180 results on '"Frédéric Petroff"'
Search Results
2. Recovering ferromagnetic metal surfaces to fully exploit chemistry in molecular spintronics
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Marta Galbiati, Sophie Delprat, Michele Mattera, Samuel Mañas-Valero, Alicia Forment-Aliaga, Sergio Tatay, Cyrile Deranlot, Pierre Seneor, Richard Mattana, and Frédéric Petroff
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Physics ,QC1-999 - Abstract
Organic spintronics is a new emerging field that promises to offer the full potential of chemistry to spintronics, as for example high versatility through chemical engineering and simple low cost processing. However, one key challenge that remains to be unlocked for further applications is the high incompatibility between spintronics key materials such as high Curie temperature Co, Ni, Fe (and their alloys) and wet chemistry. Indeed, the transition metal proneness to oxidation has so far hampered the integration of wet chemistry processes into the development of room temperature organic spintronics devices. As a result, they had mainly to rely on high vacuum physical processes, restraining the choice of available organic materials to a small set of sublimable molecules. In this letter, focusing on cobalt as an example, we show a wet chemistry method to easily and selectively recover a metallic surface from an air exposed oxidized surface for further integration into spintronics devices. The oxide etching process, using a glycolic acid based solution, proceeds without increasing the surface roughness and allows the retrieval of an oxygen-free chemically active cobalt layer. This unlocks the full potential of wet chemistry processes towards room temperature molecular spintronics with transition metals electrodes. We demonstrate this by the grafting of alkylthiols self-assembled monolayers on recovered oxidized cobalt surfaces.
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- 2015
- Full Text
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3. Artificial Graphene Spin Polarized Electrode for Magnetic Tunnel Junctions
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Victor Zatko, Regina Galceran, Marta Galbiati, Julian Peiro, Florian Godel, Lisa-Marie Kern, David Perconte, Fatima Ibrahim, Ali Hallal, Mairbek Chshiev, Benjamin Martinez, Carlos Frontera, Lluìs Balcells, Piran R. Kidambi, John Robertson, Stephan Hofmann, Sophie Collin, Frédéric Petroff, Marie-Blandine Martin, Bruno Dlubak, Pierre Seneor, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), THALES [France]-Centre National de la Recherche Scientifique (CNRS), ICN2 - Institut Catala de Nanociencia i Nanotecnologia (ICN2), Universitat Autònoma de Barcelona (UAB), SPINtronique et TEchnologie des Composants (SPINTEC), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes (UGA), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), Institut de Ciència de Materials de Barcelona (ICMAB), Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Vanderbilt University [Nashville], University of Cambridge [UK] (CAM), ANR-19-CE09-0028,MIXES,Hétérostructures de van der Waals à dimensions mixtes pour l'électronique et la spintronique(2019), ANR-19-CE24-0015,STEM2D,Emetteurs THz de type synchrotron à base de matériaux 2D ondulés(2019), European Commission, Engineering and Physical Sciences Research Council (UK), Agence Nationale de la Recherche (France), Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Ciencia e Innovación (España), Zatko, Victor, Godel, Florian, Kern, Lisa-Marie, Chshiev, Mairbek, Frontera, Carlos, Kidambi, Piran R., Hofmann, Stephan, and Dlubak, Bruno
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Mechanical Engineering ,graphene ,General Materials Science ,Bioengineering ,General Chemistry ,proximity effects ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,[SPI.NANO]Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics ,Condensed Matter Physics ,2D materials ,spin polarization - Abstract
2D materials offer the ability to expose their electronic structure to manipulations by a proximity effect. This could be harnessed to craft properties of 2D interfaces and van der Waals heterostructures in devices and quantum materials. We explore the possibility to create an artificial spin polarized electrode from graphene through proximity interaction with a ferromagnetic insulator to be used in a magnetic tunnel junction (MTJ). Ferromagnetic insulator/graphene artificial electrodes were fabricated and integrated in MTJs based on spin analyzers. Evidence of the emergence of spin polarization in proximitized graphene layers was observed through the occurrence of tunnel magnetoresistance. We deduced a spin dependent splitting of graphene's Dirac band structure (∼15 meV) induced by the proximity effect, potentially leading to full spin polarization and opening the way to gating. The extracted spin signals illustrate the potential of 2D quantum materials based on proximity effects to craft spintronics functionalities, from vertical MTJs memory cells to logic circuits., This work has received funding from the European Union’s H2020 Future and Emerging Technologies “Graphene Flagship” (Grant Core3 No. 881603), “SINFONIA” (No. 881603) projects and a Grant Agreement Marie Skłodowska Curie “ITN Spinograph” (No. 697904), as well as from EPSRC (EP/P005152/1, EP/K016636/1). This research is supported by a public grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” program Labex NanoSaclay (ANR-10-LABX-0035), as well as grants STEM2D (ANR-19-CE24-0015), MIXES (ANR-19-CE09-0028), and by the Flag-ERA JTC 2019 project “SOGraphMEM” (ANR-19-GRFI-0001-07). This work has also received fundings from the “Spanish ministry of Science and Innovation” through “Severo Ochoa” (CEX2019-000917-S) and “OXISOT” (PID2021-128410OB-I00)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).
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- 2022
4. Almost Perfect Spin Filtering in Graphene-Based Magnetic Tunnel Junctions
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Victor Zatko, Simon M.-M. Dubois, Florian Godel, Marta Galbiati, Julian Peiro, Anke Sander, Cécile Carretero, Aymeric Vecchiola, Sophie Collin, Karim Bouzehouane, Bernard Servet, Frédéric Petroff, Jean-Christophe Charlier, Marie-Blandine Martin, Bruno Dlubak, Pierre Seneor, and UCL - SST/IMCN/MODL - Modelling
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General Engineering ,General Physics and Astronomy ,General Materials Science - Abstract
We report on large spin-filtering effects in epitaxial graphene-based spin valves, strongly enhanced in our specific multilayer case. Our results were obtained by the effective association of chemical vapor deposited (CVD) multilayer graphene with a high quality epitaxial Ni(111) ferromagnetic spin source. We highlight that the Ni(111) spin source electrode crystallinity and metallic state are preserved and stabilized by multilayer graphene CVD growth. Complete nanometric spin valve junctions are fabricated using a local probe indentation process, and spin properties are extracted from the graphene-protected ferromagnetic electrode through the use of a reference Al2O3/Co spin analyzer. Strikingly, spin-transport measurements in these structures give rise to large negative tunnel magneto-resistance TMR = −160%, pointing to a particularly large spin polarization for the Ni(111)/Gr interface PNi/Gr, evaluated up to −98%. We then discuss an emerging physical picture of graphene−ferromagnet systems, sustained both by experimental data and ab initio calculations, intimately combining efficient spin filtering effects arising (i) from the bulk band structure of the graphene layers purifying the extracted spin direction, (ii) from the hybridization effects modulating the amplitude of spin polarized scattering states over the first few graphene layers at the interface, and (iii) from the epitaxial interfacial matching of the graphene layers with the spin-polarized Ni surface selecting well-defined spin polarized channels. Importantly, these main spin selection effects are shown to be either cooperating or competing, explaining why our transport results were not observed before. Overall, this study unveils a path to harness the full potential of low Resitance. Area (RA) graphene interfaces in efficient spin-based devices.
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- 2022
5. Spin filtering by proximity effects at hybridized interfaces in spin-valves with 2D graphene barriers
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Robert S. Weatherup, Simon M-M Dubois, Frédéric Petroff, Victor Zatko, Pierre Seneor, Bruno Dlubak, Jean-Christophe Charlier, Regina Galceran, Albert Fert, Stephan Hofmann, John Robertson, Marie-Blandine Martin, Florian Godel, Maëlis Piquemal-Banci, Marta Galbiati, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, UCL - SST/IMCN/MODL - Modelling, Galbiati, Marta [0000-0002-6021-5156], Godel, Florian [0000-0003-1741-2741], Weatherup, Robert S [0000-0002-3993-9045], Charlier, Jean-Christophe [0000-0002-5749-1328], Hofmann, Stephan [0000-0001-6375-1459], Dlubak, Bruno [0000-0001-5696-8991], Apollo - University of Cambridge Repository, and Weatherup, Robert S. [0000-0002-3993-9045]
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120 ,Materials science ,Science ,General Physics and Astronomy ,Genetics and Molecular Biology ,02 engineering and technology ,Materials science Nanoscience and technology ,010402 general chemistry ,01 natural sciences ,Signal ,Article ,General Biochemistry, Genetics and Molecular Biology ,law.invention ,Engineering ,Nanoscience and technology ,law ,Monolayer ,Proximity effect (superconductivity) ,128 ,639/925 ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,lcsh:Science ,Spin-½ ,[PHYS]Physics [physics] ,639/166 ,639/301 ,Multidisciplinary ,Spintronics ,Condensed matter physics ,Nanotecnologia ,Graphene ,Physics ,639/766 ,General Chemistry ,Ciència dels materials ,5104 Condensed Matter Physics ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Ferromagnetism ,General Biochemistry ,Density of states ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,119 ,0210 nano-technology ,51 Physical Sciences - Abstract
We report on spin transport in state-of-the-art epitaxial monolayer graphene based 2D-magnetic tunnel junctions (2D-MTJs). In our measurements, supported by ab-initio calculations, the strength of interaction between ferromagnetic electrodes and graphene monolayers is shown to fundamentally control the resulting spin signal. In particular, by switching the graphene/ferromagnet interaction, spin transport reveals magneto-resistance signal MR > 80% in junctions with low resistance × area products. Descriptions based only on a simple K-point filtering picture (i.e. MR increase with the number of layers) are not sufficient to predict the behavior of our devices. We emphasize that hybridization effects need to be taken into account to fully grasp the spin properties (such as spin dependent density of states) when 2D materials are used as ultimately thin interfaces. While this is only a first demonstration, we thus introduce the fruitful potential of spin manipulation by proximity effect at the hybridized 2D material / ferromagnet interface for 2D-MTJs., 2D materials are foreseen as an opportunity to tailor spintronics devices interfaces, a.k.a spinterfaces. Here, using state-of-the-art large-scale integration in spin-valves, authors demonstrate that hybridization of graphene with a metallic spin source results in strong spin filtering effects.
