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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 YBa2Cu3O7 High Tc cuprates separated by a half metallic La0.7Sr0.3MnO3 manganite ferromagnet has uncovered a novel unconventional triplet proximity effect. In this paper we examine the temperature dependence of the critical current of 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.

Memristors based on oxide tunnel junctions are promising candidates for energy efficient neuromorphic computing. However, the low power sensing of the nonvolatile resistive state is an important challenge. We report the optically induced sensing of the resistive state of a memristor based on a La_0.7Sr_0.3MnO_3/BaTiO_3/In_2O_3:SnO_2 (90:10) heterostructure with a 3 nm thick BaTiO3 ferroelectric barrier. The nonvolatile memristive response originates from the modulation of an interfacial Schottky barrier at the La_0.7Sr_0.3MnO_3/BaTiO_3 interface, yielding robust intermediate memristive states. The Schottky barrier produces a photovoltaic response when illuminated with a 3.3 eV UV LED, which depends on the state. The open circuit voltage V_oc correlates linearly with the resistance of each state, enabling active sensing of the memristive state at light power densities as low as 20 mW/cm^2 and temperatures up to 100 K. This opens up avenues for the efficient and minimally invasive readout of the memory states in hybrid devices.

Interfacial inversion symmetry breaking gives rise to electronic properties that differ substantially from those of the bulk constituent materials. Here, we report on the realization of an artificial ferromagnetic quasi-two-dimensional electron gas (q2DEG) at the (111) interfaces between LaAlO3, EuTiO3, and SrTiO3characterized by a reconstruction of the bulk quasioctahedral crystal field into a trigonal one. The q2DEG is created through a transfer of electrons to the EuTiO3layers at the interface with LaAlO3, extending into the first layers of SrTiO3, as shown by an electron-energy-loss spectroscopy map of the titanium valence with atomic column resolution. Interestingly, polarized X-ray absorption spectroscopy shows that the Eu-4f and the Ti-3d magnetic moments order ferromagnetically and exhibit the same magnetic field dependence at low temperature. In addition, the q2DEG presents a sizable in-plane orbital moment even at low magnetic field (0.1 T) possibly related to Ti-3d electrons occupying bands with the main a1gorbital character. The results show an intriguing interplay between ferromagnetism, spin-orbit coupling, and trigonal crystal field splitting in the (111) LaAlO3/EuTiO3/SrTiO3q2DEG.

Spin-pumping across ferromagnet/superconductor (F/S) interfaces has attracted much attention lately. Yet the focus has been mainly on s-wave superconductors-based systems whereas (high-temperature) d-wave superconductors such as YBa2Cu3O7-d (YBCO) have received scarce attention despite their fundamental and technological interest. Here we use wideband ferromagnetic resonance to study spin-pumping effects in bilayers that combine a soft metallic Ni80Fe20 (Py) ferromagnet and YBCO. We evaluate the spin conductance in YBCO by analyzing the magnetization dynamics in Py. We find that the Gilbert damping exhibits a drastic drop as the heterostructures are cooled across the normal-superconducting transition and then, depending on the S/F interface morphology, either stays constant or shows a strong upturn. This unique behavior is explained considering quasiparticle density of states at the YBCO surface, and is a direct consequence of zero-gap nodes for particular directions in the momentum space. Besides showing the fingerprint of d-wave superconductivity in spin-pumping, our results demonstrate the potential of high-temperature superconductors for fine tuning of the magnetization dynamics in ferromagnets using k-space degrees of freedom of d-wave/F interfaces., Comment: 20 pages, 6 figures

Ruddlesden–Popper oxides, (AO)(ABO3) n , occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen-deficient manganese Ruddlesden–Popper-related phases, La0.5Ca2.5Mn2O6.5 and La0.5Ca2.5Mn2O6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La0.5Ca2.5Mn2O7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy-loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO2] layers along [031] and [0{\bar 1}3] directions. The gradual decrease of the Mn oxidation state, accommodated by short-range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short-range order–disorder phenomena of La and Ca cations have been detected in the reduced La0.5Ca2.5Mn2O7−δ, as previously reported in the parent compound.

