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Search Results: 1 - 10 of 433629 matches for " H. Jaffrès "
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Giant Forward Scattering Asymmetry and Anomalous Tunnel Hall effect at Spin-Orbit-and Exchange-Split Interfaces
T. Huong Dang,H. Jaffrès,T. L. Hoai Nguyen,H. -J. Drouhin
Physics , 2015, DOI: 10.1103/PhysRevB.92.060403
Abstract: We report on theoretical investigations of scattering asymmetry vs. incidence of carriers through exchange barriers and magnetic tunnel junctions made of semiconductors involving spin-orbit interaction. By an analytical 2?2 spin model, we show that, when Dresselhaus interaction is included in the conduction band of antiparallel magnetized electrodes, the electrons can undergo a large difference of transmission depending on the sign of their incident in-plane wavevector. In particular, the transmission is fully quenched at some points of the Brillouin zone for specific in-plane wavevectors and not for the opposite. Moreover, it is universally scaled by a unique function independent of the spin-orbit strength. This particular feature is reproduced by a 14 ? 14 band k ? p model showing, in addition, corresponding effects in the valence band and highlighting the robustness of the effect, which even persists for a single magnetic electrode. Upon tunneling, electrons undergo an asymmetrical deflection which results in the occurrence of a transverse current, giving rise to a so-called Tunnel Hall Effect.
Use ion beam techniques to study the coupling between air and its relative humidity on iron corrosion under irradiation
S. Lapuerta,N. Moncoffre,N. Bérerd,H. Jaffrézic,N. Millard-Pinard,D. Crusset
Physics , 2005, DOI: 10.1016/j.nimb.2006.03.034
Abstract: In this paper, the role of air humidity on the iron corrosion under irradiation is studied in the context of geological disposal of nuclear wastes. The irradiation experiments are performed at room temperature using a 3 MeV extracted proton beam with a 10 nA intensity. Different atmospheres are studied: Humid air with a relative humidity (RH) fixed at 45 %, dry air and a $^{15}N\_2$ atmosphere (45% RH). The hydrogen and oxygen distribution profiles at the iron surface in contact with atmosphere are measured by using respectively ERDA (Elastic Recoil Detection Analysis) and RBS (Rutherford Backscattering Spectrometry) analysis. From these experiments it is clearly demonstrated that the coupling of O$\_2$+H$\_2$O enhances iron oxidation whereas for iron hydrogenation, humidity is sufficient whatever the atmosphere. An interpretation is given, which is based on the reaction mechanisms and the species formed by air ionisation.
Role of proton irradiation and relative air humidity on iron corrosion
S. Lapuerta,N. Moncoffre,N. Millard-Pinard,H. Jaffrézic,N. Bérerd,D. Crusset
Physics , 2005, DOI: 10.1016/j.jnucmat.2006.02.051
Abstract: This paper presents a study of the effects of proton irradiation on iron corrosion. Since it is known that in humid atmospheres, iron corrosion is enhanced by the double influence of air and humidity, we studied the iron corrosion under irradiation with a 45% relative humidity. Three proton beam intensities (5, 10 and 20 nA) were used. To characterise the corrosion layer, we used ion beam methods (Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA)) and X-ray Diffraction (XRD) analysis. The corrosion kinetics are plotted for each proton flux. A diffusion model of the oxidant species is proposed, taking into account the fact that the flux through the surface is dependent on the kinetic factor K. This model provides evidence for the dependence of the diffusion coefficient, D, and the kinetic factor, K, on the proton beam intensity. Comparison of the values for D with the diffusion coefficients for thermal oxygen diffusion in iron at 300 K suggests an enhancement due to irradiation of 6 orders of magnitude.
Spectral and Energy Efficiency Trade-Offs in Cellular Networks
Dimitrios Tsilimantos,Jean-Marie Gorce,Katia Jaffrès-Runser,H. Vincent Poor
Computer Science , 2013,
Abstract: This paper presents a simple and effective method to study the spectral and energy efficiency (SE-EE) trade-off in cellular networks, an issue that has attracted significant recent interest in the wireless community. The proposed theoretical framework is based on an optimal radio resource allocation of transmit power and bandwidth for the downlink direction, applicable for an orthogonal cellular network. The analysis is initially focused on a single cell scenario, for which in addition to the solution of the main SE-EE optimization problem, it is proved that a traffic repartition scheme can also be adopted as a way to simplify this approach. By exploiting this interesting result along with properties of stochastic geometry, this work is extended to a more challenging multi-cell environment, where interference is shown to play an essential role and for this reason several interference reduction techniques are investigated. Special attention is also given to the case of low signal to noise ratio (SNR) and a way to evaluate the upper bound on EE in this regime is provided. This methodology leads to tractable analytical results under certain common channel properties, and thus allows the study of various models without the need for demanding system-level simulations.
Anisotropic magneto-resistance in a GaMnAs-based single impurity tunnel diode: a tight binding approach
M. O. Nestoklon,O. Krebs,H. Jaffrès,S. Ruttala,J. -M. George,J. -M. Jancu,P. Voisin
Physics , 2012, DOI: 10.1063/1.3683525
Abstract: Using an advanced tight-binding approach, we estimate the anisotropy of the tunnel transmission associated with the rotation of the 5/2 spin of a single Mn atom forming an acceptor state in GaAs and located near an AlGaAs tunnel barrier. Significant anisotropies in both in-plane and out-of-plane geometries are found, resulting from the combination of the large spin-orbit coupling associated with the p-d exchange interaction, cubic anisotropy of heavy-hole dispersion and the low C2v symmetry of the chemical bonds.
