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Swirling spin textures, including topologically nontrivial states, such as skyrmions, chiral domain walls, and magnetic vortices, have garnered significant attention within the scientific community due to their appeal from both fundamental and applied points of view. However, their creation, controlled manipulation, and stability are typically constrained to certain systems with specific crystallographic symmetries, bulk or interface interactions, and/or a precise stacking sequence of materials. Recently, a new approach has shown potential for the imprint of magnetic radial vortices in soft ferromagnetic compounds making use of the stray field of YBa2Cu3O7-delta superconducting microstructures in ferromagnet/superconductor (FM/SC) hybrids at temperatures below the superconducting transition temperature (T-C). Here, we explore the lower size limit for the imprint of magnetic radial vortices in square and disc shaped structures as well as the persistence of these spin textures above T-C, with magnetic domains retaining partial memory. Structures with circular geometry and with FM patterned to smaller radius than the superconductor island facilitate the imprinting of magnetic radial vortices and improve their stability above T-C, in contrast to square structures where the presence of magnetic domains increases the dipolar energy. Micromagnetic modeling coupled with a SC field model reveals that the stabilization mechanism above T-C is mediated by microstructural defects. Superconducting control of swirling spin textures, and their stabilization above the superconducting transition temperature by means of defect engineering holds promising prospects for shaping superconducting spintronics based on magnetic textures, Helmholtz Zentrum Berlin fur Materialen und Energie, European Commission, MInisterio de Economía y Competitividad (España), Agence Nationale de la Recherche (France), Alexander von Humboldt Foundation, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub, Pagado por el autor

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

The interplay between ferromagnetism and superconductivity has attracted substantial interest due to its potential for exotic quantum phenomena and advanced electronic devices. Although ferromagnetism and superconductivity are antagonistic phenomena, ferromagnets (F) can host spin-triplet superconductivity induced via proximity with superconductors (S). To date, most of the experimental effort has been focused on single S/F/S junctions. Here, we have found the fingerprints of long-range superconducting proximity effect in micrometric weaklink arrays, formed by embedding YBa2Cu3O7 superconducting islands in a half-metallic ferromagnet La0.7Ca0.3MnO3 film. These arrays show magnetoresistance oscillations that appear at temperatures below the critical temperature of YBa2Cu3O7 for currents below a threshold, indicating their superconducting origin. This realization paves the way for device architectures displaying macroscopic quantum interference effects, which are of interest for field sensing applications, among others., Agencia Estatal de Investigación (España), Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Helmholtz Zentrum Berlin, European Commission, Agence Nationale de la Recherche (France), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub, Pagado por el autor

The magnetoresistance of La0.7Sr0.3MnO3/SrTiO3 superlattices with magnetic field rotating out-of-plane shows unexpected peaks for in-plane fields. Resistivity calculations with spin–orbit coupling reveal that orbital reconstruction at the manganite interface leads to a 2D ferromagnetic electron gas coupled antiparallel to the manganite “bulk”. These orbital and magnetic reconstructions are supported by X-ray linear dichroism and ab initio calculations., Ministerio de Economía y Competitividad (España), Depto. de Física de Materiales, 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, An unusual conducting surface state can be produced in SrTiO3 substrates by irradiation with Argon ions from a plasma source, at low energy and high doses. The effects of irradiation are analyzed here by atomic force microscopy (AFM) and aberration corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). Depth sensitive studies demonstrate the existence of a heavily damaged surface layer and an oxygen vacancy rich layer immediately underneath, both induced during the irradiation process. We find a clear dependence of the Ti oxidation state with the depth, with a very intense Ti3+ component near the surface. Oxygen vacancies act as n-type doping by releasing electrons into the lattice and producing an insulator-to-metal transition, which explains the unusual metallic behavior of these samples., Materials Sciences and Engineering Division of the US Department of Energy (DOE), ORNL’s Shared Research Equipment (ShaRE) User Program, ERC starting Investigator Award, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

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

Generation, manipulation, and sensing of magnetic domain walls are cornerstones in the design of efficient spintronic devices. Half-metals are amenable for this purpose as large low field magnetoresistance signals can be expected from spin accumulation at spin textures. Among half metals, La1−xSrxMnO3 (LSMO) manganites are considered as promising candidates for their robust half-metallic ground state, Curie temperature above room temperature (Tc = 360 K, for x = 1/3), and chemical stability. Yet domain wall magnetoresistance is poorly understood, with large discrepancies in the reported values and conflicting interpretation of experimental data due to the entanglement of various source of magnetoresistance, namely, spin accumulation, anisotropic magnetoresistance, and colossal magnetoresistance. In this work, the domain wall magnetoresistance is measured in LSMO cross-shape nanowires with single-domain walls nucleated across the current path. Magnetoresistance values above 10% are found to be originating at the spin accumulation caused by the mistracking effect of the spin texture of the domain wall by the conduction electrons. Fundamentally, this result shows the importance on non-adiabatic processes at spin textures despite the strong Hund coupling to the localized t2g electrons of the manganite. These large magnetoresistance values are high enough for encoding and reading magnetic bits in future oxide spintronic sensors., Unión Europea Horizonte 2020, Comunidad Autónoma de Madrid, Gobierno de España, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Artículo firmado por 15 autores, We have analyzed the interface structure and composition of La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 trilayers by combined polarized neutron reflectometry, aberration-corrected microscopy, and atomic column resolution electron-energy-loss spectroscopy and x-ray absorption with polarization analysis. We find the same stacking sequence at both top and bottom cuprate interfaces. X-ray magnetic circular dichroism experiments show that both cuprate interfaces are magnetic with a magnetic moment induced in Cu atoms as expected from symmetric Mn-O-Cu