Articles

2018

• M. Mattera, V. Rubio-Giménez, S. Delprat, R. Mattana, P. Seneor, S. Tatay, A. Forment-Aliaga, E. Coronado, Spontaneous growth of 2D coordination polymers on functionalized ferromagnetic surfaces. Chemical Science. 9, 8819-8828 (2018).
Résumé : The spontaneous growth of lamellar metal-alkanethiolates (LMAs) on reactive ferromagnetic surfaces as a result of surface oxidation has been observed. When alkanethiol self-assembled monolayers (SAMs) grown under an inert atmosphere over cobalt or permalloy (Ni80Fe20) are exposed to air, oxygen diffuses through the molecular layer. This induces an oxidation of metal atoms at the metal surface and a release of the resulting metal cations that migrate coordinated by the alkanethiol molecules to form lamellar structures over the SAMs. This process has been imaged in real-time, under ambient conditions, by means of different microscopy techniques. The influence of the alkyl chain length, the nature of the ferromagnet, the temperature and the atmospheric moisture on the number, area and height of the resulting features has been systematically evaluated. Remarkably, the possibility to follow the migration in real-time makes it a promising model system for the study of surface/molecule interface processes. Most importantly, the composition and crystallinity of these LMAs have been studied, evidencing that real 2D coordination polymers are formed on the surface. Hence, one could envision this strategy as a new method for the assembly of more complex low-dimensional (2D) magnetic materials based on coordination polymers.

• S. McVitie, S. Hughes, K. Fallon, S. McFadzean, D. McGrouther, M. Krajnak, W. Legrand, D. Maccariello, S. Collin, K. Garcia, N. Reyren, V. Cros, A. Fert, K. Zeissler, C. H. Marrows, A transmission electron microscope study of Néel skyrmion magnetic textures in multilayer thin film systems with large interfacial chiral interaction. Scientific Reports. 8, 5703 (2018).
Résumé : Skyrmions in ultrathin ferromagnetic metal (FM)/heavy metal (HM) multilayer systems produced by conventional sputtering methods have recently generated huge interest due to their applications in the field of spintronics. The sandwich structure with two correctly-chosen heavy metal layers provides an additive interfacial exchange interaction which promotes domain wall or skyrmion spin textures that are Néel in character and with a fixed chirality. Lorentz transmission electron microscopy (TEM) is a high resolution method ideally suited to quantitatively image such chiral magnetic configurations. When allied with physical and chemical TEM analysis of both planar and cross-sectional samples, key length scales such as grain size and the chiral variation of the magnetisation variation have been identified and measured. We present data showing the importance of the grain size (mostly < 10 nm) measured from direct imaging and its potential role in describing observed behaviour of isolated skyrmions (diameter < 100 nm). In the latter the region in which the magnetization rotates is measured to be around 30 nm. Such quantitative information on the multiscale magnetisation variations in the system is key to understanding and exploiting the behaviour of skyrmions for future applications in information storage and logic devices.

• A. Mizrahi, J. Grollier, D. Querlioz, M. D. Stiles, Overcoming device unreliability with continuous learning in a population coding based computing system. Journal of Applied Physics. 124, 152111 (2018).
Résumé : The brain, which uses redundancy and continuous learning to overcome the unreliability of its components, provides a promising path to building computing systems that are robust to the unreliability of their constituent nanodevices. In this work, we illustrate this path by a computing system based on population coding with magnetic tunnel junctions that implement both neurons and synaptic weights. We show that equipping such a system with continuous learning enables it to recover from the loss of neurons and makes it possible to use unreliable synaptic weights (i.e., low energy barrier magnetic memories). There is a trade-off between power consumption and precision because low energy barrier memories consume less energy than high barrier ones. For a given precision, there is an optimal number of neurons and an optimal energy barrier for the weights that leads to minimum power consumption.

• A. Mizrahi, T. Hirtzlin, A. Fukushima, H. Kubota, S. Yuasa, J. Grollier, D. Querlioz, Neural-like computing with populations of superparamagnetic basis functions. Nature Communications. 9, 1533 (2018).
Résumé : Population coding, where populations of artificial neurons process information collectively can facilitate robust data processing, but require high circuit overheads. Here, the authors realize this approach with reduced circuit area and power consumption, by utilizing superparamagnetic tunnel junction based neurons.

• A. M. R. Monteiro, A. D. Caviglia, N. Reyren, dans Spectroscopy of Complex Oxide Interfaces (Springer., 2018; //www.springer.com/us/book/9783319749884)Springer Series in Materials Sciencep. .
Mots-clés : Chapter.

• L. D. N. Mouafo, F. Godel, G. Melinte, S. Hajjar‐Garreau, H. Majjad, B. Dlubak, O. Ersen, B. Doudin, L. Simon, P. Seneor, J. - F. Dayen, Anisotropic Magneto‐Coulomb Properties of 2D–0D Heterostructure Single Electron Device. Advanced Materials. 30 (2018), doi:10.1002/adma.201802478.

