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Articles

2018


  • L. Soumah, N. Beaulieu, L. Qassym, C. Carrétéro, E. Jacquet, R. Lebourgeois, J. Ben Youssef, P. Bortolotti, V. Cros, A. Anane, Ultra-low damping insulating magnetic thin films get perpendicular. Nature Communications. 9, 3355 (2018).
    Résumé : A magnetic material combining both low losses and strong perpendicular magnetic anisotropy (PMA) was so far missing in the field of magnon-spintronics. The authors here report on Bismuth doped YIG nanometer thick films showing both PMA and low magnetic losses for ultra-thin PMA materials.

  • B. Tao, P. Barate, X. Devaux, P. Renucci, J. Frougier, A. Djeffal, S. Liang, B. Xu, M. Hehn, H. Jaffrès, J. - M. George, X. Marie, S. Mangin, X. Han, Z. Wang, Y. Lu, Atomic-scale understanding of high thermal stability of the Mo/CoFeB/MgO spin injector for spin-injection in remanence. Nanoscale. 10, 10213-10220 (2018).
    Résumé : Remanent spin injection into a spin light emitting diode (spin-LED) at zero magnetic field is a prerequisite for future application of spin optoelectronics. Here, we demonstrate the remanent spin injection into GaAs based LEDs with a thermally stable Mo/CoFeB/MgO spin injector. A systematic study of magnetic properties, polarization-resolved electroluminescence (EL) and atomic-scale interfacial structures has been performed in comparison with the Ta/CoFeB/MgO spin injector. The perpendicular magnetic anisotropy (PMA) of the Mo/CoFeB/MgO injector shows more advanced thermal stability than that of the Ta/CoFeB/MgO injector and robust PMA can be maintained up to 400 °C annealing. The remanent circular polarization (PC) of EL from the Mo capped spin-LED reaches a maximum value of 10% after 300 °C annealing, and even remains at 4% after 400 °C annealing. In contrast, the Ta capped spin-LED almost completely loses the remanent PC under 400 °C annealing. Combined advanced electron microscopy and spectroscopy studies reveal that a large amount of Ta diffuses into the MgO tunneling barrier through the CoFeB layer after 400 °C annealing. However, the diffusion of Mo into CoFeB is limited and never reaches the MgO barrier. These findings afford a comprehensive perspective to use the highly thermally stable Mo/CoFeB/MgO spin injector for efficient electrical spin injection in remanence.

  • N. Thiery, A. Draveny, V. V. Naletov, L. Vila, J. - P. Attané, C. Beigné, G. de Loubens, M. Viret, N. Beaulieu, J. B. Youssef, V. E. Demidov, S. O. Demokritov, A. N. Slavin, V. S. Tiberkevich, A. Anane, P. Bortolotti, V. Cros, O. Klein, Nonlinear spin conductance of yttrium iron garnet thin films driven by large spin-orbit torque. Physical Review B. 97, 060409 (2018).
    Résumé : We report high power spin transfer studies in open magnetic geometries by measuring the spin conductance between two nearby Pt wires deposited on top of an epitaxial yttrium iron garnet thin film. Spin transport is provided by propagating spin waves that are generated and detected by direct and inverse spin Hall effects. We observe a crossover in spin conductance from a linear transport dominated by exchange magnons (low current regime) to a nonlinear transport dominated by magnetostatic magnons (high current regime). The latter are low-damping magnetic excitations, located near the spectral bottom of the magnon manifold, with a sensitivity to the applied magnetic field. This picture is supported by microfocus Brillouin light-scattering spectroscopy. Our findings could be used for the development of controllable spin conductors by variation of relatively weak magnetic fields.

  • N. Thiery, V. V. Naletov, L. Vila, A. Marty, A. Brenac, J. - F. Jacquot, G. de Loubens, M. Viret, A. Anane, V. Cros, J. B. Youssef, N. Beaulieu, V. E. Demidov, B. Divinskiy, S. O. Demokritov, O. Klein, Electrical properties of epitaxial yttrium iron garnet ultrathin films at high temperatures. Physical Review B. 97, 064422 (2018).
    Résumé : We report a study on the electrical properties of 19-nm-thick yttrium iron garnet (YIG) films grown by liquid phase epitaxy on gadolinium gallium garnet single crystal. The electrical conductivity and Hall coefficient are measured in the high-temperature range [300,400] K using a Van der Pauw four-point probe technique. We find that the electrical resistivity decreases exponentially with increasing temperature following an activated behavior corresponding to a band gap of ${E}_{g}\ensuremath{\approx}2$ eV. It drops to values about $5\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{4pt}{0ex}}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at $T=400$ K, thus indicating that epitaxial YIG ultrathin films behave as large gap semiconductors. We also infer the Hall mobility, which is found to be positive ($p$ type) at 5 ${\mathrm{cm}}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{V}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{sec}}^{\ensuremath{-}1}$ and almost independent of temperature. We discuss the consequence for nonlocal spin transport experiments performed on YIG at room temperature and demonstrate the existence of electrical offset voltages to be disentangled from pure spin effects.

  • S. Tsunegi, T. Taniguchi, R. Lebrun, K. Yakushiji, V. Cros, J. Grollier, A. Fukushima, S. Yuasa, H. Kubota, Scaling up electrically synchronized spin torque oscillator networks. Scientific Reports. 8, 13475 (2018).
    Résumé : Synchronized nonlinear oscillators networks are at the core of numerous families of applications including phased array wave generators and neuromorphic pattern matching systems. In these devices, stable synchronization between large numbers of nanoscale oscillators is a key issue that remains to be demonstrated. Here, we show experimentally that synchronized spin-torque oscillator networks can be scaled up. By increasing the number of synchronized oscillators up to eight, we obtain that the emitted power and the quality factor increase linearly with the number of oscillators. Even more importantly, we demonstrate that the stability of synchronization in time exceeds 1.6 milliseconds corresponding to 105 periods of oscillation. Our study demonstrates that spin-torque oscillators are suitable for applications based on synchronized networks of oscillators.