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- 2020
6. Very Long Term Stabilization of a 2D Magnet down to the Monolayer for Device Integration
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Bernard Servet, Sophie Collin, Pierre Seneor, Aymeric Vecchiola, Marta Galbiati, Pomme Hirschauer, Bruno Dlubak, Frédéric Petroff, Florian Godel, Victor Zatko, Andrés Cantarero, Marie-Blandine Martin, Karim Bouzehouane, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, Thales Research and Technology [Palaiseau], and THALES
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010302 applied physics ,[PHYS]Physics [physics] ,Materials science ,Spintronics ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Term (time) ,Fragility ,Ferromagnetism ,Magnet ,0103 physical sciences ,Monolayer ,Materials Chemistry ,Electrochemistry ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
2D materials have recently demonstrated a strong potential for spintronic applications. This has been further reinforced by the discovery of ferromagnetic 2D layers. Nevertheless, the fragility of ...
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- 2020
7. Band-Structure Spin-Filtering in Vertical Spin Valves Based on Chemical Vapor Deposited WS
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Victor, Zatko, Marta, Galbiati, Simon Mutien-Marie, Dubois, Mauro, Och, Pawel, Palczynski, Cecilia, Mattevi, Pierre, Brus, Odile, Bezencenet, Marie-Blandine, Martin, Bernard, Servet, Jean-Christophe, Charlier, Florian, Godel, Aymeric, Vecchiola, Karim, Bouzehouane, Sophie, Collin, Frédéric, Petroff, Bruno, Dlubak, and Pierre, Seneor
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We report on spin transport in WS
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- 2019
8. Band-structure spin-filtering in vertical spin valves based on chemical vapor deposited WS2
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Sophie Collin, Jean-Christophe Charlier, Bernard Servet, Pierre Brus, Karim Bouzehouane, Pierre Seneor, Frédéric Petroff, Mauro Och, Marta Galbiati, Aymeric Vecchiola, Florian Godel, Marie-Blandine Martin, Pawel Palczynski, Odile Bezencenet, Simon M-M Dubois, Victor Zatko, Bruno Dlubak, Cecilia Mattevi, The Royal Society, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, Institut de la matière condensée et des nanosciences / Institute of Condensed Matter and Nanosciences (IMCN), Université Catholique de Louvain = Catholic University of Louvain (UCL), Imperial College London, Thales Research and Technology [Palaiseau], and THALES
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Materials science ,Tungsten disulfide ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,Transition metal ,tungsten disulfide ,Condensed Matter::Superconductivity ,spin filtering ,General Materials Science ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Nanoscience & Nanotechnology ,Electronic band structure ,2D ,Spin-½ ,[PHYS]Physics [physics] ,spintronics ,Spin filtering ,Condensed matter physics ,Spintronics ,business.industry ,General Engineering ,semiconductor ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,magnetic tunnel junction ,0104 chemical sciences ,Tunnel magnetoresistance ,Semiconductor ,chemistry ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,business - Abstract
International audience; We report on spin transport in WS2-based 2D-magnetic tunnel junctions (2D-MTJs), unveiling a band structure spin filtering effect specific to the transition metal dichalcogenides (TMDCs) family. WS2 mono-, bi-, and trilayers are derived by a chemical vapor deposition process and further characterized by Raman spectroscopy, atomic force microscopy (AFM), and photoluminescence spec-troscopy. The WS2 layers are then integrated in complete Co/Al2O3 /WS2/Co MTJ hybrid spin-valve structures. We make use of a tunnel Co/Al2O3 spin analyzer to probe the extracted spin-polarized current from the WS2/Co interface and its evolution as a function of WS2 layer thicknesses. For monolayer WS2, our technological approach enables the extraction of the largest spin signal reported for a TMDC-based spin valve, corresponding to a spin polarization of PCo/WS2 = 12%. Interestingly, for bi-and trilayer WS2, the spin signal is reversed, which indicates a switch in the mechanism of interfacial spin extraction. With the support of ab initio calculations, we propose a model to address the experimentally measured inversion of the spin polarization based on the change in the WS2 band structure while going from monolayer (direct bandgap) to bilayer (indirect bandgap). These experiments illustrate the rich potential of the families of semiconducting 2D materials for the control of spin currents in 2D-MTJs.
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- 2019
9. Perpendicular magnetic anisotropy and intralayer interactions in a single layer of CoPt nanoparticles
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Jolanta Stankiewicz, Fernando Bartolomé, L.M. García, Frédéric Petroff, Cyrile Deranlot, Adriana I. Figueroa, Julio C. Cezar, Javier Rubín, and Juan Bartolomé
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Materials science ,Condensed matter physics ,Magnetometer ,Transition temperature ,Nanoparticle ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,SQUID ,Ferromagnetism ,law ,Phase (matter) ,Coupling (piping) ,General Materials Science ,Deposition (law) - Abstract
The multilayer films [Al2O3/tCo Co/tPt Pt]N, produced by sequential deposition of Co and Pt on alumina consist in layers of CoPt alloyed nanoparticles. They show perpendicular magnetic anisotropy (PMA) below a freezing temperature Tf, an asperomagnetic-like phase below that temperature, and hard ferromagnetic ordering below a transition temperature T1 < Tf. A single layer granular film (N = 1) with deposition thicknesses tCo=0.7 nm, tPt=1.5 nm and particle diameter of 3 nm is presently studied. SQUID magnetometry shows that a single layer presents the three phases as well. Para-, aspero-and ferromagnetic phases are observed upon lowering the temperature, with transition temperatures Tf ≈ 375 K and T1 ≈ 200 K, respectively. In addition, the PMA persists, proving that there is no interlayer coupling in the multilayer system. SQUID results also reveal a core-shell structure in the CoPt nanoparticles.
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- 2019
10. Structural and magnetic properties of granular CoPd multilayers
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Javier Rubín, Cyrile Deranlot, José M. González-Calbet, L. M. García, Lorena Ruiz, N. B. Brookes, Frédéric Petroff, L. G. Vivas, Fernando Bartolomé, José F. Bartolomé, Andrei Rogalev, F. Wilhelm, Adriana I. Figueroa, Ministerio de Economía y Competitividad (España), and Diputación General de Aragón
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Materials science ,Magnetism ,Physics::Medical Physics ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Condensed Matter::Materials Science ,Paramagnetism ,0103 physical sciences ,Alloys ,010306 general physics ,Perpendicular magnetic anisotropy ,Condensed matter physics ,XMCD ,Magnetic circular dichroism ,Cobalt ,Coercivity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Ferromagnetism ,Magnetic shape-memory alloy ,Magnetic nanoparticles ,0210 nano-technology ,Palladium ,Superparamagnetism - Abstract
Multilayers of bimetallic CoPd alloyed and assembled nanoparticles, prepared by room temperature sequential sputtering deposition on amorphous alumina, were studied by means of high-resolution transmission electron microscopy, x-ray diffraction, SQUID-based magnetometry and x-ray magnetic circular dichroism. Alloying between Co and Pd in these nanoparticles gives rise to a high perpendicular magnetic anisotropy. Their magnetic properties are temperature dependent: at low temperature, the multilayers are ferromagnetic with a high coercive field; at intermediate temperature the behavior is of a soft-ferromagnet, and at higher temperature, the perpendicular magnetic anisotropy in the nanoparticles disappears. The magnetic orbital moment to spin moment ratio is enhanced compared with Co bare nanoparticles and Co fcc bulk., The financial support of the Spanish MINECO MAT2011-23791, MAT2014-53921-R and Aragonese DGA-IMANA E34 projects is acknowledged.
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- 2016
11. Phthalocyanine based molecular spintronic devices
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Jacek Arabski, Richard Mattana, Shengwei Shi, Eric Beaurepaire, Martin Bowen, Samy Boukari, Karim Bouzehouane, Clément Barraud, Pierre Seneor, Dong Jik Kim, Cyrile Deranlot, Frédéric Petroff, and R. Rakshit
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Materials science ,Condensed matter physics ,Spintronics ,Magnetoresistance ,Conductance ,chemistry.chemical_element ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Inorganic Chemistry ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Atom ,Phthalocyanine ,Molecule ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Cobalt ,Quantum tunnelling - Abstract
Molecular spintronics is an effervescent field of research, which aims at combining spin physics and molecular nano-objects. In this article, we show that phthalocyanine molecules integrated in magnetic tunnel junctions (MTJs) can lead to magnetoresistance effects of different origins. We have investigated cobalt and manganese phthalocyanine molecule based magnetic tunnel junctions. CoPc MTJs exhibit both tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR) effects of similar magnitude. However, for MnPc MTJs, a giant TAMR dominates with ratios up to ten thousands of percent. Strong features visible in the conductance suggest that spin-flip inelastic electron tunneling processes occur through the Mn atomic chain formed by the MnPc stacks. These results show that metallo-organic molecules could be used as a template to connect magnetic atomic chains or even a single magnetic atom in a solid-state device.