superexchange paths. These results supply a solid footing for the applicability of recent theories explaining the interplay between magnetism and superconductivity in this system in terms of the induced Cu spin polarization at both interfaces [J. Salafranca and S. Okamoto, Phys. Rev. Lett. 105, 256804 (2010)]., Ministerio de Ciencia e Innovación (España), Consejo Europeo de Investigación (ERC), United States Department of Energy (DOE), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2023 The Author(s). Work supported by Spanish AEI through Grant PID2020-118078RB-I00 and by Regional Government of Madrid CAM through SINERGICO Project Y2020/NMT-6661 CAIRO-CM. Work at CNRS/Thales lab supported by ERC Grant No. 647100 SUSPINTRONICS', French ANR Grant ANR-15-CE24-0008-01 SUPERTRONICS' and COST action Nanocohybri'. We acknowledge funding from Flag ERA ERA-NET To2Dox Project. J E V thanks C Ulysse and L Vila for collaboration in related projects., The proximity effect between superconductors and ferromagnets may become long range due to the generation of triplet pairs. The recent finding of a long, one micron-range unconventional Josephson effect between YBa_2Cu_3O_7 high Tc cuprates separated by a half metallic La_0.7Sr_0.3MnO_3 manganite ferromagnet has uncovered a novel unconventional triplet proximity effect. In this paper, we examine the temperature dependence of the critical current in planar Josephson junctions. We find that the critical current-normal resistance product follows the predictions of traditional superconductor-normal metal-superconductor junctions, which implies that triplet pairs in a ferromagnet are transported in the diffusive limit similarly to singlet pairs in a normal metal. This result calls for theoretical studies of the new triplet Josephson effect and underlines its potential in future superconducting spintronics., Unión Europea. H2020, Ministerio de Ciencia, Innovación (MICINN), Comunidad de Madrid, Agence nationale de la recherche (ANR), Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

Using X-ray absorption spectroscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for charge transfer at the interface between the Mott insulators Sm2CuO4 and LaFeO3 is obtained. As a consequence of the charge transfer, the Sm2CuO4 is doped with electrons and thus epitaxial Sm2CuO4/LaFeO3 heterostructures become metallic., Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, Unión Europea. FP7, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Direct evidence for charge leakage at the interface of epitaxial SrTiO3/LaMnO3 superlattices with atomically sharp interfaces is provided. The direction of charge leakage can be reversed by changing the LMO/STO thickness ratio. This result will be important for the understanding of some of the reported limitations of oxide devices involving manganite/titanate interfaces., Ministerio de Ciencia e Innovación (España), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 American Institute of Physics. One of the authors Z.S. gratefully acknowledges financial support from Flores Valles. Work supported by MCYT MAT 2002-2642, CAM GR-MAT-0771/2004, UCM PR3/04- 12399, and Fundación Ramón Areces. This research was partially sponsored by the Laboratory Directed Research and Development Program of ORNL, managed by UT-Batelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. The authors thank M. Bibes for fruitful discussion., We report large tunneling magnetoresistance in La_(0.7)Ca_(0.3)MnO_(3) (8 nm)/PrBa_(2)Cu_(3)O_(7) (2.4 nm)/La_(0.7)Ca_(0.3)MnO_(3) (50 nm) junctions. The coherent growth of the cuprate on the manganite allows the deposition of ultrathin barriers which are continuous and flat over long lateral distances. Epitaxial strain causes the top layer to be a weaker ferromagnet without a significant decrease in the spin polarization., Flores Valles, MCYT, CAM, UCM, Fundación Ramón Areces, Laboratory Directed Research and Development Program of ORNL, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© American Physical Society. CM and NMN acknowledge Spanish MINECO for Juan de la Cierva and Ramón y Cajal fellowships. This work was supported by the Spanish MINECO through Grant Nos. MAT2011-27470-C02-01 and MAT2011-27470-C02-02., La0.7Ca0.3MnO3 optimally doped epitaxial films were grown on ferroelectric BaTiO3 substrates. Electronic transport (magnetoresistance and electroresistance) and magnetic properties showed important anomalies in the temperature interval between 60 and 150 K, below the metal-insulator transition. Scanning probe microscopy revealed changes in BaTiO3 surface morphology at those temperatures. La0.7Ca0.3MnO3 thickness is a critical factor: 120-angstrom -thick films showed large anomalies sensitive to electric poling of the BaTiO3, whereas the behavior of 150-angstrom -thick films is closer to that of the reference La0.7Ca0.3MnO3 samples grown on SrTiO3. We propose that, through inhomogenous strain and electric polarization effects, the ferroelectric substrate induces an inhomogenous spin distribution in the magnetic layer. This would imply the coexistence of in-plane and out-of-plane ferromagnetic patches in La0.7Ca0.3MnO3, possibly interspersed with antiferromagnetic regions, as it has recently been theoretically predicted. Substrate poling effects are investigated, and a magnetoelectric coupling is demonstrated., Spanish MINECO, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 American Institute of Physics. We thank A. Goldman for fruitful discussions within the framework of the joint U.S.-Spain NSF Materials World Network Grant No. 709584. Work was supported by the U.S. Department of Energy, Basic Energy Science under Contract Nos. DE-AC02-06CH11357 and DE-AC02NA25396, by Spanish MICINN under Contracts “Ramon y Cajal,” Grant Nos. MAT2008-06517 and CONSOLIDER INGENIO 2010 CSD2009-00013 IMAGINE, by CAM under PHAMA Grant No. S2009/Mat-1756, and by OTKA Grant Nos. K68807 and PF63954 and the “Bolyai” program of the Hungarian Academy of Sciences., We report a memory concept utilizing ferromagnet/superconductor/ferromagnet La_(0.7)Ca_(0.3)MnO_(3)/YBa_(2)Cu_(3)O_(7)/La_(0.7)Ca_(0.3)MnO_(3) thin film hybrid structures. The orientation of the magnetic field with respect to the ferromagnetic easy axis has a strong effect on superconductivity as indicated by a strong variation in the magnetoresistance MR. MR can be controlled by rotating a small magnetic field applied in the plane of the film in a way that is determined by the in-plane biaxial magnetic anisotropy. The proposed memory device has the advantages of superconducting detection elements fast response and low dissipation, small 100–150 Oe writing fields, and resistance read-out without need for applied field., U.S.-Spain NSF Materials World Network, U.S. Department of Energy, Basic Energy Science, Spanish MICINN Contracts “Ramón y Cajal”, Consolider Ingenio 2010, CAM under PHAMA, OTKA, Hungarian Academy of Sciences, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

