Symposium CK
Functional Magnetic Oxides

Session CK-1 -Magnetic Oxide Thin Films Interfaces and Heterostructures

CK-1:IL01  Multiferroic Tunel Junctions: Revitalizing Half-doped Manganites
G. RADAELLI^{1, 2}, D. GUTIERREZ¹, F. SANCHEZ¹, R. BERTACCO², J. FONTCUBERTA¹, ¹Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, Catalonia, Spain; ²LNESS - Dipartimento di Fisica, Politecnico di Milano, Como, Italy

Half-doped manganites La0.5R0.5MnO3 have recently attracted renewed attention because their ground state (ferromagnetic (FM) / metallic or antiferromagnetic (AF) / insulator) can be radically modified by engineering the bandwidth or the carrier density. This property makes half-doped manganites ideal materials to be integrated in reconfigurable tunneling junctions with potentially large electroresistance. Progress in this direction and discrimination between strain and field-effects in ferroelectric/half-doped heterostructures, require detailed understanding of the epitaxial strain effects on the properties of ultrathin films which may modify or suppress orbital ordering.
Here we review on effects of strain and bandwidth on the magnetic and transport properties of La0.5R0.5MnO3 (R = Ca and Sr) films. The combination of both parameters allows mapping the overall phase diagram of these compounds and to guide material's selection for optimal hybrid half-doped manganite/ferroelectric tunnel junctions. Electroresistance (TER) data across ferroelectric and hybrid tunnel junctions will be reported and it will be shown that TER values exceeding 10^4 % can be obtained.


CK-1:IL02  Spin and Charge Elusive Order in Cuprate Superconductors
G. GHIRINGHELLI, Dipartimento di Fisica, Politecnico di Milano, Italy

The robust antiferromagnetic order of undoped layered cuprates evolves in a complex and still partly unknown way when charges are added to the CuO2 planes and eventually superconductivity is reached. The presence of those charges modifies the spin excitation spectrum, introduces charge channels and allows the organization of charge density fluctuations. Soft x-ray resonant spectroscopies (RIXS and XAS) are ideal techniques for the study of the magnetic and charge properties of high Tc cuprate superconductors, in single crystals, ultra-thin films and heterostructures. I will review a series of key results obtained recently in this field and present some interesting examples on other intriguing oxides.


CK-1:IL03  Photovoltaic Effect and Interface Induced Polar State in Heterojunctions of Correlated Electron Oxides
M. NAKAMURA, RIKEN-CEMS, Wako, Japan; M. KAWASAKI, Y. TOKURA, RIKEN-CEMS, Wako, Japan and Dep. of Appl. Phys. and QPEC, Univ. of Tokyo, Tokyo, Japan

The discontinuity in the polarization at the interface of two contacting insulators can be a strong driving force for the interfacial carrier accumulation. LAO/STO related junctions are one of the representative cases, where the polar catastrophe is a most prevailing scenario for the carrier accumulation. On the other hand, the observation of conductive carriers at polar/non-polar oxide heterointerface is limited to several material combinations among a lot of existing band and Mott insulators with perovskite structure. In this study, we aimed for providing some insight into this issue by investigating the photovoltaic effect of a heterojunction composed of LaFeO3 (LFO) and STO which also hosts the polar discontinuity. We found that the sign of the photocurrent reverses by changing the surface termination of Nb:STO from TiO2 to SrO, which signifies the opposite internal field within LFO between the two junctions. Meanwhile, photocurrent spectroscopy and capacitance measurements elucidate that the charge distributions in Nb:STO changes from the electron accumulation in TiO2-terminated junction to depletion in SrO-terminated one. These results are consistent with the polar catastrophe scenario and evidential for its universality even in insulating polar/non-polar heterointerfaces.


CK-1:IL04  Electric Field Control of Magnetization at Cuprate-manganite Interfaces
J. SANTAMARIA¹, F.A. CUELLAR¹, Y.H. LIU², J. SALAFRANCA^{1, 3}, E. IBORRA⁴, G. SANCHEZ-SANTOLINO¹, M. VARELA^{3, 1}, J.W. FREELAND⁵, M. ZHERNENKOV⁶, M.R. FITZSIMMONS⁶, S. OKAMOTO³, S.J. PENNYCOOK³, M. BIBES⁷, A. BARTHÉLÉMY⁷, S.G.E. TE VELTHUIS², Z. SEFRIOUI¹, C. LEON¹, ¹GFMC, Depto. Física Aplicada III, Universidad Complutense de Madrid, Madrid, Spain; ²Materials Science Division, Argonne National Laboratory, Argonne, IL, USA, ³ Materials Sci. & Technology Div., Oak Ridge National Laboratory, Oak Ridge, TN, USA; ⁴GMME Departamento de Tecnologia Electronica. ETSIT. Univ. Politecnica de Madrid, Spain; ⁵Instituto de Ciencia de Materiales de Madrid, Cantoblanco, Spain; ⁶Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA; ⁷Los Alamos National Laboratory Los Alamos, NM, USA; ⁸Unité Mixte de Physique CNRS/Thales, Palaiseau, France

The possibility of tailoring the electronic structure of interfaces between correlated oxides has driven an important effort towards the design of interfaces with specific functionalities. At oxide interfaces the strong electron correlations underlie the nucleation of emerging ground states with exciting responses. Novel forms of low dimensional magnetism may result from the atomic reconstruction at the interfaces, namely from the new superexchange path which results from the interfacial bond. The possibility of modifying the sign and strength of the superexchange interaction with an external stimulus holds an important technological promise as a new path towards tunable electronic groundstates at interfaces. In this talk I will discuss the possibility of reversible, voltage-driven magnetization switching of a manganite layer at the interface with a (non superconducting) cuprate in the absence of a magnetic field. Orbital reconstruction at the interface yields a novel form of magnetoelectric coupling between interfacial Mn spins and localized electron states in the CuO2 planes, which mediates a ferromagnetic coupling between manganite layers sandwiching the cuprate and can be controlled by the electric field. This allows toggling between bistable magnetization states (and corresponding spin-dependent resistance states in magnetic tunnel junctions) in the absence of a magnetic field. This result, apart from its fundamental importance may be relevant for data storage technology, where electric field control could enable a larger density of stored information. This route is alternative to other procedures involving voltage-controlled magnetic anisotropy, or using multiferroics via exchange bias or strain, where magnetization switching generally requires assistance from another effect or by a bias magnetic field.


