for his PhD contract (SEV-2015-0496-16-3) and its
cofunding by the ESF. SE work has been done as a part of his Ph.D.
program in Materials Science at Universitat Autònoma de Barcelona.
Electron microscopy observations carried out at the Centro Nacional
de Microscopía Electrónica at UCM (MV) supported by MICINN
grant# RTI2018-097895-B-C43., Peer reviewed

NiFe-carbon magnetic nanocomposites prepared using hybrid sebacate intercalated layered double hydroxides (LDHs) as precursors are shown to be of interest as supercapacitors. Here, the low-temperature formation mechanism of these materials has been deciphered by means of a combined study using complementary in situ (temperature-dependent) techniques. Specifically, studies involving X-ray powder diffraction, thermogravimetry coupled to mass spectrometry (TG-MS), statistical Raman spectroscopy (SRS), aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) have been carried out. The experimental results confirm the early formation of FeNi3 nanoparticles at ca. 200-250 °C, preceding the concerted collapse of the starting NiFe-LDH laminar structure over just 50 °C (from 350 to 400 °C). At the same time, the catalytic interactions between the metallic atoms and the organic molecules permit the concomitant formation of a graphitic carbon matrix leading to the formation of the final FeNi3-carbon nanocomposite. Furthermore, in situ temperature-dependent experiments in the presence of the intrinsic magnetic field of the STEM-EELS allow observing the complete metal segregation of Ni and Fe even at 400 °C. These results provide fundamental insights into the catalytic formation of carbon-based nanocomposites using LDHs as precursors and pave the way for the fine-tuning of their properties, with special interest in the field of energy storage and conversion. This journal is, Financial support from the European Union (ERC Advanced
Grant Mol-2D 788222, ERC Starting Grant 2D-PnictoChem
804110, ERC Proof of Concept Grant Hy-MAC 713704, and
COST-Action on Molecular Spintronics (MOLSPIN CA15128)),
the Spanish MINECO (Projects MAT2017-89993-R, MAT2015-
66888-C3-3-R, RTI2018-097895-B-C43 co-nanced by FEDER,
and the Unit of Excellence “Maria de Maeztu” MDM-2015-0538),
and the Generalitat Valenciana (Prometeo Program and
iDiFEDER/2018/061 co-nanced by FEDER) is gratefully
acknowledged. G. A. acknowledges the support by the Deutsche
Forschungsgemeinscha DFG (FLAG-ERA AB694/2-1) and the
Generalitat Valenciana (CIDEGENT/2018/001 grant). G. A.
received nancial support through the Postdoctoral Junior
Leader Fellowship Programme from “la Caixa” Banking Foundation.
J. R. thanks the Spanish MINECO for his predoctoral
grant. Electron microscopy observations were carried out at the
ICTS ELECMI node at Centro Nacional de Microscop´ıa Electr
´onica at the Universidad Complutense de Madrid. The authors
thank Dr Mar´ıa Dolores Jord´an Mart´ın for her kind assistance
with the XPS measurements.

This article belongs to the Special Issue Preparation, Characterization and Application of Nanowires., In the last few years, magnetic nanowires have gained attention due to their potential implementation as building blocks in spintronics applications and, in particular, in domain-wall- based devices. In these devices, the control of the magnetic properties is a must. Cylindrical magnetic nanowires can be synthesized rather easily by electrodeposition and the control of their magnetic properties can be achieved by modulating the composition of the nanowire along the axial direction. In this work, we report the possibility of introducing changes in the composition along the radial direction, increasing the degrees of freedom to harness the magnetization. In particular, we report the synthesis, using template-assisted deposition, of FeNi (or Co) magnetic nanowires, coated with a Au/Co (Au/FeNi) bilayer. The diameter of the nanowire as well as the thickness of both layers can be tuned at will. In addition to a detailed structural characterization, we report a preliminary study on the magnetic properties, establishing the role of each layer in the global collective behavior of the system., This research was funded by MCINN/AEI/ 10.13039/501100011033 under Grants PID2020-117024GB-C43, RTI2018-097895-B-C43 and PRE2019-090268, and by the Comunidad de Madrid under Grant S2018-NMT-4321. Sandra Ruiz-Gómez and Claudia Fernández-Gonzalez gratefully acknowledge the IEEE Magnetic Society Educational Seed Funding. Sandra Ruiz-Gómez also gratefully acknowledges the financial support of the Alexander von Humboldt Foundation., Peer reviewed