  • S. Delprat, M. Galbiati, S. Tatay, B. Quinard, C. Barraud, P. Seneor, R. Mattana, F. Petroff, dans Spin in organics, Z. V. Vardeny, Éd. (WORLD SCIENTIFIC, 2018; http://www.worldscientific.com/doi/abs/10.1142/9789813230170_0002)vol. 1p. 63-92.

  • J. Varignon, L. Vila, A. Barthélémy, M. Bibes, A new spin for oxide interfaces. Nature Physics. 14, 322 (2018).
    Résumé : The variety of emergent phenomena occurring at oxide interfaces has made these systems the focus of intense study in recent years. We argue that spin–orbit effects in oxide interfaces provide a versatile handle to generate, control and convert spin currents, with a view towards low-power spintronics.

  • D. - C. Vaz, A. Barthélémy, M. Bibes, Oxide spin-orbitronics: New routes towards low-power electrical control of magnetization in oxide heterostructures. Japanese Journal of Applied Physics. 57, 0902A4 (2018).

  • D. - C. Vaz, E. Lesne, A. Sander, H. Naganuma, E. Jacquet, J. Santamaria, A. Barthélémy, M. Bibes, Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures. JoVE (Journal of Visualized Experiments), e56951-e56951 (2018).
    Résumé : We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in...

  • D. Vodenicarevic, N. Locatelli, J. Grollier, D. Querlioz, Nano-oscillator-based classification with a machine learning-compatible architecture. Journal of Applied Physics. 124, 152117 (2018).
    Résumé : Pattern classification architectures leveraging the physics of coupled nano-oscillators have been demonstrated as promising alternative computing approaches but lack effective learning algorithms. In this work, we propose a nano-oscillator based classification architecture where the natural frequencies of the oscillators are learned linear combinations of the inputs and define an offline learning algorithm based on gradient back-propagation. Our results show significant classification improvements over a related approach with online learning. We also compare our architecture with a standard neural network on a simple machine learning case, which suggests that our approach is economical in terms of the number of adjustable parameters. The introduced architecture is also compatible with existing nano-technologies: the architecture does not require changes in the coupling between nano-oscillators, and it is tolerant to oscillator phase noise.



  • D. Vodenicarevic, N. Locatelli, A. Mizrahi, T. Hirtzlin, J. S. Friedman, J. Grollier, D. Querlioz, dans 2018 IEEE International Symposium on Circuits and Systems (ISCAS) (IEEE, 2018; https://ieeexplore.ieee.org/document/8351771/)p. 1-4.

  • M. Wang, W. Cai, K. Cao, J. Zhou, J. Wrona, S. Peng, H. Yang, J. Wei, W. Kang, Y. Zhang, J. Langer, B. Ocker, A. Fert, W. Zhao, Current-induced magnetization switching in atom-thick tungsten engineered perpendicular magnetic tunnel junctions with large tunnel magnetoresistance. Nature Communications. 9, 671 (2018).
    Résumé : <p>Perpendicular magnetic tunnel junctions with large tunnel magnetoresistance and low junction resistance are promising for the magnetic random access memories. Here the authors achieve the spin-transfer-torque switching in perpendicular magnetic tunnel junctions with 249% tunnel magnetoresistance and low resistance-area product.</p>

  • M. Wang, W. Cai, D. Zhu, Z. Wang, J. Kan, Z. Zhao, K. Cao, Z. Wang, Y. Zhang, T. Zhang, C. Park, J. P. Wang, A. Fert, W. Zhao, Field-free switching of a perpendicular magnetic tunnel junction through the interplay of spin–orbit and spin-transfer torques. Nature Electronics. 1, 582 (2018).
    Résumé : The interplay between spin–orbit and spin-transfer torques can be used to develop a low-power route to magnetization switching of perpendicular magnetic tunnel junctions without an external magnetic field.

  • S. Wittrock, S. Tsunegi, K. Yakushiji, A. Fukushima, H. Kubota, P. Bortolotti, U. Ebels, S. Yuasa, G. Cibiel, E. Rubiola, V. Cros, dans 2018 IEEE International Magnetics Conference (INTERMAG) (2018)p. 1-1.
    Résumé : With their very rich static and dynamical properties, magnetic vortex dynamics excited by a spin polarized current represent not only a model system to study the physical mechanisms of spin transfer phenomena but could also give birth to a new generation of multi-functional microwave spintronic devices [1]. The key property of spin-torque nano-oscillators (STNOs) is their high nonlinearity [2] which gives rise to manifold phenomena such as injection locking to an external rf signal [3], [4] or synchronization of multiple STNOs [5]-[7]. On the other hand, their large nonlinearity causes the oscillator's very poor spectral coherence and leads to a coupling between amplitude and phase noise [8]. While the noise distribution for offset frequencies far from the carrier frequency is reasonably well understood [8] and described by the general nonlinear autooscillator theory [2], low frequency noise remains under investigation as it limits the frequency stability of the oscillator. Extensively studied in GMR and TMR sensors [9]-[12], this work addresses the low frequency noise of a TMR-based spin-torque vortex oscillator in the regime of large amplitude steady oscillations. In detail, we present a precise experimental study of the TMR-based spin-torque vortex oscillator's low frequency noise, which remains poorly investigated for STNOs in the regime of large amplitude steady oscillations, as we propose here. The measured STNO's magnetic tunnel junction layer stack of PtMn/CoFe/Ru/ CoFeB/CoFe/MgO/FeB/MgO/Ta/Ru was realized by sputter deposition and nanopillar devices of 100-600nm were nanofabricated. The devices have a free running frequency from 100 MHz to 1 GHz depending on the diameter and the applied field value, with an integrated power of up to a few μW and a linewidth of typically 100 kHz. In complement to the experimental measurements, we have also developed a phenomenological theory aiming to investigate the low frequency flicker noise in these vortex-STNOs. Starting from the corresponding nonlinear Langevin equations and a colored noise distribution, we find additional noise contributions to the white noise power spectral densities. This also gives an additional coupling term between amplitude and phase noise. Noteworthy, we find that this prediction agrees well to our experimental results of the gyrotropic mode's low frequency noise (Fig. (a)). Furthermore, we analyze the noise dependence on the control parameter (the operating dc current) and the oscillator's active magnetic volume, reflected by the Hooge-formula for TMR sensors [12] and the oscillator's nonlinearity itself (Fig. (b)). S.W. acknowledges financial support from Labex FIRST-TF. EU FP7 grant (MOSAIC No. ICT-FP7-8.317950) is also acknowledged for support.