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- 2016
12. Insulator-to-Metallic Spin-Filtering in 2D-Magnetic Tunnel Junctions Based on Hexagonal Boron Nitride
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Robert S. Weatherup, Jean-Christophe Charlier, John Robertson, Stephan Hofmann, Pierre Seneor, Marie-Blandine Martin, Piran R. Kidambi, Maëlis Piquemal-Banci, Stéphane Xavier, Bruno Dlubak, Albert Fert, Abdelmadjid Anane, Sabina Caneva, Karim Bouzehouane, Regina Galceran, Florian Godel, Frédéric Petroff, Simon M-M Dubois, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, Laboratory for Photovoltaics Luxembourg, University of Luxembourg [Luxembourg], University of Cambridge [UK] (CAM), Thales Research & Technology France, THALES, Unité de Physique-Chimie et physique des matériaux (LLN), and Université Catholique de Louvain = Catholic University of Louvain (UCL)
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Materials science ,General Physics and Astronomy ,Hexagonal boron nitride ,Insulator (electricity) ,02 engineering and technology ,Chemical vapor deposition ,01 natural sciences ,chemical vapor deposition ,Metal ,Ab initio quantum chemistry methods ,0103 physical sciences ,General Materials Science ,hexagonal boron nitride ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,spintronics ,Spin filtering ,Spintronics ,Condensed matter physics ,General Engineering ,[CHIM.MATE]Chemical Sciences/Material chemistry ,021001 nanoscience & nanotechnology ,2D materials ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology - Abstract
International audience; We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into magnetic tunnel junctions (2D-MTJs) by fabricating two illustrative systems (Co/h-BN/Co and Co/h-BN/Fe) and by discussing h-BN potential for metallic spin filtering. The h-BN is directly grown by chemical vapor deposition on prepatterned Co and Fe stripes. Spin-transport measurements reveal tunnel magneto-resistances in these h-BN-based MTJs as high as 12% for Co/h-BN/h-BN/Co and 50% for Co/h-BN/Fe. We analyze the spin polarizations of h-BN/Co and h-BN/Fe interfaces extracted from experimental spin signals in light of spin filtering at hybrid chemisorbed/ physisorbed h-BN, with support of ab initio calculations. These experiments illustrate the strong potential of h-BN for MTJs and are expected to ignite further investigations of 2D materials for large signal spin devices.
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- 2018
13. Spin-Dependent Hybridization Phenomena in Organic and Molecular Spintronics Devices
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Frédéric Petroff, Sophie Delprat, Clément Barraud, Marta Galbiati, Pierre Seneor, Richard Mattana, Sergio Tatay, and Benoit Quinard
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Physics ,Spintronics ,Condensed matter physics ,Spin (physics) - Published
- 2018
14. Investigating magnetic proximity effects at ferrite/Pt interfaces
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Frédéric Petroff, Stéphane Collin, Jean-Baptiste Moussy, Andrei Rogalev, Vicent Cros, Richard Mattana, F. Wilhelm, Abdelmadjid Anane, Cyrile Deranlot, Manuel Collet, Katharina Ollefs, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), THALES [France]-Centre National de la Recherche Scientifique (CNRS), Laboratoire Nano-Magnétisme et Oxydes (LNO), Service de physique de l'état condensé (SPEC - UMR3680), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, European Synchrotron Radiation Facility (ESRF), and Centre National de la Recherche Scientifique (CNRS)-THALES
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[PHYS]Physics [physics] ,Materials science ,Physics and Astronomy (miscellaneous) ,Magnetic domain ,Spintronics ,Condensed matter physics ,Yttrium iron garnet ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferromagnetic resonance ,Magnetic susceptibility ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,Nuclear magnetic resonance ,Ferromagnetism ,Magnetic shape-memory alloy ,chemistry ,Magnet ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology - Abstract
International audience; Spintronic devices based on pure spin currents have drawn a lot of attention during the last few years for low energy device design. One approach to generate pure spin currents is to combine a metallic or insulating ferromagnetic layer with a non-magnetic metallic layer with a large spin-orbit coupling. A recent controversy has arisen in the possible role of magnetic proximity effects at ferromagnetic/ non-magnetic interfaces, which can hamper the understanding of pure spin current generation mechanisms. While magnetic proximity effects have been frequently observed at ferromagnetic metal/non-magnetic interfaces, there are only a few studies on ferromagnetic insulator/non-magnetic interfaces. Regarding the use of ferromagnetic insulators, the focus has been mainly on yttrium iron garnet (YIG). However, investigation of induced magnetic moments at YIG/Pt interfaces has engendered contradictory results. Here, we propose to study insulating ferrites for which electronic and magnetic properties can be modulated. Magnetic proximity effects have been investigated at MnFe 2 O 4 /Pt, CoFe 2 O 4 /Pt, and NiFe 2 O 4 /Pt interfaces by X-ray circular magnetic dichroism (XMCD) measurements at the Pt L 3 edge. Although hybridization with Pt seems to be different among the ferrites, we do not detect any XMCD signal as the signature of an induced magnetism in Pt. We have then studied the Fe 3 O 4 ferrite below and above the Verwey transition temperature. No XMCD signal has been measured in the insulating or conducting phase of Fe 3 O 4. This suggests that the absence of magnetic proximity effects at ferrite/Pt interfaces is not linked to the insulating character or not of the ferrites.
- Published
- 2017
15. Simple and advanced ferromagnet/molecule spinterfaces
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F. Djedhloul, Fatima Ibrahim, Hashim Jabbar, Philippe Ohresser, Fabrice Scheurer, Kai Chen, Edwige Otero, Jacek Arabski, Clément Barraud, P. Le Fèvre, Richard Mattana, Samar Hajjar-Garreau, Wulf Wulfhekel, Samy Boukari, Ufuk Halisdemir, François Bertran, E. Urbain, Hironari Isshiki, Frédéric Petroff, Moritz Peter, Martin Bowen, Mebarek Alouani, Pierre Seneor, A. Taleb-Ibrahimi, P. Wetzel, Loïc Joly, Cyrile Deranlot, Michał Studniarek, Eric Beaurepaire, V. Da Costa, Fadi Choueikani, Stéphane Fusil, D. Xenioti, Hervé Bulou, G. Garreau, Jinjie Chen, Karim Bouzehouane, V. Davesne, Wolfgang Weber, and Manuel Gruber
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Materials science ,Condensed matter physics ,Spin polarization ,Fermi level ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Organic semiconductor ,Condensed Matter::Materials Science ,symbols.namesake ,Exchange bias ,Ferromagnetism ,Spin crossover ,0103 physical sciences ,symbols ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Quantum tunnelling - Abstract
Spin-polarized charge transfer between a ferromagnet and a molecule can promote molecular ferromagnetism 1, 2 and hybridized interfacial states3, 4. Observations of high spin-polarization of Fermi level states at room temperature5 designate such interfaces as a very promising candidate toward achieving a highly spin-polarized, nanoscale current source at room temperature, when compared to other solutions such as half-metallic systems and solid-state tunnelling over the past decades. We will discuss three aspects of this research. 1) Does the ferromagnet/molecule interface, also called an organic spinterface, exhibit this high spin-polarization as a generic feature? Spin-polarized photoemission experiments reveal that a high spin-polarization of electronics states at the Fermi level also exist at the simple interface between ferromagnetic cobalt and amorphous carbon6. Furthermore, this effect is general to an array of ferromagnetic and molecular candidates7. 2) Integrating molecules with intrinsic properties (e.g. spin crossover molecules) into a spinterface toward enhanced functionality requires lowering the charge transfer onto the molecule8 while magnetizing it1,2. We propose to achieve this by utilizing interlayer exchange coupling within a more advanced organic spinterface architecture. We present results at room temperature across the fcc Co(001)/Cu/manganese phthalocyanine (MnPc) system9. 3) Finally, we discuss how the Co/MnPc spinterface’s ferromagnetism stabilizes antiferromagnetic ordering at room temperature onto subsequent molecules away from the spinterface, which in turn can exchange bias the Co layer at low temperature10. Consequences include tunnelling anisotropic magnetoresistance across a CoPc tunnel barrier11. This augurs new possibilities to transmit spin information across organic semiconductors using spin flip excitations12.
- Published
- 2016
16. Perpendicular magnetic anisotropy in granular multilayers of COPD alloyed nanoparticles
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Matthieu Chorro, Andrei Rogalev, Adriana I. Figueroa, L. M. García, Cyrile Deranlot, Lorena Ruiz, F. Wilhelm, N. B. Brookes, Sakura Pascarelli, José F. Bartolomé, Frédéric Petroff, Javier Rubín, José M. González-Calbet, Fernando Bartolomé, L. G. Vivas, Ministerio de Economía y Competitividad (España), and Diputación General de Aragón
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010302 applied physics ,Materials science ,Magnetic circular dichroism ,Order (ring theory) ,ComputingMilieux_LEGALASPECTSOFCOMPUTING ,02 engineering and technology ,Coercivity ,Type (model theory) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic anisotropy ,Crystallography ,Ferromagnetism ,Data_GENERAL ,0103 physical sciences ,Absorption (logic) ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS ,Superparamagnetism - Abstract
Under the terms of the Creative Commons Attribution license.-- et al., Co-Pd multilayers obtained by Pd capping of pre-deposited Co nanoparticles on amorphous alumina are systematically studied by means of high-resolution transmission electron microscopy, x-ray diffraction, extended x-ray absorption fine structure, SQUID-based magnetometry, and x-ray magnetic circular dichroism. The films are formed by COPD alloyed nanoparticles self-organized across the layers, with the interspace between the nanoparticles filled by the non-alloyed Pd metal. The nanoparticles show atomic arrangements compatible with short-range chemical order of L10 strucure type. The collective magnetic behavior is that of ferromagnetically coupled particles with perpendicular magnetic anisotropy, irrespective of the amount of deposited Pd. For increasing temperature three magnetic phases are identified: hard ferromagnetic with strong coercive field, soft-ferromagnetic as in an amorphous asperomagnet, and superparamagnetic. Increasing the amount of Pd in the system leads to both magnetic hardness increment and higher transition temperatures. Magnetic total moments of 1.77(4) μB and 0.45(4) μB are found at Co and Pd sites, respectively, where the orbital moment of Co, 0.40(2) μB, is high, while that of Pd is negligible. The effective magnetic anisotropy is the largest in the capping metal series (Pd, Pt, W, Cu, Ag, Au), which is attributed to the interparticle interaction between de nanoparticles, in addition to the intraparticle anisotropy arising from hybridization between the 3d-4d bands associated to the Co and Pd chemical arrangement in a L10 structure type., The financial support of the Spanish Ministerio de Economía MAT2014-53921-R and Aragonese DGA-IMANA E34 projects is acknowledged.