Bi-doped Cu alloys are promising materials in the field of Spintronics due to the possibility of having efficient charge to spin conversion via spin Hall effect. To explore this effect, in particular at the nanoscale, it is essential to have a growth method that allows the control of crystal quality, cluster formation and microstructure. In this paper, we demonstrate that electrochemical deposition is a suitable method for the synthesis of these nanomaterials. We report the growth, by template assisted electrodeposition, of high quality, homogeneous nanowires of a diluted alloy of Bi dispersed into a Cu matrix, in which Bi concentration can be easily varied by tuning electrolyte composition. Structural analysis shows that Bi does not cluster but incorporate into the Cu matrix. The short-range order is nevertheless affected by the deposition potential. Cu is basically metallic, and Cu–Cu nearest-neighbor distances are those of bulk Cu, so Bi enters into the Cu structure substitutionally. Using low overpotential, we demonstrate the possibility of growing single crystal nanowires., This work has been partially funded by MAT2017-87072-C4-2-P and RTI2018-097895-B-C43 from the Ministerio de Ciencia e Innovación (MINECO-FEDER). We acknowledge The European Synchrotron (ESRF), MINECO and CSIC for provision of synchrotron radiation facilities, BM25-SpLine staff for the technical support beyond their duties and the financial support for the beamline (PIE-2010-OE-013-200014). We thank the CAI de Difracción de Rayos X, Universidad Complutense de Madrid, for XRD measurements. Electron microscopy observations were carried out at the Centro Nacional de Microscopía Electrónica node of the ICTS-ELECMI. A.S. acknowledges financial support from Comunidad de Madrid for an Atracción de Talento Investigador Contract (2017-t2/IND5395)., Peer reviewed

[EN] Epsilon iron oxide (ε-FeO) coatings on Si(100) substrates are obtained by an easy one-pot sol-gel recipe assisted by glycerol in an acid medium. Glycerol, given its small dimensions, enables the formation of ε-FeO nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 °C. The structural and compositional evolution up to 1200 °C is studied by confocal Raman microscopy and X-ray absorption spectroscopy techniques, correlating the existing magnetic properties. We report a novel characterization method, which allows monitoring the evolution of the precursor micelles as well as the intermediate and final phases formed. Furthermore, the inherent industrial technology transfer of the sol-gel process is also demonstrated with the ε-FeO polymorph, impelling its application in the coatings form., This work has been supported by the Ministerio de Ciencia e Innovación (MCINN, Spain) through the projects PIE: 2021-60-E-030, PIE: 2010-6-OE-013, PID2019-104717RB-I00 (2020–2022), MAT2017-86540-C4-1-R, RTI2018-095856-B-C21 (2019–2021), RTI2018-097895-B-C43 and RTI2018-095303-A-C52. The authors are grateful to The ESRF (France), MCINN and Consejo Superior de Investigaciones Científicas (CSIC, Spain) for the provision of synchrotron radiation
facilities and to the BM25-SpLine Staff for their valuable help. A.S.and A.M.-N acknowledge financial support from Comunidad de
Madrid (Spain) for an “Atracción de Talento Investigador” Contract 2017-t2/IND5395 and 2018-T1/IND-10360, respectively

[EN] Fe3C/few-layered graphene core/shell nanoparticles embedded in a carbon matrix are synthesized by a novel two-step surfactant sol-gel strategy, where the processes of hydrolysis, polycondensation and drying take place in a one-pot. The present approach is based on the combined action of oleic acid and oleylamine, which act sterically on the precursor micelles when a densification temperature is performed in a reducing atmosphere. The structural and magnetic evolution of the formed compounds is investigated, ranging from iron oxides such as Fe3O4 and FeO, to the formation of pure Fe3C/C samples from 700 ºC onwards. Interestingly, Fe3C nanoparticles with a size of ~20 nm crystallize immersed in the carbon matrix and the surrounding environment forms an oriented encapsulation built by few-layered graphene. The nanostructures show a saturation magnetization of ~43 emu/g and a moderate coercivity of ~500 Oe. Thereby, an innovative chemical route to produce single phase Fe3C nanoparticles is described, and an effective method of few-layered graphene passivation is proposed, yielding a product with a high magnetic response and high chemical stability against environmental corrosion., Ministerio de Ciencia de Innovación (MCINN), Spain, through the projects: MAT2015–65445-C2–1-R, MAT2017–86450-C4–1-R, MAT2015–67557-C2–1-P,
RTI2018–095856-B-C21, RTI2018–095303-A-C52, PIE: 2021-60-E030, PIE: 2010–6-OE-013; and Comunidad de Madrid, Spain, by S2013/MIT-2850 NANOFRONTMAG and S2018/NMT-4321 NANOMAGCOST. The authors are also grateful for the electron microscopy characterization performed in the Centro Nacional de Microscopía Electrónica at the Universidad Complutense de Madrid (ICTS ELECMI, UCM), support from MCINN grant # RTI2018–097895-B-43. C.G.-M. acknowledges the financial support from MICINN through the “Juan de la Cierva” Program (FJC2018–035532-I).