Origin of the hydrogen involved in iron corrosion under irradiation
S. Lapuerta,N. Millard-Pinard,N. Moncoffre,N. Bérerd,H. Jaffrézic,G. Brunel,D. Crusset,Th. Mennecart
Physics , 2005, DOI: 10.1016/j.surfcoat.2006.01.094
Abstract: In the perspective of long term geological storage, high level nuclear wastes will be overpacked in low carbon steel containers. In that context, we have studied the influence of oxygen dissolved in water on iron corrosion. Therefore, leaching experiments were performed in desaerated D$\_2$O and in aerated H$\_2$O and a kinetic study of iron corrosion under proton irradiation was lead in aqueous media with two different dissolved oxygen concentrations. The leaching experiments underline the major role of dissolved oxygen in oxydoreduction reactions which take place as far as iron is in contact with water. But the kinetic study of iron corrosion under irradiation put in evidence the balance between the oxydoreduction reactions and the corrosion rate induced by radicals species generated by water radiolysis. In addition, to check if, in the atomic % concentration range, hydrogen diffuse from the air/Fe interface through the foil an irradiation experiment was performed in argon. It proved that no hydrogen permeation occurs at a concentration level of the atomic percent.
Perpendicular magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers via the Spin Hall Effect of Pt
J. -C. Rojas-Sánchez,P. Laczkowski,J. Sampaio,S. Collin,K. Bouzehouane,N. Reyren,H. Jaffrès,A. Mougin,J. -M. George
Physics , 2015,
Abstract: We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]$_3$/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 0.3 TA/m$^2$. In these experiments we demonstrate a full control of each stage: i)the {\O}rsted field controls the domain nucleation and ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and N\'eel like due to the interfacial Dzyaloshinskii-Moriya interaction.
Spin precession and inverted Hanle effect in a semiconductor near a finite-roughness ferromagnetic interface
S. P. Dash,S. Sharma,J. C. Le Breton,H. Jaffrès,J. Peiro,J. -M. George,A. Lema?tre,R. Jansen
Physics , 2011, DOI: 10.1103/PhysRevB.84.054410
Abstract: Although the creation of spin polarization in various non-magnetic media via electrical spin injection from a ferromagnetic tunnel contact has been demonstrated, much of the basic behavior is heavily debated. It is reported here for semiconductor/Al2O3/ferromagnet tunnel structures based on Si or GaAs that local magnetostatic fields arising from interface roughness dramatically alter and even dominate the accumulation and dynamics of spins in the semiconductor. Spin precession in the inhomogeneous magnetic fields is shown to reduce the spin accumulation up to tenfold, and causes it to be inhomogeneous and non-collinear with the injector magnetization. The inverted Hanle effect serves as experimental signature. This interaction needs to be taken into account in the analysis of experimental data, particularly in extracting the spin lifetime and its variation with different parameters (temperature, doping concentration). It produces a broadening of the standard Hanle curve and thereby an apparent reduction of the spin lifetime. For heavily doped n-type Si at room temperature it is shown that the spin lifetime is larger than previously determined, and a new lower bound of 0.29 ns is obtained. The results are expected to be general and occur for spins near a magnetic interface not only in semiconductors but also in metals, organic and carbon-based materials including graphene, and in various spintronic device structures.
Mixed Layer Depth Seasonality within the Coral Sea Based on Argo Data
Jasmine B. D. Jaffrés
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0060985
Abstract: The worldwide deployment of Argo floats has enabled much more detailed studies of global and regional seas over the last decade. Here, the seasonal variability of the mixed layer depth (MLD) within the Coral Sea was examined with CTD profiles from Argo floats. Multiple threshold values for both temperature and density have been employed to determine the most suitable threshold values for the Coral Sea. A threshold value of 0.04 kg/m3 for density and 0.2°C for temperature appear the most fitting for this region. Although MLD and isothermal layer depth (ILD) coincide quite well in most cases, the relatively common presence of temporary, non-seasonal barrier layers induces an ILD that is significantly deeper than the MLD. Consequently, an MLD estimation based on density is more appropriate. A distinct seasonality in the MLD is evident throughout the Coral Sea, but is generally more pronounced in higher southern latitudes (20–30°S). Salinity inversions are rare and mainly occur in the south-eastern Coral Sea, while barrier layers are more commonly associated with the north-eastern Coral Sea, a region characterised by high rainfall. The significance of regional currents is evident in the north-western Coral Sea, where temperature and ocean heat content is relatively low due to a northward moving boundary current. Shallow bathymetry, in turn, is linked to the absence of Argo data on the continental shelf and in the central Coral Sea.
Spin Pumping and Inverse Spin Hall Effect in Platinum: The Essential Role of Spin-Memory Loss at Metallic Interfaces
J. -C. Rojas-Sánchez,N. Reyren,P. Laczkowski,W. Savero,J. -P. Attané,C. Deranlot,M. Jamet,J. -M. George,L. Vila,H. Jaffrès
Physics , 2013, DOI: 10.1103/PhysRevLett.112.106602
Abstract: Through combined ferromagnetic resonance, spin-pumping and inverse spin Hall effect experiments in Co|Pt bilayers and Co|Cu|Pt trilayers, we demonstrate consistent values of spin diffusion length $\ell_{\rm sf}^{\rm Pt}=3.4\pm0.4$ nm and of spin Hall angle $\theta_{\rm SHE}^{\rm Pt}=0.051\pm0.004$ for Pt. Our data and model emphasize on the partial depolarization of the spin current at each interface due to spin-memory loss. Our model reconciles the previously published spin Hall angle values and explains the different scaling lengths for the ferromagnetic damping and the spin Hall effect induced voltage.
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