- Published
- 2016
17. Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers
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Bruno Dlubak, Albert Fert, Sabina Caneva, Frédéric Petroff, John Robertson, Regina Galceran, Maëlis Piquemal-Banci, Stephan Hofmann, Abdelmadjid Anane, Marie-Blandine Martin, Piran R. Kidambi, Pierre Seneor, Karim Bouzehouane, S. Xavier, Robert S. Weatherup, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), THALES-Centre National de la Recherche Scientifique (CNRS), University of Cambridge [UK] (CAM), Thales Research and Technology [Palaiseau], THALES, and Centre National de la Recherche Scientifique (CNRS)-THALES
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[PHYS]Physics [physics] ,Materials science ,Physics and Astronomy (miscellaneous) ,Magnetoresistance ,business.industry ,Nanotechnology ,02 engineering and technology ,Chemical vapor deposition ,Nitride ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surface coating ,Tunnel magnetoresistance ,Electrical resistivity and conductivity ,Monolayer ,Optoelectronics ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,0210 nano-technology ,business ,Quantum tunnelling ,ComputingMilieux_MISCELLANEOUS - Abstract
We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.
- Published
- 2016
18. Self-assembled monolayers based spintronics: from ferromagnetic surface functionalization to spin-dependent transport
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Sophie Delprat, Karim Bouzehouane, Cyrile Deranlot, Frédéric Petroff, Pierre Seneor, Eric Jacquet, Marta Galbiati, Clément Barraud, Richard Mattana, Sophie Collin, and Sergio Tatay
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Phosphorous Acids ,Surface Properties ,Electrical Equipment and Supplies ,Nanotechnology ,Electrons ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Molecular engineering ,Lanthanum ,Monolayer ,General Materials Science ,Alkyl ,chemistry.chemical_classification ,Spintronics ,Magnetic Phenomena ,Self-assembled monolayer ,Oxides ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,3. Good health ,0104 chemical sciences ,Tunnel magnetoresistance ,chemistry ,Ferromagnetism ,Manganese Compounds ,Strontium ,Magnets ,Surface modification ,0210 nano-technology - Abstract
Chemically functionalized surfaces are studied for a wide range of applications going from medicine to electronics. Whereas non-magnetic surfaces have been widely studied, functionalization of magnetic surfaces is much less common and has almost never been used for spintronics applications. In this article we present the functionalization of La2/3Sr1/3MnO3, a ferromagnetic oxide, with self-assembled monolayers for spintronics. La2/3Sr1/3MnO3 is the prototypical half-metallic manganite used in spintronics studies. First, we show that La2/3Sr1/3MnO3 can be functionalized by alkylphosphonic acid molecules. We then emphasize the use of these functionalized surfaces in spintronics devices such as magnetic tunnel junctions fabricated using a nano-indentation based lithography technique. The observed exponential increase of tunnel resistance as a function of alkyl chain length is a direct proof of the successful connection of molecules to ferromagnetic electrodes. For all alkyl chains studied we obtain stable and robust tunnel magnetoresistance, with effects ranging from a few tens to 10 000%. These results show that functionalized electrodes can be integrated in spintronics devices and open the door to a molecular engineering of spintronics.
- Published
- 2016
19. Self-Assembled Monolayer-Functionalized Half-Metallic Manganite for Molecular Spintronics
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Karim Bouzehouane, Pascale Jégou, Cyrile Deranlot, Alicia Forment-Aliaga, Frédéric Petroff, Albert Fert, Marta Galbiati, Richard Mattana, Sergio Tatay, Pierre Seneor, Clément Barraud, and Eric Jacquet
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Materials science ,Macromolecular Substances ,Surface Properties ,Molecular Conformation ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Materials Testing ,Monolayer ,General Materials Science ,Particle Size ,Thin film ,Magnetite Nanoparticles ,Alkyl ,chemistry.chemical_classification ,Spintronics ,General Engineering ,Self-assembled monolayer ,021001 nanoscience & nanotechnology ,Manganite ,0104 chemical sciences ,Organic semiconductor ,Semiconductors ,chemistry ,Surface modification ,Spin Labels ,Crystallization ,0210 nano-technology - Abstract
(La,Sr)MnO(3) manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-assembled monolayers, with the phosphonic group coordinated to the surface and alkyl chains tilted from the surface vertical by 43° (C12P) and 27° (C18P). We have electrically characterized these SAMs in nanodevices and found that they act as tunnel barriers, opening the door toward the integration of alkylphosphonic acid//LSMO SAMs into future molecular/organic spintronic devices such as spin OLEDs.
- Published
- 2012
20. Unveiling Self-Assembled Monolayers' Potential for Molecular Spintronics: Spin Transport at High Voltage
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Eric Jacquet, Clément Barraud, Sergio Tatay, Albert Fert, Marta Galbiati, Pierre Seneor, Frédéric Petroff, Richard Mattana, Cyrile Deranlot, and Karim Bouzehouane
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Materials science ,Condensed matter physics ,Spintronics ,Magnetoresistance ,Mechanical Engineering ,High voltage ,Biasing ,Self-assembled monolayer ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Tunnel magnetoresistance ,Magnetics ,Semiconductors ,Mechanics of Materials ,0103 physical sciences ,Monolayer ,Organometallic Compounds ,Nanoparticles ,General Materials Science ,Electronics ,010306 general physics ,0210 nano-technology ,Spin (physics) - Abstract
Molecular magnetic tunnel junctions using self-assembled monolayers (SAMs) as tunnel barriers show stable and efficient spin transport properties. Large tunnel magnetoresistance with a flat bias voltage dependence of the magnetoresistance is observed in La(2/3) Sr(1/3) MnO(3) /dodecylphosphonic acid SAM/Co nanocontacts. This opens the door to spintronic tailoring though SAM engineering and could also lead to new venues for spin injection in organic devices.
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- 2012
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21. From ensemble average to single (nano-) objects properties by X-ray microdiffraction: a short review on structure determination (local strain, composition, ...) and objects manipulation (AFM-coupled)
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Ana Diaz, A. V. Ramos, Mário Rodrigues, Th. Scheller, R. Paniago, Cristian Mocuta, Frédéric Petroff, Antoine Barbier, J. Chevrier, J. Stangl, Bärbel Krause, G. Bauer, Richard Mattana, Angelo Malachias, T. H. Metzger, Thomas W. Cornelius, K. Mundboth, Cyrile Deranlot, Stefan Stanescu, O. Dhez, M.-J. Guittet, and Jean-Baptiste Moussy
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Diffraction ,Coupling ,Materials science ,Nanostructure ,business.industry ,Dispersity ,Resolution (electron density) ,Metals and Alloys ,Condensed Matter Physics ,Sample (graphics) ,Signal ,Optics ,Nano ,Materials Chemistry ,Physical and Theoretical Chemistry ,business - Abstract
In standard diffraction experiments, ensembles of objects are characterized yielding averaged, statistical properties (meaningful only if the ensemble is monodisperse). Focused x-ray beams are used here to localize single nanostructures, identifying and probing individual objects one by one. In a scanning mode, a 2-dimensional image of the sample is recorded, which allows the reproducible alignment of a specific nanostructure for analysis. The x-ray scattered signal is analyzed and modelled, to give access to the shape, strain and composition inside the single object with sub-micron resolution. Combination of x-ray microdiffraction technique with other micro-probe experiments on the very same individual object (simultaneous coupling of x-ray diffraction measurements with atomic force microscopy (AFM)) is also shown; we prove the possibility to interact with the objects and to address elastic properties for individual nano-structures out of an ensemble.
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- 2010
22. Molecular spintronics: the role of spin-dependent hybridization
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Benoit Quinard, Sophie Delprat, Sergio Tatay, Pierre Seneor, Frédéric Petroff, Marta Galbiati, Richard Mattana, Clément Barraud, Unité Mixte de Physique CNRS-Thales (UMPhy CNRS-Thales), Thales Research & Techology-Centre National de la Recherche Scientifique (CNRS), Laboratoire Matériaux et Phénomènes Quantiques (MPQ (UMR_7162)), Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), and Centre National de la Recherche Scientifique (CNRS)-THALES
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Materials science ,Acoustics and Ultrasonics ,Spintronics ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,0210 nano-technology ,Spin (physics) ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
- Published
- 2018
23. Anisotropic magneto-Coulomb effects and magnetic single-electron-transistor action in a single nanoparticle
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Albert Fert, Cyrile Deranlot, Frédéric Petroff, Stéphane Fusil, Anne Bernand-Mantel, Pierre Seneor, and Karim Bouzehouane
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Physics ,Magnetoresistance ,Condensed matter physics ,Transistor ,General Physics and Astronomy ,Nanoparticle ,Coulomb blockade ,Physicist ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,law.invention ,Condensed Matter::Materials Science ,Ferromagnetism ,law ,Coulomb ,Condensed Matter::Strongly Correlated Electrons ,Magneto - Abstract
Anisotropies in the response of ferromagnetic electrodes attached to a gold nanoparticle lead to Coulomb blockade and spin-valve-like magnetoresistance phenomena. Such behaviour could allow the development of magnetically gated single-electron transistors composed of just two terminals.
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- 2009
24. Crystalline structure of oxide-based epitaxial tunnel junctions
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Frédéric Petroff, Antoine Barbier, Stefan Stanescu, Cyrile Deranlot, Jean-Baptiste Moussy, Richard Mattana, M.-J. Guittet, Christophe Gatel, A. V. Ramos, and Cristian Mocuta
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Diffraction ,Materials science ,business.industry ,Oxide ,General Physics and Astronomy ,Crystal structure ,Epitaxy ,law.invention ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Tunnel effect ,Optics ,chemistry ,Tunnel junction ,law ,Optoelectronics ,General Materials Science ,Physical and Theoretical Chemistry ,Photolithography ,business ,Lithography - Abstract
Epitaxial metal/oxide based magnetic tunnel-junctions (MTJ) are valuable model systems to investigate the influence of the crystallinity of individual layers on the magnetic properties. We have non-destructively studied the effect of the optical lithography procedure on the crystalline structure of MTJ’s with lateral spatial resolution by performing local x-ray diffraction experiments using a microfocused x-ray spot. We demonstrate that the lithography process produces distortion effects on the crystalline structure of the layers near the edges of the lithographed junction. These distortions are present on all the constituent layers and are most probably driven by the elastic constants of the materials. They translate into tilts of the crystalline planes in the vicinity of the edges and propagate towards the center of the junction; the tilt’s amplitude (up to several degrees) and sign (concave or convex) depend on the junction’s shape, size and the type of materials (interfaces) used. We report results for junctions made with two types of metal-oxide interfaces (Co/CoFe2O4 and Co/Fe3O4), with sizes from 10 to 150 μm and various shapes (square-, rectangle- and disk-like).
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- 2009
25. Anisotropy Enhancement in Co Granular Multilayers by Capping
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Fabrice Wilhelm, Andrei Rogalev, Fernando Luis, Fernando Bartolomé, Frédéric Petroff, Peter Bencok, N. B. Brookes, Juan Bartolomé, Cyrile Deranlot, and L.M. García
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Materials science ,Condensed matter physics ,Magnetic circular dichroism ,Mechanical Engineering ,Nanoparticle ,Electron ,Condensed Matter Physics ,Nanocrystalline material ,Metal ,Magnetic anisotropy ,Nuclear magnetic resonance ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,General Materials Science ,Thin film ,Anisotropy - Abstract
The effect of capping with Cu, Au and Pt of an array of Co nanoparticles is revised. The magnetic surface anisotropy KS was found to be the dominant contribution to the effective anisotropy Keff of the particles. Recent X-ray Magnetic Circular Dichroism (XMCD) measurements show that there is hybridization between the 3d Co electrons and the d and 4p electrons of the capping metal. By comparison to the mechanisms which give rise to the surface anisotropy in thin films, it is argued that this hybridization governs the modification of KS, and hence, of Keff.
- Published
- 2008
26. Copper spacer thickness dependence of the exchange bias in IrMn/Cu/Co ultrathin films
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Frédéric Petroff, Julian Penkov Geshev, Luis Gustavo Pereira, Luiz Carlos Camargo Miranda Nagamine, Cyrile Deranlot, Sabrina Nicolodi, Joao Edgar Schmidt, and Alexandre da Cas Viegas
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Materials science ,Condensed matter physics ,Annealing (metallurgy) ,Analytical chemistry ,chemistry.chemical_element ,Coercivity ,Condensed Matter Physics ,Copper ,Electronic, Optical and Magnetic Materials ,Magnetization ,Magnetic anisotropy ,Exchange bias ,chemistry ,Antiferromagnetism ,Anisotropy - Abstract
The exchange-bias, H EB and coercivity, H C of IrMn / Cu ( t Cu ) / Co films have been investigated as a function of the Cu spacer thickness, t Cu before and after magnetic annealing. A large increase of H EB and a significant decrease of H C with the treatment were observed for the samples with t Cu ⩽ 1.0 nm . H C ( t Cu ) and H EB ( t Cu ) showed a general trend of rapid decrease for all samples. The phenomenological models used to derive the anisotropy and exchange coupling parameters from the magnetization data indicated that the antiferromagnetic part of the interface is fully spin-compensated for the as-made films and nearly uncompensated for the treated ones. The annealing, despite the H EB and H C changes, did not alter the Co anisotropy but only improved the interfacial IrMn spins alignment.
- Published
- 2007
27. Shaped angular dependence of the spin-transfer torque and microwave generation without magnetic field
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Luis Gustavo Pereira, Frédéric Petroff, Albert Fert, Vincent Cros, Giancarlo Faini, Olivier Boulle, Julie Grollier, Cyrile Deranlot, and Józef Barnaś
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Physics ,Condensed Matter - Materials Science ,Spintronics ,Condensed matter physics ,Field (physics) ,Spin-transfer torque ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,General Physics and Astronomy ,Magnetic field ,Magnetization ,Torque ,Microwave ,Nanopillar - Abstract
The generation of oscillations in the microwave frequency range is one of the most important applications expected from spintronics devices exploiting the spin-transfer phenomenon, which is the reorientation of the magnetization of a ferromagnetic domain by spin-polarized current. Here we report transport and microwave power measurements on specially designed nanopillars, for which a non-standard angular dependence of the spin-transfer torque is predicted by theoretical models. We observe a new kind of current-induced dynamics that is characterized by large angle precessions in the absence of any applied field. This is also predicted by simulations including a ‘wavy’ angular dependence of the torque. This type of nanopillar, which is able to generate microwave oscillations in zero applied magnetic field, could represent an interesting method for the implementation of spin-transfer oscillators. We also emphasize the theoretical implications of our results on the angular dependence of the torque.
- Published
- 2007
28. Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions
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Frédéric Petroff, Pierre Seneor, Stéphane Fusil, Clément Barraud, Dong Jik Kim, Martin Bowen, Jacek Arabski, Cyrile Deranlot, C. Kieber, Samy Boukari, Richard Mattana, Hashim Jabbar, Eric Beaurepaire, Rajib Rakshit, and Karim Bouzehouane
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Tunnel magnetoresistance ,Spin polarization ,Spintronics ,Condensed matter physics ,Ferromagnetism ,Field (physics) ,Electric field ,General Physics and Astronomy ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Anisotropy ,Spin (physics) - Abstract
Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co/CoPc/Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance.
- Published
- 2015
29. Influence of alkylphosphonic acid grafting on the electronic and magnetic properties of La2/3Sr1/3MnO3 surfaces
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Martin Aeschlimann, F. Coloma, Marta Galbiati, Norman Haag, Fadi Choueikani, Richard Mattana, Mirko Cinchetti, Vincent Cros, Frédéric Petroff, Edwige Otero, Sergio Tatay, Pierre Seneor, Sophie Delprat, Philippe Ohresser, Eric Jacquet, Clément Barraud, Universidad de Alicante. Servicios Técnicos de Investigación, and Materiales Avanzados
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Materials science ,Spintronics ,Magnetism ,General Physics and Astronomy ,Nanotechnology ,Self-assembled monolayer ,Self-assembled monolayers ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Ferromagnetism ,Monolayer ,Surface modification ,Work function ,Ultraviolet photoelectron spectroscopy - Abstract
Self-assembled monolayers (SAMs) are highly promising materials for molecular engineering of electronic and spintronics devices thanks to their surface functionalization properties. In this direction, alkylphosphonic acids have been used to functionalize the most common ferromagnetic electrode in organic spintronics: La2/3Sr1/3MnO3 (LSMO). However, a study on the influence of SAMs grafting on LSMO electronic and magnetic properties is still missing. In this letter, we probe the influence of alkylphosphonic acids-based SAMs on the electronic and magnetic properties of the LSMO surface using different spectroscopies. We observe by X-ray photoemission and X-ray absorption that the grafting of the molecules on the LSMO surface induces a reduction of the Mn oxidation state. Ultraviolet photoelectron spectroscopy measurements also show that the LSMO work function can be modified by surface dipoles opening the door to both tune the charge and spin injection efficiencies in organic devices such as organic light-emitting diodes. The research leading to these results was financially supported by the EU project NMP3-SL-2011-263104 HINTS and ANR agency (MELAMIN 2011-NANO-021). S.T. acknowledges the European Union FP7 CIG Marie Curie Actions under project SAMSFERE (FP7/2012–321739) and the Spanish MICINN for his JdC contract. P.S. wishes to thank the Institut Universitaire de France for a junior Fellowship. The research leading to these results was partly funded by the SFB/TRR 88 ‘3MET’ from the DFG. Experiments were performed on the “DEIMOS” beamline at SOLEIL Synchrotron, France (project No. 20100960).
- Published
- 2015
30. Tuning the magnetic anisotropy of Co nanoparticles by metal capping
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Frédéric Petroff, Andrei Rogalev, Fernando Bartolomé, Fernando Luis, Henri Jaffrès, Fabrice Wilhelm, Peter Bencok, Cyrile Deranlot, M. J. Martínez, José F. Bartolomé, Luis Miguel García, and N. B. Brookes
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Materials science ,Condensed matter physics ,General Physics and Astronomy ,Thermal fluctuations ,Nanoparticle ,Electron ,Metal ,Magnetization ,Magnetic anisotropy ,Nuclear magnetic resonance ,visual_art ,visual_art.visual_art_medium ,Anisotropy ,Layer (electronics) - Abstract
The magnetic anisotropy of Co clusters with diameters ranging from 1.1 nm to 4.5 nm turns out to be significantly larger than in bulk and strongly increasing with decreasing cluster size. The dominating role of the surface can be used to modify the anisotropy by changing the electronic properties of the matrix surrounding the clusters. We find that capping the clusters by a metallic (Cu and Au) layer significantly enhances the anisotropy, thus also stabilizing the magnetization against thermal fluctuations. The observed anisotropy enhancement is attributed to the bonding of the Co 3d electrons to the conduction band of the capping layer, which depends on the electronic band structures of both metals.
- Published
- 2006
31. Magnetic relaxation of Co nanoclusters in a bias magnetic field
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José F. Bartolomé, Fernando Luis, and Frédéric Petroff
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Spin–spin relaxation ,Magnetic anisotropy ,Magnetization ,Condensed matter physics ,Magnetic moment ,Chemistry ,Relaxation (NMR) ,Spin–lattice relaxation ,General Materials Science ,Condensed Matter Physics ,Magnetic susceptibility ,Superparamagnetism - Abstract
We report ac magnetic susceptibility data measured on two samples of Co nano-particles, with average diameters and 3.1?nm, respectively. The temperatures Tmax of the maxima of the real and imaginary components of the susceptibility shift in opposite directions when an increasing bias magnetic field H is applied. We show that the increase of Tmax of with H is caused by the non-linear field dependence of the equilibrium magnetization and that only provides reliable information about the magnetic relaxation mechanisms in a bias field. Our data show that the magnetization reversal takes place via a classical thermally activated relaxation process. The influence that inter-cluster dipolar interactions have on the relaxation time depends on H. At zero field, the magnetic relaxation is slower than in the limit of no interactions. By contrast, as the magnetic moments of the particles become gradually polarized by H, the relaxation approaches the theoretical predictions for non-interacting particles.
- Published
- 2004
32. Time and layer resolved magnetic domain imagig of FeNi/Cu/Co trilayers using x-ray photoelectron emission microscopy (invited)
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Jan Vogel, A. Fontaine, Yan Pennec, J. Kirschner, Frédéric Petroff, Julio Camarero, Stefania Pizzini, Wolfgang Kuch, Marlio Bonfim, and Keiki Fukumoto
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Condensed Matter::Materials Science ,Magnetization dynamics ,Materials science ,Magnetic domain ,Condensed matter physics ,Ferromagnetism ,Magnetic circular dichroism ,Astrophysics::High Energy Astrophysical Phenomena ,Resolution (electron density) ,General Physics and Astronomy ,Synchrotron radiation ,Magnetic hysteresis ,Electron spectroscopy - Abstract
We have performed magnetic domain imaging with spatial, temporal, and layer resolution using x-ray photoelectron emission microscopy. The element selectivity of x-ray magnetic circular dichroism allows the magnetization dynamics of the different magnetic layers in spin-valve-like FeNi/Cu/Co trilayers to be studied separately, using the time structure of synchrotron radiation. The unique possibilities of this technique have been used to study the influence of the intrinsic magnetic properties of the different layers on the magnetization dynamics and the interlayer magnetic coupling.
- Published
- 2004
33. On the use of exchange biased top electrodes in magnetic tunnel junctions
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Daniel Lacour, Frédéric Petroff, J. Humbert, Olivier Durand, Annie Vaures, Jean-Luc Maurice, F. Nguyen Van Dau, P. Etienne, H. Jaffrès, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, and Thales Research & Technology
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Materials science ,Tantalum ,chemistry.chemical_element ,02 engineering and technology ,01 natural sciences ,Magnetic tunnel junctions ,Tunnel effect ,Nuclear magnetic resonance ,Spin-dependent tunnelling ,Tunnel junction ,0103 physical sciences ,Texture (crystalline) ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Thin film ,010302 applied physics ,Condensed matter physics ,PACS: 75.70.-i ,61.66.-f ,75.30.Gw ,Bilayer ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Exchange bias ,Ferromagnetism ,chemistry ,0210 nano-technology - Abstract
International audience; We have investigated the magnetic behavior and the structural properties of ferromagnetic-antiferromagnetic systems (NiFe-IrMn and Co-IrMn) deposited directly on a thin tantalum buffer layer (bottom configuration) or above a thin Al 2 O 3 tunnel barrier layer (top configuration). In the bottom configuration, the bilayer system exhibits higher magnetic performances than in the top configuration in terms of thermal stability. We have performed a detailed structural study by X-ray diffraction and high-resolution transmission electron microscopy which allow us to establish a clear correlation between the situation of the bilayer with respect to the tunnel barrier, its texture and its magnetic properties. r
- Published
- 2004
34. Resonant diffuse X-ray scattering from magnetic multilayers
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Andreas Scholl, Eric M. Gullikson, Renaud Delaunay, Coryn F. Hague, Piero Torelli, Carlo Spezzani, Maurizio Sacchi, and Frédéric Petroff
- Subjects
Materials science ,Magnetoresistance ,Magnetic domain ,Condensed matter physics ,magnetoresistive multilayers ,Scattering ,X-ray ,chemistry.chemical_element ,X-ray scattering ,magnetic domains ,Condensed Matter Physics ,Copper ,Electronic, Optical and Magnetic Materials ,law.invention ,Diffuse scattering ,soft X-rays ,chemistry ,Transition metal ,law ,Electrical and Electronic Engineering ,Electron microscope - Abstract
We have measured field-dependent resonant diffuse scattering from a magnetoresistive Co/Cu multilayer. We have observed that the magnetic domain size in zero field depends on the magnetic history of the sample. The results of the X-ray scattering analysis have been compared to PEEM images of the magnetic domains.
- Published
- 2004
35. Hot-electron transport in 3-terminal devices based on magnetic tunnel junctions
- Author
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Van Dau, H. Jaffrès, Michel Hehn, Daniel Lacour, François Montaigne, Frédéric Petroff, P. Rottländer, F. Nguyen, Alain Schuhl, Institut Jean Lamour (IJL), Université de Lorraine (UL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), and THALES-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Electron mobility ,Materials science ,Magnetoresistance ,General Physics and Astronomy ,02 engineering and technology ,01 natural sciences ,law.invention ,Tunnel effect ,Nuclear magnetic resonance ,Triode ,law ,Tunnel junction ,Condensed Matter::Superconductivity ,0103 physical sciences ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,Quantum tunnelling ,Diode ,Common emitter ,[PHYS]Physics [physics] ,Spin polarization ,Condensed matter physics ,Transistor ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Tunnel magnetoresistance ,Ferromagnetism ,Electrode ,0210 nano-technology ,Voltage - Abstract
Summary form only given. Magnetic field-dependent electrical characteristics of magnetic tunnel junction-based 3-terminal devices have been measured on M/sub 1//I/sub 1//M/sub 2//I/sub 2//M/sub 3/ stacks where M are ferromagnetic electrodes and I are insulating barriers (Al/sub 2/O/sub 3/ or TaO). A spin polarised current is pumped from the voltage biased M/sub 1//I/sub 1//M/sub 2/ junction and injected in the I/sub 2//M/sub 3/ collector junction. The collected current in M/sub 3/ is then dependent on the voltages applied to each tunnel junction, the orientation of the electrode magnetisations and the thickness of the M/sub 2/ electrode. Besides the fundamental interest in measuring the properties of nonequilibrium spin-dependent hot electron transport, 3-terminal devices appear to be good candidates for a new generation of magnetic field-dependent devices. The control of hot electron transmission in a double tunnel junction is the keystone to ensure asymmetric diodes or hot electron magnetic field-dependent transistors. Experimental results have been compared to computations made in the framework of the parabolic band model.
- Published
- 2002
36. Experimental evidence of the ferrimagnetic ground state of Sr 2 FeMoO 6 probed by X-ray magnetic circular dichroism
- Author
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M. Besse, Andrei Rogalev, Albert Fert, P. Decorse, Alberto Tagliaferri, Walter Temmerman, Agnès Barthélémy, Jan Vogel, Vincent Cros, Sarnjeet S. Dhesi, Henri Jaffrès, Frédéric Petroff, P. Berthet, Zdzislawa Szotek, Peter Bencok, Alessandro Mirone, and N. B. Brookes
- Subjects
Delocalized electron ,Materials science ,Condensed matter physics ,Magnetic moment ,Magnetic structure ,X-ray magnetic circular dichroism ,Magnetic circular dichroism ,Ferrimagnetism ,General Physics and Astronomy ,Condensed Matter::Strongly Correlated Electrons ,Ground state ,Computer Science::Digital Libraries ,Single crystal - Abstract
We have investigated the magnetic structure of a Sr2FeMoO6 single crystal by X-ray magnetic circular dichroism at the L2,3 edges of Fe and Mo sites. The spin magnetic moments we find on Fe (3.05μB) and Mo ( − 0.32μB) give, for the first time, a direct confirmation of their ferrimagnetic ordering. The presence of a finite spin moment on Mo together with only very small orbital moments on both Fe and Mo confirms that the predicted half-metallicity of the Sr2FeMoO6 compound is due to a configuration with five localized d electrons forming a high-spin moment on Fe and one s antiparallel delocalized electron shared between the Mo and the other sites.
- Published
- 2002
37. Growth of Au clusters on amorphous Al2O3: are small clusters more mobile than atoms?
- Author
-
Frédéric Petroff, Julian Carrey, Jean-Luc Maurice, and Annie Vaures
- Subjects
Chemistry ,Annealing (metallurgy) ,Nucleation ,Crystal growth ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Amorphous solid ,law.invention ,Condensed Matter::Materials Science ,Crystallography ,Sputtering ,Transmission electron microscopy ,Chemical physics ,law ,Materials Chemistry ,Cluster (physics) ,Electron microscope - Abstract
We study the growth by sputtering of Au clusters on amorphous Al2O3 using transmission electron microscopy (TEM). The weak decrease of the cluster density with temperature is a clear sign that the defects of the substrate strongly influence the growth. We observe two phenomena which cannot be explained in a classical model of nucleation on defects: (i) there is some missing material in TEM micrographs that can re-appear after annealing at room temperature, and (ii) there is a delay in the nucleation of clusters. Moreover, in the case of clusters visible by TEM, we show by comparing the observed growth with kinetic Monte-Carlo simulations that clusters detach from defects above a critical size. We propose that a similar behavior explains the blockade and re-appearance of the invisible material, and the delay in nucleation: a large density of clusters nucleate on traps that release them at a size below TEM resolution (≃1 nm in these experiments).
- Published
- 2002
38. Field sensing using the magnetoresistance of IrMn exchange-biased tunnel junctions
- Author
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F. Nguyen Van Dau, H. Jaffrès, Frédéric Petroff, J. Humbert, Annie Vaures, Daniel Lacour, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), THALES-Centre National de la Recherche Scientifique (CNRS), Institut Jean Lamour (IJL), and Université de Lorraine (UL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
010302 applied physics ,Materials science ,Condensed matter physics ,Magnetoresistance ,Field (physics) ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic field ,Magnetic anisotropy ,Exchange bias ,0103 physical sciences ,Thermal ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,0210 nano-technology ,Vicinal ,Quantum tunnelling - Abstract
International audience; An original concept of high sensitivity magnetic field sensor using the spin-dependent tunneling effect has been investigated. The required crossed-biased configuration is obtained by combining both shape energy originating from vicinal step bunched Si substrates and unidirectional exchange anisotropy supplied by an Ir 20 Mn 80 film in the ''top-biased'' geometry. We demonstrate a linear and reversible signal at room temperature and above. The smooth loss of sensitivity at higher temperature is shown to be correlated to the thermal dependence of the exchange bias property when IrMn is deposited above the insulating Al 2 O 3 barrier.
- Published
- 2002
39. Magnetic Proximity Effect Free Spin Hall Magnetoresistance in YIG∖Pd
- Author
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Andrei Rogalev, Eric Jacquet, F. Wilhelm, O. d'Allivy Kelly, Abdelmadjid Anane, Martin Collet, Katharina Ollefs, Vincent Cros, Richard Mattana, P. Bortolotti, and Frédéric Petroff
- Subjects
Physics ,Condensed matter physics ,Magnetoresistance ,Magnetic circular dichroism ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Signal ,Ferromagnetic resonance ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Magnetization ,0103 physical sciences ,Proximity effect (audio) ,Spin Hall effect ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology ,Spin (physics) - Abstract
Magnetic Proximity Effect (MPE) at the interface of Y3Fe5O[Formula: see text] (YIG)[Formula: see text]Pd is investigated using X-ray Magnetic Circular Dichroism (XMCD) at the Pd-edges. No evidence of MPE is found even for Pd film thicknesses down to 0.5[Formula: see text]nm. The same bilayers have been thereafter used for inverse spin Hall Effect (ISHE) measurements using the spin-pumping technique. A large signal can be observed at the ferromagnetic resonance. The angular dependence of the Pd dc resistance has been measured as a function of the YIG magnetization direction. It shows the expected dependences for the spin Hall magnetoresistance (SMR). Our methodology allows to state that ISHE and SMR are intrinsic phenomena whose underlying physics is uncorrelated to MPE.
- Published
- 2017
40. Sub-nanometer Atomic Layer Deposition for Spintronics in Magnetic Tunnel Junctions Based on Graphene Spin-Filtering Membranes
- Author
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Karim Bouzehouane, Heejun Yang, Frédéric Petroff, Bruno Dlubak, Robert S. Weatherup, Albert Fert, Abdelmadjid Anane, Stephan Hofmann, Marie-Blandine Martin, John Robertson, Cyrile Deranlot, and Pierre Seneor
- Subjects
spintronics ,Materials science ,Fabrication ,Spintronics ,Spin polarization ,Graphene ,graphene ,General Engineering ,General Physics and Astronomy ,Nanotechnology ,Dielectric ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,magnetic tunnel junction ,Article ,dielectrics ,law.invention ,Tunnel magnetoresistance ,Atomic layer deposition ,law ,Condensed Matter::Superconductivity ,atomic layer deposition ,General Materials Science ,spin filter ,Quantum tunnelling - Abstract
We report on the successful integration of low-cost, conformal, and versatile atomic layer deposited (ALD) dielectric in Ni–Al2O3–Co magnetic tunnel junctions (MTJs) where the Ni is coated with a spin-filtering graphene membrane. The ALD tunnel barriers, as thin as 0.6 nm, are grown layer-by-layer in a simple, low-vacuum, ozone-based process, which yields high-quality electron-transport barriers as revealed by tunneling characterization. Even under these relaxed conditions, including air exposure of the interfaces, a significant tunnel magnetoresistance is measured highlighting the robustness of the process. The spin-filtering effect of graphene is enhanced, leading to an almost fully inversed spin polarization for the Ni electrode of −42%. This unlocks the potential of ALD for spintronics with conformal, layer-by-layer control of tunnel barriers in magnetic tunnel junctions toward low-cost fabrication and down-scaling of tunnel resistances.
- Published
- 2014
- Full Text
- View/download PDF
41. Structural and magnetic properties of granular Co-Pt multilayers with perpendicular magnetic anisotropy
- Author
-
Cyrile Deranlot, Sakura Pascarelli, Lorena Ruiz, N. B. Brookes, Adriana I. Figueroa, Fernando Bartolomé, Andrei Rogalev, Frédéric Petroff, L. M. García, José M. González-Calbet, Oana Bunau, José F. Bartolomé, A. Smekhova, Jolanta Stankiewicz, Fabrice Wilhelm, Peter Bencok, Ministerio de Economía y Competitividad (España), CSIC-UZA - Instituto de Ciencia de Materiales de Aragón (ICMA), Diputación General de Aragón, Universidad de Zaragoza, European Commission, and Consejo Superior de Investigaciones Científicas (España)
- Subjects
Condensed Matter::Materials Science ,Magnetic anisotropy ,Materials science ,Extended X-ray absorption fine structure ,Condensed matter physics ,Ferromagnetism ,Magnetic circular dichroism ,Coercivity ,Condensed Matter Physics ,High-resolution transmission electron microscopy ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Superparamagnetism - Abstract
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., We present a study of granular Co-Pt multilayers by means of high-resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS), SQUID-based magnetic measurements, anomalous Hall effect (AHE), and x-ray magnetic circular dichroism (XMCD). We describe these granular films as composed of particles with a pure cobalt core surrounded by an alloyed Co-Pt interface, embedded in a Pt matrix. The alloy between the Co and Pt in these granular films, prepared by room temperature sputter deposition, results from interdiffusion of the atoms. The presence of this alloy gives rise to a high perpendicular magnetic anisotropy (PMA) in the granular films, as consequence of the anisotropy of the orbital moment in the Co atoms in the alloy, and comparable to that of highly-ordered CoPt L10 alloy films. Their magnetic properties are those of ferromagnetically coupled particles, whose coupling is strongly temperature dependent: at low temperatures, the granular sample is ferromagnetic with a high coercive field; at intermediate temperatures the granular film behaves as an amorphous asperomagnet, with a coupling between the grains mediated by the polarized Pt, and at high temperatures, the sample has a superparamagnetic behavior. The coupling/decoupling between the grains in our Co-Pt granular films can be tailored by variation of the amount of Pt in the samples., The financial support of the Spanish Ministerio de Economía y Competitividad (MINECO)MAT2011-23791 and Aragonese DGA-IMANA E34 (cofunded by Fondo Social Europeo) projects is acknowledged. Authors also acknowledge the Servicio General de Apoyo a la Investigacón-SAI, Universidad de Zaragoza. A. I. F. acknowledges a Spanish Consejo Superior de Investigaciones Científicas (CSIC) JAE2008-Predoc grant.
- Published
- 2014
42. Suppression of the critical thickness threshold for conductivity at the LaAlO3/SrTiO3 interface
- Author
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Henri Jaffrès, Rossitza Pentcheva, Philippe Ohresser, Fadi Choueikani, Frédéric Petroff, David Doennig, Manuel Bibes, Edouard Lesne, Nicolas Reyren, Vicent Cros, Alain Barthélémy, Richard Mattana, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), and Department of Physics and Center for Nanointegration, University of Duisburg-Essen (CENIDE)
- Subjects
Multidisciplinary ,Materials science ,Condensed matter physics ,Oxide ,General Physics and Astronomy ,Nanotechnology ,Heterojunction ,02 engineering and technology ,General Chemistry ,Substrate (electronics) ,Conductivity ,Physik (inkl. Astronomie) ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Perpendicular ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,Thin film ,010306 general physics ,0210 nano-technology ,Perovskite (structure) - Abstract
International audience; Perovskite materials engineered in epitaxial heterostructures have been intensely investigated during the last decade. The interface formed by an LaAlO 3 thin film grown on top of a TiO 2-terminated SrTiO 3 substrate hosts a two-dimensional electronic system and has become the prototypical example of this field. Although controversy exists regarding some of its physical properties and their precise origin, it is universally found that conductivity only appears beyond an LaAlO 3 thickness threshold of four unit cells. Here, we experimentally demonstrate that this critical thickness can be reduced to just one unit cell when a metallic film of cobalt is deposited on top of LaAlO 3. First-principles calculations indicate that Co modifies the electrostatic boundary conditions and induces a charge transfer towards the Ti 3d bands, supporting the electrostatic origin of the electronic system at the LaAlO 3 /SrTiO 3 interface. Our results expand the interest of this low-dimensional oxide system from in-plane to perpendicular transport and to the exploration of elastic and inelastic tunnel-type transport of (spin-polarized) carriers.