CK-1:IL06  Ultrafast Magnetic Dynamics in Nickelates Heterostructures
A.D. CAVIGLIA^{1, 2}, M. FÖRST¹, R. SCHERWITZL³, V. KHANNA^{1, 4, 11}, H. BROMBERGER¹, R. MANKOWSKY¹, R. SINGLA¹, Y.-D. CHUANG⁶, W.S. LEE⁷, O. KRUPIN⁹, W.F. SCHLOTTER⁸, J.J. TURNER⁸, G.L. DAKOVSKI⁸, M.P. MINITTI⁸, J. ROBINSON⁸, V. SCAGNOLI¹⁰, S.B. WILKINS⁵, S.A. CAVILL¹¹, M. GIBERT³, S. GARIGLIO³, P. ZUBKO³, J.-M. TRISCONE³, J.P. HILL⁵, S.S. DHESI¹¹, A. CAVALLERI^1,4, ¹Max-Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany; ²Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands; ³DPMC, University of Geneva, Switzerland; ⁴Department of Physics, Clarendon Laboratory, University of Oxford, UK; ⁵Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY, USA; ⁶Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA, USA; ⁷The Stanford Institute for Materials and Energy Sciences (SIMES), Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory and Stanford University, Menlo Park, CA, USA; ⁸Linac Coherent Light Source, Stanford Linear Accelerator Center (SLAC) National Accelerator Laboratory, Menlo Park, CA, USA; ⁹European XFEL GmbH, Hamburg, Germany; ¹⁰Swiss Light Source, Paul Scherrer Institute, Villigen PSI, Switzerland; ¹¹Diamond Light Source, Chilton, Didcot, Oxfordshire, UK

Using ultrafast resonant soft X-ray diffraction, we demonstrate optical melting of antiferromagnetic order in the correlated electron insulator NdNiO3. Time-dependent analysis of the resonant spectra allows us to follow the temporal evolution of the charge imbalance between adjacent Ni sites. A direct correlation between the melting of magnetic order and charge rebalancing is found.
Furthermore, we report on experiments in which femtosecond mid-infrared radiation is used to excite the lattice of complex oxide heterostructures. By tuning the excitation energy to a vibrational mode of the substrate, magnetic melting is observed in an epitaxial NdNiO3 thin film. The propagation of a melting front across the interface is measured by femtosecond x-ray scattering at a free-electron laser. Vibrational excitation, extended here to a wide class of heterostructures and interfaces, may be conducive to new strategies for electronic phase control at THz repetition rates.


CK-1:IL07  Relationship between Composition, Structure and Magnetic Properties in MBE-grown La2MnNiO6 Double Perovskite Films
S.A. CHAMBERS, Y. DU, T.C. DROUBAY, V. SHUTTHANANDAN, M. BOWDEN, R. COLBY, Pacific Northwest National Laboratory Richland, WA, USA

We are early in the investigation of LaNiO3 (LNO)/LaMnO3 (LMO) superlattices deposited on SrTiO3(001) and (111) by MBE. Bulk LNO is a metal without magnetic order, whereas bulk LMO is an A-type antiferromagnetic Mott insulator. For the perfect double perovskite structure, we expect a saturation moment of 5 mB/formula unit (f.u.) based on the expectation of parallel spin alignment of Mn4+ (d3: t2g3eg0) and Ni2+ (d8: t2g6eg2) via superexchange. In situ XPS, calibrated by ex situ RBS, was used to determine the stoichiometry and cation valences. Nominally stoichiometric films grown so far consist mostly of Mn4+ and Ni2+. (001)-oriented films deposited by co-evaporation are ferromagnetic with Tc = 130K and a saturation moment of 1.5 mB/f.u. These results suggest the presence of LaMn1-xNixO3, a disordered regular perovskite. (111)-oriented films deposited by shuttered evaporation are ferromagnetic with a saturation moment of 2.2 mB/f.u. at 10K. These films show two ferromagnetic phases with Tc = 150K and 300K. Magnetic measurements are suggestive of disordered regions of Ni2+ and Mn4+ along with antiphase boundaries in the double perovskite. The low-TC phase has been attributed to LMNO with Ni3+ and Mn3+. Structural measurements are about to commence and will be described in the talk.


CK-1:IL08  Probing Magnetism of Thin Film Oxides with Advanced Electron Microscopy
C. MAGEN, L.A. RODRÍGUEZ, L. MARÍN, I. LUCAS, L. MORELLÓN, M.R. IBARRA, Instituto de Nanociencia de Aragón, University of Zaragoza, Zaragoza, Spain; E. SNOECK, CEMES-CNRS, Toulouse, France; S. FAROKHIPOOR, C.J.M. DAUMONT, B. NOHEDA, Zernike Institute for Advanced Materials, Univ. Groningen, Netherlands; J.M. DE TERESA, P.A. ALGARABEL, ICMA, University of Zaragoza-CSIC, Zaragoza, Spain

Recent trends in Nanomagnetism and Spintronics have evidenced that the lattice distortions driven by epitaxial growth of thin films is a successful strategy in the pursuit of tailored (multi)ferroic properties in oxide thin films, and particularly ferromagnetism.
The design of new strain-engineered oxides requires the combination of the most advanced thin film growth techniques available with an accurate and local characterization of the physical properties, especially at the interfaces, such as strain, the presence of misfit dislocations and other defects, chemical composition/diffusion and electronic state). In this task advanced electron microscopy has demonstrated unique capabilities to probe magnetism at the nanoscale, even with atomic resolution.
In this lecture we present several examples of this potential. In particular, we will focus on the analysis of strain-induced magnetism of epitaxial TbMnO3 thin films by means of atomic resolution chemical mapping by aberration corrected STEM-EELS, and the observation of the formation of non-ferromagnetic layers in La0.67Ca0.33MnO3 thin films as a function of the strain by means of electron holography techniques.


CK-1:IL09  Magnetic Effects in Spin-triplet Superconductors - Ferromagnets Heterostructures
M. CUOCO, CNR-SPIN, Fisciano (Salerno), Italy and Dipartimento di Fisica "E.R. Caianiello'', Università di Salerno, Fisciano (Salerno), Italy

We discuss the magnetic properties of spin-triplet superconductors (TSC) interfaced to ferromagnets (FM) focusing on two effects: i) the spin-orbital coupling at the FM-TSC interface [1], ii) the magnetic Andreev states at their edge if the system allows for singlet pairing in a subdominant channel [2].
In a TSC-FM heterostructure, the orientation of the FM moment relative to the TSC vector order parameter is either parallel or perpendicular to the TSC vector order parameter, depending on the alignment of the TSC gap with respect to the interface, thus evidencing a unique form of spin-orbital coupling. [1] When the interface is spin active the scenario is different and other processes can play the decisive role in setting the overall magnetic profile [3].
Novel magnetic effects can occur at the edge of a TSC if triplet and singlet pairing get mixed and have a non-uniform spatial profile [2].
[This research has received funding from the EU -FP7/2007-2013 grant agreement N. 264098 - MAMA].
[1] P. Gentile, M. Cuoco, A. Romano, C. Noce, D. Manske, P. M. R. Brydon, Phys. Rev. Lett. 111, 097003 (2013).
[2] A. Romano, P. Gentile, C. Noce, I. Vekhter, M. Cuoco, Phys. Rev. Lett. 110, 267002 (2013).
[3] D. Terrade, P. Gentile, M. Cuoco, and D. Manske, Phys. Rev. B 88, 054516 (2013).


CK-1:IL10  Emergent Phenomena in Two-dimensional Electron Gases at Oxide Interfaces
S. STEMMER, University of California, Santa Barbara, CA, USA

Two-dimensional electron gases (2DEGs) at interfaces between two insulating oxides can exhibit unique properties, such as strong electron correlations, superconductivity and magnetism. In this presentation, we will discuss emergent properties at interfaces and quantum wells formed between Mott insulating rare earth titanates (SmTiO3, GdTiO3), and the band insulator SrTiO3. Such interfaces exhibit a high-density 2DEG, of approximately ½ electron per surface unit cell, providing ~ 3×1014 cm-2 mobile charge per interface. We discuss recent advances in controlling growth and interface properties. We show that the subband structure can be probed using quantum oscillations and tunneling studies. We investigate electron correlation effects and metal-insulator transitions in narrow quantum wells bound by two such interfaces, and the role of coupling to the lattice. We next discuss tuning of the properties of the correlated electron system using interfacial proximity effects. We show that ferromagnetism in the high-density 2DEG can be induced by proximity to the ferrimagnetic GdTiO3. Antiferromagnetic coupling is obtained by interfaces with SmTiO3.
This work was performed in collaboration with Clayton Jackson, Santosh Raghavan, Pouya Moetakef, Jack Zhang, and S. James Allen.


CK-1:L11  Ferromagnetism in the 2DEG Formed at the Polar and Non-polar LaAlO3/SrTiO3 Interfaces
J.I. BELTRÁN, M.C. MUNOZ, Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, Cantoblanco, Madrid, Spain

We investigate the electronic properties of the interface between LaAlO3 and SrTiO3 in oxide heterostructures (HSs) grown along the polar (100) and (111) and non-polar (110) crystallographic directions. Using first-principles methods, the effect of local correlations is considered within the LDA+U scheme. We found that in the absence of defects the polar HSs support an interfacial 2DEG, while in the case of HSs grown along the (110) direction, a metallic interface results either from the formation of oxygen vacancies or from the La-Sr intermixing near the interface. We discuss the variuos origins of the interface 2DEG formed in HSs with different orientations and therefore elucidate the microscopic mechanisms responsible for the appearance of a conducting oxide interface. Moreover, our results predict different orbital nature of the carriers at the (100), (111) and (110) interfaces and show that ferroelectric-like distortions determine the dimensionality of the 2DEG. Finally, we discuss the conditions that stabilize a spontaneous ferromagnetic phase showing that electronic correlations energetically favored the stability of this ordered phase.

 
CK-1:L12  Design of a Polar Magnetic Metal with Highly Anisotropic Thermopower
J.M. RONDINELLI, Drexel University, Department of Materials Science and Engineering, Philadelphia, PA, USA

The metallic features in materials, which provide low-resistance channels for electrical conduction, lead to effective screening of local electric dipole moments. Itinerant electrons disfavor both their formation and cooperative ordering. Consequently, most metals with a finite density of states and partial band occupation exhibit centric (inversion symmetric) crystal structures. Despite this contraindication, noncentrosymmetric metals (NCSM) lacking inversion were proposed more than fifty years ago, with some examples discovered serendipitously later. Here we describe a design framework to alleviate the property disparities and accelerate NCSM discovery: The primary ingredient relies on the removal of inversion symmetry through displacements of atoms whose electronic degrees of freedom are decoupled from the states at the Fermi level. Density functional theory calculations validate our crystal-chemistry strategy, and predict a polar-NCS perovskite ruthenate to be metallic and robust to spin-orbit interactions. Motivated by recent suggestions that degenerately doped ferroelectrics exhibit advantageous thermoelectric responses, we show that the thermopower in this polar metal exhibits large anisotropy for particular doping regimes along the polar axis.


CK-1:L13  Unexpected High Conductivity at Twin Boundaries in LSMO Thin Films
LL. BALCELLS, M. PARADINAS, R. GALCERAN, Z. KONSTANTINOVIC, A. POMAR, F. SANDIUMENGE, C. OCAL, B. MARTINEZ, Instituto de Ciencia de Materiales de Barcelona - CSIC, Campus UAB, Bellaterra, Spain; R. MORENO, N. DOMINGO, J. SANTISO, ICN2, Institut Catala de Nanociencia I Nanotecnologia, Campus UAB, Bellaterra, Spain

High quality La2/3Sr2/3MnO3 thin films prepared by sputtering are studied by Conducting Scanning Force and Magnetic Force Microscopy. Film surface consists of one unit cell steps separating atomically flat terraces, with a surface roughness on the terraces lower than 0.3Å. In spite of the extremely flat surface morphology observed, simultaneously acquired topography and current maps revealed a considerably intensity along lines superimposed on a uniform current background. These enhanced conducting lines were not randomly distributed but forming domains with periodic arrays with perpendicular orientations. Line periodicity within each domain coincides with the lateral size of each crystallographic twin as observed by XRD and SEM, thus confirm that the observed lines correspond to the precise position of the twin boundaries. I-V characteristics indicate an important enhancement of the electronic response at the twin boundaries locations. Values of the measured current for a given voltage may differ by one order of magnitude. A clear magnetic signature is also detected at the twin boundaries locations. The origin of this large difference is still under consideration, but it seems that an increase in the density of states at the boundaries might have an important contribution.

 
Session CK-2 - Electronic Structure and Correlation Effects

CK-2:IL02  Electronic Structure of Double Perovskites: Compounds with Promises
T. SAHA-DASGUPTA, Department of Condensed Matter Physics and Materials Science, S.N.Bose National Centre for Basic Sciences, Kolkata, India

Double perovskite compounds with general formula ABB'O6, have attracted lot of attention recently due to a variety of properties exhibited by them. In this talk, we will report our recent study on a series of double-perovskite compounds, exhibiting rare ferromagnetic insulating state in La2NiMnO6 [1], hybridization driven antiferromagnetic metallic state in La-doped Sr2FeMoO6 [2], magneto-capacitive properties [3], large magneto-optic Kerr signals [4], as well as multiferroic behavior in 3d-5d double perovskites [5,6].
[1] Hena Das, Umesh V. Waghmare, T. Saha-Dasgupta, D. D. Sarma, Phys. Rev. Lett. 100, 186402 (2008).
[2] Prabuddha Sanyal, Hena Das, T. Saha-Dasgupta, Phys. Rev. B 80, 224412 (2009); S. Jana et al., Phys. Rev. B 86, 054433 (2012).
[3] Hena Das, Umesh V. Waghmare, T. Saha-Dasgupta, D. D. Sarma, Phys. Rev. B 79, 144403 (2009).
[4] Hena Das, Molly De-Raychaudhury, T. Saha-Dasgupta, Appl. Phys. Lett. 92, 201912 (2008).
[5] Hena Das, Prabuddha Sanyal, T. Saha-Dasgupta, D.D. Sarma, Phys. Rev. B 83, 104418 (2011).
[6] Hena Das, Saurabh Ghosh, Craig Fennie, Martha Greenblatt, T. Saha-Dasgupta (communicated).


CK-2:L04  Quantum Mechanical Simulation of Magnetic Alloys: s, p, and d Model Hamiltonians
M.E.A. COURY, W.M.C. FOULKES, A.P. HORSFIELD, Imperial College London, London, UK; S.L. DUDAREV, P.W. MA, EUROATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, UK

The Hubbard Hamiltonian is a widely used method to simulate strongly correlated materials [1]. In the presented work we take a bottom up approach. We derive a multi-orbital Hubbard Hamiltonian, which is exact for single atoms, and find its mean field approximation, suitable for a tight binding model. This work corrects a long series of mistakes in the literature regarding the tensorial form of the multi-orbital Hubbard Hamiltonians. It is shown that for on-site Coulombic interactions, 1 parameter suffices for the s-orbital case, 2 suffice for the p-orbital case and 3 suffice for the d-orbital case. These interactions are written down in terms of rotationally invariant operators and sizeable terms have been found that are not included in the literature.
The inclusion of the rotationally invariant operators of the on-site Coulombic interactions in the mean field Hamiltonian gives rise to their symmetry breaking in certain limits of the self-consistent solutions. These symmetry broken solutions and the effect of the inclusion of the new terms is examined in the context of magnetism and orbital ordering.
[1] Dagotto, E., Hotta, T., & Moreo, A. (2001). Colossal magnetoresistant materials: the key role of phase separation. Physics Reports, 344(1), 1-153.


CK-2:L05  Competing Charge Orders in Magnetite Ultrathin Films
I. BERNAL, S. GALLEGO, Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain

Magnetite (Fe3O4) is a half-metallic ferrimagnet with high critical temperature and large magnetic moment. The strong electron correlations lead to a rich scenario of phase transitions at low temperatures where charge order plays a crucial role: the Verwey transition at 120 K, with the opening of an insulating gap accompanied by a structural distortion, or the development of a ferroelectric polarization at 40 K.
Modification of the Verwey transition has been pursued in thin films, under pressure or strain, or introducing defects, always causing a decrease of the Verwey temperature. However, the existence of an insulating gap at different Fe3O4(001) terminations at ambient conditions could translate the rich Verwey physics to higher temperatures.
By means of ab-initio calculations, we will demonstrate that low dimensionality introduces a competition between surface and bulk charge orders, while preserving the magnetic properties. This is accompanied by a structural distortion involving the surface and subsurface layers, that ultimately manifests in a phase diagram distinct from the bulk one. We will also evidence the existence of a threshold thickness for the emergence of the two Fe valence states required for charge order and half-metallicity.

 
Session CK-3 - Spin Transport and Interplay between Spin, Charge and Lattice Degree of Freedom

CK-3:IL01  Spin Pumping from Insulators
E. SAITOH, WPI-AIMR,Tohoku University, Sendai, Japan, and Institute for Materials Research, Tohoku University, Sendai, Japan

Utilization of a spin current, a flow of electrons’ spins in a solid, is the key technology in spintronics that will allow the achievement of efficient magnetic memories and computing devices. In this science and technology, generation and detection of spin currents are necessary. Here, we review inverse spin-Hall effect and spin-current-generation phenomena recently discovered both in metals and insulators: inverse spin-Hall effect, spin pumping, and spin Seebeck effect.
1. Spin pumping and spin torque in a Mott insulator system
We found that spin pumping and spin torque effects appear also at an interface between Pt and an insulator YIG.. This means that we can connect a spin current carried by conduction electrons and a spin-wave spin current flowing in insulators. We demonstrate electric signal transmission by using these effects and interconversion of the spin currents [1].
2. Spin Seebeck effect
We have observed, by using the inverse spin-Hall effect [2], spin voltage generation from a heat current in a NiFe, named the spin-Seebeck effect [3]. Surprisingly, spin-Seebeck effect was found to appear even in insulators [4], a situation completely different from conventional charge Seebeck effect. The result implies an important role of elementary excitation in solids beside charge in the spin Seebeck effect.
[1] Y. Kajiwara & E. Saitoh et al.  Nature 464 (2010) 262.
[2] E. Saitoh et al.,  Appl. Phys. Lett. 88 (2006) 182509.
[3] K. Uchida & E. Saitoh et al.,  Nature 455 (2008)778.
[4] K. Uchida & E. Saitoh et al.,  Nature materials 9 (2010) 894 - 897.


CK-3:IL02  Towards Efficient Spin Injection at the LaAlO3/SrTiO3 Interface
E. LESNE¹, N. REYREN¹, D. DOENNIG², R. MATTANA¹, F. CHOUEIKANI³, V. CROS¹, F. PETROFF¹, J.-M. GEORGE¹, S. COLLIN¹, C. DERANLOT¹, P. OHRESSER³, R. PENTCHEVA², M. BIBES¹, H. JAFFRÈS¹, A. BARTHÉLÉMY¹, ¹Unité Mixte de Physique CNRS/Thales, Palaiseau, France and Université Paris-Sud, Orsay, France; ²Department of Earth and Environmental Sciences, Section Crystallography and Center of Nanoscience, University of Munich, Munich, Germany; ³Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin, Gif sur Yvette, France

It has been a long-lasting goal to realize a prototypical spin-field effect transistor. The high-mobility quasi-two-dimensional electron system (2DES) that forms at the LaAlO3/SrTiO3 interface provides a potentially suitable channel to study lateral spin transport in a non-magnetic oxide.
We present results of electrical spin injection in this 2D system. In a non-local, three-terminal measurement geometry, we analyze the voltage variation associated with the precession of the injected spin accumulation (Hanle and inverted Hanle effects). Back-gating experiments reveal that the spin accumulation signal is amplified by resonant tunneling through localized states. In order to favor direct tunneling, the barrier width must be reduced. However it is found that conductivity only appears beyond an LaAlO3 thickness threshold of four unit cells (uc), therefore leading to a very large barrier resistance. We provide a way to realize efficient Co/LaAlO3/SrTiO3 spin injectors (detectors) with LaAlO3 thickness down to a single uc. To clarify the origin of the conduction in such structures, we performed X-ray absorption spectroscopy experiments which indicate, together with first principle calculations (DFT), a transfer of electrons toward the Ti 3d bands with preferential dxy occupancy.


CK-3:L03  Growth and Properties of Low Dimensional Magneto-electric Ba2CuGe2O7 Single Crystals
R. FITTIPALDI¹, V. GRANATA¹, M. CIOMAGA HATNEAN², G. BALAKRISHNAN², A. VECCHIONE¹, ¹CNR - SPIN U.O.S. Salerno and Dipartimento di Fisica - Università di Salerno, Fisciano (SA), Italy; ²University of Warwick, Coventry, UK

Non-centrosymmetric antiferromagnets (AF) can host a number of properties including multiferroicity, skyrmions, topologically stable particle-like chiral objects. Ba2CuGe2O7 is one example for its complex magnetic behaviour [1,2]. It has been investigated by neutrons showing the incommensurate AF double-k cycloid spin structure detected below about TN = 3K in zero applied field. A rich phase diagram emerges from the application of magnetic fields with transitions identified as magnetic structure change to spin cone and commensurate AF. We report the synthesis of Ba2CuGe2O7 single crystals by floating-zone technique. The morphology and chemical composition of the crystals were investigated by SEM with energy and wavelength dispersive spectrometry. The crystallographic properties were analyzed by X-ray diffraction through reciprocal space mapping, rocking curve and pole figures measurements. The microstructure has been investigated by electron back scattered diffraction technique. The obtained crystals showed being suitable exploring the complex magnetoelectric phase diagram. dc magnetic susceptibility down to 1.5K at different applied magnetic field will be presented.
[1] H. Murakawa et al. Phys. Rev. Lett. 2009, 103, 147201; [2] S. Mülhbauer et al. Phys. Rev. B 2012, 86, 024417.


CK-3:IL05  Chirality in Charge and Orbital Ordered Materials
J. VAN WEZEL, University of Bristol, Bristol, UK

Helical arrangements of spins are common among magnetic materials. The first material to harbor a corkscrew pattern of charge density on the other hand, was discovered only relatively recently. This difference can be directly attributed to the nature of the involved order parameters: whereas rotating a magnetic vector around a propagation vector trivially yields a helical pattern, the purely scalar charge density cannot straightforwardly support a chiral state.
Here, I will resolve the paradox of how chiral charge order can nonetheless arise in certain charge density wave materials. It is shown that the emergence of chirality is accompanied by the simultaneous formation of charge and orbital order. This rather generic mechanism has been suggested to underlie the emergence of broken inversion symmetry in a broad class of charge ordered materials, which includes transition metal dichalcogenides like 1T-TiSe2 and 2H-TaS2, but also elemental metals like Te and Po, and potentially even some cuprate superconductors.
It will also be shown how the onset of this type of combined charge and orbital order can be observed experimentally, using a combination of X-ray diffraction, electrical resistivity and specific heat measurements.


CK-3:IL06  Magnetic Excitations, CDW and Phonon Anomalies in Cuprates: New Insights from Inelastic x-ray Scattering
M. LE TACON, MPI-FKF, Stuttgart, Germany

I will present an overview of recent results obtained in superconducting cuprates obtained by various x-ray scattering experiments. In the search for the mechanism of HTSC, intense effort has been focused on the evolution of the spin excitation spectrum on doping from the AF to the superconducting state of the cuprates. We used RIXS to show that a large family of superconductors (YBCO) exhibits damped spin excitations (paramagnons) with dispersions and spectral weights closely similar to those of magnons in undoped cuprates, and surprisingly observe their persistence up to very high doping. In addition, RIXS is also sensitive to charge. The greatly enhanced sensitivity of the scattering signal to the valence electron system led us to the discovery of a fluctuating charge density wave competing with the superconducting order at low doping levels. Finally, we used high resolution IXS to study low energy phonons with wavevectors near the CDW ordering vector and found that they exhibit extremely large superconductivity induced renormalizations. This provides important insights regarding the long-standing debate of the role of the electron-phonon interaction, a major factor influencing the competition between collective instabilies in correlated-electron materials.


CK-3:L07  Control of the Magnetic Properties of LaMnO3 Epitaxial Thin Films Grown by Pulsed Laser Deposition
J. ROQUETA, J. SANTISO, ICN2, Institut Catala de Nanociencia I Nanotecnologia, Campus UAB, Bellaterra, Barcelona, Spain; A. POMAR, LL. BALCELLS, C. FRONTERA, Z. KONSTANTINOVIC, F. SANDIUMENGE, B. MARTÍNEZ, Instituto de Ciencia de Materiales de Barcelona, ICMAB-CSIC; Campus UAB, Bellaterra, Spain

LaMnO3 (LMO), the parent compound of colossal magnetoresistance based manganites has gained renewed attention as a building block in heterostructures with unexpected properties [1]. In its bulk phase, stoichiometric LMO is an A-type antiferromagnetic (AFM) insulator (TN=140K) with orthorhombic structure that easily accommodate an oxygen excess by generating cationic (La or Mn) vacancies. As a result, a fraction of Mn 3+ converts into Mn 4+ leading to a double-exchange mediated ferromagnetic (FM) behavior. In thin films, however, the unambiguously growth of the AFM phase has been elusive up to now and thin films with FM ordering are usually reported [1]. In this work, we have systematically studied the growth of LaMnO3 thin films by pulsed laser deposition on SrTiO3 (001) substrates under different oxygen partial pressures. We found that there is a progressive evolution of the structure (explored by XRD) and magnetic properties (SQUID measurements) of the films as a function of PO2. At high PO2 usual FM behavior is observed. On the contrary, at very low PO2, the results obtained for unit cell volume (close to stoichiometric bulk values) and magnetic moment (0.2 uB per Mn) place our films inside the antiferromagnetic phase.
1. M. Gibert et al., Nat Mat 11(2012) 195.

 
Session CK-4 - Multiferroic and Magnetoelectric Compounds

CK-4:IL01  Novel Effects at the Domain Walls of Multiferroic Materials
J. INIGUEZ, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, Spain

Ferroelectric and ferroelastic domain walls (DWs) are becoming the focus of renewed excitement. Modern experimental techniques permit an unprecedented control on nano-domain structures, and it is now possible to produce materials with a large volume fraction occupied by the DWs themselves. Also, recent experiments show that DWs can display distinct properties not present in the domains. For example, measurements of increased conductivity and photovoltaic activity in materials like BiFeO3 suggest that the DWs could serve as active elements in electronics and energy applications. As a result, a lot of effort is being devoted to the engineering and optimization of the DWs.
Understanding the novel DW behaviours remains a great challenge, and atomistic first-principles theory is called to play a key role in the field. We have employed a variety of tools, ranging from accurate quantum-mechanical methods to approximate model potentials for large-scale simulations, to investigate DW-related phenomena. In this talk I will present some of our most striking results, including the discovery of novel structures and structural transitions at the DWs of well-known (multi)ferroic oxides, the tuning of DW properties with epitaxial strain, and ideas for inducing novel orders confined at the walls.


CK-4:IL02  Multiferroics Studied by Resonant x-ray Scattering
C. MAZZOLI¹, A. BOMBARDI², G. GHIRINGHELLI¹, ¹Politecnico di Milano, Italy; ²Diamond Light Source, UK

Multifunctional materials whose properties derive from electronic degrees of freedom, like Multiferroics and Magneto-electrics for example, are extremely appealing for possible futuristic applications in fields as different as information technologies, sensors and energy harvesting, as well as extremely challenging battles for material scientists and solid state physicists. For long time the investigation and modelling of such complex systems was essentially out of the scope but in the last ten years the scientific community has produced an enormous effort to investigate and engineer electronic problems down to the microscopic level. In this panorama, Resonant X-ray Scattering experiments (both elastic and inelastic) have shown its privileged point of view, being able to unravel tiny electronic handles responsible for macroscopic phenomenology of interest: new and exotic orderings can be investigated, sublattice order parameters spotted and finally coupling mechanisms of electronic origin revealed. In my talk, I will surf on the last contributions of Resonant X-ray Scattering on this class of materials, showing how the complementarity with neutrons and the specificity of X-rays provides the scientific community with fundamental information otherwise essentially inaccessible.


CK-4:L03  Dielectric Properties of Novel Multiferroic Systems
S. KROHNS, P. LUNKENHEIMER, A. RUFF, A. LOIDL, Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, Germany; J. MÜLLER, M. LANG, Institute of Physics, Goethe-University Frankfurt, Germany; A.V. PROKOFIEV, Institute of Solid State Physics, Vienna University of Technology, Austria

In the last decade, various mechanisms for coupled polar and magnetic ordering, so called multiferroicity, were discovered. Especially in case of strong magnetoelectric coupling, multiferroic systems can pave the way for new generations of sensors and actuators. Therefore, mechanisms for multiferroicity as spin-driven ferroelectricity or electric-dipole-driven magnetism and new multiferroic systems, e.g., artificial heterostructures, are in the focus of current research aiming to find compounds with material properties that are suitable for application.
Dielectric spectroscopy and non-linear electrical measurements are powerful tools to analyze the electronic properties of multiferroic systems giving new insights into the underlying physics, which is prerequisite for their optimization. Here, we thoroughly discuss the dielectric properties of two important multiferroic systems: At first, we give a brief review on a recently discovered multiferroic charge-transfer-salt systems [1]. In addition, we address the question if there is a high-temperature polar phase in the prototypical spin-driven multiferroic system LiCuVO4 [2].
[1] P. Lunkenheimer et al., Nat. Mater. 11, 755 (2012).
[2] F. Schrettle et al., Phys. Rev. B 77, 144101 (2008).


CK-4:IL06  Multifunctional Interfaces in Ferroic Oxides
D. MEIER, M. FIEBIG, ETH Zuerich, Zuerich, Switzerland

In ferroic oxide materials natural interfaces spontaneously arise in the form of domain walls. Just like artificially constructed interfaces such domain walls are a rich source for fascinating physics resulting from their low symmetry, geometric confinement, electrostatics, and strain. In addition, they can be created, moved, and erased at will offering great potential for novel device paradigms and new opportunities for interface engineering.
Particularly interesting are domain walls in multiferroics, where the interplay of electric and magnetic (or structural) long-range order gives rise to rather exotic interface states. Here, I will present two examples of multiferroic domain walls with specific functionalities: (i) Hybrid walls with inseparably entangled magnetic and electric order parameters and (ii) charged walls that owe their stability to the presence of topologically protected structural singularities. Results gained by cathode-lens microscopy, scanning-probe microscopy, and nonlinear optics will be discussed providing insight to the domain wall physics on nano- to mesoscopic length scales.


CK-4:L07  Novel LiNbO3-Type ScFeO3 with Weak Ferromagnetic Behavior at Room Temperature
T. KAWAMOTO, K. FUJITA, T. MATOBA, K. TANAKA, Kyoto Univ., Kyoto, Kyoto, Japan; I. Yamada, Osaka Prefecture Univ., Sakai, Osaka, Japan and JSP-PRESTO, Chiyoda-ku, Tokyo, Japan; S. KIM, P. GAO, X. PAN, UMich, Ann Arbor, MI, USA; H. Etani, T. Irifune, Ehime Univ., Matsuyama, Ehime, Japan

LiNbO3 (LN)-type magnetic oxides have attracted much attention because they are categorized as a multiferroic material, which shows both ferromagnetic and ferroelectric properties. Although a number of LN-type oxides are stabilized via high-pressure synthesis, there are no reports on LN-type oxides with long-range magnetic ordering at room temperature. In this study, we report on the synthesis of novel LN-type ScFeO3 temperature from bixbyite-type ScFeO3 via high-pressure and high-temperature treatment at 15 GPa and 1450 ºC. The high-angle annular dark-field scanning transmission electron microscopic image directly shows the fully ordered arrangement of Sc and Fe ions, unlike the polar corundum-type ScFeO3. The structural refinement and 57Fe Mössbauer spectroscopy indicate that this compound is a rare example of LN-type oxide with only trivalent ions on the A and B sites. In-situ XRD measurement demonstrates that the bixbyite phase transforms into perovskite phase under 15 GPa and 800 ºC, implying that LN phase stems from perovskite phase upon decompression. LN-type ScFeO3 exhibits weak ferromagnetic behavior below　545 K due to the canting of antiferromagnetically coupled Fe3+ moments.


Session CK-5 - Coexistence of Superconductivity and Magnetism; Oxides with Diluted Magnetic Moments

CK-5:IL02  Impurity Effect on the Interplay Between Magnetism and Superconductivity in 1111 Iron-pnictides
S. SANNA, Physics Department, University of Pavia, Pavia, Italy

I shall review on the evolution of the magnetic and superconducting ground states of REFeAsO_(0.89)F_(0.11) with RE= La, Nd, Sm (RE1111) as a function of diamagnetic Ru and paramagnetic Mn impurities, at constant optimum charge doping [1-3]. This is an alternative and complementary approach respect to the usual studies done versus charge doping or pressure. It will be shown that spin dilution by Ru for Fe substitution causes the recovery of static magnetism nanoscopically coexisting with superconductivity around the 1/4 Ru:Fe content. By tuning the RE radii it results that the stronger the static magnetism the more significant are both the electron localization effects and the degradation of the superconducting state. For all the RE1111 families superconductivity survives up to the relatively high diamagnetic Ru:Fe dilution of 60%.
On the contrary, only a tiny 0.2% of paramagnetic Mn causes the total suppression of superconductivity in La1111 with a concomitant recovery of strong static magnetism and electron localization effects.
The implication of these results on the possible pairing mechanisms underlying those materials will be discussed.
[1] S. Sanna et al., PRL 107, 227003 (2011)
[2] P. Bonfà et al., PRB B 85, 054518 (2012)
[3] S. Sanna et al., PRB 87, 134518 (2013)


CK-5:IL03  Phase Diagrams of Fe Based Superconductors
B. BUECHNER, Institut fuer Festkoerperforschung, IFW Dresden and Institut fuer Festkoerperphysik, TU Dresden, Dresden, Germany

Using a broad spectrum of experimental techniques, such as NMR, µSR, ARPES, magnetometry, thermodynamics, x-ray diffraction, and transport measurements, we studied the interplay between magnetism and superconductivity in several classes of iron pnictide superconductors. In LaO1-xFxAsFe and other 1111 type materials an intimate interplay between magnetism and electronic properties is evident. Moreover, measurements of the electrical field gradient by NQR yield clear-cut evidence for nanoscale order of charges and/or orbitals which are reminiscent to the famous stripe order in cuprates. The phase diagram of Co doped NaFeAs is very similar to that of the 1111 and 122 type pnictides. In contrast, LiFeAs, a second member of the 111 type pnictide shows quite different behaviour. From our measurements on pristine material as well as hole and electron doped compounds we do not find any evidence for strong antiferromagnetic correlations. Instead, measurements of NQR, µSR, magnetisation and magnetic resonance reveal a weak ferromagnetic order in hole doped LiFeAs. Based on our determination of the phase diagram and the results from spectroscopic studies the possible relationship between this unusual ferromagnetic state and superconductivity in stoichiometric LiFeAs is discussed.


CK-5:IL04  NMR Studies in Multilayered Cuprates and Fe Pnictides: Toward Understanding the Mechanism of High Temperature Superconductors
H. MUKUDA, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan

We present resent progress on our NMR experiments of two high-temperature superconductors, cuprates and iron-pnictides. In the cuprates, the ground-state phase diagram of a disorder-free CuO_2 plane has been experimentally revealed by site-selective NMR on multilayered cuprates(n=2~6). A critical hole density (p_c(AFM)), at which the AFM order on a CuO2 plane disappears, increases from 0.075 to 0.11 as the interlayer magnetic coupling becomes stronger in increasing from n = 3 to 6. Recent NMR study on n=6~8 suggests that the p_c(AFM) will saturate around optimally-doped region of SC even when the interlayer coupling is sufficiently strong.
In Fe-pnictides, NMR studies on many LaFeAsO-based compounds have revealed that the low-energy antiferromagnetic spin fluctuations (AFMSF) are one of the key factors to increase the Tc. However, in Fe-pnicitide with high-Tc (50 K), the low-energy AFMSF does not increase critically in the normal state. We discuss the origin of superconductivity through the relation between Tc and other parameters such as local structure of Fe-As plane, Fermi surface topology, AFMSF, and so on.
[1] H.Mukuda et al., J. Phys. Soc. Jpn 81, 011008 (2012)
[2] H.Mukuda et al., Phys. Rev. Lett. 109, 157001 (2012)


CK-5:IL05  Computational Nano-materials Design of Dynamically Created New Functional Ordered Oxide Nano-superstructures by Spinodal Nano-decomposition: Design vs. Experimental Realizations
H. KATAYAMA-YOSHIDA, Graduate School of Engineering Science, Osaka University, Osaka, Japan

Based on ab initio electronic structure calculation and multi-scale simulation, we discuss the design of magnetic mechanism and the self-organized Spinodal Nano-Decomposition in dilute magnetic oxides in ZnO, MgO, SrO, BaO, CaO, NiO , and Re-RAM with d0 ferromagnetism. By controlling the dimensionality (2D and 3D) of the crystal growth, crystal growth speed, substrate temperatures, and seeding in the self-organized nanostructure formation, we design the shape controlled quantum-dot (Dairiseki-Phase) and quantum nanowire (Konbu-Phase), and the new functionality such a Re-RAM, and high-blocking temperature in super-para-magnetism. We compare our recent computational nano-materials design data with the recent available experimental verifications.
References:
[1]. K. Sato et al., Rev. of Mod. Phys., 82, (2010) 1633.
[2]. M. Toyoda, et al., Physica B 376, (2006) 647.
[3]. Nguyen Dang Vu, et al., Appl. Phys. Express, 4, (2011) 015203.
[4]. K. Kenmochi, et al., J. Phys. Soc. Jpn, 73, (2004) 2952.
[5]. M. Seike et al., Jpn. J. Appl. Phys.50 (2011) 090204.; ibid 51 (2012) 050201.
[6]. K. Oka et al., J. Am. Chem.Soc. 134 (2012) 2535.


CK-5:IL06  Room Temperature Ferromagnetic Oxide Semiconductor
T. FUKUMURA, Department of Chemistry, University of Tokyo, Tokyo, Japan

Electrically induced ferromagnetism at room temperature in (Ti,Co)O2 demonstrated a principal role of electron carriers in the high temperature ferromagnetism and also a possibility of room temperature operation of spintronic devices [1]. Subsequent chemical carrier-doping study unveiled the presence of various magnetic and electronic phases as a function of carrier density [2]. These results indicate close interplay between the electronic conduction and the magnetism [3,4]. In this paper, we shall talk about current understanding of the ferromagnetism and recent progress toward room temperature semiconductor spintronics.
References
[1] Y. Yamada et al., Science 332, 1065 (2011).
[2] Y. Yamada et al., Appl. Phys. Lett. 99, 242502 (2011).
[3] T. Fukumura et al., Spin 2, 1230005 (2012).
[4] T. Fukumura et al., in "Functional Metal Oxides: New Science and Novel Applications" ed. by S. Ogale, M. Blamire, T. Venkatesan, (Wiley, Weinheim, 2013).

 
Session CK-6 - Novel Synthesis, Characterization and Application

CK-6:IL01  High-pressure Synthesis, Crystal Structure, and Physical Properties of Novel Iron-based Perovskite Oxides
I. YAMADA, Nanoscience and Nanotechnology Research Center, Research Institutes for the Twenty-First Century, Osaka Prefecture University, Sakai, Japan

ACu3Fe4O12 (A: alkaline earth, rare earth, R) perovskite oxides are synthesized under high pressures above 10 GPa, demonstrating various types of structural transformations and electronic properties because of instability of unusual high valence ions (Fe4+ and Fe3.75+) [1-4]. CaCu3Fe4O12 and LnCu3Fe4O12 (R = Y, Dy, Ho, Er, Tm, Yb, Lu) show charge disproportionation (2Fe4+ → Fe3+ + Fe5+) and ferrimagnetic transitions. On the other hand, SrCu3Fe4O12 and RCu3Fe4O12 (R = La, Pr, Nd, Sm, Eu, Gd, Tb) exhibit intersite charge transfer (Cu2+ + Fe4+ → Cu3+ + Fe3+) and antiferromagnetic transitions. Structure analysis based on bond valence models for RCu3Fe4O12 reveals that the metal-oxygen bond strains in these compounds govern the types of phase transitions and are classified into two types: Overbonding or compression stress (underbonding or tensile stress) in the R-O (Fe-O) bond is dominant for the compounds with larger Ln ions (R = La-Tb), while the opposite type of bond strains are found for those with smaller Ln ions (R = Y, Dy-Lu).
References
[1] I. Yamada et al., Angew. Chem. Int. Ed. 47, 7032-7035 (2008).
[2] Y. W. Long et al., Nature 458, 60-63 (2009).
[3] I. Yamada et al., Angew. Chem., Int. Ed. 50, 6579-6582 (2011).
[4] H. Etani et al., J. Am. Chem. Soc. 135, 6100-6106 (2013).


CK-6:IL02  Synthesis of Epitaxial Ultrathin Films Prepared by Polymer-Assisted Deposition
J.M. VILA-FUNGUEIRIÑO, B. RIVAS-MURIAS, F. RIVADULLA, Center for research in Biological Chemistry and Molecular Materials (CQIUS), University of Santiago de Compostela, Santiago de Compostela, Spain

Chemical methods of thin-film deposition are an affordable and versatile alternative to physical deposition techniques (PLD, Sputtering, MBE, etc.). But when compared to these techniques, chemical methods show poorest control of the thickness and stoichiometry, a larger interface and surface roughness, and difficult fabrication of homogeneous films and multilayers over large areas. These problems limited the applicability of chemical deposition methods for the study of the phenomena that occur at clean interfaces with a broken symmetry (spin, orbital, etc), or their use in highly demanding applications.
We will describe a simple chemical deposition method to synthesize high quality epitaxial thin and ultrathin films of different materials. A precursor solution of a hydrosoluble polymer (polyethileneimine or chitosan) and the stoichiometric proportions of the metallic salts, is spun-coated on a substrate and annealed at high temperature. The results are homogeneous films, free of defects over large areas, with smooth surfaces and interfaces, comparable to these obtained by physical methods. We will discuss the structural, magnetic and transport properties of films sythesized by this method, including different functional oxides, heteroepitaxial bilayers, nitrides and pure elements


CK-6:IL03  SPINWIRE®, Magnetism for Security and Traffic Management
X. MARTI, J. GARCES, IGS Reserach, La Pobla de Mafumet (Tarragona), Spain

One hundred thousand outdoor parking slots and over a thousand kilometers of streets are counted in downtown Barcelona. Yet, reality shows up as long hours driving towards the scarce free parking spots. In IGSresearch we believe that the smart solution to improve the mobility and parking in large cities cannot deal with both issues separately. Moreover, relying on one hundred thousand replaceable battery-powered devices is unfeasible.
SPINWIRE® is a new cost-effective flexible cable combining vehicle sensing, information processing, broadcasting and energy supply. The wire, 20 mm thick, is installed below the ground, protected from vandalism, and plugged to conventional energy sources available in cities using the ubiquitous pre-existing pipes and service lines. Alternatively, a quick 20 mm deep rack is trenched and covered at the speed of a meter per minute. The information can be extracted from any segment of the wire and sent to ground traffic control authorities.
IGSresearch solutions are already guiding municipalities of Reus and Tarragona (both with above hundred thousand inhabitants) and has been requested by large multinational companies like REPSOL or BASF. Follow us at www.igsresearch.com

 
Poster Presentations

CK:P01  Resistance Noise in Ultra-thin Films of LaNiO3
J. SCOLA, A. SENEGAS, B. BERINI, Y. DUMONT, Groupe d'Étude de la Matiere Condensée (GEMaC), UMR 8635 du CNRS, UVSQ, Versailles Cedex, France

The LaNiO3 compound with perovskite structure has been described as a correlated electron system with important electron-electron interactions from the observed behaviour in specific heat, magnetic susceptibility and electrical resistivity measurements. The Ni 3d t2g and the O 2p electrons hybridize and form a strongly delocalized states screen the Coulomb repulsion of the Ni 3d eg electrons thus enabling them to contribute to the electrical and heat transport through quasiparticule excitations. The very small mean free path can be related to the essentially dynamical character of the conduction process and is in agreement with the description of the metallic phase in nickelates in terms of a fluctuating medium where conducting and insulating regions coexist.
In ultra-thin films a localisation-induced metal-insulator transition occurs as the thickness is decreased below a threshold value. Here, we present resistance fluctuations measured in a series of ultra-thin films of LaNiO3 grown on SrTiO3, close to the metal-insulator transition. A particular attention was paid to the oxygen stoichiometry. The electrical properties were determined by DC transport. The noise regime is studied for different thicknesses and the role of the electron-electron interaction is discussed.