  • H. Yang, O. Boulle, V. Cros, A. Fert, M. Chshiev, Controlling Dzyaloshinskii-Moriya Interaction via Chirality Dependent Atomic-Layer Stacking, Insulator Capping and Electric Field. Scientific Reports. 8, 12356 (2018).
    Résumé : Using first-principles calculations, we demonstrate several approaches to control Dzyaloshinskii-Moriya Interaction (DMI) in ultrathin films with perpendicular magnetic anisotropy. First, we find that DMI is significantly enhanced when the ferromagnetic (FM) layer is sandwiched between nonmagnetic (NM) layers inducing additive DMI in NM1/FM/NM2 structures. For instance, when two NM layers are chosen to induce DMI of opposite chirality in Co, e.g. NM1 representing Au, Ir, Al or Pb, and NM2 being Pt, the resulting DMI in NM1/Co/Pt trilayers is enhanced compared to Co/Pt bilayers. Moreover, DMI can be significantly enhanced further in case of using FM layer comprising Fe and Co layers. Namely, it is found that the DMI in Ir/Fe/Co/Pt structure can be enhanced by 80% compared to that of Co/Pt bilayers reaching a very large DMI amplitude of 5.59 meV/atom. Our second approach for enhancing DMI is to use oxide capping layer. We show that DMI is enhanced by 60% in Oxide/Co/Pt structures compared to Co/Pt bilayers. Moreover, we unveiled the DMI mechanism at Oxide/Co interface due to Rashba effect, which is different to Fert-Levy DMI at FM/NM interfaces. Finally, we demonstrate that DMI amplitude can be modulated using an electric field with an efficiency factor comparable to that of the electric field control of perpendicular magnetic anisotropy in transition metal/oxide interfaces. These approaches of DMI controlling pave the way for skyrmion and domain wall motion-based spintronic applications.

  • H. Yang, G. Chen, A. A. C. Cotta, A. T. N’Diaye, S. A. Nikolaev, E. A. Soares, W. A. A. Macedo, K. Liu, A. K. Schmid, A. Fert, M. Chshiev, Significant Dzyaloshinskii–Moriya interaction at graphene–ferromagnet interfaces due to the Rashba effect. Nature Materials. 17, 605 (2018).
    Résumé : Authors investigate graphene/cobalt and graphene/nickel interfaces, and observe a non-zero Dzyaloshinskii–Moriya interaction that they attribute to the Rashba effect; calculations suggest the effect can be enhanced in van der Waals heterostructures.


  • J. Zang, V. Cros, A. Hoffmann, Éd., dans Topology in Magnetism, J. Zang, V. Cros, A. Hoffmann, Éd. (Springer International Publishing, Cham, 2018; http://link.springer.com/10.1007/978-3-319-97334-0)vol. 192 of Springer Series in Solid-State Sciencesp. .

  • B. Zimmermann, W. Legrand, D. Maccariello, N. Reyren, V. Cros, S. Blügel, A. Fert, Dzyaloshinskii-Moriya interaction at disordered interfaces from ab initio theory: Robustness against intermixing and tunability through dusting. Applied Physics Letters. 113, 232403 (2018).
    Résumé : The Dzyaloshinskii-Moriya interaction (DMI), which is essential for the stabilization of topologically non-trivial chiral magnetic textures such as skyrmions, is particularly strong in heterostructures of ultra-thin magnetic materials and heavy elements. We explore by density-functional theory calculations the possibility to modify the magnetic properties at Co/Pt interfaces with chemical disorder. In these systems, we find a particular robustness of the DMI against intermixing. Upon dusting the interface with a third element (all 4d transition metals and B, Cu, Au, and Bi), a strong reduction of the DMI is predicted. This opens up possibilities to tune the DMI through the degrees of intermixing and dusting.

2017


  • F. Abreu Araujo, L. Piraux, Spin-Transfer-Torque Driven Vortex Dynamics in Electrodeposited Nanowire Spin-Valves. SPIN. 07, 1740007 (2017).

  • A. Agbelele, D. Sando, C. Toulouse, C. Paillard, R. - D. Johnson, R. Rüffer, A. - F. Popkov, C. Carrétéro, P. Rovillain, J. - M. Le Breton, B. Dkhil, M. Cazayous, Y. Gallais, M. - A. Méasson, A. Sacuto, P. Manuel, A. - K. Zvezdin, A. Barthélémy, J. Juraszek, M. Bibes, Strain and Magnetic Field Induced Spin‐Structure Transitions in Multiferroic BiFeO3. Advanced Materials. 29, 1602327 (2017).
    Résumé : The magnetic‐field‐dependent spin ordering of strained BiFeO3 films is determined using nuclear resonant scattering and Raman spectroscopy. The critical field required to destroy the cycloidal modulation...

