• S. Tsunegi, E. Grimaldi, R. Lebrun, H. Kubota, A. S. Jenkins, K. Yakushiji, A. Fukushima, P. Bortolotti, J. Grollier, S. Yuasa, V. Cros, Self-Injection Locking of a Vortex Spin Torque Oscillator by Delayed Feedback. Scientific Reports. 6, 26849 (2016).
    Résumé : The self-synchronization of spin torque oscillators is investigated experimentally by re-injecting its radiofrequency (rf) current after a certain delay time.
    Mots-clés : Spinorbitronics.

  • F. Töpler, A. Hönemann, K. Tauber, D. - V. Fedorov, M. Gradhand, I. Mertig, A. Fert, Nonlocal anomalous Hall effect in ternary alloys based on noble metals. Phys. Rev. B. 94, 140413 (2016).
    Résumé : We present a theoretical study of the nonlocal anomalous Hall effect induced by heavy-metal impurities in dilute magnetic alloys based on noble metals. The results of our first-principles calculations are shown in comparison to those obtained within a model consideration via Matthiessen's rule. Based on the transport properties of the constituent binary alloys, we reveal optimal host-impurity combinations to enhance the phenomenon. In particular, this allows us to explain experimental findings showing a strong effect in Cu-based alloys but a vanishing effect in the case of the Au host.

  • A. Vecchiola, P. Chrétien, S. Delprat, K. Bouzehouane, O. Schneegans, P. Seneor, R. Mattana, S. Tatay, B. Geffroy, Y. Bonnassieux, D. Mencaraglia, F. Houzé, Wide range local resistance imaging on fragile materials by conducting probe atomic force microscopy in intermittent contact mode. Applied Physics Letters. 108, 243101 (2016).
    Résumé : An imaging technique associating a slowly intermittent contact mode of atomic force microscopy (AFM) with a home-made multi-purpose resistance sensing device is presented. It aims at extending the widespread resistance measurements classically operated in contact mode AFM to broaden their application fields to soft materials (molecular electronics, biology) and fragile or weakly anchored nano-objects, for which nanoscale electrical characterization is highly demanded and often proves to be a challenging task in contact mode. Compared with the state of the art concerning less aggressive solutions for AFM electrical imaging, our technique brings a significantly wider range of resistance measurement (over 10 decades) without any manual switching, which is a major advantage for the characterization of materials with large on-sample resistance variations. After describing the basics of the set-up, we report on preliminary investigations focused on academic samples of self-assembled monolayers with various thicknesses as a demonstrator of the imaging capabilities of our instrument, from qualitative and semi-quantitative viewpoints. Then two application examples are presented, regarding an organic photovoltaic thin film and an array of individual vertical carbon nanotubes. Both attest the relevance of the technique for the control and optimization of technological processes.

  • L. G. Vivas, J. Rubín, A. I. Figueroa, F. Bartolomé, L. M. García, C. Deranlot, F. Petroff, L. Ruiz, J. M. González-Calbet, S. Pascarelli, N. - B. Brookes, F. Wilhelm, M. Chorro, A. Rogalev, J. Bartolomé, Perpendicular magnetic anisotropy in granular multilayers of CoPd alloyed nanoparticles. Phys. Rev. B. 93, 174410 (2016).
    Résumé : Co-Pd multilayers obtained by Pd capping of pre-deposited Co nanoparticles on amorphous alumina are systematically studied by means of high-resolution transmission electron microscopy, x-ray diffraction, extended x-ray absorption fine structure, SQUID-based magnetometry, and x-ray magnetic circular dichroism. The films are formed by CoPd alloyed nanoparticles self-organized across the layers, with the interspace between the nanoparticles filled by the non-alloyed Pd metal. The nanoparticles show atomic arrangements compatible with short-range chemical order of $\textbackslashmathrm{L}{1}_{0}$ strucure type. The collective magnetic behavior is that of ferromagnetically coupled particles with perpendicular magnetic anisotropy, irrespective of the amount of deposited Pd. For increasing temperature three magnetic phases are identified: hard ferromagnetic with strong coercive field, soft-ferromagnetic as in an amorphous asperomagnet, and superparamagnetic. Increasing the amount of Pd in the system leads to both magnetic hardness increment and higher transition temperatures. Magnetic total moments of 1.77(4) ${\textbackslashensuremath{\textbackslashmu}}_{B}$ and 0.45(4) ${\textbackslashensuremath{\textbackslashmu}}_{B}$ are found at Co and Pd sites, respectively, where the orbital moment of Co, 0.40(2) ${\textbackslashensuremath{\textbackslashmu}}_{B}$, is high, while that of Pd is negligible. The effective magnetic anisotropy is the largest in the capping metal series (Pd, Pt, W, Cu, Ag, Au), which is attributed to the interparticle interaction between de nanoparticles, in addition to the intraparticle anisotropy arising from hybridization between the $3d\textbackslashchar21{}4d$ bands associated to the Co and Pd chemical arrangement in a $\textbackslashmathrm{L}{1}_{0}$ structure type.

