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Spin transfer in a magnetic insulator

Abstract : The generation and detection of pure spin currents circulating in magnetic insulator materials are at the heart of insulating spintronics. It have proven its worth by enabling transport of spin information across large distances, much further than in metals, thanks to the absence of decay mechanism through the delocalized electrons. Spin currents here propagate over localized magnetic moments via spin-waves (SW), or their quanta the magnons, with characteristic frequencies ranging from GHz to THz and associated wavelengths from µm to nm. Recently, considerable attention in the field of insulating spintronics has been given Yttrium Iron garnets (YIG), which is a ferrimagnetic insulator with the lowest known amount of magnetic damping. My thesis work focuses on spin waves transport in high-quality ultra-thin films exploiting spin-orbit tools to interconvert the spin signal into an electrical signal. By injecting a high current density in Pt electrodes deposited few microns apart on top of a YIG film, a pure magnon current propagating in the YIG can be induced/detected via the direct/inverse spin Hall effect. The main contribution of my work is a wide investigating of the spin transfer at large energies. We have found that the spin conductance in this system can cross several regimes that involve a strong change in the magnon distribution. Throughout various techniques such as Brillouin light scattering spectroscopy, spin Seebeck and spin Hall magnetoresistance measurements, we provide a complete analysis of the different phenomena surrounding the spin transport at large energy in thin YIG films and we will show that our experimental findings do not support yet the emergence of the new collective behaviors, such as Bose-Einstein condensation at room temperature.
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Nicolas Thiery. Spin transfer in a magnetic insulator. Materials Science [cond-mat.mtrl-sci]. Université Grenoble Alpes, 2019. English. ⟨NNT : 2019GREAY064⟩. ⟨tel-03092264⟩

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