Controlling shot noise in double-barrier magnetic tunnel junctions

We demonstrate that shot noise in Fe/MgO/Fe/MgO/Fe double-barrier magnetic tunnel junctions is determined by the relative magnetic configuration of the junction and also by the asymmetry of the barriers. The proposed theoretical model, based on sequential tunneling through the system and including spin relaxation, successfully accounts for the experimental observations for bias voltages below 0.5V, where the influence of quantum well states is negligible. A weak enhancement of conductance and shot noise, observed at some voltages (especially above 0.5V), indicates the formation of quantum well states in the middle magnetic layer. The observed results open up new perspectives for a reliable magnetic control of the most fundamental noise in spintronic structures.Comment: 8 pages, 4 figure

Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice

Magnetic frustration effects in artificial kagome arrays of nanomagnets are investigated using x-ray photoemission electron microscopy and Monte Carlo simulations. Spin configurations of demagnetized networks reveal unambiguous signatures of long range, dipolar interaction between the nanomagnets. As soon as the system enters the spin ice manifold, the kagome dipolar spin ice model captures the observed physics, while the short range kagome spin ice model fails.Comment: 4 pages, 4 figures, 1 tabl

Advances in the control of electrophoretic process parameters to tune the ytterbium disilicate coatings microstructure

Suspensions of ytterbium disilicate in isopropanol were prepared using iodine dispersant. Their zeta potential, electrical conductivity, and pH dependence with iodine concentration is detailed. Electrophoretic deposition was performed on silicon substrates at various voltages (100‐200 V) and times (until 10 minutes) and the growth dynamic was investigated. It was observed that the deposited mass reaches a maximum value for [I2] = 0.2 g/L, and the coating microstructure becomes porous at higher iodine concentrations. Current density and voltage measurements allowed to correlate this behavior to the increase of free protons concentration in the suspension. In these conditions, it was proved that porosity increases with the increase in applied voltage, and a compaction occurs as the deposition time increases. This has been related to the coating resistance increase and subsequent decrease in effective voltage in the suspension. The denser coatings (20% of porosity) were obtained in the case of suspension without iodine, at the minimum applied voltage and for the longest deposition times

Comparison of three optical diagnostic techniques for the measurement of boron atom density in a H 2 /B 2 H 6 microwave plasma

International audienc

Detection of Hydrogen Atoms by Two Photons Absorption Laser Induced Fluorescence in a High Power Density H2/CH4 Microwave Plasma

posterInternational audienceMicrowave Plasma Assisted Chemical Vapour Deposition (MPACVD) is widely used for the production of diamond films, for which hydrogen atoms and methyl radicals have been shown to constitute the key species for growing crystal diamond [1]. The growth of very high purity and quality diamond at elevated deposition rate relies on high production of H atoms and CH3 radicals in a very clean system at very high power density. That is the reason why understanding the physical and chemical processes involved in diamond deposition and how the experimental conditions impact the growth mechanisms at high pressure / high power (> 100 hPa, > 2 kW) requires in particular the determination of H plasma concentration. Following Optical Emission Spectroscopy (OES) used previously [2], Two-Photons Absorption Induced Fluorescence (TALIF) technique has been implemented to study a H2/CH4 CVD plasma under high pressures and high microwave power densities. Indeed, this laser technique is a powerful and spatially resolved tool for chemical characterization of plasma [3]

Determination of absolute atomic hydrogen densities by TALIF in a H2/CH4 microwave plasma at high power and high pressure

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Atomic Hydrogen density and temperature measurements by Two-Photon Absorption Laser Induced Fluorescence in a High Power Density H2/CH4 Microwave Plasma

posterInternational audienceIn the context of monocrystalline diamond plasma deposition, the atomic hydrogen densities and temperatures have been determined by two-photon absorption laser induced fluorescence in a H2/CH4 microwave plasma at high pressure (>200 mbar) and high microwave power (>2000 W). Absolute H densities were obtained by a calibration method that consists in measuring the TALIF signal emitted from Kr gas at a well-known pressure. H temperatures were estimated from Doppler broadening of the absorption line. In plasmas containing 1% CH4, the measured H densities and temperatures in the plasma bulk are in the ranges 1-3x1017 cm-3 and 3000-3500 K respectively. As the pressure rises from 200 mbar to 400 mbar, the maximum H density increases and shifts closer to the substrate, and the H molar fraction and H temperature increase in the plasma bulk

Determination of absolute atomic hydrogen densities by Two-Photon Absorption Laser Induced Fluorescence in a H2/CH4 Microwave Plasma at High Pressure and High Microwave Power

oralInternational audienceIn the context of monocrystalline diamond plasma deposition, the atomic hydrogen densities have been determined by two-photon absorption laser induced fluorescence in a H2/CH4 microwave plasma at high pressure (200 hPa) and high microwave power (3000 W). H-atom densities were estimated by a calibration method that consists in normalizing the H-atom TALIF intensity by the intensity from Kr atoms in a pure krypton gas at a known pressure. In the range of pressures studied, the value of the H-atom fluorescence yield, which is necessary for the calculation of absolute densities, cannot be determined experimentally, but is estimated from a model calculation that solves the rate equations describing the population changes in the various H n=3 sublevels. In plasmas containing 1% CH4, the H-atom densities reach values ≥ 1.9×1023 m-3, and the gas temperature in the plasma bulk is ~3000 K

Soft matter electrolytes based on polymethylmetacrylate dispersions in lithium bis(trifluoromethanesulfonyl)imide/1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids

Ion transport in a polymer–ionic liquid (IL) soft matter composite electrolyte is discussed here in detail in the context of polymer–ionic liquid interaction and glass transition temperature. The dispersion of polymethylmetacrylate (PMMA) in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) resulted in transparent composite electrolytes with a “jelly-like” consistency. The composite ionic conductivity measured over the range −30 °C to 60 °C was always lower than that of the neat BMITFSI/BMIPF6 and LiTFSI-BMITFSI/LiTFSI-BMIPF6 electrolytes but still very high (>1 mS/cm at 25 °C up to 50 wt% PMMA). While addition of LiTFSI to IL does not influence the glass Tg and Tm melting temperature significantly, dispersion of PMMA (especially at higher contents) resulted in increase in Tg and disappearance of Tm. In general, the profile of temperature-dependent ionic conductivity could be fitted to Vogel–Tamman–Fulcher (VTF) suggesting a solvent assisted ion transport. However, for higher PMMA concentration sharp demarcation of temperature regimes between thermally activated and solvent assisted ion transport were observed with the glass transition temperature acting as the reference point for transformation from one form of transport mechanism to the other. Because of the beneficial physico-chemical properties and interesting ion transport mechanism, we envisage the present soft matter electrolytes to be promising for application in electrochromic devices