The aim of this work is to clarify how in-plane magnetic anisotropy and magnetoelasticity depend on the thickness of Ga-rich FeGa layers. Samples with an Fe72Ga28 composition were grown by sputtering in the ballistic regime in oblique incidence. Although for these growth conditions uniaxial magnetic anisotropy could be expected, in-plane anisotropy is only present when the sample thickness is above 100 nm. By means of differential X-ray absorption spectroscopy, we have determined the influence of both Ga pairs and tetragonal cell distortion on the evolution of the magnetic anisotropy with the increase of FeGa thickness. On the other hand, we have used the cantilever beam technique with capacitive detection to also determine the evolution of the magnetoelastic parameters with the thickness increase. In this case, experimental results can be understood considering the grain distribution. Therefore, the different physical origins for anisotropy and magnetoelasticity open up the possibility to independently tune these two characteristics in Ga-rich FeGa films.

Spin Hall and Rashba-Edelstein effects, which are spin-to-charge conversion phenomena due to spin-orbit coupling (SOC), are attracting increasing interest as pathways to manage rapidly and at low consumption cost the storage and processing of a large amount of data in spintronic devices as well as more efficient energy harvesting by spin-caloritronics devices. Materials with large SOC, such as heavy metals (HMs), are traditionally employed to get large spin-to-charge conversion. More recently, the use of graphene (gr) in proximity with large SOC layers has been proposed as an efficient and tunable spin transport channel. Here, we explore the role of a graphene monolayer between Co and a HM and its interfacial spin transport properties by means of thermo-spin measurements. The gr/HM (Pt and Ta) stacks have been prepared on epitaxial Ir(111)/Co(111) structures grown on sapphire crystals, in which the spin detector (i.e., top HM) and the spin injector (i.e., Co) are all grown in situ under controlled conditions and present clean and sharp interfaces. We find that a gr monolayer retains the spin current injected into the HM from the bottom Co layer. This has been observed by detecting a net reduction in the sum of the spin Seebeck and interfacial contributions due to the presence of gr and independent from the spin Hall angle sign of the HM used.

Among the hybrid organic-inorganic perovskites MAPbX(3) (MA: methyl-ammonium CH3-NH3+, X=halogen), the triiodide specimen (MAPbI(3)) is still the material of choice for solar energy applications. Although it is able to absorb light above its 1.6 eV bandgap, its poor stability in humid air atmosphere has been a major drawback for its use in solar cells. However, we discovered that this perovskite can be prepared by ball milling in a straightforward way, yielding specimens with a superior stability. This fact allowed us to take atomic-resolution STEM images for the first time, with sufficient quality to unveil microscopic aspects of this material. We demonstrated full Iodine content, which might be related to the enhanced stability, in a more compact PbI6 framework with reduced unit-cell volume. A structural investigation from neutron powder diffraction (NPD) data of an undeuterated specimen was essential to determine the configuration of the organic MA unit in the 100-298 K temperature range. A phase transition is identified, from the tetragonal structure observed at RT (space group I4/mcm) to an orthorhombic (space group Pnma) phase where the methyl-ammonium organic units are fully localized. Our NPD data reveal that the MA changes are gradual and start before reaching the phase transition. Optoelectronic measurements yield a photocurrent peak at an illumination wavelength of 820 nm, which is redshifted by 30 nm with respect to previously reported measurements on MAPbI(3) perovskites synthesized by crystallization from organic solvents.

Graphene-based magnetic epitaxial heterostructures, where an ultrathin layer of a ferromagnetic metal is sandwiched between a heavy metal and a graphene monolayer, have been widely studied due to their easily tunable interfacial driven spin-orbit interactions. The interplay between orbital hybridization and symmetry breaking at the interfaces in systems like graphene/Co grown epitaxially on Pt results in enhanced perpendicular magnetic anisotropy and sizeable antisymmetric exchange interaction, enabling the possibility to stabilize thermally stable chiral spin textures and their manipulation with external stimuli. However, in order to properly exploit the functionality of such heterostructures, the crystal structure, composition, and integrity of the ultrathin ferromagnetic metallic layer must be understood down to the atomic level. For this aim, the characterization of thermally activated atomic processes taking place during growth, along with changes likely taking place during future device performance derived from Joule heating, is a must. In this work, we use in situ atomic resolution electron microscopy and spectroscopy techniques to investigate thermally activated interdiffusion phenomena at Co/Pt interfaces in the range of 300–773 K. We show how significant alloying takes place at the Co/Pt interface for higher annealing temperatures. Such interdiffusion affects the magnetic properties of the layers, enhancing the layer coercivity. Such direct visualization of the thermally induced interdiffusion effects offers a pathway for optimizing graphene-based magnetic epitaxial systems for robust device integration