Metallic surface layers are fabricated by doping (100) SrTiO3 (STO) single crystals with oxygen vacancies generated by bombardment with Ar ions from an rf plasma source. The presence of oxygen vacancies is confirmed by cathodoluminescence and x-ray photoemission spectroscopy. This technique produces a surface electron gas with high values of the sheet carrier density (n2D = 2.45×1017 cm−2). A strong increase (300%) of the low-temperature magnetoresistance is observed when the magnetic field is rotated away from the surface, characteristic of orbital effects of confined electrons. We estimate the width of the confinement region to be in the 200–300 nm range. When a magnetic field is applied in the surface plane and parallel to the current direction, a large negative magnetoresistance is found below the structural transition of the STO, which is discussed in terms of spin-orbit scattering. On further reduction of temperature, there is a change to a positive magnetoresistance regime due to the scattering of charge carriers at the disordered surface region., Ministerio de Ciencia e Innovación, Comunidad de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2011 American Physical Society. Este artículo está firmado por 13 autores. Work at UCM was supported by Spanish MICINN Grant No. MAT 2008 06517, Consolider Ingenio CSD2009- 00013 (IMAGINE), and CAM S2009-MAT 1756 (PHAMA). Work at ORNL was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. M. V. acknowledges ERC starting Grant No. 239739 STEMOX., We report on the magnetic coupling of La_(0.7)Sr_(0.3)MnO_(3) layers through SrTiO_(3) spacers in La_(0.7)Sr_(0.3)MnO_(3)/SrTiO_(3) epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO_(3) controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm., Spanish MICINN, CAM, Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy, ERC, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2002 The American Physical Society. We thank P. Lunkenheimer, A. Kulkarni, A. Pradel, C. Cramer, and H. Jain for sending their experimental data. The work performed at NRL was supported by ONR. C. León is supported in Spain by CICYT Grant No. MAT2001-3713- C04., Experimental frequency-dependent conductivity relaxation spectra of a number of molten, glassy, and crystalline ionic conductors that show both the presence of the near constant loss (NCL) and the cooperative ion hopping contribution are analyzed. On decreasing frequency, the NCL appears first but terminates at some frequency v_(x1). At still a lower frequency v_(x2) the cooperative ion hopping dispersion takes over. The independent ion hopping frequency v_(0) of the coupling model is calculated from the parameters characterizing the cooperative ion hopping dispersion. It is found for all ionic conductors that v_(x1)>>v_(0), and v_(0) always fall inside the frequency region v_(x1) > v > v_(x2). The empirical results leads to a qualitative theory for the origin of the NCL, which gives physical meanings of the two crossover frequencies v_(x1) and v_(x2), as well as explaining the role of the independent hopping frequency v_(0), in determining them. The weak temperature dependence of the NCL has been recaptured by the qualitative theory. An improved understanding is gained of the evolution of the ion dynamics from early times when the cages decay very slowly with time, giving rise to the near constant loss, to long times when ions move cooperatively, leading finally to dc conductivity., ONR, CICYT, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 American Institute of Physics. The work at UCM was supported by MEC MAT 2005—06024 C02 and work at UMN was supported by NSF DMR., Electrical transport properties of heteroepitaxial p-n junctions made of La_(0.8)Sr_(0.2)CoO_(3) and SrTi_(0.99)Nb_(0.01)O_(3) were studied. Junctions display highly rectifying current-voltage characteristics over a wide temperature range (20–300 K). Two distinct transport mechanisms are identified: tunneling assisted by interface states at T<130 K and diffusion/recombination at higher temperatures. Capacitance-voltage characteristics are used to determine the junction built-in potential at different frequencies. A capacitance relaxation is found due to charge trapping at interface states. Interface states, which deeply affect transport, are discussed in connection to charge-transfer processes related to the polarity mismatch at the interface., MEC, NSF DMR, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 The American Physical Society. This work was supported by MCYT MAT 2002-2642 and CAM 07N/0032/2002., We investigate the zero-magnetic-field dynamic scaling in Bi_(2)Sr_(2)CaCu_(2)O_(8) thin films from nonlinear currentvoltage sI-Vd characteristics and by using the concavity criterion recently proposed by Strachan et al. [Phys. Rev. Lett. 87, 067007 (2001)]. We find that fresh samples show a BKT-like transition with z=0.8, smaller than expected for a conventional Berezinskii-Kosterlitz-Thouless transition. The effect of sample size and finite Josephson coupling are discussed. We examine the effect of thermally-induced disorder in the oxygen sublattice finding that the BKT-like transition is suppressed by point disorder., MCYT, CAM, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

We report on the magnetic coupling of La0.7Sr0.3MnO3 layers through SrTiO3 spacers in La0.7Sr0.3MnO3/SrTiO3 epitaxial heterostructures. Combined aberration-corrected microscopy and electron-energy-loss spectroscopy evidence charge transfer to the empty conduction band of the titanate. Ti d electrons interact via superexchange with Mn, giving rise to a Ti magnetic moment as demonstrated by x-ray magnetic circular dichroism. This induced magnetic moment in the SrTiO3 controls the bulk magnetic and transport properties of the superlattices when the titanate layer thickness is below 1 nm., MICINN, CAM, U.S. Department of Energy, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2003 American Institute of Physics. The authors thank Professor A. Várez for sample preparation. One of the authors (A.R.) thanks another (E.R.) for his hospitality during the stay in Bayreuth., We report on the temperature dependence of the ionic conductivity at low temperatures in the crystalline lithium ionic conductor Li_(0.18)La_(0.61)TiO_(3). Time domain measurements of the electric modulus have been performed to investigate ion dynamics in the frequency range 1025 – 102 Hz and for conductivity values in the range 10214 – 1028 S/cm. Ionic conductivity shows an Arrhenius temperature dependence below 300 K and down to 120 K, in contrast to the non-Arrhenius behavior found at higher temperatures, demonstrating that the temperature dependence of ionic conductivity in Li_(0.18)La_(0.61)TiO_(3) cannot be described by a Vogel–Fulcher–Tamman law., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 The American Physical Society. M. V. was partially supported by a research grant of the Fundación Universidad Carlos III de Madrid. Financial support from CICYT Grant No. MAT99-1706E is also acknowledged. M. V. is thankful for the hospitality received during her stay at the LBNL/NCEM. W. G. acknowledges support from the Max Kade Foundation for his stay at Berkeley. Work at LBNL/NCEM was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098., Charge neutrality and stoichiometry impose severe restrictions on the mechanisms of epitaxial growth of complex oxides. The fundamental question arises of what is the minimum growth unit when sample thickness is reduced beyond the size of the unit cell. We have investigated the growth mechanism of YBa_(2)Cu_(3)O_(7) cuprate superconductor, using a consistent approach based on the growth of noninteger numbers of YBa_(2)Cu_(3)O_(7) layers in YBa_(2)Cu_(3)O_(7)/PrBa_(2)Cu_(3)O_(7) superlattices. Ex situ chemical and structural analysis evidence a 2D block-by-block mechanism in which the minimum growth units are complete unit cell blocks, growing coherently over large lateral distances., Fundación Universidad Carlos III de Madrid, CICYT, Max Kade Foundation, Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