  • P. Barate, S. - H. Liang, T. T. Zhang, J. Frougier, B. Xu, P. Schieffer, M. Vidal, H. Jaffrès, B. Lépine, S. Tricot, F. Cadiz, T. Garandel, J. - M. George, T. Amand, X. Devaux, M. Hehn, S. Mangin, B. Tao, X. F. Han, Z. - G. Wang, X. Marie, Y. Lu, P. Renucci, Bias Dependence of the Electrical Spin Injection into GaAs from Co-Fe-B/MgO Injectors with Different MgO Growth Processes. Phys. Rev. Applied. 8, 054027 (2017).
    Résumé : In view of future spintronic and spin-optronic devices, such as spin light-emitting diodes and spin lasers, it is important to understand the dependence of electrical spin injection on bias in bipolar devices based on GaAs. Focusing on the efficiency of Co-Fe-B/MgO spin injectors, the authors investigate the influence of the MgO growth process on this bias dependence, using MgO tunnel barriers fabricated by different techniques. The bias dependence of spin injection efficiency, and the compromise between high intensity and high circular polarization of electroluminescence, depend strongly on the characteristics of the interface, which can be engineered by the growth process.
    Mots-clés : Semiconductors and Spintronics.

  • S. Boyn, J. Grollier, G. Lecerf, B. Xu, N. Locatelli, S. Fusil, S. Girod, C. Carrétéro, K. Garcia, S. Xavier, J. Tomas, L. Bellaiche, M. Bibes, A. Barthélémy, S. Saïghi, V. Garcia, Learning through ferroelectric domain dynamics in solid-state synapses. Nature Communications. 8, 14736 (2017).
    Résumé : Accurate modelling of memristor dynamics is essential for the development of autonomous learning in artificial neural networks. Through a combined theoretical and experimental study of the polarization switching process in ferroelectric memristors, Boynet al.

  • L. Bégon-Lours, V. Rouco, A. Sander, J. Trastoy, R. Bernard, E. Jacquet, K. Bouzehouane, S. Fusil, V. Garcia, A. Barthélémy, M. Bibes, J. Santamaría, J. - E. Villegas, High-Temperature-Superconducting Weak Link Defined by the Ferroelectric Field Effect. Phys. Rev. Applied. 7, 064015 (2017).
    Résumé : Josephson junctions are the cornerstones of numerous applications, and fabricating them from high-temperature superconductors has received much attention in recent years. The authors exploit the local field-effect doping of a cuprate superconducting film by a ferroelectric overlayer, where domain structure is “written” at will using an atomic force microscope. The key advantage of this approach is that it creates devices that are planar and can be reconfigured by “rewriting” the ferroelectric.

  • N. - B. Caballero, I. - F. Aguirre, L. - J. Albornoz, A. - B. Kolton, J. - C. Rojas-Sanchez, S. Collin, J. - M. George, R. - D. Pardo, V. Jeudy, S. Bustingorry, J. Curiale, Excess velocity of magnetic domain walls close to the depinning field. Phys. Rev. B. 96, 224422 (2017).
    Résumé : Magnetic field driven domain wall velocities in [Co/Ni] based multilayers thin films have been measured using polar magneto-optic Kerr effect microscopy. The low field results are shown to be consistent with the universal creep regime of domain wall motion, characterized by a stretched exponential growth of the velocity with the inverse of the applied field. Approaching the depinning field from below results in an unexpected excess velocity with respect to the creep law. We analyze these results using scaling theory to show that this speeding up of domain wall motion can be interpreted as due to the increase of the size of the deterministic relaxation close to the depinning transition. We propose a phenomenological model to accurately fit the observed excess velocity and to obtain characteristic values for the depinning field ${H}_{d}$, the depinning temperature ${T}_{d}$, and the characteristic velocity scale ${v}_{0}$ for each sample.

  • M. Cabero, K. Nagy, F. Gallego, A. Sander, M. Rio, F. A. Cuellar, J. Tornos, D. Hernandez-Martin, N. M. Nemes, F. Mompean, M. Garcia-Hernandez, A. Rivera-Calzada, Z. Sefrioui, N. Reyren, T. Feher, M. Varela, C. Leon, J. Santamaria, Modified magnetic anisotropy at LaCoO3/La0.7Sr0.3MnO3 interfaces. APL Materials. 5, 096104 (2017).
    Résumé : Controlling magnetic anisotropy is an important objective towards engineering novel magnetic device concepts in oxide electronics. In thin film manganites, magnetic anisotropy is weak and it is primarily determined by the substrate, through induced structural distortions resulting from epitaxial mismatch strain. On the other hand, in cobaltites, with a stronger spin orbit interaction, magnetic anisotropy is typically much stronger. In this paper, we show that interfacing La0.7Sr0.3MnO3 (LSMO) with an ultrathin LaCoO3 (LCO) layer drastically modifies the magnetic anisotropy of the manganite, making it independent of the substrate and closer to the magnetic isotropy characterizing its rhombohedral structure. Ferromagnetic resonance measurements evidence a tendency of manganite magnetic moments to point out-of-plane suggesting non collinear magnetic interactions at the interface. These results may be of interest for the design of oxide interfaces with tailored magnetic structures for new oxide devices.