Black phosphorus (BP) allotrope has an orthorhombic crystal structure with a narrow bandgap of 0.35 eV. This material is promising for 2D technology since it can be exfoliated down to one single layer: the well-known phosphorene. In this work, bulk BP was synthesized under high-pressure conditions at high temperatures. A detailed structural investigation using neutron and synchrotron X-ray diffraction revealed the occurrence of anisotropic strain effects on the BP lattice; the combination of both sets of diffraction data allowed visualization of the lone electron pair 3s(2). Temperature-dependent neutron diffraction data collected at low temperature showed that the a axis (zigzag) exhibits a quasi-temperature-independent thermal expansion in the temperature interval from 20 up to 150 K. These results may be a key to address the anomalous behavior in electrical resistivity near 150 K. Thermoelectric properties were also provided; low thermal conductivity from 14 down to 6 Wm(-1) K-1 in the range 323-673 K was recorded in our polycrystalline BP, which is below the reported values for single-crystals in literature.

Neutron powder diffraction and thermoelectric characterization of SnSe:Kx intermetallic alloys are presented. Nanostructured ingots were prepared by arc-melting elemental tin and selenium along with potassium hydride. Up to x = 0.1 of K can be incorporated into SnSe. Rietveld refinement of the diffractograms locates potassium on the Sn site in the high-temperature Cmcm structure. However, in the low-temperature Pnma structure, K cannot be localized by difference Fourier maps, indicating the incorporation of K in a disordered form in the interlayer space. STEM-EELS indicates the incorporation of K into the SnSe grains. The resistivity upon K-doping at intermediate temperatures decreases by 1–2 orders of magnitude, but at high temperature is higher than the undoped SnSe. The Seebeck coefficient of K-doped SnSe remains p-type and almost temperature independent (400 μV/K for x = 0.1). The ultralow thermal conductivity of undoped SnSe decreases further upon K-doping to below 0.3 W/m K.

Interfaces 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., The authors acknowledge the financial support from the Spanish Minister of Science and Innovation (MICINN) through the projects PID2019-106165GB-C21, PID2019-106165GB-C22, and PID2019-106229RB-I00. They also acknowledge funding from Generalitat de Catalunya through the 2017-SGR-292 and 2017-SGR-776 projects. In addition, research at UCM was supported by MINECO/FEDER MAT2015-66888-C3-3-R and RTI2018-097895-B-C43 grants. ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, funded by the Spanish Research Agency (AEI, Grant SEV-2017-0706). M.E. thanks the Spanish MICINN and AEI/FSE for Ramón y Cajal contract (RYC2018-024396-I). A.L.O. acknowledges support from the Universidad Pública de Navarra (Grant PJUPNA2020). STEM-EELS observations carried out at the Centro Nacional de Microscopía Electrónica at Universidad Complutense de Madrid, Spain (ICTS ELECMI).

Hybrid nanoparticles allow exploiting the interplay of confinement, proximity between different materials and interfacial effects. However, to harness their properties an in-depth understanding of their (meta)stability and interfacial characteristics is crucial. This is especially the case of nanosystems based on functional oxides working under reducing conditions, which may severely impact their properties. In this work, the in-situ electron-induced selective reduction of Mn₃O₄ to MnO is studied in magnetic Fe₃O₄/Mn₃O₄ and Mn₃O₄/Fe₃O₄ core/shell nanoparticles by means of high-resolution scanning transmission electron microscopy combined with electron energy-loss spectroscopy. Such in-situ transformation allows mimicking the actual processes in operando environments. A multi-stage image analysis using geometric phase analysis combined with particle image velocity enables direct monitoring of the relationship between structure, chemical composition and strain relaxation during the Mn₃O₄ reduction. In the case of Fe₃O₄/Mn₃O₄ core/shell the transformation occurs smoothly without the formation of defects. However, for the inverse Mn₃O₄/Fe₃O₄O core/shell configuration the electron beam-induced transformation occurs in different stages that include redox reactions and void formation followed by strain field relaxation via formation of defects. This study highlights the relevance of understanding the local dynamics responsible for changes in the particle composition in order to control stability and, ultimately, macroscopic functionality.

Interfaces 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.