We acknowledge financial support by Spanish MICINN through grants MAT2011-27470-C01 and Consolider Ingenio 2010 - CSD2009-00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama) and by the ERC starting Investigator Award, grant #239739 STEMOX. RS wishes to acknowledge the MICINN (Spain) for granting a Ramon y Cajal fellowship. MAF is Research Fellow of CONICET (Argentine). Financial support of CONICET is gratefully acknowledged. OJD acknowledges a postdoctoral fellowship from JCCM. JS acknowledges a Juan de la Cierva fellowship from MICINN (Spain). The authors thank Dr. Hugo Schlich from Mateck GmbH for providing information about the process of bicrystals production, Masashi Watanabe for the Digital Micrograph PCA plug-in and J. Luck for help with specimen preparation, and A. de Andrés for helpful discussion and assistance on experimental matters. Electron microscopy observations at ORNL (SJP, MV) were sponsored by the Materials Sciences and Engineering Division of the U.S. Department of Energy (DOE) and and through the Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, DOE-BES. ESM measurements (SVK, SJ, AK) were performed at the Center for Nanophase Materials Sciences and supported by the Division of Scientific User Facilities of the U.S. Department of Energy (DOE)., The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Besides the possible effect of the modified chemical bonding, this negative charge gives rise to an additional barrier for ion transport at the grain boundary., Ministerio de Ciencia e Innovación (MICINN), Comunidad de Madrid, Consolider Ingenio 2010, ERC starting Investigator Award, CONICET, JCCM, Materials Sciences and Engineering Division of the U.S. Department of Energy (DOE), Center for Nanophase Materials Sciences (CNMS), Scientific User Facilities Division, DOE-BES, Division of Scientific User Facilities of the U.S. Department of Energy (DOE), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 1996 American Institute of Physics., The use of Kramers–Kronig transforms is proposed for the treatment of admittance spectroscopy data of junctions when significant shunt conductance or series resistance is present. An algorithm has been implemented to calculate the transformations numerically and the validity of the method developed has been tested using simulated data. Two experimental systems, p-n junctions into InP made by ion implantation, and atomic-layer-epitaxy-grown CdS/CdTe heterojunctions, have been characterized using this procedure., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2011 American Physical Society. Artículo firmado por 13 autores. We acknowledge financial support from MICINN grants MAT2008-06517-C02-01, CSD2009-00013, MAT2008-06517-C02-02, and PI2010-60E013 and provision of beamtime by the European Synchrotron Radiation Facility., We report the observation between 40 and 120 K of anomalous magnetic hysteresis loops in thin epitaxial films of La_(0.7)Ca_(0.3)MnO_(3) grown on ferroelectric BaTiO_(3). These hysteresis loops display extremely unusual features: after switching at coercivity, the magnetization overshoots the eventual high-field value. We study the strains in the film and substrate with x-ray diffraction and propose a model of two magnetic moment populations with different magnetoelastic anisotropies. The relative weights of both populations can be estimated by comparison with twin samples of La_(0.7)Ca_(0.3)MnO_(3) films on nonferroelectric SrTiO_(3). We propose that the observed magnetization overshoots the result from differences in the magnetostriction balance as the applied magnetic field increases. The picture of a nonuniform strain field in La_(0.7)Ca_(0.3)MnO_(3) on BaTiO_(3), caused by the corrugation of the ferroelectric domains in the rhombohedric phase of BaTiO_(3), is compatible with the magnetic granular behavior observed in the temperature and field dependences of the magnetization as well as in the low temperature magnetoresistance exhibited by the epitaxial film., MICINN, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2006 The American Physical Society. Work at Universidad Complutense de Madrid was supported by MCYT MAT 2005-06024-C02-02, CAM GRMAT-0771/2004, UCM PR3/04-12399 and Fundación Ramón Areces. M. A. López de la Torre acknowledges financial support through JCCM projects PBI-02-015 and PAI-05- 013. We thank A. Quijano and J. J Palacios for helpful discussions., We report the observation of a paramagnetic contribution to the field cooled magnetization that develops below the superconducting transition temperature T_(c) in measurements performed on YBa_(2)Cu_(3)O_(7)/La_(0.7)Ca_(0.3)MnO_(3) superlattices. The effect has been detected only for samples whose manganite layers are magnetically granular. We discuss our observation of this paramagnetic Meissner effect (Wohlleben effect) in terms of an inhomogeneous superconducting state at the interface with the magnetically granular manganite layers., MCYT, CAM, UCM, Fundación Ramón Areces, JCCM, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2016 Elsevier B.V. This research has been financed by the “Ministerio de Ciencia e Innovación” (MICINN, Spain) and by the “Fundación Neurociencias y Envejecimiento” (Spain) through grants MAT2010-18432 and 4153592, 4143942 respectively as well as by the MAT2013-40722-R project., Li_(1+x)M_(x)Ti_(2−x)(PO_(4))_(3) powders with x = 0 and 0.3 and M = Al, Cr and Fe have been sintered by conventional sintering (CS) and Spark Plasma Sintering (SPS), and the electrical properties have been compared. The use of SPS allows preparing samples with higher density at lower temperature and shorter time than the CS, avoiding segregation of secondary phases and with reduced crystallite size. The introduction of aluminum, chromium and iron in the LiTi_(2)(PO_(4))_(3) (LTP) clearly enhances ionic conductivity even if the samples have similar densities. Despite the different level of density reached with CS and SPS, the activation energies of dc and grain boundary contributions are very similar and the differences in ionic conductivity are determined by pre-exponential factors. The samples produced by SPS showed a well-defined grain boundary meaning a more homogenous electrical contact., Ministerio de Ciencia e Innovación (MICINN, Spain), Fundación Neurociencias y Envejecimiento (Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2002 The American Physical Society., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2014 AIP Publishing LLC. We acknowledge financial support by Spanish MICINN through Grants MAT2011-27470-C02 and Consolider Ingenio 2010-CSD2009-00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama). We