  • F. Cadiz, D. Lagarde, S. H. Liang, B. Tao, J. Frougier, Y. Lu, B. Xu, H. Jaffrès, Z. Wang, X. Han, M. Hehn, S. Mangin, J. - M. George, H. Carrere, T. Amand, X. Marie, B. Urbaszek, P. Renucci, dans Spintronics X (International Society for Optics and Photonics, 2017; https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10357/103571D/Very-efficient-electrical-spin-injection--detection-into-quantum-dots/10.1117/12.2273746.short)vol. 10357p. 103571D.
    Résumé : In this paper, we demonstrate a very efficient electrical spin injection into an ensemble of InAs/InGaAs quantum dots at zero magnetic field. The circular polarization of the electroluminescence coming from the dots, which are embedded into a GaAs-based Spin Light Emitting diode reaches a value as large as 20% at low temperature. In this device, no external magnetic field is required in order to inject or read spin polarization thanks to the use of an ultrathin CoFeB electrode (1.1 nm), as well as p-doped quantum dots (with one hole per dot in average) as an optical probe. The electroluminescence circular polarization of the dots follows the hysteresis loop of the magnetic layer and decreases as a function of bias for large voltages. In a reverse way, we have also investigated the possibility to use such a device as a photodetector presenting a photon helicity-dependent photocurrent. We observe a weak asymmetry of photocurrent under right and left polarized light that follows the hysteresis cycle of the magnetic layer, and the effect decreases for increasing temperatures and can be controlled by the bias.

  • S. Cervera, M. Trassinelli, M. Marangolo, C. Carrétéro, V. Garcia, S. Hidki, E. Jacquet, E. Lamour, A. Lévy, S. Macé, C. Prigent, J. - P. Rozet, S. Steydli, D. Vernhet, Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation. Phys. Rev. Materials. 1, 065402 (2017).
    Résumé : Magnetic refrigeration based on the magnetocaloric effect at room temperature is one of the most attractive alternatives to the current gas compression/expansion method routinely employed. Nevertheless, in giant magnetocaloric materials, optimal refrigeration is restricted to the narrow temperature window of the phase transition (${T}_{c}$). In this work, we present the possibility of varying this transition temperature in the same giant magnetocaloric material by ion irradiation. We demonstrate that the transition temperature of iron rhodium thin films can be tuned by the bombardment of ions of ${\textbackslashmathrm{Ne}}ˆ{5+}$ with varying fluences up to ${10}ˆ{14}$ ions ${\textbackslashmathrm{cm}}ˆ{\textbackslashensuremath{-}2}$, leading to optimal refrigeration over a large 270\textbackslashchar21{}380 K temperature window. The ${T}_{c}$ modification is found to be due to the ion-induced disorder and to the density of new pointlike defects. The variation of the phase transition temperature with the number of incident ions opens new perspectives in the conception of devices using giant magnetocaloric materials.

  • J. - Y. Chauleau, E. Haltz, C. Carrétéro, S. Fusil, M. Viret, Multi-stimuli manipulation of antiferromagnetic domains assessed by second-harmonic imaging. Nature Materials. 16, 803–807 (2017).
    Résumé : Sub-coercive electric fields and sub-picosecond light pulses are shown to enable low-power manipulation of antiferromagnetic domains in the multiferroic BiFeO3.

  • M. Collet, O. Gladii, M. Evelt, V. Bessonov, L. Soumah, P. Bortolotti, S. O. Demokritov, Y. Henry, V. Cros, M. Bailleul, V. E. Demidov, A. Anane, Spin-wave propagation in ultra-thin YIG based waveguides. Applied Physics Letters. 110, 092408 (2017).
    Résumé : Spin-wave propagation in microfabricated 20 nm thick, 2.5 μm wide Yttrium Iron Garnet (YIG) waveguides is studied using propagating spin-wave spectroscopy (PSWS) and phase resolved micro-focused Brillouin Light Scattering (μ-BLS) spectroscopy. We demonstrate that spin-wave propagation in 50 parallel waveguides is robust against microfabrication induced imperfections and extract spin-wave propagation parameters for the Damon-Eshbach configuration in a wide range of excitation frequencies. As expected from its low damping, YIG allows for the propagation of spin waves over long distances; the attenuation lengths is 25 μm at μ 0 H = 45 mT. Moreover, direct mapping of spin waves by μ-BLS allows us to reconstruct the spin-wave dispersion relation and to confirm the multi-mode propagation in the waveguides, glimpsed by propagating spin-wave spectroscopy.
    Mots-clés : Magnonics.

  • M. Collet, R. Mattana, J. - B. Moussy, K. Ollefs, S. Collin, C. Deranlot, A. Anane, V. Cros, F. Petroff, F. Wilhelm, A. Rogalev, Investigating magnetic proximity effects at ferrite/Pt interfaces. Applied Physics Letters. 111, 202401 (2017).
    Résumé : Spintronic devices based on pure spin currents have drawn a lot of attention during the last few years for low energy device design. One approach to generate pure spin currents is to combine a metallic or insulating ferromagnetic layer with a non-magnetic metallic layer with a large spin-orbit coupling. A recent controversy has arisen in the possible role of magnetic proximity effects at ferromagnetic/non-magnetic interfaces, which can hamper the understanding of pure spin current generation mechanisms. While magnetic proximity effects have been frequently observed at ferromagnetic metal/non-magnetic interfaces, there are only a few studies on ferromagnetic insulator/non-magnetic interfaces. Regarding the use of ferromagnetic insulators, the focus has been mainly on yttrium iron garnet (YIG). However, investigation of induced magnetic moments at YIG/Pt interfaces has engendered contradictory results. Here, we propose to study insulating ferrites for which electronic and magnetic properties can be modulate...