  • L. - G. Vivas, A. I. Figueroa, F. Bartolomé, J. Rubin, L. - M. Garcia, C. Deranlot, F. Petroff, L. Ruiz, J. - M. Gonzalez-Calbet, N. - B. Brookes, F. Wilhelm, A. Rogalev, J. Bartolomé, dans Journal of Magnetism and Magnetic Materials (2016)vol. 400p. 248–252.

  • D. Vodenicarevic, N. Locatelli, J. Grollier, D. Querlioz, (IEEE, 2016)p. 2015–2022.
    Résumé : Coupled oscillator-based networks are an attractive approach for implementing hardware neural networks based on emerging nanotechnologies. However, the readout of the state of a coupled oscillator network is a difficult challenge in hardware implementations, as it necessitates complex signal processing to evaluate the degree of synchronization between oscillators, possibly more complicated than the coupled oscillator network itself. In this work, we focus on a coupled oscillator network particularly adapted to emerging technologies, and evaluate two schemes for reading synchronization patterns that can be readily implemented with basic CMOS circuits. Through simulation of a simple generic coupled oscillator network, we compare the operation of these readout techniques with a previously proposed full statistics evaluation scheme. Our approaches provide results nearly identical to the mathematical method, but also show better resilience to moderate noise, which is a major concern for hardware implementations. These results open the door to widespread realization of hardware coupled oscillator-based neural systems.

  • H. Yu, O. d’Allivy Kelly, V. Cros, R. Bernard, P. Bortolotti, A. Anane, F. Brandl, F. Heimbach, D. Grundler, Approaching soft X-ray wavelengths in nanomagnet-based microwave technology. Nature Communications. 7 (2016), doi:10.1038/ncomms11255.
    Résumé : Seven decades after the discovery of collective spin excitations in microwave-irradiated ferromagnets, there has been a rebirth of magnonics. However, magnetic nanodevices will enable smart GHz-to-THz devices at low power consumption only, if such spin waves (magnons) are generated and manipulated on the sub-100 nm scale. Here we show how magnons with a wavelength of a few 10 nm are exploited by combining the functionality of insulating yttrium iron garnet and nanodisks from different ferromagnets. We demonstrate magnonic devices at wavelengths of 88 nm written/read by conventional coplanar waveguides. Our microwave-to-magnon transducers are reconfigurable and thereby provide additional functionalities. The results pave the way for a multi-functional GHz technology with unprecedented miniaturization exploiting nanoscale wavelengths that are otherwise relevant for soft X-rays. Nanomagnonics integrated with broadband microwave circuitry offer applications that are wide ranging, from nanoscale microwave components to nonlinear data processing, image reconstruction and wave-based logic.
    Mots-clés : Magnonics.

  • S. Zhang, A. Fert, Conversion between spin and charge currents with topological insulators. Phys. Rev. B. 94, 184423 (2016).
    Résumé : Injection of a spin current into the surface or interface states of a topological insulator (TI) induces a charge current (inverse Edelstein effect or IEE) and, inversely, a charge current flowing at the surface or interface states of a TI generates a nonzero spin density (Edelstein Effect or EE) from which a spin current can be ejected into an adjacent layer. The parameters characterizing the efficiency of these conversions between spin and charge currents have been derived in recent experiments. By using a spinor distribution function for a momentum-spin locked TI, we determine a number of spin transport properties of TI-based heterostructure and find that the spin to charge conversion in IEE is controlled by the relaxation of an out-of equilibrium distribution in the TI states while the charge to spin conversion in EE depends on the electron transmission rate at the interface of the TI.
    Mots-clés : Spinorbitronics.


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