thank Patrizia De Marco, Francesco Perrozzi, and Luca Ottaviano for their help and guidance in preparing the graphene samples. We thank Susana Álvarez and Alicia de Andrés for help with preliminary Raman spectroscopy experiments, We report on the fabrication and magnetotransport characterization of hybrid graphene-based nanodevices with epitaxial nanopatterned La_(0.7)Sr_(0.3)MnO_(3) manganite electrodes grown on SrTiO_(3)(100). The few-layer graphene was deposited onto the predefined manganite nanowires by using a mechanical transfer technique. These nanodevices exhibit resistive switching and hysteretic transport as measured by current-voltage curves. The resistance can be reversibly switched between high and low states, yielding a consistent non-volatile memory response. The effect is discussed in terms of changes in the concentration of oxygen vacancies at the space charge region of the Schottky barriers building at the contacts., Minsiterio de Ciencia e Innovación (MICINN), Consolider Ingenio 2010, Comunidad de Madrid, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 Macmillan Publishers Limited. We thank Andrew Millis and Giniyat Khaliullin for stimulating discussions. J.G.-B. thanks the Spanish Ministry of Science and Innovation (MICINN) for financial support through the Specialization in International Organizations fellowship. This work was supported by Spanish MICINN Grant MAT 2008 06517, Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA). Work at ORNL was supported by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Some XMCD experiments were conducted with the approval of JASRI (proposal no. 2007B1516) and supported by UK EPSRC Grants EP/F062729 and EP/G056463/1., In systems with strong electron-lattice coupling, such as manganites, orbital degeneracy is lifted, causing a null expectation value of the orbital magnetic moment. Magnetic structure is thus determined by spin–spin superexchange. In titanates, however, with much smaller Jahn–Teller distortions, orbital degeneracy might allow non-zero values of the orbital magnetic moment, and novel forms of ferromagnetic superexchange interaction unique to t_2g electron systems have been theoretically predicted, although their experimental observation has remained elusive. In this paper, we report a new kind of Ti^3+ ferromagnetism at LaMnO_3/SrTiO_3 epitaxial interfaces. It results from charge transfer to the empty conduction band of the titanate and has spin and orbital contributions evidencing the role of orbital degeneracy. The possibility of tuning magnetic alignment (ferromagnetic or antiferromagnetic) of Ti and Mn moments by structural parameters is demonstrated. This result will provide important clues for understanding the effects of orbital degeneracy in superexchange coupling., Ministerio de Ciencia e Innovación (MICINN), España, Specialization in International Organizations, Consolider Ingenio, U.S. Department of Energy, EE.UU., Engineering and Physical Sciences Research Council (EPSRC), Reino Unido, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2003 The American Physical Society. We thank M. A. Alario for fruitful conversations. Financial support by Spanish CICYT Grant No. MAT 2000-1468 is also acknowledged., We report on the effect of oxygen disorder in the CuO chains on the superconducting properties of oxygen depleted YBa_(2)Cu_(3)O_(x)(YBCO). While moderate disorder, induced thermally, depresses the critical temperature as a result of a reduced carrier concentration, strong oxygen disorder and chain fragmentation induced by low energy (80 keV) He^(+) irradiation suppresses the critical temperature beyond the values expected from the reduction of the carrier density. This provides an experimental evidence of pair breaking by chain disorder and outlines the importance of chain states in the pairing mechanism in the YBCO family., Spanish CICYT, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2015 Macmillan Publishers Limited. We acknowledge financial support from the European Research Council (ERC Advanced Grant FEMMES, No. 267579) and the Labex NanoSaclay project FIRET. The ALICE project is supported by the BMBF Contract No. 05K10PC2. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 226716. Work at UCM was supported by grants MAT2011-27470-C02 and Consolider Ingenio 2010—CSD2009- 00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama) and by the ERC starting Investigator Award, grant #239739 STEMOX. Microscopy at ORNL (M.V.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. We thank N.M. Nemes and M. Garcı´a- Herna´ndez for collaboration and assistance with the preliminary magnetic characterization of the LSMO/LFO structures and V. Garcia for his constructive comments. Author contributions: F.Y.B., J.S., A.B. and M.B. designed and conceived the experiment. F.Y.B. and A.R.-C. were involved in sample growth and characterization. F.Y.B. and C.V were involved in lithography process and transport measurements. S.V. conceived the synchrotron experiments. F.Y.B., S.V., R.A., J.T., A.A.U¨ . and A.R.-C. were involved in synchrotron measurements and data analysis. M.V. and S.J.P. performed electron microscopy. M.N.G. and M.B performed tunnelling magneto-resistance simulations. F.Y.B., M.N.G., C.V., Z.S., C.L., J.E.V., J.S., A.B. and M.B analyzed the data and discussed the manuscript. F.Y.B. and M.B. wrote the article with inputs from all co-authors. Competing financial interests: The authors declare no competing financial interests., At interfaces between complex oxides, electronic, orbital and magnetic reconstructions may produce states of matter absent from the materials involved, offering novel possibilities for electronic and spintronic devices. Here we show that magnetic reconstruction has a strong influence on the interfacial spin selectivity, a key parameter controlling spin transport in magnetic tunnel junctions. In epitaxial heterostructures combining layers of antiferromagnetic LaFeO_3 (LFO) and ferromagnetic La_0.7Sr_0.3MnO_3 (LSMO), we find that a net magnetic moment is induced in the first few unit planes of LFO near the interface with LSMO. Using X-ray photoemission electron microscopy, we show that the ferromagnetic domain structure of the manganite electrodes is imprinted into the antiferromagnetic tunnel barrier, endowing it with spin selectivity. Finally, we find that the spin arrangement resulting from coexisting ferromagnetic and antiferromagnetic interactions strongly influences the tunnel magnetoresistance of LSMO/LFO/LSMO junctions through competing spin-polarization and spin-filtering effects., Unión Europea. FP7, Comunidad Autónoma de Madrid, Ministerio de Economía y Competitividad (MINECO), Labex NanoSaclay project FIRET, ALICE Project (BMBF), Bundesministerium für Bildung und Forschung (BMBF), Alemania, European Research Council, Programa Consolider-Ingenio (Imagine), MINECO, España, ERC starting Investigator Award STEMOX, US Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division, PHOTONIC ADVANCED MATERIALS: PHAMA 2.0-CM PROGRAMME, Consejo Superior de Investigaciones Científicas (CSIC), España, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© Sociedad Española de Cerámica y Vidrio. National Meeting on Electroceramics (9. 2009. Madrid). Este trabajo ha sido realizado gracias al proyecto PR34/07-15895 BSCH-UCM., Haciendo uso de la química sol-gel, se han preparado ortofosfatos de composición LiTi_(2)(PO_(4))_(3) y Li_(1.05)(Cr/Fe)_(0.05)Ti_(1.95)(PO_(4))_(3) a temperaturas moderadas mediante el método Pechini. Estas fases han sido caracterizadas estructural y microestructuralmente por difracción de rayos X de polvo y microscopía electrónica de barrido (SEM), encontrándose que todas cristalizan en una estructura tipo NASICON, con parámetros de red muy similares. El dopaje con Fe y Cr permite aumentar la densidad de las muestras en la sinterización, mejorando de forma apreciable su conductividad iónica. Se ha observado un incremento de hasta cuatro órdenes de magnitud en la conductividad a temperatura ambiente obteniéndose una energía de activación de 0.29 eV para el material dopado con Cr., Compounds of formula Li_(1+x)M^(III)_(x)Ti_(2-x)(PO_(4))_(3) with M^(III)=Cr,Fe and x=0 and 0.05 have been prepared at soft temperatures using the Pechini synthesis method, based on sol-gel chemistry. The structural and microstructural characterization by X-ray diffraction and Scanning Electron Microscopy (SEM), shows that all of them crystallize in a NASICON-type structure with similar lattice parameters. Doping with Fe and Cr, causes an increase of the density of the samples after sinterization what clearly improves the ionic conductivity of the original material, LiTi_(2)(PO_(4))_(3) until values of 9x10^(-4) S cm^(-1) at room temperature in the chromium-doped material., BSCH-UCM, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2013 American Physical Society. Work at Argonne National Laboratory and use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357. Work at UCM was supported by the Spanish MICINN through Grant No. MAT2011- 27470-C02, Consolider Ingenio 2010 - CSD2009-00013 (Imagine), and by CAM through Grant No. S2009/MAT- 1756 (Phama). This work has benefited from the use of the Lujan Neutron Scattering Center at LANSCE, which is funded by the Department of Energy’s Office of Basic Energy Sciences. Los Alamos National Laboratory is operated by Los Alamos National Security LLC under DOE through Contract No. DE-AC52-06NA25396., We report a strong effect of interface-induced magnetization on the transport properties of magnetic tunnel junctions consisting of ferromagnetic manganite La_(0.7)Ca_(0.3)MnO_(3) and insulating cuprate PrBa_(2)Cu_(3)O_(7). Contrary to the typically observed steady increase of the tunnel magnetoresistance with decreasing temperature, this system exhibits a sudden anomalous decrease at low temperatures. Interestingly, this anomalous behavior can be attributed to the competition between the positive spin polarization of the manganite contacts and the negative spin-filter effect from the interface-induced Cu magnetization., Comunidad de Madrid, Ministerio de Ciencia en Innovación (MICINN), U.S. Department of Energy, Office of Basic Energy Sciences, Los Alamos National Security LLC, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2005 The American Physical Society. Authors from CINVESTAV-IPN thank CONACYT for fi- nancial support. Authors from Universidad Complutense acknowledge financial support from MCYT. K.J.M. thanks CINVESTAV-IPN for financial support during her stay at Universidad Complutense., We report on dispersive conductivity measurements in the oxygen ion conductor Gd_(2)(Ti_(2−y)Zr_(y))O_(7). Increasing Zr content leads to higher concentration of oxygen vacancies and results in higher activation energies for long-range ion transport, whilst the microscopic energy barrier for single ion hopping remains constant. We find evidence that, besides oxygen binding energy, enhanced cooperativity in oxygen ion dynamics determines the activation energy for long-range diffusion., CONACYT, MCYT, CINVESTAV-IPN, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2014 Macmillan Publishers Limited. We acknowledge financial support by the Spanish MICINN through grants MAT2011- 27470-C02 and Consolider Ingenio 2010–CSD2009-00013 (Imagine), by CAM through grant S2009/MAT-1756 (Phama) and by the ERC starting Investigator Award, grant #239739 STEMOX (G.S.-S.). Work at Argonne National Laboratory (Y.L. and S.G.E.t.V.) was supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. Research (J.F.) and X-ray experiments carried out at the Advanced Photon Source and X-ray experiments carried out at Advanced Light Source were supported by DOE, Office of Science, BES. We thank Masashi Watanabe for the Digital Micrograph PCA plug-in. Research at ORNL was sponsored by the US Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division (SO) and through the Center for Nanophase Materials Sciences (CNMS), which is sponsored by the Scientific User Facilities Division, DOE-BES (MV). Research (MRF) and neutron scattering experiments at the Lujan Center for Neutron Scattering, the Los Alamos National Laboratory were supported by DOE, Office of Science, BES. the Los Alamos National Laboratory is operated by the Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396. We thank C.H. Zhu and P. Shafer for support during XMCD experiments conducted at ALS., Electric-field control of magnetism has remained a major challenge which would greatly impact data storage technology. Although progress in this direction has been recently achieved, reversible magnetization switching by an electric field requires the assistance of a bias magnetic field. Here we take advantage of the novel electronic phenomena emerging at interfaces between correlated oxides and demonstrate reversible, voltage-driven magnetization switching without magnetic field. Sandwiching a non-superconducting cuprate between two manganese oxide layers, we find a novel form of magnetoelectric coupling arising from the orbital reconstruction at the interface between interfacial Mn spins and localized states in the CuO2 planes. This results in a ferromagnetic coupling between the manganite layers that can be controlled by a voltage. Consequently, magnetic tunnel junctions can be electrically toggled between two magnetization states, and the corresponding spin-dependent resistance states, in the absence of a magnetic field., Spanish MICINN, Consolider Ingenio 2010, CAM, ERC starting Investigator Award, US Department of Energy (DOE), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 The American Physical Society. This work was supported by MCYT MAT 2002-2642 and CAM 07N/0032/2002 and Fundación Ramón Areces., Here we examine the ferromagnetic/superconducting proximity effect in half-metallic ferromagnetic La_(0.7)Ca_(0.3)MnO_(3) and high-T_(c) superconducting YBa_(2)Cu_(3)O_(7) artificial structures. We have found experimental evidence for the coupling between superconducting layers through ferromagnetic spacers in superlattices. This is consistent with a long-range proximity effect in half-metal ferromagnet/d-wave superconductor structures., MCYT, CAM, Fundación Ramón Areces, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 American Institute of Physics., We report on complex admittance measurements on ZrO_(2):Y_(2)O_(3) (YSZ) thin films in the parallel plate geometry. Highly textured YSZ thin films, grown by rf sputtering, allow measuring complex admittance free of the effect of charge blocking at grain boundaries. We have examined low-temperature (close to room temperature) regime dominated by association of oxygen vacancies. Complex admittance analyzed in terms of the modulus formalism supplies information on correlation effects in ion motion and allows obtaining an association energy for the oxygen vacancies of 0.45 eV, in agreement with previous theoretical calculations., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 The American Physical Society. The work performed at the Naval Research Laboratory was supported by ONR. We thank J. Ullrich for help in the dielectric measurements and J. Santamaría and C. T. Moynihan for helpful discussions., Electrical relaxation data of crystalline yttria-stabilized zirconia are used to analyze the permittivity change observed in the spectra of the real part of the permittivity in ionic conducting materials. It is found that this permittivity change is independent of both temperature and mobile-ion concentration, and it is determined solely by the degree of interaction among ions in the relaxation process. This finding is at odds with an expression for the permittivity change in the framework of a proposed universal ac conductivity scaling law for glassy ionic conductors. On the other hand, not only the total permitivity change, but also the particular frequency dependence of the permittivity spectra is found to be consistent with the analysis of electrical relaxation in terms of the electric modulus. The results of this work give further support to the use of the electric modulus in describing electrical relaxation in ionic conductors., ONR, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2001 The American Physical Society. Financial support from CICYT Grant Nos. MAT94-0604, MAT97-0675, and MAT99-1706E is acknowledged. Z.S. thanks AECI for financial support., Epitaxial YBa_(2)Cu_(3)O_(7) thin films, grown by high-pressure dc sputtering, are irradiated with He^(+) ions at 80 keV with doses between 10^(14) and 10^(15) cm^(-2). Irradiation reduces the critical temperature but it does not modify the carrier concentration. Angle-dependent resistivity is used to show that the mass anisotropy does not change upon irradiation. The melting transition in magnetic fields applied parallel to the c axis is analyzed by I-V critical scaling, and all irradiated and nonirradiated samples show a three-dimensional vortex glass transition with the same critical exponents. The dissipation in the liquid state is analyzed in terms of the activation energy of the magnetoresistance in a perpendicular magnetic field. While as-grown samples show an activation energy depending as 1/H on the applied magnetic field, irradiated samples show a dependence as 1/H^(0.5), characteristic of plastic deformation of vortices. This is discussed in terms of the point disorder introduced by ion irradiation., CICYT, AECI, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2002 The American Physical Society. We thank Professor Ivan Schuller for helpful conversations and interesting suggestions. This work was supported by Spanish CICYT MAT 2000 1468. Work at LBNL/NCEM was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098., We report on the growth mechanism of YBa_(2)Cu_(3)O_(7-x). Our study is based on an analysis of ultrathin YBa_(2)Cu_(3)O_(7-x) (YBCO) layers in c-axis-oriented YBa_(2)Cu_(3)O_(7-x)/PrBa_(2)Cu_(3)O_(7)superlattices. We have found that the release of epitaxial strain in very thin YBCO layers triggers a change in the dimensionality of the growth mode. Ultrathin epitaxially strained YBCO layers with thickness below 3 unit cells grow in a blockby-block two -dimensional mode that is coherent over large lateral distances. Meanwhile, when the thickness increases and the strain relaxes, layer growth turns three-dimensional, resulting in rougher layers and interfaces., Spanish CICYT, Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

©2009 IEEE-Institute of Electrical and Electronics Engineers. N. N. M. acknowledges the “Ramon y Cajal” fellowship of the Spanish Ministry of Science and Education. This work was supported in part by SPIN-MAT06024 C01 and C02 and by Marie-Curie-IRG grant No. 024861, and by OTKA PF63954, K68807 and NK60984., The magnetic properties of La_0.7Ca_0.3Mn_O3 (LCMO) manganite thin films were studied with magnetometry and ferromagnetic resonance as a function of film thickness. They maintain the colossal magnetoresistance behavior with a pronounced metal-insulator transition around 150-200 K, except for the very thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain ferromagnetic, without a decrease in saturation magnetization, indicating an absence of dead-layers, although below approximately 6 nm the films remain insulating at low temperature. Magnetization hysteresis loops reveal that the magnetic easy axes lie in the plane of the film for thicknesses in the range of 4-15 nm. Ferromagnetic resonance studies confirm that the easy axes are in-plane, and find a biaxial symmetry in-plane with two, perpendicular easy axes. The directions of the easy axes with respect to the crystallographic directions of the cubic SrTiO_3 substrate differ by 45 deg in 4- and 15-nm-thick LCMO films., Unión Europea. FP7, Ministerio de Educación y Ciencia (MEC), España, Programa Ramón y Cajal, Acciones Marie Skłodowska-Curie (UE), Hungarian Scientific Research Fund (OTKA), Hungría, Depto. de Física de Materiales, Fac. de Ciencias Físicas, TRUE, pub

© 2010 The American Physical Society. We acknowledge financial support by Junta de Comunidades de Castilla-La Mancha through Project No. PAI-05- 013, by CAM under Grant No. S2009/MAT-1756 Phama, by Spanish MICINN through Grants No. MAT2008-06517- C02, No. MAT2008-06542-C04, and No. FIS2009-12964- C05-04, and Consolider Ingenio 2010 under Grant No. CSD2009-00013 Imagine. We thank J. Garcia-Barriocanal for helpful discussions. We are indebted to the staff of SpLine for their help during the experimental work at ESRF., We report on the effect of grain size on the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling. Complex impedance measurements, as a function of temperature and frequency are performed on 10 mol % yttria-stabilized zirconia nanocrystalline samples with grain sizes ranging from 900 to 17 nm. Bulk ionic conductivity decreases dramatically for grain sizes below 100 nm, although its activation energy is essentially independent of grain size. The results are interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries is on the order of 1 nm for large micron-sized grains but extends up to 7 nm when decreasing the grain size down to 17 nm. This gives rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity., Junta de Comunidades de Castilla-La Mancha, CAM, Spanish MICINN, Consolider Ingenio 2010, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 1998 The American Physical Society., We present complex admittance measurements on single-crystal yttria-stabilized zirconia and polycrystalline Li_(0.5)La_(0.5)TiO_(3) over the frequency range 5 Hz to 30 MHz and at temperatures ranging between 150 and 650 K. Electric-field relaxation in both fast ionic conductors can be described using Kohlrausch-Williams-Watts decay functions, but departures are observed at high frequencies and low temperatures. Electric modulus data obey the Dixon Nagel scaling that has been proposed to be universal in describing the relaxation processes in supercooled liquids. Our data provide broader universality to the Dixon-Nagel scaling, and are interpreted in terms of the influence of mobile ions positional disorder on the relaxation dynamics., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© EDP Sciences. The authors are grateful to C. Cantoni for the bulk YSZ sample, M. Watanabe for the PCA plug in for Digital Micrograph and J. Luck for sample preparation. Research at Oak Ridge National Laboratory was sponsored by the US Department of Energy, Office of Science, Materials Sciences and Engineering Division (MPO, MV, SJP). Research at Vanderbilt was supported in part by the US Department of Energy Grant DEFG02- 09ER46554 (TJP, STP) and the McMinn Endowment (STP). Research at Universidad Complutense was supported by the Spanish Ministry for Science and Innovation, and the Madrid Regional Government. Computations were performed at the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory., Colossal ionic conductivity was recently discovered in YSZ/SrTiO_(3) multilayers and was explained in terms of strain- and interface-enhanced disorder of the O sublattice. In the present paper we use a combination of scanning transmission electron microscopy and electron energy loss spectroscopy (EELS) and theoretical EELS simulations to confirm the presence of a disordered YSZ O sublattice in coherent YSZ/SrTiO_(3) multilayers. O K-edge fine structure simulated for the strained disordered O sublattice phase of YSZ possesses blurred-out features compared to that of ordered cubic bulk YSZ, and experimental EELS fine structure taken from the strained YSZ of coherent YSZ/SrTiO_(3) thin films is similarly blurred out. Elemental mapping is shown to be capable of resolving ordered YSZ O sublattices. Elemental mapping of O in the coherent YSZ/STO multilayers is presented in which the O sublattice is seen to be clearly resolved in the STO but blurred out in the YSZ, indicating it to be disordered. In addition, we present imaging and EELS results which show that strained regions exist at the incoherent interfaces of YSZ islands in STO with blurred out fine structure, suggesting these incoherent regions may also support high ionic conductivities. Recently, Cavallaro et al. reported electronic conductivities in samples of incoherent disconnected islands embedded in STO that are similar to the islands described herein. The presence of a region of O depleted STO at the interface with incoherent YSZ islands is revealed by EELS elemental mapping, implying the n-type doping of STO/YSZ nanocomposites with disconnected incoherent YSZ islands., US Department of Energy, Office of Science, Materials Sciences and Engineering Division, McMinn Endowment, Spanish Ministry for Science and Innovation, Madrid Regional Government, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

The local order around Zr and Y atoms of nanocrystalline yttria-stabilized zirconia (YSZ) powders with different grain sizes has been investigated by x-ray absorption spectroscopies. The samples were prepared by means of mechanical alloying with or without subsequent sintering treatment and also by milling commercial YSZ. Our study is motivated by the interest in the electrical properties of grain boundaries and the controversy about the level of disorder in the intergrain regions in nanocrystalline YSZ. The x-ray absorption near edge structure (XANES) analysis indicates that the local order of all the sintered samples is independent of the grain size. This is confirmed by the analysis of the extended x-ray absorption fine structure, which points out also that, in contrast to that found in sintered samples, the local order around the cation in the samples milled without further sintering treatment extends only to the first coordination shell. Finally, the results of ab initio Zr K-edge XANES calculations lead us to conclude that the observed changes of the shape of the white line are not related to a phase transformation but reflects the short-range order present in the as-milled samples., Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 The American Physical Society. This work has been carried out with the financial support of Mexican Conacyt Grant No. SEP-2003-C02-44075 and Spanish MCYT Contracts No. MAT2005-06024-C02 and No. MAT2008-06517-C02. M.R.D.G. thanks Conacyt for financial support. K.L. Ngai was supported in part by ONR under Program Element and Project 61153N., In this work we evaluate the effect of cation size on the dc activation energy needed for oxygen ion migration, E_(dc), in highly disordered pyrochlore-type ionic conductors A_(2)B_(2)O_(7). Twenty six compositions with the general formula, Ln_(2)Zr_(2−y)Ti_(y)O_(7), Ln_(1.7)Mg_(0.3)Zr_(2)O_(7) (Ln=Y, Dy, and Gd), and Gd_(2−y)La_(y)Zr_(2)O_(7), were prepared by mechanical milling, and their electrical properties were measured by using impedance spectroscopy as a function of frequency and temperature. By using the coupling model we also examine the effect of cation radii R_(A) and R_(B) on the microscopic potential-energy barrier, E_(a), which oxygen ions encounter when hopping into neighboring vacant sites. We find that, for a fixed B-site-cation radius R_(B), both activation energies decrease with increasing A-site-cation size, R_(A), as a consequence of the increase in the unit-cell volume. In contrast, for a given R_(A) size, the E_(dc) of the Ln_(2)Zr_(2−y)Ti_(y)O_(7) series increases when the average R_(B) size increases. This behavior is associated with enhanced interactions among mobile oxygen ions as the structural disorder increases with R_(B)., Mexican Conacyt, Spanish MCYT, Conacyt ONR under Program Element, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2016 Author(s). We thank J. Pearson for assistance with SQUID magnetometry study. Work at ORNL is supported by the Division of Scientific User Facilities of the Office of Basic Energy Sciences (BES), US Department of Energy (DOE). Work at MSD, ANL was supported by the U.S. DOE, Office of Science, BES, Materials Sciences and Engineering Division. Research at UCM was supported by Spanish MICINN through Grant Nos. MAT2014-52405-C02-01 and Consolider Ingenio 2010-CSD2009-00013 (Imagine), by CAM through Grant No. S2014/MAT-PHAMA II. This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We also thank Diamond Light Source for access to beamline I10., In artificial multiferroics hybrids consisting of ferromagnetic La_(0.7)Sr_(0.3)MnO_(3) (LSMO) and ferroelectric BaTiO_(3) epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. The Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. However, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures., Division of Scientific User Facilities of the Office of Basic Energy Sciences (BES), US Department of Energy (DOE), U.S. DOE, Office of Science, BES, Materials Sciences and Engineering Division, Spanish MICINN, Consolider Ingenio 2010, CAM, Argonne National Laboratory, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub