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Topological materials are of high interest due to the promise to obtain low power and fast memory devices based on efficient spin-orbit torque switching or spin-orbit magnetic state read-out. In particular, sputtered polycrystalline Bi$_x$Se$_{1-x}$ is one of the materials with more potential for this purpose since it is relatively easy to fabricate and has been reported to have a very high spin Hall angle. We study the spin-to-charge conversion in Bi$_x$Se$_{1-x}$ using the spin pumping technique coming from the ferromagnetic resonance in a contiguous permalloy thin film. We put a special emphasis on the interfacial properties of the system. Our results show that the spin Hall angle of Bi$_x$Se$_{1-x}$ has an opposite sign to the one of Pt. The charge current arising from the spin-to-charge conversion is, in contrast, lower than Pt by more than one order of magnitude. We ascribe this to the interdiffusion of Bi$_x$Se$_{1-x}$ and permalloy and the changes in chemical composition produced by this effect, which is an intrinsic characteristic of the system and is not considered in many other studies.

Second Harmonic Generation (SHG) from BiFeO3 nanocrystals is investigated for the first time to determine their potential as biomarkers for multiphoton imaging. Nanocrystals are produced by an auto-combustion method with TRIS as a fuel. Stable colloidal suspensions with mean particle diameters in the range 100-120 nm are then obtained after wet-milling and sonication steps. SHG properties are determined using two complementary experimental techniques, Hyper Rayleigh Scattering and nonlinear polarization microscopy. BiFeO3 shows a very high second harmonic efficiency with an averaged coefficient of 79+-12 pm/V. From the nonlinear polarization response of individual nanocrystals, relative values of the independent dij coefficients are also determined and compared with recent theoretical and experimental studies. Additionally, the particles show a moderate magnetic response, which is attributed to gamma-Fe2O3 impurities. A combination of high nonlinear optical efficiency and magnetic response within the same particle is of great interest for future bio-imaging and diagnostic applications.

The aim of this work is the elaboration of an integrated optical amplifier for telecommunication. The amplifying function is essential for data transmission in the mid and long distances. First of all, we will see the role of the component in optical telecommunications networks as well as the theory of the physical amplification process applied to the two materials used (PbSe nanocristals and Erbium doped particles). After material preparation and optical characterization of PMMA resin doped with PbSe nanocristals, we report on device elaboration with the various steps of simulation and manufacture. Optical properties of this waveguiding amplifier will be report: propagation and coupling losses, on-off and net gain., Le but de ce travail est la réalisation d'un composant intégré pour l'amplification optique des signaux de télécommunications. La fonction d'amplification est primordiale dans tous les types de transmissions de données à moyenne et longue distance. Nous verrons tout d'abord le rôle du composant dans les réseaux de télécommunications optiques, ainsi que la théorie des processus d'amplification appliquée aux deux matériaux utilisés (Nanocristaux de PbSe et particules dopées Erbium). Après la fabrication et la caractérisation optique de la résine de PMMA dopée aux nanocristaux de PbSe, nous décrirons l'élaboration du composant incluant les différentes étapes de simulation et de fabrication. Les propriétés optiques de ce guide amplificateur seront déterminées : pertes de propagation et de couplage, gain on-off et gain net.

Offre de Transfert Technologique de l’Université de Lorraine et enveloppe Soleau

International audience

International audience