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Fellowship PRE2018-084818, The wealth of complex polar topologies1–10 recently found in nanoscale ferroelectrics results from a delicate balance between the intrinsic tendency of the materials to develop a homogeneous polarization and the electric and mechanical boundary conditions imposed on them. Ferroelectric–dielectric interfaces are model systems in which polarization curling originates from open circuit-like electric boundary conditions, to avoid the build-up of polarization charges through the formation of fuxclosure11–14 domains that evolve into vortex-like structures at the nanoscale15–17 level. Although ferroelectricity is known to couple strongly with strain (both homogeneous18 and inhomogeneous19,20), the efect of mechanical constraints21 on thin-flm nanoscale ferroelectrics has been comparatively less explored because of the relative paucity of strain patterns that can be implemented experimentally. Here we show that the stacking of freestanding ferroelectric perovskite layers with controlled twist angles provides an opportunity to tailor these topological nanostructures in a way determined by the lateral strain modulation associated with the twisting. Furthermore, we fnd that a peculiar pattern of polarization vortices and antivortices emerges from the fexoelectric coupling of polarization to strain gradients. This fnding provides opportunities to create two-dimensional high-density vortex crystals that would enable us to explore previously unknown physical efects and functionalities., European Comission, Agencia Estatal de Investigación (España), Comunidad de Madrid, Ministerio de Ciencia e Innovación (España), Luxembourg National Research Fund, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub, Pagado por el autor

Está depositada una versión preprint del artículo, The peculiar features of domain walls observed in ferroelectrics make them promising active elements for next-generation non-volatile memories, logic gates and energy-harvesting devices. Although extensive research activity has been devoted recently to making full use of this technological potential, concrete realizations of working nanodevices exploiting these functional properties are yet to be demonstrated. Here, we fabricate a multiferroic tunnel junction based on ferromagnetic La0.7Sr0.3MnO3 electrodes separated by an ultrathin ferroelectric BaTiO3 tunnel barrier, where a head-to-head domain wall is constrained. An electron gas stabilized by oxygen vacancies is confined within the domain wall, displaying discrete quantum-well energy levels. These states assist resonant electron tunnelling processes across the barrier, leading to strong quantum oscillations of the electrical conductance., Ministerio de Economía y Competitividad (España), Comunidad Autónoma de Madrid, United States Department of Energy (DOE), BBVA Foundation, European Research Council (ERC), Red Española de Superconputación (RES), Universite Paris Saclay (DAlembert Program), Centre National de la Recherche Scientifique (CNRS), CeSViMa (Madrid), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2014 AIP Publishing LLC. Financial support by the Spanish Government [Project Nos. MAT2011-29269-CO3 and NANOSELECT CSD2007- 00041] and Generalitat de Catalunya (No. 2009 SGR 00376) is acknowledged., We show that yttria-stabilized zirconia (YSZ) films deposited on structurally dissimilar SrTiO_(3)(110) substrates exhibit two-dimensional layer-by-layer growth. We observed that, up to a thickness of about 15 nm, the square (001) basal plane of the cubic YSZ grows epitaxially on the rectangular (110) crystallographic plane of SrTiO3 substrates, with [110]YSZ(001)//[001]SrTiO_(3)(110) epitaxial relationship. Thus, the heterointerface presents symmetry discontinuity between the YSZ(001) film and the lower surface symmetry SrTiO_(3)(110) substrate. Beyond this specific case, we envisage similar approaches to develop other innovative oxide interfaces showing similar crystal symmetry discontinuities., Ministerio de Economía y Competitividad (MINECO), Generalitat de Catalunya, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

El texto completo de este trabajo no se encuentra disponible por no haber sido facilitado aún por su autor, por restricciones de copyright, o por no existir una versión digital. Artículo firmado por 26 autores, The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing. Josephson coupling over micrometres and at tens of kelvins is demonstrated across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7., Unión Europea, Gobierno de España, IDEX Paris-Saclay, Agence Nationale de la Recherche (ANR), Flag ERA ERA-NET To2Dox project, Ministry of Science and Higher Education of the Russian Federation, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

