Readout of a antiferromagnetic spintronics systems by strong exchange coupling of Mn2Au and Permalloy

In antiferromagnetic spintronics, the read-out of the staggered magnetization or Neel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Neel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-estabished read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are retained. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Neel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.Comment: 9 pages, 5 figure

Reconstruction polarimétrique d'environnements circumstellaires à partir des données ESO/VLT-SPHERE IRDIS

International audienceLa reconstruction des environnements des étoiles jeunes par imagerie directe est un dé car leur émission est noyée dans les résidus de lumière stellaire malgré l'utilisation d'un coronographe. Il est cependant possible de les démélanger en exploitant leurs di érences d'états de polarisation. Dans ce papier, nous présentons une méthode régularisée de reconstruction des environnements circumstellaires polarisés, à partir des données d'IRDIS (Infrared Dual Imager and Spectrograph), instrument de SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) installé sur l'un des télescopes du VLT (Very Large Tescope) de l'ESO (European Southern Observatory). Nous discutons des mérites de di érentes régularisations selon le cas astrophysique étudié

RHAPSODIE: Reconstruction of High-contrAst Polarized SOurces and Deconvolution for cIrcumstellar Environments

Context. Polarimetric imaging is one of the most effective techniques for high-contrast imaging and characterization of circumstellar environments. These environments can be characterized through direct-imaging polarimetry at nearinfrared wavelengths. The Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)/IRDIS instrument installed on the Very Large Telescope in its dual-beam polarimetric imaging (DPI) mode, offers the capability to acquire polarimetric images at high contrast and high angular resolution. However dedicated image processing is needed to get rid of the contamination by the stellar light, of instrumental polarization effects, and of the blurring by the instrumental point spread function. Aims. We aim to reconstruct and deconvolve the near-infrared polarization signal from circumstellar environments. Methods. We use observations of these environments obtained with the high-contrast imaging infrared polarimeter SPHERE-IRDIS at the Very Large Telescope (VLT). We developed a new method to extract the polarimetric signal using an inverse approach method that benefits from the added knowledge of the detected signal formation process. The method includes weighted data fidelity term, smooth penalization, and takes into account instrumental polarization Results. The method enables to accurately measure the polarized intensity and angle of linear polarization of circumstellar disks by taking into account the noise statistics and the convolution by the instrumental point spread function. It has the capability to use incomplete polarimetry cycles which enhance the sensitivity of the observations. The method improves the overall performances in particular for low SNR/small polarized flux compared to standard methods. Conclusions. By increasing the sensitivity and including deconvolution, our method will allow for more accurate studies of these disks morphology, especially in the innermost regions. It also will enable more accurate measurements of the angle of linear polarization at low SNR, which would lead to in-depth studies of dust properties. Finally, the method will enable more accurate measurements of the polarized intensity which is critical to construct scattering phase functions

The influence of nanoparticles embedded in a matrix on the responses of composite structures to low velocity impacts

cited By 0International audienceIn passive safety structures, the use of composite materials has increased significantly for many years because of their high specific properties and high energy absorption capacities. The purpose of this experimental study was to describe the behavior of Kevlar woven composite materials under low-velocity impacts. Different matrices (with and without nano-reinforcement) were considered. The role of the nano-reinforcement is to bring significant improvement with low concentration, thereby avoiding sacrificing other desirable properties. Tests were performed with a drop-weight tower on square plates clamped in a circular fixture. A video camera fixed underneath the plate during impact was used to record the damage that occurred during impact. Macroscopic impact scenarios were proposed based on the correlations between the photographs, displacement, and loading histories. Cross sections of the damaged areas were inspected with an optical microscope in order to reveal the micro-mechanisms that were involved in the dissipation of the impact energy. © 2012 Lavoisier

GSURE criterion for unsupervised regularized reconstruction in tomographic diffractive microscopy

International audienceWe propose an unsupervised regularized inversion method for reconstruction of the 3D refractive index map of a sample in tomographic diffractive microscopy. It is based on the minimization of the generalized Stein’s unbiased risk estimator (GSURE) to automatically estimate optimal values for the hyperparameters of one or several regularization terms (sparsity, edge-preserving smoothness, total variation). We evaluate the performance of our approach on simulated and experimental limited-view data. Our results show that GSURE is an efficient criterion to find suitable regularization weights, which is a critical task, particularly in the context of reducing the amount of required data to allow faster yet efficient acquisitions and reconstructions

A fibrous cellulose paste formulation to manufacture structural parts using 3D printing by extrusion

International audienceAn optimized paste based on short natural cellulose fibers combined with carboxymethyl cellulose at a high dry content (42 wt.%) was implemented as a bio-based material for 3D printing by extrusion. The homogeneous paste exhibited a pronounced thinning behavior and yield stress; it was extruded using a screw extrusion-based direct ink writing system and could easily flow through a small nozzle. The optimized formulation enabled accurate additive manufacturing of parts using a natural air-drying process with or without an ethanol bath. We characterized the anisotropic shrinkage that occurred during the drying of 3D printed parts and proposed a compensation method to account for it. The obtained results emphasized that cellulose had a strong potential to be used as a raw material for 3D printing of cheap, lightweight, robust, and recyclable parts

Damage investigation and modeling of 3D woven ceramic matrix composites from X-ray tomography in-situ tensile tests

The present paper proposes an investigation of the failure events in a melt-infiltrated SiC/SiC composite. In-situ X-ray microtomography tensile tests were performed at room temperature and at 1250 • C in air. Digital Volume Correlation has been used to identify the damage mechanisms within the material at increasing loads and to propose a damage scenario. Realistic finite element meshes have been constructed from the 3D images to numerically reproduce the experiments at the meso-scale. Elastic simulations exhibit stress concentrations in the planes containing the weft tows. The first cracks and subsequent damage localization were found to appear within these planes thanks to the analysis of the in-situ tomographic data