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.

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International audience; Superconductor/Ferromagnet (S/F) hybrid systems show interesting magneto-transport behaviors that result from the transfer of properties between both constituents. For instance, magnetic memory can be transferred from the F into the S through the pinning of superconducting vortices by the ferromagnetic textures. The ability to tailor this type of induced behavior is important to broaden its range of application. Here we show that engineering the F magnetization reversal allows tuning the strength of the vortex pinning (and memory) effects, as well as the field range in which they appear. This is done by using magnetic multilayers in which Co thin films are combined with different heavy metals (Ru, Ir, Pt). By choosing the materials, thicknesses, and stacking order of the layers, we can design the characteristic domain size and morphology, from out-of-plane magnetized stripe domains to much smaller magnetic skyrmions. These changes strongly affect the magneto-transport properties. The underlying mechanisms are identified by comparing the experimental results to a magnetic pinning model. * javier.villegas@cnrs-thales.fr 2

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 nanometer-thick 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 ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ bottom electrode and ${\mathrm{BaTiO}}_{3}$ 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 neuromorphic computing.

International audience; In transition metal perovskites (ABO3) most physical properties are tunable by structural parameters such as the rotation of the BO6 octahedra. Examples include the Néel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scan-dates. Since oxides often host large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in SrTiO3-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remain unknown. In this Letter, we identify a bismuth-based perovskite with a giant, electrically-switchable Rashba interaction whose amplitude can be controlled by both the ferroelectric polarization and the breathing mode of oxygen octahedra. This particular structural parameter arises from the strongly covalent nature of the Bi-O bonds, reminiscent of the situation in perovskite nickelates. Our results not only provide novel strategies to craft agile spin-charge converters but also highlight the relevance of covalence as a powerful handle to design emerging properties in complex oxides.

One of the most desirable attributes of non-volatile memories and memristors is a fast and non-destructive read out of their resistive state. Prototypical ferroelectric (FE) memories use the bulk photovoltaic response associated to the polarization of FE films to address this requirement by optically sensing binary memory cells. A more advanced type of non-volatile memories is FE tunnel junctions (FTJs). They feature resistive state ratios R_High/R_Low up to 10^6, with a continuum of resistive states accessible, making them promising candidates for neuromorphic computing applications. A novel approach is presented to achieve the optical sensing of the resistive state in a La_(0.7)Sr_(0.3)MnO_3/BaTiO_3/ITO FTJ, by using the Schottky barrier forming in the La_(0.7)Sr_(0.3)MnO_3/BaTiO_3/ITO interface to dramatically enhance the optical response of the 5 nm BaTiO3 (BTO) barrier. Illumination with UV light exceeding the BTO bandgap through the top transparent ITO electrode generates a photovoltaic response in the R_High state, with an open circuit voltage V_oc of 400 mV at 20 K, enabling the optical sensing of the resistive state. In the R_Low state, the Schottky barrier is removed and the photoresponse disappears.

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.

This work reports on magnetocapacitance (MC) effects in epitaxial heterostructures of nominally 15 unit cells (u.c.) LaMnO3 (LMO) and 2 u.c. SrTiO3 (STO) with an alternating layer-repetition rate of 8: (LMO15/STO2)8. Epitaxial multilayer growth at high temperatures (900 °C) activates a selective inter-diffusion of La3+ and Sr2+ cations across the interfaces, which gives rise to Sr p-doping of the LMO and La n-doping of the STO layers. MC effects at the buried La1–xSrxMnO3/SrxLa1–xTiO3 (LSMO/SLTO) interfaces are probed by frequency, temperature and magnetic field dependent AC impedance spectroscopy. The technique is shown to be appropriate to account for the separate analysis of different resistance and capacitance contributions at the buried interfaces. As a result of the La/Sr inter-diffusion process, Schottky barriers are formed at the LSMO/SLTO interfaces, which give rise to massive MC of up to ≈ −200% in the out-of-plane film direction. The capacitance of the manganite-titanate LSMO/SLTO interfaces may be coupled indirectly to the resistance of the LSMO layers, because the Schottky space-charge layers and their capacitance can be modulated by varying the concentration of highly mobile charge carriers in the LSMO with a magnetic field.

Strong electronic correlations can produce remarkable phenomena such as metal–insulator transitions and greatly enhance superconductivity, thermoelectricity or optical nonlinearity. In correlated systems, spatially varying charge textures also amplify magnetoelectric effects or electroresistance in mesostructures. However, how spatially varying spin textures may influence electron transport in the presence of correlations remains unclear. Here we demonstrate a very large topological Hall effect (THE) in thin films of a lightly electron-doped charge-transfer insulator, (Ca,Ce)MnO3. Magnetic force microscopy reveals the presence of magnetic bubbles, whose density as a function of magnetic field peaks near the THE maximum. The THE critically depends on carrier concentration and diverges at low doping, near the metal–insulator transition. We discuss the strong amplification of the THE by correlation effects and give perspectives for its non-volatile control by electric fields., The authors thank V. Cros, V. Dobrosavljevic, J. Iñiguez, J.-V. Kim, D. Maccariello, J. Matsuno, I. Mertig, N. Nagaosa and N. Reyren for useful discussions, J.-Y. Chauleau and M. Viret for second harmonic generation experiments, N. Jaouen for resonant magnetic X-ray diffraction, J. Varignon for preparing Fig. 1a and J.-M. George for his help with some magnetotransport measurements. This research received financial support from the ERC Consolidator grant ‘MINT’ (contract no. 615759) and ANR project ‘FERROMON’. This work was also supported by a public grant overseen by the ANR as part of the ‘Investissement d’Avenir’ programme (LABEX NanoSaclay, ref. ANR-10-LABX-0035) through projects ‘FERROMOTT’ and ‘AXION’ and by the Spanish Government through project no. MAT2014-56063-C2-1-R and MAT2017-85232-R (AEI/FEDER, UE), and Severo Ochoa SEV-2015-0496 and the Generalitat de Catalunya (2014SGR 734 project). B.C. acknowledges grant no. FPI BES-2012-059023, R.C. acknowledges support from CNPq-Brazil, and J.S. thanks the University Paris-Saclay (D’Alembert programme) and CNRS for financing his stay at CNRS/Thales. Work at Rutgers was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, US Department of Energy under award no. DE-SC0018153. H.K. is supported by JSPS KAKENHI grants nos. 25400339, 15H05702 and 17H02929. K.N. is supported by a Grant-in-Aid for JSPS Research Fellow grant no. 16J05516, and by a Program for Leading Graduate Schools ‘Integrative Graduate Education and Research in Green Natural Sciences’.

When ferromagnetic films become ultrathin, key properties such as the Curie temperature and the saturation magnetization are usually depressed. This effect is thoroughly investigated in magnetic oxides such as half-metallic manganites, but much less in ferrimagnetic insulating perovskites such as rare-earth titanates RTiO3 , despite their appeal to design correlated 2D electron gases. Here, the magnetic properties of epitaxial DyTiO3 thin films are reported. While films thicker than about 50 nm show a bulk-like response, at low thickness a surprising increase of the saturation magnetization is observed. This behavior is described using a classical model of a "dead layer" but assuming that this layer is actually "living," that is, it responds to the magnetic field with a strong paramagnetic susceptibility. Through depth-dependent X-ray absorption and photoemission spectroscopy, it is shown that the "living-dead layer" corresponds to surface regions where magnetic (S = 1/2) Ti3+ ions are replaced by nonmagnetic Ti4+ ions. Hysteresis cycles at the Dy M 5 and Ti L 3 edges indicate that the surface Ti4+ ions decouple the Dy3+ ions, thus unleashing their strong paramagnetic response. Finally, it is shown how capping the DyTiO3 film can help increase the Ti3+ content near the surface and thus recover a better ferrimagnetic behavior.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from correlations between transition metal and oxygen ions. Strong correlations thus offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metaloxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence., Work supported by ERC Consolidator grant MINT (Contract No. 615759)

Ferroelectric field-effect doping has emerged as a powerful approach to manipulate the ground state of correlated oxides, opening the door to a different class of field-effect devices. However, this potential is not fully exploited so far, since the size of the field-effect doping is generally much smaller than expected. Here we study the limiting factors through magnetotransport and scanning transmission electron and piezoresponse force microscopy in ferroelectric/superconductor (YBa₂Cu₃O_(7-δ)/BiFeO₃) heterostructures, a model system showing very strong field effects. Still, we find that they are limited in the first place by an incomplete ferroelectric switching. This can be explained by the existence of a preferential polarization direction set by the atomic terminations at the interface. More importantly, we also find that the field-effect carrier doping is accompanied by a strong modulation of the carrier mobility. Besides making quantification of field effects via Hall measurements not straightforward, this finding suggests that ferroelectric poling produces structural changes (e.g., charged defects or structural distortions) in the correlated oxide channel. Those findings have important consequences for the understanding of ferroelectric field effects and for the strategies to further enhance them.

When ferromagnetic films become ultrathin, key properties such as the Curie temperature and the saturation magnetization are usually depressed. This effect is thoroughly investigated in magnetic oxides such as half-metallic manganites, but much less in ferrimagnetic insulating perovskites such as rare-earth titanates RTiO

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 and SrTiO3 has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LaAlO3 thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. In this paper, the chemical, electronic, and transport properties of LaAlO3/SrTiO3 samples capped with different metals grown in a system combining pulsed laser deposition, sputtering, and in situ X-ray photoemission spectroscopy are investigated. The results show that for metals with low work function a q2DES forms at 1-2 uc of LaAlO3 and is accompanied by a partial oxidation of the metal, a phenomenon that affects the q2DES properties and triggers the formation of defects. In contrast, for noble metals, the critical thickness is increased above 4 uc. The results are discussed in terms of a hybrid mechanism that incorporates electrostatic and chemical effects., Work supported by ERC Consolidator grant MINT (Contract No. 615759)

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO

Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBaCuO (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics., A.M.G. was supported partially by US National Science Foundation Award DMR-1420013 through the Minnesota Materials Research Science and Engineering Center and by US National Science Foundation Award DMR-1209578. J.G.-B. acknowledges support from the Ministerio de Economía, Industria y Competitividad (MINECO) through the Ramon y Cajal Program and through MINECO Award PCIN-2013-061. Calculations were performed using computer resources from Genci Grand Équipement National de Calcul Intensif under Centre Informatique National de l’Enseignement Suprieur Grants c2015097211 and c2016097211. Work at Universidad Complutense de Madrid was supported by the Spanish MINECO through Grants MAT2014-52405-C02-01 and Consolider Ingenio 2010-CSD2009-00013 (Imagine) and by Comunidad Autonoma de Madrid (CAM) through Grant CAM S2013/MIT-2740. The SpLine beamline is supported financially by the Spanish MINECO and Consejo Superior de Investigaciones Cientificas under Grant PIE 2010 6 OE 013. P.S. acknowledges the support from Fundação de Amparo à Pesquisa do Estado de São Paulo Projects 2012/18397-2 and 2013/12537-9.

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 LaSrMnO electrodes separated by an ultrathin ferroelectric BaTiO 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., Work supported by Spanish MINECO through grants MAT2014-52405-C02-01 and MAT2014-52405-C02-02, MAT2015-066888-C3-1-R, MAT2015-066888-C3-3-R (MINECO/FEDER) and CAM S2013/MIT-2740. Research at ORNL sponsored by the US Department of Energy (DOE), Basic Energy Sciences (BES), M.V. acknowledges support from Fundación BBVA. G.S. and M.C. acknowledge support from ERC Starting Investigator Grant #239739 STEMOX. J.I.B. acknowledges the Spanish Supercomputing Network (RES) and CeSViMa (project FI-2016-2-0006). J.S. thanks Université Paris Saclay (DÁlembert Program) and CNRS for financing his stay at CNRS Thales.

The magnetoresistance (MR) effect is widely employed in technologies that pervade our world from magnetic reading heads to sensors. Diverse contributions to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are revealed in materials depending on the specific system and measuring configuration. Half-metallic manganites hold promise for spintronic applications but the complexity of competing interactions has not permitted the understanding and control of their magnetotransport properties to enable the realization of their technological potential. Here we report on the ability to induce a dominant switchable magnetoresistance in La0.7Sr0.3MnO3 epitaxial films, at room temperature (RT). By engineering an extrinsic magnetic anisotropy, we show a large enhancement of anisotropic magnetoresistance (AMR) which leads to, at RT, signal changes much larger than the other contributions such as the colossal magnetoresistance (CMR). The dominant extrinsic AMR exhibits large variation in the resistance in low field region, showing high sensitivity to applied low magnetic fields. These findings have a strong impact on the real applications of manganite based devices for the high-resolution low field magnetic sensors or spintronics., Comment: 10 pages, 6 figures

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 Sm 2CuO4/LaFeO3 heterostructures become metallic. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Work at UCM supported by Spanish MICINN Grant MAT 2011 27470, Consolider Ingenio CSD2009-00013 (IMAGINE), CAM S2009-MAT 1756 (PHAMA) and ERC starting Investigator Award, grant #239739 STEMOX. R.S. wishes to acknowledge the Ministerio de Ciencia e Innovación (MICINN) for granting a Ramon y Cajal Fellowship.

The new field of nano-ionics is expected to yield large improvements in the performance of oxide-based energy generation and storage devices based on exploiting size effects in ion conducting materials. The search for novel materials with enhanced ionic conductivity for application in energy devices has uncovered an exciting new facet of oxide interfaces. With judicious choice of the constituent materials, oxide heterostructures can exhibit enhanced ion mobility compared to the bulk counterparts. Here we review recent experimental and theoretical progress on enhancement of oxide-ion conductivity arising in oxide ultrathin layers and at their interfaces, and describe the different scenarios, space-charge effects, epitaxial strain, and atomic reconstruction at the interface, proposed to account for the observed conductivity enhancement

Electron energy loss spectroscopy in the scanning transmission electron microscope has long been used to perform elemental mapping but has not previously exhibited depth sensitivity. The key to depth resolution with optical sectioning is the transfer of sufficiently high lateral spatial frequencies. By performing spectrum imaging with atomic resolution we achieve nanometer scale depth resolution, enabling us to optically section an oxide heterostructure spectroscopically. Such 3D elemental mapping is sensitive to atomic scale changes in structure and composition and is more interpretable than Z-contrast imaging alone.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Memristive switching serves as the basis for a new generation of electronic devices. Conventional memristors are two-terminal devices in which the current is turned on and off by redistributing point defects, e.g., vacancies. Memristors based on alternative mechanisms have been explored, but achieving both high on/off ratio and low switching energy, as needed in applications, remains a challenge. This study reports memristive switching in La0.7Ca0.3MnO3/PrBa2Cu3O7bilayers with an on/off ratio greater than 103and results of density functional theory calculations in terms of which it is concluded that the phenomenon is likely the result of a new type of interfacial magnetoelectricity. More specifically, this study shows that an external electric field induces subtle displacements of the interfacial Mn ions, which switches on/off an interfacial magnetic “dead layer”, resulting in memristive behavior for spin-polarized electron transport across the bilayer. The interfacial nature of the switching entails low energy cost, about of a tenth of atto Joule for writing/erasing a “bit”. The results indicate new opportunities for manganite/cuprate systems and other transition metal oxide junctions in memristive applications.

The penetration of a superconducting current from a superconductor into a half-metallic ferromagnet is usually forbidden. Resonances in the conductance spectra of superconductor/half-metal heterostructures suggest this restriction is lifted by the occurrence of unconventional equal-spin Andreev reflection.

In the version of this Letter originally published, Hiroshi Kohno’s affiliation was incorrectly listed as Department of Earth and Space Science, Graduate School of Science, Osaka University, Osaka, Japan; it should have been Department of Physics, Nagoya University, Nagoya, Japan. This has been corrected in all versions of the Letter.

Towards cooler solid oxide fuel cells: Disorder and dimensionality (see picture) play an important role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity. Reducing the operation temperature of solid oxide fuel cells is a major challenge towards their widespread use for power generation. This has triggered an intense materials research effort involving the search for novel electrolytes with higher ionic conductivity near room temperature. Two main directions are being currently followed: the use of doping strategies for the synthesis of new bulk materials and the implementation of nanotechnology routes for the fabrication of artificial nanostructures with improved properties. In this paper, we review our recent work on solid oxide fuel cell electrolyte materials in these two directions, with special emphasis on the importance of disorder and reduced dimensionality in determining ion conductivity. Substitution of Ti for Zr in the A2Zr2−yTiyO7 (A=Y, Dy, and Gd) series, directly related to yttria stabilized zirconia (a common fuel cell electrolyte), allows controlling ion mobility over wide ranges. In the second scenario we describe the strong enhancement of the conductivity occurring at the interfaces of superlattices made by alternating strontium titanate and yttria stabilized zirconia ultrathin films. We conclude that cooperative effects in oxygen dynamics play a primary role in determining ion mobility of bulk and artificially nanolayered materials and should be considered in the design of new electrolytes with enhanced conductivity.

We evaluate in this work the effect of Gd substitution on the dc activation energy, Edc, and ionic conductivity of the pyrochlore-type gadolinium zirconate, P-Gd2Zr2O7. Several compositions with the general formulae Gd2−yLnyZr2O7 (Ln =E r 3+ ,Y

Different compositions in the Gd2-yLayZr2O7 solid solution (0 {less than or equal to} y {less than or equal to} 1) were prepared at room-temperature, by mechanically milling stoichiometric mixtures of the corresponding oxides. We found that irrespective of their lanthanum content, as-prepared powder samples consist of single-phase anion deficient fluorite materials, although post-milling thermal treatments at 1200ºC facilitates the long-range ordering of cations and anion vacancies characteristic of pyrochlores for y {greater than or equal to} 0.4. Interestingly, activation energy for oxygen migration in the series decreases from 1.13 {plus minus} 0.02 eV (Gd2Zr2O7) to 0.84 {plus minus} 0.03 eV (GdLaZr2O7) as La-content and the RA/RB ratio increase. These results are explained in terms of weaker ion-ion interactions in better ordered and highlight the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.

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.

We report on the influence of structural disorder on the oxide-ion conductivity of Dy2(Ti1� yZry)2O7 (y = 0.55 and 0.90). A significant disorder is induced by mechanical milling synthesis of the samples, and, depending on the Zr/Ti, a partial and progressive structural ordering can be achieved by subsequent annealing at temperatures between 800 and 1500 C. Ionic conductivity is relatively high for both compositions (up to 10 � 4 S/cm at 900 K), and the activation energies for dc conductivity (in the range 1.02–1.32 eV) are found to be larger in samples with more structural disorder. This result is quantitatively explained, by using Ngai’s coupling model, in terms of the enhancement of interactions between mobile oxygen vacancies in a more disordered structure. 2007 Elsevier B.V. All rights reserved.

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 0.5 nm. 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 grainboundary. Fil: Frechero, Marisa Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Complutense de Madrid; España Fil: Rocci, M.. Universidad Complutense de Madrid; España Fil: Sanchez Santolino, G.. Universidad Complutense de Madrid; España Fil: Kumar, Amit. Oak Ridge National Laboratory. Center for Nanophase Materials Sciences; Estados Unidos Fil: Salafranca, Juan. Universidad Complutense de Madrid; España Fil: Schmidt, Rainer. Universidad Complutense de Madrid; España Fil: Diaz Guillen, M.R.. Universidad Complutense de Madrid; España Fil: Durá, O. J.. Universidad Complutense de Madrid; España Fil: RiveraCalzada, A.. Universidad Complutense de Madrid; España Fil: Mishra, R.. Vanderbilt University; Estados Unidos Fil: Jesse, Stephen. Oak Ridge National Laboratory. Center for Nanophase Materials Sciences; Estados Unidos Fil: Pantelides, S.T.. Vanderbilt University; Estados Unidos Fil: Kalinin, Sergei. Oak Ridge National Laboratory. Center for Nanophase Materials Sciences; Estados Unidos Fil: Varela, M.. Universidad Complutense de Madrid; España Fil: Pennycook, Steve. University Of Tennessee; Estados Unidos Fil: Santamaria, J.. Universidad Complutense de Madrid; España Fil: Leon, C.. Universidad Complutense de Madrid; España

The design of artificial vortex pinning landscapes is a major goal toward large scale applications of cuprate superconductors. Although disordered nanometric inclusions have shown to modify their vortex phase diagram and to produce enhancements of the critical current (MacManus-Driscoll, J. L.; Foltyn, S. R.; Jia, Q. X.; Wang, H.; Serquis, A.; Civale, L.; Maiorov, B.; Hawley, M. E.; Maley, M. P.; Peterson, D. E. Nat. Mater. 2004, 3, 439?443 and Yamada, Y.; Takahashi, K.; Kobayashi, H.; Konishi, M.; Watanabe, T.; Ibi, A.; Muroga, T.; Miyata, S.; Kato, T.; Hirayama, T.; Shiohara, Y. Appl. Phys. Lett. 2005, 87, 1-3), the effect of ordered oxide nanostructures remains essentially unexplored. This is due to the very small nanostructure size imposed by the short coherence length, and to the technological difficulties in the nanofabrication process. Yet, the novel phenomena occurring at oxide interfaces open a wide spectrum of technological opportunities to interplay with the superconductivity in cuprates. Here, we show that the unusual long-range suppression of the superconductivity occurring at the interface between manganites and cuprates affects vortex nucleation and provides a novel vortex pinning mechanism. In particular, we show evidence of commensurate pinning in YBCO films with ordered arrays of LCMO ferromagnetic nanodots. Vortex pinning results from the proximity induced reduction of the condensation energy at the vicinity of the magnetic nanodots, and yields an enhanced friction between the nanodot array and the moving vortex lattice in the liquid phase. This result shows that all-oxide ordered nanostructures constitute a powerful, new route for the artificial manipulation of vortex matter in cuprates., Work at UCM supported by grants MAT2014-52405-C02-01 and Consolider Ingenio 2010-CSD2009-00013 (Imagine), by CAM through grant CAM S2013/MIT-2740. Work done at ICMM supported by Spanish MINECO (Ministry for Economy and Competitiveness) grants MAT2011-27470-C02-02, MAT2014-52405-C02-02, and Consolider Ingenio CSD2009-00013 (Imagine). J.V. acknowledges European Research Council, ERC, grant No. 647100 “SUSPINTRONICS”.

Iron oxychloride has been lithiated by the reaction with n -butyllithium and thereafter exposed to air. Lithium intercalation increases several orders of magnitude of the electrical conductivity of the pristine material although the intercalate remains a semiconductor. This phase, after being exposed to atmospheric humidity becomes an ionic conductor, with a conductivity comparable to that of some molten salts, and does not show electronic conduction in the whole range of temperatures of measurement (150–300 K), a strong non-Arrhenius behaviour being observed. Impedance spectroscopy and NMR techniques, among others, have been used to follow this behaviour.

Different compositions in a solid solution of general formula Dy2(Ti1−yZry)2O7, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y ⩾ 0.4 , which, as observed in the similar Y2(Ti1−yZry)2O7, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y > 0.6 , reaching a maximum value of ∼5×10−3 for Dy2Zr2O7 at 900 °C.

The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7−x/La0.67Ca0.33MnO3 superlattices has been analyzed by scanning transmission electron microscopy and high spatial resolution electron energy loss spectroscopy. Individual layers are flat over long lateral distances. The interfaces are coherent, free of defects, exhibiting no roughness, and are located at the BaO plane of the superconductor. Concerning chemical disorder, EELS measurements show the absence of measurable chemical interdiffusion within experimental error bars.