CRUE-CSIC (Acuerdos Transformativos 2021) ©2021 The Author(s). Published by Elsevier 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 Investigations 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, Epsilon iron oxide (epsilon-Fe_2O_3) 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 epsilon-Fe_2O_3 nanoparticles with a size of a few nanometers and the highest purity is reached in coatings after a densification treatment at 960 degrees C. The structural and compositional evolution up to 1200 degrees 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 epsilon-Fe_2O_3 polymorph, impelling its application in the coatings form., Ministerio de Ciencia e Innovacion (MICINN), Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2021 The Royal Society of Chemistry This work was partially supported by the Spanish MINECO projects MAT2014-54425-R (MINECO/FEDER, UE), MAT2017-82970-C2-R (AEI/FEDER, UE), MAT2017-83468-R (AEI/FEDER, UE), MAT2017-87134-C02-01-R (AEI/FEDER, UE) and MAT2017-87134-C02-02-R (AEI/FEDER, UE), the Spanish MICINN project PID2020-115159GB-I00/AEI/10.13039/501100011033 and by the Aragon Regional Government (Projects No. E12-20R and E28-20R). E. A-E acknowledges the Spanish MINECO and the European Social Fund for an FPI (Formacion de Personal Investigador, 2015) grant. R. B. acknowledges funding support from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 665919. This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge Diamond Light Source for time on I20-Scanning under Proposal SP-17266. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation Horizon 2020. The authors acknowledge funding from the project Quantox of QuantERA ERA-NET Cofund of Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. The authors would like to acknowledge the use of Servicio General de Apoyo a la InvestigacionSAI, Universidad de Zaragoza. The authors would like to acknowledge the use of the diffractometers at the Instituto de Nanociencia de Aragon and C. Munuera for AFM images., A metal-insulator transition is observed in spin-orbit-coupled IrO_2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t similar to 1.5-2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros-Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO_2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator., Unión Europea. H2020, Ministerio de Economía y Competitividad (MINECO) /FEDER, Ministerio de Economía y Competitividad (MINECO), Ministerio de Ciencia e Innovación (MICINN), Gobierno de Aragón, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

©2021 The Author(s) We are indebted to Dr. Santiago Sanchez-Cortes from the Instituto de Estructura de la Materia (Consejo Superior de Investigaciones Cientificas, CSIC-Spain) who kindly offered his lab and assistance to obtain the Raman spectra. We thank Dr. Jacob P.C. Ruff from the Cornell High Energy Synchrotron Source (CHESS) for his assistance with CHESS data. This work is based upon research conducted at the Spanish National Centre for Electron Microscopy and at the Cornell High Energy Synchrotron Source (CHESS) which is supported by the National Science Foundation under award DMR-1332208. Additional support was provided by the Ministry of Science and Education of Spain and the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canada Foundation for Innovation (CFI) and the Ontario Ministry of Research, Science and Innovation., The phase transition from graphite to diamond is an appealing object of study because of many fundamental and also, practical reasons. The out-of-plane distortions required for the transition are a good tool to understand the collective behaviour of layered materials (graphene, graphite) and the van der Waals forces. As today, two basic processes have been successfully tested to drive this transition: strong shocks and high energy femtolaser excitation. They induce it by increasing either pressure or temperature on graphite. In this work, we report a third method consisting in the irradiation of graphite with ultraviolet photons of energies above 4.4 eV. We show high resolution electron microscopy images of pyrolytic carbon evidencing the dislocation of the superficial graphitic layers after irradiation and the formation of crystallite islands within them. Electron energy loss spectroscopy of the islands show that the sp(2) to sp(3) hybridation transition is a surface effect. High sensitivity X-ray diffraction experiments and Raman spectroscopy confirm the formation of diamond within the islands., Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

A metal–insulator transition is observed in spin–orbit-coupled IrO2 thin films upon reduction of the film thickness. In the epitaxially grown samples, the critical thickness (t ∼ 1.5–2.2 nm) is found to depend on growth orientation (001), (100) or (110). Interestingly from the applied point of view, the insulating behavior is found even in polycrystalline ultrathin films. By analyzing the experimental electrical response with various theoretical models, we find good fits to the Efros–Shklovskii-VRH and the Arrhenius-type behaviors, which suggests an important role of electron correlations in determining the electrical properties of IrO2. Our magnetic measurements also point to a significant role of magnetic order. Altogether, our results would point to a mixed Slater- and Mott-type of insulator.

The phase transition from graphite to diamond is an appealing object of study because of many fundamental and also, practical reasons. The out-of-plane distortions required for the transition are a good tool to understand the collective behaviour of layered materials (graphene, graphite) and the van der Waals forces. As today, two basic processes have been successfully tested to drive this transition: strong shocks and high energy femtolaser excitation. They induce it by increasing either pressure or temperature on graphite. In this work, we report a third method consisting in the irradiation of graphite with ultraviolet photons of energies above 4.4 eV. We show high resolution electron microscopy images of pyrolytic carbon evidencing the dislocation of the superfcial graphitic layers after irradiation and the formation of crystallite islands within them. Electron energy loss spectroscopy of the islands show that the sp2 to sp3 hybridation transition is a surface efect. High sensitivity X-ray difraction experiments and Raman spectroscopy confrm the formation of diamond within the islands.

© 2019 American Physical Society Artículo firmado por más de once autores. Authors acknowledge received funding from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. This work was supported by Spanish MINECO through Grants No. MAT2014-52405-C02, No. MAT2017-87134-C02, No. MAT2015-72795-EXP, and by Comunidad de Madrid through S2013/336 MIT-2740. Work at Argonne National Laboratory (PNR experiments and analysis) was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The neutron scattering experiment was conducted at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Beam time support provided at Alice (BMBF Project No. 05K10PC2) is acknowledged. Financial support for developing and building the PM2-VEKMAG beam line and VEKMAG end station was provided by HZB and BMBF (05K10PC2, 05K10WR1, 05K10KE1), respectively. Steffen Rudorff is acknowledged for technical support. J. S. thanks Scholarship program Alembert funded by the IDEX Paris-Saclay, ANR-11-IDEX-0003-02., The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a La_0.7Sr_0.3MnO_3/BaTiO_3/La_0.7Sr_0.3MnO_3 multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics., Union Europea. H2020, Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Bundesministerium für Bildung und Forschung (BMBF), Université Paris-Saclay, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© Amer Chemical Soc. P.P. acknowledges Prof. A. Fert for fruitful discussions and interesting suggestions. This work has been supported by MINECO (Ministerio de Economía y Competitividad) through FLAGERA Graphene Flagship (‘SOgraph’ No. PCIN-2015-111) and through Projects FIS2016-78591-C3-1-R (SKYTRON), FIS2015-67287-P, MAT2012-39308, MAT2015-66888-C3-3-R, MAT2014-59315-R, FIS2013-45469-C4-3-R, FIS2016-78591- C3-2-R (AEI/FEDER, UE) and by the Comunidad de Madrid through Project S2013/MIT-2850 NANOFRONTMAG-CM. Financial support from the ERC PoC2015 MAGTOOLS is also acknowledged. IMDEA-Nanociencia acknowledges support from the ‘Severo Ochoa’ Program for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). Trabajo realizado por más de diez autores., A major challenge for future spintronics is to develop suitable spin transport channels with long spin lifetime and propagation length. Graphene can meet these requirements, even at room temperature. On the other side, taking advantage of the fast motion of chiral textures, that is, Neel-type domain walls and magnetic skyrmions, can satisfy the demands for high- density data storage, low power consumption, and high processing speed. We have engineered epitaxial structures where an epitaxial ferromagnetic Co layer is sandwiched between an epitaxial Pt(111) buffer grown in turn onto MgO(111) substrates and a grapheme layer. We provide evidence of a graphene-induced enhancement of the perpendicular magnetic anisotropy up to 4 nm thick Co films and of the existence of chiral left-handed Neel-type domain walls stabilized by the effective Dzyaloshinskii-Moriya interaction (DMI) in the stack. The experiments show evidence of a sizable DMI at the gr/Co interface, which is described in terms of a conduction electron mediated Rashba-DMI mechanism and points opposite to the spin orbit coupling-induced DMI at the Co/Pt interface. In addition, the presence of graphene results in (i) a surfactant action for the Co growth, producing an intercalated, flat, highly perfect face-centered cubic film, pseudomorphic with Pt and (ii) an efficient protection from oxidation. The magnetic chiral texture is stable at room temperature and grown on insulating substrate. Our findings open new routes to control chiral spin structures using interfacial engineering in graphene-based systems for future spin- orbitronics devices fully integrated on oxide substrates., Ministerio de Economía y Competitividad (MINECO), AEI/FEDER, Comunidad de Madrid, European Research Council (ERC), "Severo Ochoa" Program for Centres of Excellence in RD (MINECO), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Los óxidos complejos son una familia de compuestos de óxidos de metales de transición con un amplio espectro de propiedades para su aplicación en electrónica de óxidos, como son: ferromagnetismo, antiferromagnetismo, superconductividad, ferroelectricidad, etc. En particular, son buenos candidatos para dispositivos reales, ya que las interfases de estos materiales generan un escenario prometedor gracias a la interacción entre sus efectos eléctricos y magnéticos [1]. Las distintas interacciones entre los distintos grados de libertad como son la carga, el espín, la red cristalina y los orbitales dan lugar a una amplia variedad de fases electrónicas. Por tanto, la combinación de estas propiedades en heteroestructuras de alta calidad cristalina pueden dar lugar a diferentes estados electrónicos [2]. El comportamiento de los electrones en estos sistemas está sujeto a las interacciones culombianas con primeros vecinos y, por tanto, los materiales no se pueden describir con el modelo clásico de bandas. Un ejemplo de este tipo de comportamiento es el que se da en los aislantes de Mott, en los que la repulsión culombiana es suficientemente intensa para inducir un estado aislante a pesar de que la teoría de bandas prediga exactamente lo opuesto para una ocupación parcial de las bandas [3]. Es bien sabido que este tipo de materiales crecen con deficiencias de oxígeno, las cuales pueden dar lugar a cambios en sus las propiedades físicas, ya sea por el efecto electrónico de dopado o por los cambios estructurales que puedan generar en la red cristalina. Por ejemplo, el LaMnO3 estequiometrico es un aislante antiferromagnético que presenta ferromagnetismo cuando la red es deficiente en oxígeno [4]. Otros estudios demuestran que la familia de cobaltitas (La,Sr)CoO3 en película delgada sobre sustratos de NdGaO3 y (La,Sr)(Al,Ta)O3 tiene diferentes imanaciones de saturación [5]. Es estos experimentos se ha demostrado que, la diferencia en el contenido de vacantes de oxígeno en las pelíc, The quest for novel functionalities in strongly correlated oxide systems has often been determined by reducing dimensionality and designing nanostructured systems that exploit new physical effects. Any physical phenomena occurring within nanometric length scales are often ruled by the properties of small active regions, such as interfaces, point or extended defects, etc. In the growth process of oxide based heterostructures, the oxygen content constitutes a degree of freedom that can strongly affect the physical properties. Thus, the study of interfacial effects driven by oxygen vacancies is of great interest in order to pursue new functionalities aimed at designing future devices. Under these premises, in this thesis we have grown and characterized a number of systems comprised of complex oxide heterostructures where the O stoichiometry is tuned to produce physical behaviors not present in bulk. The local atomic structure and chemical properties of our samples have been probed with one of the most powerful techniques available currently to explore materials in real space with atomic resolution: aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). By means of spatially resolved analyses of slight fluctuations of the local crystalline structure, composition or electronic environment imposed by the presence of O point defects defects, we have been able to explain a number of physical effects in oxide interfaces of interest in hot fields such as spintronics or energy materials, establishing the link between the atomic local structure and the macroscopic world...

Los óxidos complejos son una familia de compuestos de óxidos de metales de transición con un amplio espectro de propiedades para su aplicación en electrónica de óxidos, como son: ferromagnetismo, antiferromagnetismo, superconductividad, ferroelectricidad, etc. En particular, son buenos candidatos para dispositivos reales, ya que las interfases de estos materiales generan un escenario prometedor gracias a la interacción entre sus efectos eléctricos y magnéticos [1]. Las distintas interacciones entre los distintos grados de libertad como son la carga, el espín, la red cristalina y los orbitales dan lugar a una amplia variedad de fases electrónicas. Por tanto, la combinación de estas propiedades en heteroestructuras de alta calidad cristalina pueden dar lugar a diferentes estados electrónicos [2]. El comportamiento de los electrones en estos sistemas está sujeto a las interacciones culombianas con primeros vecinos y, por tanto, los materiales no se pueden describir con el modelo clásico de bandas. Un ejemplo de este tipo de comportamiento es el que se da en los aislantes de Mott, en los que la repulsión culombiana es suficientemente intensa para inducir un estado aislante a pesar de que la teoría de bandas prediga exactamente lo opuesto para una ocupación parcial de las bandas [3]. Es bien sabido que este tipo de materiales crecen con deficiencias de oxígeno, las cuales pueden dar lugar a cambios en sus las propiedades físicas, ya sea por el efecto electrónico de dopado o por los cambios estructurales que puedan generar en la red cristalina. Por ejemplo, el LaMnO3 estequiometrico es un aislante antiferromagnético que presenta ferromagnetismo cuando la red es deficiente en oxígeno [4]. Otros estudios demuestran que la familia de cobaltitas (La,Sr)CoO3 en película delgada sobre sustratos de NdGaO3 y (La,Sr)(Al,Ta)O3 tiene diferentes imanaciones de saturación [5]. Es estos experimentos se ha demostrado que, la diferencia en el contenido de vacantes de oxígeno en las pelíc, The quest for novel functionalities in strongly correlated oxide systems has often been determined by reducing dimensionality and designing nanostructured systems that exploit new physical effects. Any physical phenomena occurring within nanometric length scales are often ruled by the properties of small active regions, such as interfaces, point or extended defects, etc. In the growth process of oxide based heterostructures, the oxygen content constitutes a degree of freedom that can strongly affect the physical properties. Thus, the study of interfacial effects driven by oxygen vacancies is of great interest in order to pursue new functionalities aimed at designing future devices. Under these premises, in this thesis we have grown and characterized a number of systems comprised of complex oxide heterostructures where the O stoichiometry is tuned to produce physical behaviors not present in bulk. The local atomic structure and chemical properties of our samples have been probed with one of the most powerful techniques available currently to explore materials in real space with atomic resolution: aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). By means of spatially resolved analyses of slight fluctuations of the local crystalline structure, composition or electronic environment imposed by the presence of O point defects defects, we have been able to explain a number of physical effects in oxide interfaces of interest in hot fields such as spintronics or energy materials, establishing the link between the atomic local structure and the macroscopic world...

© 2017 Author(s). Work at UCM supported by Spanish MINECO through Grant Nos. MAT2014-52405-C02- 01 and MAT2014-52405-C02-02 and by CAM through Grant No. CAM S2013/MIT-2740. M.V. and M.C. acknowledge support from Fundación BBVA and from MINECO through Grant No. MAT2015-066888-C3-3-R. J.S. thanks the University Paris-Saclay (D’Alembert program) and CNRS for financing his stay at CNRS/Thales. T.F. acknowledges support from the Hungarian Research Fund OTKA No. K107228., Controlling magnetic anisotropy is an important objective towards engineering novel magnetic device concepts in oxide electronics. In thin film manganites, magnetic anisotropy is weak and it is primarily determined by the substrate, through induced structural distortions resulting from epitaxial mismatch strain. On the other hand, in cobaltites, with a stronger spin orbit interaction, magnetic anisotropy is typically much stronger. In this paper, we show that interfacing La0.7Sr0.3MnO3 (LSMO) with an ultrathin LaCoO3 (LCO) layer drastically modifies the magnetic anisotropy of the manganite, making it independent of the substrate and closer to the magnetic isotropy characterizing its rhombohedral structure. Ferromagnetic resonance measurements evidence a tendency of manganite magnetic moments to point out-of-plane suggesting non collinear magnetic interactions at the interface. These results may be of interest for the design of oxide interfaces with tailored magnetic structures for new oxide devices., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Fundación BBVA, University Paris-Saclay (D’Alembert program), CNRS, Hungarian Research Fund OTKA, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

REVIEW Programa Ramon y Cajal (RYC-2012-11709), In this chapter we will review a few examples of applications of atomic resolution aberration corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to complex oxide materials. These are most challenging systems where subtle changes in structure or chemistry may result in colossal responses in macroscopic physical behavior. Here, we will review how atomic resolution compositional mapping can be achieved in manganite thin films and single crystals, highlighting the importance of considering artifacts during quantification. Besides, minor changes in near edge fine structure may take place when the crystalline environment, and hence nearest neighbor configuration, is modified. These can also be tracked by atomic resolution EELS, as will be shown through the study of binary Fe oxides. Also, examples regarding the study of distributions of point defects such as 0 vacancies in cobaltite thin films will be discussed. In these materials, a combination of epitaxial strain and defects may promote physical behaviors not present in bulk, such as the stabilization of unexpected spin state superlattices. Last, a study of extended defects such as dislocation lines will be reviewed. In particular, we will show how chemical segregation at dislocation cores in yttria-stabilized zirconia grain boundaries results in the generation of static O vacancies that affect the local electrostatic potential and hence, the macroscopic ionic conduction properties., European Commission, Fundación BBVA, Ministerio de Economia y Competitividad (España), Universidad Complutense de Madrid, Depto. de Física de Materiales, Fac. de Ciencias Físicas, Instituto Pluridisciplinar (IP), TRUE, pub

Los óxidos complejos son una familia de compuestos de óxidos de metales de transición con un amplio espectro de propiedades para su aplicación en electrónica de óxidos, como son: ferromagnetismo, antiferromagnetismo, superconductividad, ferroelectricidad, etc. En particular, son buenos candidatos para dispositivos reales, ya que las interfases de estos materiales generan un escenario prometedor gracias a la interacción entre sus efectos eléctricos y magnéticos [1]. Las distintas interacciones entre los distintos grados de libertad como son la carga, el espín, la red cristalina y los orbitales dan lugar a una amplia variedad de fases electrónicas. Por tanto, la combinación de estas propiedades en heteroestructuras de alta calidad cristalina pueden dar lugar a diferentes estados electrónicos [2]. El comportamiento de los electrones en estos sistemas está sujeto a las interacciones culombianas con primeros vecinos y, por tanto, los materiales no se pueden describir con el modelo clásico de bandas. Un ejemplo de este tipo de comportamiento es el que se da en los aislantes de Mott, en los que la repulsión culombiana es suficientemente intensa para inducir un estado aislante a pesar de que la teoría de bandas prediga exactamente lo opuesto para una ocupación parcial de las bandas [3]. Es bien sabido que este tipo de materiales crecen con deficiencias de oxígeno, las cuales pueden dar lugar a cambios en sus las propiedades físicas, ya sea por el efecto electrónico de dopado o por los cambios estructurales que puedan generar en la red cristalina. Por ejemplo, el LaMnO3 estequiometrico es un aislante antiferromagnético que presenta ferromagnetismo cuando la red es deficiente en oxígeno [4]. Otros estudios demuestran que la familia de cobaltitas (La,Sr)CoO3 en película delgada sobre sustratos de NdGaO3 y (La,Sr)(Al,Ta)O3 tiene diferentes imanaciones de saturación [5]. Es estos experimentos se ha demostrado que, la diferencia en el contenido de vacantes de oxígeno en las pelíc

Los óxidos complejos son una familia de compuestos de óxidos de metales de transición con un amplio espectro de propiedades para su aplicación en electrónica de óxidos, como son: ferromagnetismo, antiferromagnetismo, superconductividad, ferroelectricidad, etc. En particular, son buenos candidatos para dispositivos reales, ya que las interfases de estos materiales generan un escenario prometedor gracias a la interacción entre sus efectos eléctricos y magnéticos [1]. Las distintas interacciones entre los distintos grados de libertad como son la carga, el espín, la red cristalina y los orbitales dan lugar a una amplia variedad de fases electrónicas. Por tanto, la combinación de estas propiedades en heteroestructuras de alta calidad cristalina pueden dar lugar a diferentes estados electrónicos [2]. El comportamiento de los electrones en estos sistemas está sujeto a las interacciones culombianas con primeros vecinos y, por tanto, los materiales no se pueden describir con el modelo clásico de bandas. Un ejemplo de este tipo de comportamiento es el que se da en los aislantes de Mott, en los que la repulsión culombiana es suficientemente intensa para inducir un estado aislante a pesar de que la teoría de bandas prediga exactamente lo opuesto para una ocupación parcial de las bandas [3]. Es bien sabido que este tipo de materiales crecen con deficiencias de oxígeno, las cuales pueden dar lugar a cambios en sus las propiedades físicas, ya sea por el efecto electrónico de dopado o por los cambios estructurales que puedan generar en la red cristalina. Por ejemplo, el LaMnO3 estequiometrico es un aislante antiferromagnético que presenta ferromagnetismo cuando la red es deficiente en oxígeno [4]. Otros estudios demuestran que la familia de cobaltitas (La,Sr)CoO3 en película delgada sobre sustratos de NdGaO3 y (La,Sr)(Al,Ta)O3 tiene diferentes imanaciones de saturación [5]. Es estos experimentos se ha demostrado que, la diferencia en el contenido de vacantes de oxígeno en las pelíc

Ionic conductor complex oxides poise a most interesting promise as electrolytes for solid oxide fuel cells (SOFC). In particular, high quality thin films, superlattices and interfaces may exhibit a dramatic enhancement of the ionic conductivity, since such heterostructures may accommodate large amounts of strain. Coherently strained interfaces provide a very interesting playground towards the search of enhanced diffusivities near room temperature, aimed at improving devices for energy generation and storage. In this work, thin films of ZrO_2:Y_2O_3 (YSZ) and ZrO_2:Y_2O_3/YAlO_3 (YSZ/YAP) superlattices have been grown on different YAP substrates in order to tune the degree of epitaxial strain in the system. Different characterization techniques, as X-ray diffraction or scanning transmission electron microscopy have been used to study the role of the growth orientation and the interface strain in transport properties [RESUMEN] Los óxidos de metales de transición son una amplia familia de materiales, entre los que destacan los sólidos iónicos por su aplicaciones como materiales para la generación y almacenamiento de energía. En concreto, en películas delgadas de alta calidad en su estructura aparecen nuevas propiedades como una gran mejora en la conductividad iónica, fundamental para su utilización en celdas de combustible de electrolito sólido (SOFC: solid oxide fuel cells). Se ha demostrado que estos materiales se pueden combinar en heteroestructuras soportando grandes tensiones sin romper en islas o dominios estructurales. En estos sistemas, las interfases coherentemente tensionadas presentan un campo de estudio muy prometedor en la búsqueda de conductores iónicos con difusividades mayores cerca de temperatura ambiente. En este trabajo se han crecido láminas delgadas de ZrO_2:Y_2O_3 (YSZ) y superredes de ZrO_2:Y_2O_3/ YAlO_3 (YSZ/YAP) sobre distintos sustratos de YAlO3 (YAP) para su posterior caracterización mediante técnicas como difracción de rayos X y microscopía

The authors acknowledge received funding from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. Work supported by Spanish MINECO through Grants No. MAT2014-52405-C02, No. MAT2017-87134-C02, No. MAT2015-066888-C3-1-3-R, and No. RTI2018-097895-B-C41 (-C43), Grant No. Santander-UCM PR87/19-22603, and computational support from Grant No. FI-2019-1-0012. J. S. thanks for the scholarship program Alembert funded by the IDEX Paris-Saclay, Grant No. ANR-11-IDEX-0003-02., The persistence of ferroelectricity in ultrathin layers relies critically on screening or compensation of polarization charges which otherwise destabilize the ferroelectric state. At surfaces, charged defects play a crucial role in the screening mechanism triggering novel mixed electrochemical-ferroelectric states. At interfaces, however, the coupling between ferroelectric and electrochemical states has remained unexplored. Here, we make use of the dynamic formation of the oxygen vacancy profile in the nanometerthick barrier of a ferroelectric tunnel junction to demonstrate the interplay between electrochemical and ferroelectric degrees of freedom at an oxide interface. We fabricate ferroelectric tunnel junctions with a La_0.7Sr_0.3MnO_3 bottom electrode and BaTiO_3 ferroelectric barrier. We use poling strategies to promote the generation and transport of oxygen vacancies at the metallic top electrode. Generated oxygen vacancies control the stability of the ferroelectric polarization and modify its coercive fields. The ferroelectric polarization, in turn, controls the ionization of oxygen vacancies well above the limits of thermodynamic equilibrium, triggering the build up of a Schottky barrier at the interface which can be turned on and off with ferroelectric switching. This interplay between electronic and electrochemical degrees of freedom yields very large values of the electroresistance (more than 10^6% at low temperatures) and enables a controlled switching between clockwise and counterclockwise switching modes in the same junction (and consequently, a change of the sign of the electroresistance). The strong coupling found between electrochemical and electronic degrees of freedom sheds light on the growing debate between resistive and ferroelectric switching in ferroelectric tunnel junctions, and moreover, can be the source of novel concepts in memory devices and neuromorphie computing., Unión Europea, Ministerio de Economía, Comercio y Empresa (España), Ministerio de Ciencia, Innovación y Universidades (España), Universidad Complutense de Madrid/Banco de Santander, Universidad París-Saclay/ IDEX, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

