Influence of ambient air on the flowing afterglow of an atmospheric pressure Ar/O2 radiofrequency plasma

The influence of ambient air on the flowing afterglow of an atmospheric pressure Ar/O2 radiofrequency plasma has been investigated experimentally. Spatially resolved mass spectrometry and laser induced fluorescence on OH radicals were used to estimate the intrusion of air in between the plasma torch and the substrate as a function of the torch-to-substrate separation distance. No air is detected, within the limits of measurement uncertainties, for separation distances smaller than 5 mm. For larger distances, the effect of ambient air can no longer be neglected, and radial gradients in the concentrations of species appear. The Ar 4p population, determined through absolute optical emission spectroscopy, is seen to decrease with separation distance, whereas a rise in emission from the N2(C-B) system is measured. The observed decay in Ar 4p and N2(C) populations for separation distances greater than 9 mm is partly assigned to the increasing collisional quenching rate by N2 and O2 molecules from the entrained air. Absorption measurements also point to the formation of ozone at concentrations from 1014 to 10 15 cm - 3, depending both on the injected O2 flow rate and the torch-to-substrate separation distance. © 2013 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Symmetry-state features in a global analysis of the temperature-dependent spin transport in Fe/MgO/Fe junctions

International audienceThe temperature dependence of the spin polarized tunnel conductance is investigated with Fe/MgO/Fe tunnel junctions with different structural properties and interfacial chemistry. A global quantitative model is proposed for analyzing the tunnel conductance in both parallel and antiparallel configuration. Three contributions to the temperature dependence can be distinguished. The first one is governed by the Bloch law for the temperature dependence of the magnetization of the electrodes. The second one is unpolarized and follows a power-law associated with a hopping mechanism. Although these two mechanisms are predominant in the decrease of tunnel magnetoresistance with temperature, a third contribution must be considered. This term results from a thermally activated decrease of the effective spin polarization, introduced by an Arrhenius law. It appears in either the parallel or antiparallel conductance, depending on the interface chemical doping, and could then be related to a symmetry dependent diffusion process. Finally, this global analysis appears universal, as it can well fit the temperature dependence of all samples

Fe/MgO/Fe (100) textured tunnel junctions exhibiting spin polarization features of single crystal junctions

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Metalliclike behavior of the exchange coupling in (001) Fe/MgO/Fe junctions

International audienceExchange magnetic coupling between Fe electrodes through a thin MgO interlayer in epitaxial junctions has been investigated as a function of temperature, MgO thickness, and interface quality. Depending on the MgO thickness, which has been varied from 1.5 to 4 monolayers, two opposite temperature dependences are clearly disentangled. For a thin MgO spacer, the main component decreases with temperature following a metalliclike behavior. On the contrary, for the thickest MgO layers, the main component increases with temperature, following an Arrhenius law. Moreover, the insertion of a monoatomic roughness at the bottom MgO interface, induced by the addition of a fraction of a Fe monolayer, exacerbates the metallic features as an oscillatory behavior from antiferromagnetic to ferromagnetic is observed. These results allow questioning the simple tunneling mechanism usually invoked for MgO coupling, and suggest a crossover behavior of the thin MgO spacer from metallic to insulating with a progressive opening of the gap

Symmetry Dependent Scattering by Minority Interface Resonance States in Single-crystal Magnetic Tunnel Junctions

Symmetry dependent scattering effect by minority interface resonance states (IRS) has been evidenced in full-epitaxial Fe/MgO/Fe magnetic tunnel junctions (MTJs). Two types of samples with and without carbon doped bottom Fe/MgO interface were fabricated to represent two different types of IRS in the minority channel in the vicinity of the Fermi level. By analysis of the first- principles calculated local density of states (LDOS) and the temperature dependence of conductance in parallel configuration at low bias, we show that the IRS in the carbon free sample is dominated by the delta5 symmetry. This has a major contribution on the majority deltai to delta5 channel scattering and explains the enhancement of the delta5 conductance in the parallel configuration at low temperature. Furthermore, the spectral composition of the IRS in the carbon doped interface is found to be dominated by the delta1 symmetry, which is responsible for the suppression of delta5 channel in the parallel conductance.Comment: We recently find that the explication in this paper is not correct. We are continuing to study the mechanis