Recent works provide evidence for a large orbital Rashba-Edelstein effect at the interface between Cu and its oxide. Here, we experimentally demonstrate that a very large enhancement of both the net torque and the spin-pumping voltage (up to a factor of two) can be obtained with the insertion of a Pt layer whose large spin-orbit coupling helps to convert a pure orbital current into a spin current. These two reciprocal phenomena, observed simultaneously for the first time in the same Co/Pt/Cu/CuOx samples, are in agreement and their orbital angular momentum nature associated to a charge-to-orbit (orbit-to-charge) conversion at the Cu/CuOx interface constitutes a robust interpretation. To disentangle spin and orbital currents in these systems, we also measure the ferromagnet thickness dependence of the net torques and observe a clear increase of the corresponding dephasing length, indicating the contribution of pure orbital currents acting on the magnetization. From the Cu thickness dependence, we also verify that the conversion occurs at the Cu/CuOx interface through the orbital Rashba effect as observed in both torque and spin-pumping measurements.
Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions among others. The presentation will focus on the behavior of chiral DWs at ultrashort timescale after optical pumping in perpendicularly magnetized asymmetric multilayers. The magnetization dynamics is probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). In the first 2 picosecond, a transient reduction of the CD-XRMS asymmetry ratio is attributed to the spin current-induced coherent and incoherent torques within the continuously dependent spin texture of the DWs. On the one hand, this time-varying change of the DW texture shortly after the laser pulse is identified as a distortion of the homochiral Néel shape toward a transient mixed Bloch-Néel-Bloch texture along a direction transverse to the DW due to the coherent torque. On the other hand, the overall effect of the spin current incoherent torque results in an average loss of angular momentum that induces an increase of the spin relaxation processes within the DW at the ps timescale. It leads to a faster remagnetization inside the DWs compared to domains.
Generation and detection of pure spin currents circulating in magnetic insulator materials have proven its worth by enabling transport of spin information across large distances, much further than in metals, thanks to the abscence 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. Most of the work so far has focus on Yttrium Iron garnets (YIG), which is a ferrimagnetic insulator with the lowest known amount of magnetic damping. In this talk, I will present recent result of 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. In this work, I will mainly focus on investigating the behavior at large energies. We have found that the magnon tranresistance in this system can cross several regimes that involve 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 in thin YIG films and we will show that our experimental findings do not support yet the emergence of new collective behaviors, such as Bose-Einstein condensation at room temperature.
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