• K. Nakazawa, M. Bibes, H. Kohno, Topological Hall Effect from Strong to Weak Coupling. Journal of the Physical Society of Japan. 87, 033705 (2018).
Résumé : The topological Hall effect (THE) of electrons coupled to a noncoplanar spin texture has been studied so far for the strong- and weak-coupling regimes separately; the former in terms of the Berry phase and the latter by perturbation theory. In this letter, we present a unified treatment in terms of spin gauge field by considering not only the adiabatic (Berry phase) component of the gauge field but also the nonadiabatic component. While only the adiabatic contribution is important in the strong-coupling regime, it is completely canceled by a part of the nonadiabatic contribution in the weak-coupling regime, where the THE is governed by the remaining nonadiabatic terms. We found a new weak-coupling region that cannot be accessed by a simple perturbation theory, where the Hall conductivity is proportional to M, with 2M being the exchange splitting of the electron spectrum.

• E. Pawlowski Recoba, J. Kermorvant, D. Crété, Y. Lemaître, B. Marcilhac, C. Ulysse, F. Couëdo, C. Feuillet-Palma, N. Bergeal, J. Lesueur, Static and radio frequency magnetic response of high T c superconducting quantum interference filters made by ion irradiation. Superconductor Science and Technology. 31, 095005 (2018).
Mots-clés : Supra.

• D. Perconte, F. A. Cuellar, C. Moreau-Luchaire, M. Piquemal-Banci, R. Galceran, P. - R. Kidambi, M. - B. Martin, S. Hofmann, R. Bernard, B. Dlubak, P. Seneor, J. - E. Villegas, Tunable Klein-like tunnelling of high-temperature superconducting pairs into graphene. Nature Physics. 14, 25 (2018).
Résumé : \textlessp\textgreaterProximity effects enable superconductivity to leak into normal metals. In graphene, a Klein-like tunnelling of superconducting pairs from a high-temperature superconductor allows the proximity effects to be tuned by electric fields.\textless/p\textgreater

• D. Pinna, F. A. Araujo, J. - V. Kim, V. Cros, D. Querlioz, P. Bessiere, J. Droulez, J. Grollier, Skyrmion Gas Manipulation for Probabilistic Computing. Physical Review Applied. 9, 064018 (2018).
Résumé : Stochastic computing (SC), a radical rethinking of computation, defines operations on streams of random bits; it trades precision for large advantages in speed. Implementation has been thwarted, though, by the lack of an efficient means to properly decorrelate bitstreams at each logic gate in an SC circuit. This study harnesses recent advances in manipulating magnetic skyrmions to propose a technique for telegraph-signal reshuffling that is tailor-made for SC applications. Leveraging the two-dimensional diffusive character of skyrmion motion shows how useful these exotic magnetic textures can be in tackling problems that require compact, scalable, energy-efficient device architectures.

• M. Piquemal-Banci, R. Galceran, F. Godel, S. Caneva, M. - B. Martin, R. - S. Weatherup, P. - R. Kidambi, K. Bouzehouane, S. Xavier, A. Anane, F. Petroff, A. Fert, S. M. M. Dubois, J. - C. Charlier, J. Robertson, S. Hofmann, B. Dlubak, P. Seneor, Insulator-to-Metallic Spin-Filtering in 2D-Magnetic Tunnel Junctions Based on Hexagonal Boron Nitride. ACS Nano. 12, 4712 (2018).
Résumé : Insulator-to-Metallic Spin-Filtering in 2D-Magnetic Tunnel Junctions Based on Hexagonal Boron Nitride

• D. Preziosi, L. Lopez-Mir, X. Li, T. Cornelissen, J. - H. Lee, F. Trier, K. Bouzehouane, S. Valencia, A. Gloter, A. Barthélémy, M. Bibes, Direct Mapping of Phase Separation across the Metal–Insulator Transition of NdNiO3. Nano Letters. 18, 2226 (2018).
Résumé : Direct Mapping of Phase Separation across the Metal–Insulator Transition of NdNiO3

• M. Romera, P. Talatchian, S. Tsunegi, F. A. Araujo, V. Cros, P. Bortolotti, J. Trastoy, K. Yakushiji, A. Fukushima, H. Kubota, S. Yuasa, M. Ernoult, D. Vodenicarevic, T. Hirtzlin, N. Locatelli, D. Querlioz, J. Grollier, Vowel recognition with four coupled spin-torque nano-oscillators. Nature. 563, 230 (2018).
Résumé : A network of four spin-torque nano-oscillators can be trained in real time to recognize spoken vowels, in a simple and scalable approach that could be exploited for large-scale neural networks.

• D. Sando, C. Carrétéro, M. - N. Grisolia, A. Barthélémy, V. Nagarajan, M. Bibes, Revisiting the Optical Band Gap in Epitaxial BiFeO3 Thin Films. Advanced Optical Materials. 6, 201700836 (2018).

• G. Singh, A. Jouan, L. Benfatto, F. Couëdo, P. Kumar, A. Dogra, R. C. Budhani, S. Caprara, M. Grilli, E. Lesne, A. Barthélémy, M. Bibes, C. Feuillet-Palma, J. Lesueur, N. Bergeal, Competition between electron pairing and phase coherence in superconducting interfaces. Nature Communications. 9, 407 (2018).
Résumé : <p>The nature of the doping dependent superconducting transition remains elusive for a two dimensional electron gas at the LaAlO<sub>3</sub>/SrTiO<sub>3</sub> interface. Here, Singh et al. report superfluid stiffness and the superconducting gap energy at such interface as a function of carrier density.</p>

• 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. .
Mots-clés : Chapter.

• 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).
Mots-clés : Magnonics.

• 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.

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