The authors acknowledge funding received from the project Quantox of QuantERA ERA-NET Cofund in Quantum Technologies (Grant Agreement No. 731473) implemented within the European Union's Horizon 2020 Programme. This work was supported by Spanish MINECO through Grant No. MAT2017-87134-C02. V.R. acknowledges the European Union's Horizon 2020 research and innovation programme (Marie Skodowska-Curie IF Grant Agreement No. OXWALD 838693) and the Spanish Ministry of Science, Innovation and Universities through a Juan de la Cierva Incorporacion fellowship (Grant No. IJC2018-035192-I). G.S.-S. acknowledges the financial support from Spanish MICIU (Grant Nos. RTI2018-099054-J-I00 and MICINN IJC2018-038164-I)., Magnetoelectric coupling in artificial multiferroic interfaces can be drastically affected by the switching of oxygen vacancies and by the inversion of the ferroelectric polarization. Disentangling both effects is of major importance toward exploiting these effects in practical spintronic or spinorbitronic devices. We report on the independent control of ferroelectric and oxygen vacancy switching in multiferroic tunnel junctions with a La_(0.7)Sr_(0.3)MnO_3 bottom electrode, a BaTiO_3 ferroelectric barrier, and a Ni top electrode. We show that the concurrence of interface oxidation and ferroelectric switching allows for the controlled inversion of the interface spin polarization. Moreover, we show the possibility of a spin-memristor where the controlled oxidation of the interface allows for a continuum of memresistance states in the tunneling magnetoresistance. These results signal interesting new avenues toward neuromorphic devices where, as in practical neurons, the electronic response is controlled by electrochemical degrees of freedom., Unión Europea, Ministerio de Economía, Comercio y Empresa (España), Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia, Innovación y Universidades (España) - Programa Juan de la Cierva, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

The anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, by skew or side-jump scattering due to chiral features of the disorder scattering, or by an intrinsic contribution directly linked to the topological properties of the Bloch states. Here we show that the AHE can be artificially engineered in materials in which it is originally absent by combining the effects of symmetry breaking, spin orbit interaction and proximity-induced magnetism. In particular, we find a strikingly large AHE that emerges at the interface between a ferromagnetic manganite (La_(0.7)Sr_(0.3)MnO_3) and a semimetallic iridate (SrIrO_3). It is intrinsic and originates in the proximity-induced magnetism present in the narrow bands of strong spin-orbit coupling material SrIrO_3, which yields values of anomalous Hall conductivity and Hall angle as high as those observed in bulk transition-metal ferromagnets. These results demonstrate the interplay between correlated electron physics and topological phenomena at interfaces between 3d ferromagnets and strong spin-orbit coupling 5d oxides and trace an exciting path towards future topological spintronics at oxide interfaces. The anomalous Hall effect (AHE) occurs in ferromagnets caused by intrinsic and extrinsic mechanisms. Here, Yoo et al. report large anomalous Hall conductivity and Hall angle at the interface between a ferromagnet La_(0.7)Sr_(0.3M)nO_3 and a semimetallic SrIrO_3, due to the interplay between correlated physics and topological phenomena., Unión Europea - Horizonte 2020, Ministerio de Economía, Comercio y Empresa (España), Agence nationale de la recherche, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub