Suchergebnisse

We have studied the interaction between magnetism and superconductivity in a pseudo-spin-valve structure consisting of a Co/Cu/Py/Nb-layer sequence. We are able to control the magnetization reversal process and monitor it by means of the giant magnetoresistance effect during transport measurements. By placing the superconducting Nb-film on the top of the permalloy (Py) electrode instead of putting it in between the two ferromagnets, we minimize the influence of spin scattering or spin accumulation onto the transport properties of Nb. Magnetotransport data reveal clear evidence that the stray fields of domain walls (DWs) in the pseudo-spin valve influence the emerging superconductivity close to the transition temperature by the occurrence of peaklike features in the magneto-resistance characteristic. Direct comparison with magnetometry data shows that the resistance peaks occur exactly at the magnetization reversal fields of the Co and Py layers where DWs are generated. For temperatures near the superconducting transition the amplitude of the DW-induced magnetoresistance increases with decreasing temperature, reaching values far beyond the size of the giant magnetoresistive response of our structure in the normal state. 2012 American Physical Society. ; We acknowledge the Diputación Foral de Giupuzkoa Ref. 99/11, program Red Guipuzkoana de Ciencia Tecnologia e Innovacion, funding from the Basque Government under Program No. PI2009-17 and UPV/EHU Project IT-366-07, and the Spanish Ministry of Science and Innovation under Projects No. MAT2009-07980 and FIS2011-28851-C02-02. ; Peer Reviewed

We overviewed the correlation between the structure, magnetic and transport properties of magnetic microwires prepared by the Taylor-Ulitovsky method involving rapid quenching from the melt and drawing of the composite (metallic core, glass coated) wire. We showed that this method can be useful for the preparation of different families of magnetic microwires: soft magnetic microwires displaying Giant magnetoimpedance (GMI) effect, semi-hard magnetic microwires, microwires with granular structure exhibiting Giant Magnetoresistance (GMR) effect and Heusler-type microwires. Magnetic and transport properties of magnetic microwires depend on the chemical composition of metallic nucleus and on the structural features (grain size, precipitating phases) of prepared microwires. In all families of crystalline microwires, their structure, magnetic and transport properties are affected by internal stresses induced by the glass coating, depending on the quenching rate. Therefore, properties of glass-coated microwires are considerably different from conventional bulk crystalline alloys. ; This work was supported by Spanish Ministry of Economy and Competitiveness (MINECO) under Projects MAT2013-47231-C2-1-P and MAT2013-47231-C2-2-P. The authors thank for technical and human support provided by SGIker (Magnetic Measurements Gipuzkoa) of UPV/EHU. VZ and AZ wish to acknowledge the support under Program of Mobility of the Researchers of the Basque Government (grants MV-2016-1-0025 and MV-2016-1-0018 respectively).

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'. ; Peer reviewed

The spin Hall magnetoresistance (SMR) emerged as a reference tool to investigate the magnetic properties of materials with an all-electrical setup. Its sensitivity to the magnetization of thin films and surfaces may turn it into a valuable technique to characterize van der Waals magnetic materials, which support long-range magnetic order in atomically thin layers. However, realistic surfaces can be affected by defects and disorder, which may result in unexpected artifacts in the SMR, rather than the sole appearance of electrical noise. Here, we study the SMR response of heterostructures combining a platinum (Pt) thin film with the van der Waals antiferromagnet MnPSe3 and observe a robust SMR-like signal, which turns out to originate from the presence of strong interfacial disorder in the system. We use transmission electron microscopy (TEM) to characterize the interface between MnPSe3 and Pt, revealing the formation of a few nanometer-thick platinum–chalcogen amorphous layer. The analysis of the transport and TEM measurements suggests that the signal arises from a disordered magnetic system formed at the Pt/MnPSe3 interface, washing out the interaction between the spins of the Pt electrons and the MnPSe3 magnetic lattice. Our results show that the damaged interfaces can yield an important contribution to SMR, questioning a widespread assumption on the role of disorder in such measurements. ; The authors also thank SGIker Medidas Magneticas Gipuzkoa (UPV/EHU/ ERDF, EU) for the technical and human support. This work is supported by the European Union H2020 under the Marie Sklodowska-Curie Actions (796817-ARTEMIS and 748971-SUPER2D) and by the Spanish MICINN under project nos. RTI2018-094861-B-I00, PID2019-108153GA-I00, and the Maria de Maeztu Units of Excellence Programme (MDM-2016-0618 and CEX2020-001038-M). J.M.G.-P. and M.X.A.-P. thank the Spanish MICINN for a Ph.D. fellowship (grants no. BES-2016-077301 and PRE-2019-089833, respectively). M.G. acknowledges support from la Caixa Foundation for a Junior Leader ...

3 páginas, 3 figuras.-- et al. ; Epitaxial discontinuous Fe/MgO multilayers have been grown by pulsed laser deposition on MgO(001) single-crystal substrates. The multilayers with 0.6 nm nominal Fe layers thickness are superparamagnetic and demonstrate tunneling magnetoresistance (TMR) in the current-in-plane configuration. Increasing deposition temperature causes an improvement in crystal quality and is accompanied by higher TMR ratios. The maximum value (9.2% TMR at room temperature and 18 kOe magnetic field) trebles that of polycrystalline samples deposited simultaneously on glass substrates. A model formula for TMR ratio that includes both spin-dependent tunneling and spin-filtering effect is proposed to explain these results. ; Financial support by Spanish Ministry of Science (through project No. MAT2008-06567-C02 including FEDER funding) and by the Aragón Regional Government (through projects E26 and PI059/08) is acknowledged. Work of A.V. and G.N.K. was supported by Portuguese FCT through "Ciencia 2008" and "Ciencia 2007" programs, respectively. ; Peer reviewed

4 pages, 3 figures. ; We have investigated the transport and magnetotransport properties in Fe/MgO multilayers around the Fe percolation threshold as a function of the temperature and the nominal thickness of iron layer (t). Electrical resistivity measurements allowed us to disclose the charge transport mechanisms involved, which are closely related to the degree of discontinuity in the Fe layers. The samples with Fe thickness below percolation threshold (t ∼ 0.8 nm) exhibit isotropic magnetoresistance (MR), which can be understood considering spin-polarized electron tunneling between nanometer-sized, superparamagnetic Fe grains. The MR ratio increases with decreasing temperature from ∼ 3% at room temperature to ∼ 10% at 30 K. The temperature dependence of MR can be explained satisfactorily in terms of a modified Mitani's model. ; Financial support by Spanish Ministry of Science (through Project Nos. MAT2008-06567-C02 and CIT- 420000-2008-19 including FEDER funding) and by the Aragón Regional Government (through Project Nos. E26 and PI059/08) is acknowledged. ; Peer reviewed

The magnetoresistance (MR) was measured at 200, 250 and 300 K in magnetic fields up to B=12 T for a nanocrystallized Fe63.5Cr 10Nb3Cu1Si13.5B9 alloy. Both the longitudinal (LMR) and transverse (TMR) component of the magnetoresistance decreased from B=0 to about 0.1 T. This could be ascribed to a giant MR (GMR) effect due to spin-dependent scattering of conduction electrons along their path between two FeSi nanograins via the non-magnetic matrix. Such a scattering may occur if the nanograin moments are not or only weakly coupled in the absence of a strong exchange coupling (due to the high Cr content in the matrix) and/or only weak dipoledipole coupling is present (due to sufficiently large separations between the nanograins). For larger fields, the GMR saturated and a slightly nonlinear increase in MR with B was observed due to a contribution by the residual amorphous matrix. The anisotropic MR effect (AMR≡LMR-TMR) was negative for all fields and temperatures investigated. By measuring the MR of melt-quenched Fe100-xSix solid solutions with x=15, 18, 20, 25 and 28, the observed AMR could be identified as originating from the FeSi nanograins having a D03 structure. © 2010 Elsevier B.V. All rights reserved. ; This work was supported by the Hungarian Scientific Research Fund (OTKA) through Grant T 038383 as well as by the Hungarian–Spanish Bilateral Cooperation through Grant TéT E-21/04, moreover by the Spanish Government and EU FEDER (Project MAT 2007-65227) and the PAI of the Regional Government of Andalucía (Project P06-FQM-01823). The authors thank Dr. A. Rodriguez Pierna (E.U.I.T.I. of San Sebastian, University of the Basque Country, Spain) for kindly providing the original amorphous Fe63.5Cr10Nb3Cu1Si13.5B9 alloy ribbon. M.C. is grateful to the European Commission for financial support under a Marie Curie Intra-European Fellowship for Career Development. ; Peer Reviewed

Galceran, Regina et al. ; © 2015 American Physical Society. We report on magnetotransport properties on La0.7Sr0.3MnO3/MgO/Fe tunnel junctions grown epitaxially on top of (001)-oriented SrTiO3 substrates by sputtering. It is shown that the magnetoresistive response depends critically on the MgO/Fe interfacial properties. The appearance of an FeOX layer by the interface destroys the Δ1 symmetry filtering effect of the MgO/Fe system and only a small negative tunneling magnetoresistance (TMR) (∼-3%) is measured. However, in annealed samples a switchover from positive TMR (∼+25% at 70 K) to negative TMR (∼-1%) is observed around 120 K. This change is associated with the transition from semiconducting at high T to insulating at low T taking place at the Verwey transition (TV∼120K) in Fe3O4, thus suggesting the formation of a very thin slab of magnetite at the MgO/Fe interface during annealing treatments. These results highlight the relevance of interfacial properties on the tunneling conduction process and how it can be substantially modified through appropriate interface engineering. ; We acknowledge financial support from the Spanish MINECO through grants (MAT2012-33207, MAT2011-27470-C02, MAT2012-37638 and Consolider Ingenio 2010 - CSD2009-00013 (Imagine)), from CAM through Grant No. S2009/MAT-1756 (Phama) and Basque Government (PI2011-1). Financial support from EC through FEDER program and Marie Curie Actions (256470-ITAMOSCINOM) is also acknowledged. C.M.B. thanks the Spanish MINECO for the financial support through the RyC program ; Peer Reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y3Fe5O12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. ; This work was supported by the European Union 7th Framework Programme under NMP Project No. 263104-HINTS and the European Research Council (Project No. 257654-SPINTROS), by the Spanish Ministry of Economy and Competitiveness under Projects No. MAT2012-37638, No. FIS2011-28851-C02-02, No. FIS2014-55987-P, and No. MAT2013-46593-C6-4-P, and by the Basque Government under UPV/EHU Projects No. IT-756-13 and No. IT-621-13. M. I. and E. S. thank the Basque Government and the Spanish Ministry of Education, Culture and Sport, respectively, for a Ph.D. fellowship (Grants No. BFI-2011-106 and No. FPU14/03102). ; Peer Reviewed

We report the spin Hall magnetoresistance (SMR) in Pt deposited on a tensile-strained LaCoO3 (LCO) thin film, which is a ferromagnetic insulator with a Curie temperature Tc=85K. The SMR displays a strong magnetic-field dependence below Tc, with the SMR amplitude continuing to increase (linearly) with increasing the field far beyond the saturation value of the ferromagnet. The SMR amplitude decreases gradually with raising the temperature across Tc and remains measurable even above Tc. Moreover, no hysteresis is observed in the field dependence of the SMR. These unusual behaviors indicate that a low-dimensional magnetic system forms at the surface of LCO and that the LCO/Pt interface decouples magnetically from the rest of the LCO thin film. Transmission electron microscopy analysis of the heterostructure reveals that an ultrathin Co-rich layer forms at the LCO surface upon deposition of Pt, which is separated from the rest of the LCO film by a ∼1-nm La/O-rich layer, thus supporting the presence of a low-dimensional ferromagnetic system. To explain the magnetoresistance measurements, we revisit the derivation of the SMR corrections and relate the spin-mixing conductances to the spin-spin correlation functions and microscopic quantities describing the magnetism at the interface. Comparisons between theory and experiment confirm the existence of a low-dimensional Heisenberg ferromagnet at the interface. Our results pave the way for exploring complex magnetic textures of insulating films by simple transport measurements. ; This work was supported by the European Union 7th Framework Programme under the Marie Curie Actions (607904- 13-SPINOGRAPH), the European Research Council (257654-SPINTROS), and the European Regional Development Fund (ERDF), by the Spanish Ministry of Economy, Industry and Competitiveness (MAT2015-65159-R, FIS2014-55987-P, MAT2013-46593-C6-4-P, MAT2016-80762-R and FIS2017-82804-P), by the Basque Government (UPV/EHU Project IT-756-13 and IT-621-13), by the Regional Council of Gipuzkoa (100/16), and by the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09).

Studies of magnetic properties and GMI effect of amorphous Co-Fe rich microwires reveal that they present GMI effect at GHz frequencies. Magnetic field dependences of GMI effect are affected by the post-processing conditions. In particular, we observed that in Co-Fe rich microwires stress-annealing allows improvement of frequency dependence of GMI ratio at high frequencies. We discussed observed experimental dependences considering both different magnetic structure and the anisotropy in the bulk and near the surface and close analogy between giant magnetoimpedance and ferromagnetic resonance. ; This work was supported by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE), by the Government of the Basque Country under PIBA 2018-44 and Elkartek (RTM 4.0) projects and by the University of Basque Country under the scheme of "Ayuda a Grupos Consolidados" (Ref.: GIU18/192). The authors thank for technical and human support provided by SGIker of UPV/EHU (Medidas Magnéticas Gipuzkoa) and European funding (ERDF and ESF)

When Glencore, the world's biggest commodities brokerage firm, went public in May 2011, the initial public offering (IPO) on the London and Hong Kong stock exchanges made headlines for weeks in the Financial Times and the trade-industry press, which devoted endless columns to the company's astonishing valuation of nearly $60 billion -- higher than Boeing or Ford Motor Co. The massive new wealth turned nearly 500 employees into overnight multimillionaires and made billionaires of at least five senior executives, including CEO Ivan Glasenberg. The firm was forced to pull back the curtain on its famously secretive doings to go public, and what it revealed shocked even seasoned commodities traders. Glencore turned out to be far more globally dominant than analysts had realized. What the IPO filing did not make clear was just how Glencore, founded four decades ago by Marc Rich, a defiant friend of dictators and spies who later became one of the world's richest fugitives, achieved this kind of global dominance. The answer -- pieced together for this article over a year of reporting that included numerous interviews with past and current Glencore employees and a review of leaked corporate records, dossiers prepared by private investigative firms, court documents, and various international investigations -- is at once simpler and far more complicated than it appears. Like all traders, Glencore makes its money at the margins, but Glencore, even more so than its competitors, profits by working in the globe's most marginal business regions and often, investigators have found, at the margins of what is legal. Adapted from the source document.