  • M. Collet, L. Soumah, P. Bortolotti, M. Munoz, V. Cros, A. Anane, dans AIP Advances (2017)vol. 7p. 055924.
    Résumé : We have investigated the spin Seebeck effect (SSE) generated by current induced-heating in ultra-thin yttrium iron garnet film (20 nm) covered by an 8 nm thick Pt layer. By passing current in the Pt layer, an out-of-plane temperature gradient is established that, in turn, generates an out-of-equilibrium magnons population. The resulting pure spin current is detected using the inverse spin Hall effect (ISHE) measured in the Pt electrode. A lock-in detection scheme is used to separate the SSE signal from other magneto-galvanic effect. Indeed, the SSE signal is obtained as the second harmonic voltage response, while spin Hall magnetoresistance (SMR) is measured as the first harmonic response to the ac excitation current. Interestingly, the amplitude of the SSE in such thin YIG film is comparable to what has been reported for much thicker films.
    Mots-clés : Magnonics.

  • O. Copie, J. Varignon, H. Rotella, G. Steciuk, P. Boullay, A. Pautrat, A. David, B. Mercey, P. Ghosez, W. Prellier, Chemical Strain Engineering of Magnetism in Oxide Thin Films. Advanced Materials. 29 (2017), doi:10.1002/adma.201604112.

  • A. Cornia, P. Seneor, Spintronics: The molecular way. Nature Materials. 16, 505–506 (2017).
    Résumé : Molecular spintronics is an interdisciplinary field at the interface between organic spintronics, molecular magnetism, molecular electronics and quantum computing, which is advancing fast and promises large technological payoffs.

  • V. E. Demidov, S. Urazhdin, G. de Loubens, O. Klein, V. Cros, A. Anane, S. O. Demokritov, Magnetization oscillations and waves driven by pure spin currents. Physics Reports. 673, 1–31 (2017).

  • S. Deng, H. Butt, K. Jiang, B. Dlubak, P. - R. Kidambi, P. Seneor, S. Xavier, A. - K. Yetisen, Graphene nanoribbon based plasmonic Fresnel zone plate lenses. RSC Adv. 7, 16594–16601 (2017).
    Résumé : A graphene-based metamaterial lens is theoretically proposed by combining plasmonic nanoribbons with Fresnel Zone Plate (FZP) architecture to realize wavelength-selective and tunable lensing. The plasmonic FZP lens shows higher focal intensity and efficiency compared to conventional FZP. As compared with normal graphene FZP, the lensing effect of the plasmonic FZP can be enhanced by 83 times. When compared with Au thin film based FZP lenses, the graphene plasmonic lenses can achieve comparable lensing effects, but with a thinner geometry and with an additional advantage of being wavelength selective and tuneable. The analyses of selectivity and tunability of the plasmonic lens show that the plasmonic lens functions as a filter with broadband incident light or as a switch which can be turned on and off via changing the Fermi levels. The diffraction between neighboring graphene nanoribbons and the effect of the substrate on the lensing effect is also discussed. The plasmonic effect of the nanoribbons only contributes to the focal intensity without affecting the diffraction properties of Fresnel zone plate lenses such as focal lengths. This plasmonic FZP lens is an ideal combination of near and far field optics. However, the complex interaction of diffractions within and between the FZP rings could lead to a significant change of the lensing effect, which opens the possibility of creating innovative graphene metamaterial devices. The findings in this work can be used for developing wavelength-selective electro-optical applications operating in the infrared and terahertz ranges.

  • O. d’Allivy Kelly, M. Collet, E. Jacquet, R. Mattana, F. Petroff, P. Bortolotti, V. Cros, A. Anane, F. Wilhelm, K. Ollefs, A. Rogalev, Magnetic Proximity Effect Free Spin Hall Magnetoresistance in YIG/Pd. SPIN. 07, 1740005 (2017).

  • A. Fert, N. Reyren, V. Cros, Magnetic skyrmions: advances in physics and potential applications. Nature Reviews Materials. 2, 17031 (2017).
    Résumé : Magnetic skyrmions are topologically protected spin whirls that hold promise for applications because they can be controllably moved, created and annihilated. In this Review, the underlying physics of the stabilization of skyrmions at room temperature and their prospectives

  • T. Fördös, H. Jaffrès, K. Postava, M. - S. Seghilani, A. Garnache, J. Pištora, H. - J. Drouhin, Eigenmodes of spin vertical-cavity surface-emitting lasers with local linear birefringence and gain dichroism. Phys. Rev. A. 96, 043828 (2017).
    Résumé : We present a general method for the modeling of semiconductor lasers such as a vertical-cavity surface-emitting laser and a vertical-external-cavity surface-emitting laser containing multiple quantum wells and involving anisotropies that may reveal (i) a local linear birefringence due to the strain field at the surface or (ii) a birefringence in quantum wells due to phase amplitude coupling originating from the reduction of the biaxial ${D}_{2d}$ symmetry group to the ${C}_{2v}$ symmetry group at the III-V ternary semiconductor interfaces. From a numerical point of view, a scattering S-matrix recursive method is implemented using a gain or amplification tensor derived analytically from the Maxwell-Bloch equations. It enables one to model the properties of the emission (threshold, polarization, and mode splitting) from the laser with multiple quantum well active zones by searching for the resonant eigenmodes of the cavity. The method is demonstrated on real laser structures and is presently used for the extraction of optical permittivity tensors of surface strain and quantum wells in agreement with experiments. The method can be generalized to find the laser eigenmodes in the most general case of circular polarized pumps (unbalance between the spin-up and spin-down channels) and/or dichroism allowing an elliptically polarized light emission as recently demonstrated experimentally when the linear birefringence is almost compensated [Joly et al., Opt. Lett. 42, 651 (2017)].
    Mots-clés : Semiconductors and Spintronics.