- Published
- 2014
43. Structural and magnetic properties of Co/AlN multilayers
- Author
-
Annie Vaures, J. P. Dallas, Agnès Traverse, Frédéric Petroff, Didier Zanghi, and Jean-Luc Maurice
- Subjects
Absorption spectroscopy ,General Physics and Astronomy ,chemistry.chemical_element ,Chemical interaction ,Ceramic matrix composite ,Crystallography ,chemistry ,Chemical engineering ,Sputtering ,visual_art ,visual_art.visual_art_medium ,Magnetic nanoparticles ,Ceramic ,Cobalt ,Metal clusters - Abstract
Granular Co/AlN multilayers, with Co thicknesses varying from 0.2 to 3 nm, were prepared by sputtering. The goal was to prepare Co clusters embedded in a ceramic matrix and to study their magnetic properties. The local surrounding of the Co atoms was characterized via x-ray absorption spectroscopy. The magnetic properties were found to depend markedly on the Co thickness. The findings can be explained in terms of strong chemical interaction between Co and AlN.
- Published
- 2001
44. Growth of Au Clusters on AmorphousAl2O3: Evidence of Cluster Mobility above a Critical Size
- Author
-
Julian Carrey, Frédéric Petroff, Annie Vaures, and Jean-Luc Maurice
- Subjects
Range (particle radiation) ,Materials science ,Condensed matter physics ,Transmission electron microscopy ,Monte Carlo method ,Nucleation ,Cluster (physics) ,General Physics and Astronomy ,Substrate (electronics) ,Deposition (law) ,Amorphous solid - Abstract
We study the 3D growth of clusters during the deposition of Au atoms on amorphous ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$. By comparing transmission electron microscopy images of the growth with Monte Carlo simulations, we show that nucleation takes place on substrate defects, but that further stages of growth imply that clusters leave the defects after they have reached a given critical size, and diffuse. An interesting consequence of this property is that, in contrast to intuition, and in a certain range of size, larger clusters are more mobile than smaller ones in this system.
- Published
- 2001
45. Study of the magnetic order in a Co/Cr multilayer by magnetic Bragg diffraction at the Co 2p resonance
- Author
-
A. Mirone, Annie Vaures, Gerrit van der Laan, E. Dudzik, Maurizio Sacchi, Hermann A. Dürr, and Frédéric Petroff
- Subjects
Materials science ,Condensed matter physics ,business.industry ,Scattering ,Bragg's law ,Resonance ,Bragg peak ,Dielectric ,Inelastic scattering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Optics ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,business ,Anisotropy - Abstract
We have measured the resonant scattering from an antiferromagnetic Co/Cr multilayer at photon energies close to the cobalt 2p→3d transitions. The cobalt dielectric tensor has an anisotropic component, enhanced by resonance, which depends on the magnetic order and follows its modulation inside the sample. We have studied the vertical distribution of this component through the dependence of the reflectivity on the scattering angle. Using s-polarized light, we have observed the signature of the cobalt–cobalt antiferromagnetic coupling as an half-integer-order Bragg peak. Experimental results have been analyzed by numerical simulation.
- Published
- 2000
46. Structural and magnetic properties of Fex–C1−x nanocomposite thin films
- Author
-
Frédéric Petroff, A. Naudon, David Babonneau, Thierry Cabioc’h, and J. Briatico
- Subjects
Magnetization ,Crystallography ,Materials science ,Extended X-ray absorption fine structure ,Annealing (metallurgy) ,Analytical chemistry ,General Physics and Astronomy ,Magnetic nanoparticles ,Coercivity ,Microstructure ,Magnetic susceptibility ,Superparamagnetism - Abstract
Iron–carbon nanocomposite thin films with iron concentrations ranging from 12 to 74 at. % were grown by ion-beam sputtering codeposition at different substrate temperatures. The microstructure of the films was characterized by transmission electron microscopy, atomic force microscopy, extended x-ray absorption fine structure, and grazing incidence small-angle x-ray scattering. A granular morphology consisting of body-centered-cubic iron-rich nanoparticles (2–5 nm in diameter and 3–8 nm in height with a relatively sharp size distribution) regularly distributed within a more or less graphitic matrix was obtained. Structural properties as well as magnetic ones were found to depend strongly on composition, substrate temperature, and postdeposition treatments (annealing or Ar+ irradiation). The temperature dependence of the susceptibility exhibited a superparamagnetic response with blocking temperature in the range of 13–180 K. The maximum low-temperature (5 K) coercivity value obtained in this study was 850 O...
- Published
- 2000
47. Evidence for a high-spin Fe phase in Fe/Pd(001) multilayers
- Author
-
Marco Finazzi, Vincent Cros, Frédéric Petroff, Alfonso Cebollada, Jan Vogel, N. B. Brookes, Alain Fontaine, Wilfried Grange, Jose Menendez, and Jean-Paul Kappler
- Subjects
symbols.namesake ,Materials science ,Transition metal ,Condensed matter physics ,Magnetic moment ,Magnetic circular dichroism ,Phase (matter) ,symbols ,General Physics and Astronomy ,Van der Waals radius ,Spin (physics) ,Magnetic dipole ,XANES - Abstract
We have investigated by X-ray Magnetic Circular Dichroism (XMCD) the Fe spin and orbital magnetic moments in Fe/Pd(001) multilayers with nominal Fe thicknesses up to 3 Atomic Layers (AL). We find a strong enhancement of both spin and orbital moments (mspin ≈ 2.8 μB and morb ≈ 0.3 μB) compared to bulk Fe in excellent agreement with theoretical calculations. For 1 AL of Fe, the magnetic dipole term was deduced using the Stohr and Konig method and found to be non-negligible (20% of mspin). We further show that, for 3 AL of Fe, the high spin phase is correlated to a fcc-like crystalline structure with a large atomic volume of Fe ( ≈ 12.4 A3).
- Published
- 2000
48. Clusters obtained by sputter deposition of cobalt atoms on alumina
- Author
-
J. Briatico, L. F. Schelp, Jean-Luc Maurice, Frédéric Petroff, Julian Carrey, and Annie Vaures
- Subjects
Physics and Astronomy (miscellaneous) ,Extended X-ray absorption fine structure ,Chemistry ,Metals and Alloys ,Mineralogy ,chemistry.chemical_element ,Coulomb blockade ,Sputter deposition ,Condensed Matter Physics ,Molecular physics ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Electrical resistivity and conductivity ,Percolation ,Cluster (physics) ,General Materials Science ,Cobalt - Abstract
We report on aggregation of Co on a smooth amorphous alumina surface, during sputter deposition of Co atoms at room temperature. The atomic structure of the Co grains appears to be size dependent: hep in the larger bean-shaped clusters (greater than 3 nm), and often fee in the smaller, almost spherical clusters. The deposits show relatively narrow distributions of the cluster sizes and of the intercluster distances, which results in a noticeable local order and explains how charge blocking (the so-called Coulomb blockade) could be observed in large sets of such particles by Schelp et al. (1997, Phys. Rev. B, 56, R5747). Electrical percolation occurs at a nominal thickness of about 2 nm.
- Published
- 1999
49. Structure of cobalt cluster films obtained by sputter deposition on alumina
- Author
-
Annie Vaures, Julian Carrey, Frédéric Petroff, D. Imhoff, Jean-Luc Maurice, and J. Briatico
- Subjects
Materials science ,chemistry ,Extended X-ray absorption fine structure ,Sputtering ,Electron energy loss spectroscopy ,Cluster (physics) ,Analytical chemistry ,chemistry.chemical_element ,Sputter deposition ,Cobalt ,Cobalt oxide ,Atomic and Molecular Physics, and Optics ,Amorphous solid - Abstract
We report on the structure of cobalt cluster films obtained by aggregation of metal atoms sputter-deposited on amorphous alumina. The cluster layers were encapsulated with a second amorphous alumina layer, also made by sputtering in the same chamber. Electron energy loss spectroscopy (EELS) indicates that encapsulation with sputtered alumina keeps the clusters free from cobalt oxide. Transmission electron microscopy (TEM) exhibits relatively narrow distributions of the cluster sizes and of the inter-cluster distances, which results in a noticeable local order. Size distributions appear quasi-Gaussian, but TEM misses an important number of small particles. Extended X-ray absorption fine structure (EXAFS) data shows that the actual average sizes are smaller, and Monte Carlo simulations suggest that the actual distributions could be bimodal, with a secondary peak in the small-size range.
- Published
- 1999
50. Tunnel magnetoimpedance in cobalt discontinuous films
- Author
-
E.L Rosa, Frédéric Petroff, Annie Vaures, Jean-Luc Maurice, and L. F. Schelp
- Subjects
Condensed Matter::Materials Science ,Tunnel effect ,Tunnel magnetoresistance ,Materials science ,Magnetoresistance ,Condensed matter physics ,Percolation ,Relaxation (NMR) ,Condensed Matter Physics ,Electrical impedance ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Dielectric spectroscopy - Abstract
We present the impedance and its variation in magnetic fields for discontinuous Co films sandwiched by Al2O3. The Co nominal thickness varies from 0.7 to 2.5 nm and the room temperature impedance has been measured from fractions of Hz to 100 kHz. The samples present a distribution of relaxation times with a maximum width below the percolation point. For a given frequency, an external magnetic field induces a variation in the modulus and in the phase of the impedance. The evolution of the tunnel magnetoimpedance, whose real part is the usual tunnel magnetoresistance, as a function of frequency is presented and can be described in terms of the variations in the relaxation time.
- Published
- 1999
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