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

Microstructural control of new generation thermal barrier coatings via a sol-gel route : cyclic oxidation behaviour

International audienceFor several years, turbojet engineers have been searching to increase the efficiency of engines in order to enhance their performances. This can be achieved via the increase of engine service temperature which may dramatically damage the materials used, namely for turbine blades made of single crystal nickel based superalloys. To protect and extend lifetime of those materials, they are generally coated with thermal barriers either deposited using the so-called EB-PVD or APS process, respectively resulting in typically directional columnar and lamellar microstructures. In this study, an alternative process is proposed. It consists to elaborate thermal barriers by sol-gel route, a room temperature method based on soft chemistry, object of several research investigations, showing a real interest for the synthesis of materials with controlled morphology and composition [1,2]. Relative to elaboration step, an initial sequence consists in coating the superalloy with an yttria stabilised zirconia composite sol by dip-coating at controlled speed. This allows to obtain a homogeneous coating with an equi-distributed porosity. Two types of commercial dispersants have been investigated for the implementation in the composite sol, Beycostat C213 and the PVP whose active chemical groups are similar but formulations and physicochemical characteristics are different. After adjustements of the parameters of both synthesis sintering heat treatment, ceramic coating shows a satisfactorily controlled microstructure. According to the nature of the dispersant incorporated, it is shown that the width of micro-cracks of ceramics varies, this controlled micro-cracking being nevertheless favourable for accommodating thermomechanical constraints exerted on the TBC during cyclic oxidation. The next step includes the reinforcement of the micro-crack network. Indeed, filling grooves with additional material has the virtue to strengthen the TBC and ultimately increase the lifetime of the system. The shaping technique used to reinforce the network is the spray-coating. The sols are loaded in powder and the content is adapted to the width of cracks to fill. To evaluate the effect of the reinforcement, several characterisations including cyclic oxidation and microstructure analysis ( SEM, image analysis, surface profilometry) are carried out for the two systems based respectively on C213 and PVP dispersant. The cyclic oxidation experiments (1100°C-1h) allow to compare the behaviour of thermal barrier coatings processed through the sol-gel route to that of standard EB-PVD TBC. Preliminary promising results unambiguously show that lifetimes of both systems are very similar

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

Folded fully depleted FET using Silicon-On-Nothing technology as a highly W-scaled planar solution

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Electrochromism of non-stoichiometric NiO thin film: as single layer and in full device

Electrochromic properties, known as a reversible modulation of the optical properties under an applied voltage, of NiO thin films are discussed in respect of the film stoichiometry. Using radio-frequency magnetron sputtering, non-stoichiometric "NiO" thin films of good crystallinity were grown at room temperature from low oxygen partial pressure [i.e., above 2 % P(O2/Ar + O2)]. A further increase in oxygen partial pressure leads to conductive brownish films containing a large amount of Ni3+. 2 %-Ni1- x O thin films exhibit significant EC performance in lithium-based electrolyte with a transmittance modulation of 25 %. If it is generally accepted that this optical modulation is due to an insertion of small cations, the presence of additional surface phenomena is also shown. The cycling of full device, based on the association of WO3 and "NiO" in temperature up to 60 °C and down to -35 °C confirms expected increase and decrease in capacity while surprisingly the optical switch from a transparent to a neutral gray color appears slightly modified