  • R. Galceran, E. Gaufres, A. Loiseau, M. Piquemal-Banci, F. Godel, A. Vecchiola, O. Bezencenet, M. - B. Martin, B. Servet, F. Petroff, B. Dlubak, P. Seneor, Stabilizing ultra-thin black phosphorus with in-situ-grown 1 nm-Al2O3 barrier. Applied Physics Letters. 111, 243101 (2017).
    Résumé : Exfoliated black phosphorus is a 2D semiconductor with promising properties for electronics, spintronics, and optoelectronics. Nevertheless, its rapid degradation in air renders its integration and use in devices particularly challenging—even more so for smaller thicknesses for which the degradation rate is tremendously enhanced. In order to effectively protect the thinnest flakes, we present here an approach based on an in-situ dielectric capping to avoid all contact with air. Optical microscopy, Raman spectroscopy, and atomic force microscopy studies confirm that 1 nm of Al2O3 efficiently passivates exfoliated black phosphorus (below 5 layers) on Si/SiO2 substrates. Such an ultrathin and transparent passivation layer can act as a tunnel barrier allowing for black phosphorus devices processing without passivation layer removal.

  • M. Geahel, I. Jouanny, D. Gorse-Pomonti, M. Poirier-Quinot, J. Briatico, C. - J. van der Beek, Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films. Condensed Matter. 2, 27 (2017).
    Résumé : We have investigated the effect of different types of disorder on the propagation, roughness, and scaling properties of magnetic flux fronts in a type II superconductor. A progression from the usual (Kardar–Parisi–Zhang-type) scaling to multiscaling is observed as the disorder strength is increased. A hierarchy of disorder strengths is established for YBa 2 Cu 3 O 7 − δ thin films. The results cast light on the physical origin of the roughening of flux fronts, and they are of interest for the design and elimination of flux noise in microscopic superconducting thin-film devices.
    Mots-clés : Supra.

  • J. Gonzalez Sutter, L. Neñer, H. Navarro, G. Leyva, S. Fusil, K. Bouzehouane, N. Haberkorn, M. Sirena, Oxygen influence in the magnetic and the transport properties of ferroelectric/ferromagnetic heterostructures. Thin Solid Films. 639, 42 (2017).
    Résumé : Oxygen vacancies in oxides nanostructures are the origin of many intriguing phenomena. We have studied the influence of the oxygen pressure in the tunneling properties of a ferroelectric barrier, Ba0.25Sr0.75TiO3 (BSTO), grown over a ferromagnetic electrode. A phenomenological model description was used to obtain critical information about the structure and electrical properties of ultra-thin BSTO layers using conductive atomic force microscopy. The BSTO layers present good insulation properties. Reducing the oxygen content increases the conductivity of the samples. The tunneling of the current carriers is probably the main conduction mechanism for samples with higher barrier thicknesses.

  • I. Gross, W. Akhtar, V. Garcia, L. J. Martínez, S. Chouaieb, K. Garcia, C. Carrétéro, A. Barthélémy, P. Appel, P. Maletinsky, J. - V. Kim, J. - Y. Chauleau, N. Jaouen, M. Viret, M. Bibes, S. Fusil, V. Jacques, Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer. Nature. 549, 252–256 (2017).
    Résumé : Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin–orbit effects that enable efficient spin–charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen–vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen–vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.

  • F. Hellman, A. Hoffmann, Y. Tserkovnyak, G. Beach, E. Fullerton, C. Leighton, A. - H. MacDonald, D. - C. Ralph, D. - A. Arena, H. Dürr, P. Fischer, J. Grollier, J. - P. Heremans, T. Jungwirth, A. - V. Kimel, B. Koopmans, I. - N. Krivorotov, S. - J. May, A. Petford-Long, J. - M. Rondinelli, N. Samarth, I. - K. Schuller, A. - N. Slavin, M. D. Stiles, O. Tchernyshyov, A. Thiaville, B. - L. Zink, Interface-induced phenomena in magnetism. Reviews of Modern Physics. 89, 025006 (2017).
    Résumé : This article reviews static and dynamic interfacial effects in magnetism, focusing on interfacially driven magnetic effects and phenomena associated with spin-orbit coupling and intrinsic symmetry breaking at interfaces. It provides a historical background and literature survey, but focuses on recent progress, identifying the most exciting new scientific results and pointing to promising future research directions. It starts with an introduction and overview of how basic magnetic properties are affected by interfaces, then turns to a discussion of charge and spin transport through and near interfaces and how these can be used to control the properties of the magnetic layer. Important concepts include spin accumulation, spin currents, spin-transfer torque, and spin pumping. An overview is provided to the current state of knowledge and existing review literature on interfacial effects such as exchange bias, exchange-spring magnets, the spin Hall effect, oxide heterostructures, and topological insulators. The article highlights recent discoveries of interface-induced magnetism and noncollinear spin textures, nonlinear dynamics including spin-transfer torque and magnetization reversal induced by interfaces, and interfacial effects in ultrafast magnetization processes.
  • A. Joly, G. Baili, M. Alouini, J. - M. George, I. Sagnes, D. Dolfi, (Ieee, New York, 2017)p. .

  • A. Joly, G. Baili, M. Alouini, J. - M. George, I. Sagnes, G. Pillet, D. Dolfi, Compensation of the residual linear anisotropy of phase in a vertical-external-cavity-surface-emitting laser for spin injection. Opt. Lett., OL. 42, 651–654 (2017).
    Résumé : We report on the compensation of the linear anisotropy of phase in a vertical-external-cavity surface-emitting laser from 21 to 0.5 mrad with an intracavity PLZT electro-optical ceramic. It allows dynamic and accurate control of the laser linear anisotropy, as well as dynamic control of the laser polarization eigenstates. At the birefringence compensation point, we observe an elliptical polarization state with 41° of ellipticity, rotated from its initial position of 32°. The experimental observations are in close agreement with the theoretical predictions. Finally, we are able to demonstrate control of the polarization state with spin injection.

  • J. - V. Kim, M. - W. Yoo, Current-driven skyrmion dynamics in disordered films. Applied Physics Letters. 110, 132404 (2017).
    Résumé : A theoretical study of the current-driven dynamics of magnetic skyrmions in disordered perpendicularly magnetized ultrathin films is presented. The disorder is simulated as a granular structure, in which the local anisotropy varies randomly from grain to grain. The skyrmion velocity is computed for different disorder parameters and ensembles. Similar behavior is seen for spin-torques due to in-plane currents and the spin Hall effect, where a pinning regime can be identified at low currents with a transition towards the disorder-free case at higher currents, similar to domain wall motion in disordered films. Moreover, a current-dependent skyrmion Hall effect and fluctuations in the core radius are found, which result from the interaction with the pinning potential.

  • M. Kreissig, R. Lebrun, F. Protze, K. - J. Merazzo, J. Hem, L. Vila, R. Ferreira, M. - C. Cyrille, F. Ellinger, V. Cros, U. Ebels, P. Bortolotti, dans AIP Advances (2017)vol. 7p. 056653.
    Résumé : Spin-torque nano-oscillators (STO) are candidates for the next technological implementation of spintronic devices in commercial electronic systems. For use in microwave applications, improving the noise figures by efficient control of their phase dynamics is a mandatory requirement. In order to achieve this, we developed a compact phase locked loop (PLL) based on custom integrated circuits (ICs) and demonstrate that it represents an efficient way to reduce the phase noise level of a vortex based STO. The advantage of our approach to phase stabilize STOs is that our compact system is highly reconfigurable e.g. in terms of the frequency divider ratio N, RF gain and loop gain. This makes it robust against device to device variations and at the same time compatible with a large range of STOs. Moreover, by taking advantage of the natural highly non-isochronous nature of the STO, the STO frequency can be easily controlled by e.g. changing the divider ratio N.

  • P. Laczkowski, Y. Fu, H. Yang, J. - C. Rojas-Sanchez, P. Noel, V. T. Pham, G. Zahnd, C. Deranlot, S. Collin, C. Bouard, P. Warin, V. Maurel, M. Chshiev, A. Marty, J. - P. Attane, A. Fert, H. Jaffrès, L. Vila, J. - M. George, Large enhancement of the spin Hall effect in Au by side-jump scattering on Ta impurities. Phys. Rev. B. 96, 140405 (2017).
    Résumé : We present measurements of the spin Hall effect (SHE) in AuW and AuTa alloys for a large range of W or Ta concentrations by combining experiments on lateral spin valves and ferromagnetic-resonance/spin-pumping techniques. The main result is the identification of a large enhancement of the spin Hall angle (SHA) by the side-jump mechanism on Ta impurities, with a SHA as high as $+0.5$ (i.e., $50%$) for about 10% of Ta. In contrast, the SHA in AuW does not exceed $+0.15$ and can be explained by intrinsic SHE of the alloy without significant extrinsic contribution from skew or side-jump scattering by W impurities. The AuTa alloys, as they combine a very large SHA with a moderate resistivity (smaller than $85\textbackslashphantom{\textbackslashrule{0.28em}{0ex}}\textbackslashensuremath{\textbackslashmu}\textbackslashmathrm{\textbackslashensuremath{\textbackslashOmega}}\textbackslashphantom{\textbackslashrule{0.16em}{0ex}}\textbackslashtext{cm}$), are promising for spintronic devices exploiting the SHE.

  • R. Lebrun, J. Grollier, F. Abreu Araujo, P. Bortolotti, V. Cros, A. Hamadeh, X. de Milly, Y. Li, G. De Loubens, O. Klein, S. Tsunegi, H. Kubota, K. Yakushiji, A. Fukushima, S. Yuasa, Driven energy transfer between coupled modes in spin-torque oscillators. Phys. Rev. B. 95, 134444 (2017).
    Résumé : The mutual interaction between the different eigenmodes of a spin-torque oscillator can lead to a large variety of physical mechanisms from mode hopping to multimode generation, that usually reduce their performances as radio-frequency devices. To tackle this issue for the future applications, we investigate the properties of a model spin-torque oscillator that is composed of two coupled vortices with one vortex in each of the two magnetic layers of the oscillator. In such double-vortex system, the remarkable properties of energy transfer between the coupled modes, one being excited by spin transfer torque while the second one being damped, result into an alteration of the damping parameters. As a consequence, the oscillator nonlinear behavior is concomitantly drastically impacted. This efficient coupling mechanism, driven mainly by the dynamic dipolar field generated by the spin transfer torque induced motion of the vortices, gives rise to an unusual dynamical regime of self-resonance excitation. These results show that mode coupling can be leveraged for controlling the synchronization process as well as the frequency tunability of spin-torque oscillators.

  • R. Lebrun, S. Tsunegi, P. Bortolotti, H. Kubota, A. S. Jenkins, M. Romera, K. Yakushiji, A. Fukushima, J. Grollier, S. Yuasa, V. Cros, Mutual synchronization of spin torque nano-oscillators through a long-range and tunable electrical coupling scheme. Nature Communications. 8, 15825 (2017).
    Résumé : The spintronics based complex network is promising for next generation computing systems but hampered by short-range spin-wave coupling. The authors make progress by achieving long range and tunable mutual synchronization of two spin-torque oscillators with improved emission
    Mots-clés : Spinorbitronics.

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