• D. Q. To, T. H. Dang, H. Nguyen, V. Safarov, J. - M. George, H. - J. Drouhin, H. Jaffrès, Spin-Orbit Currents, Spin-Transfer Torque and Anomalous Tunneling in III–V Heterostructures Probed by Advanced 30- and 40-Bands $k\cdotp$ Tunneling Methods. IEEE Transactions on Magnetics. 55, 1-7 (2019).
    Résumé : On the basis of tunneling magnetoresistance (TMR) spin-transfer torque (STT) experiments in (Ga,Mn)As/GaAs/(Ga,Mn)As submicronic magnetic tunnel junctions, we have analyzed the anatomy of the spin-current profiles within the heterostructures, location of strong spin-orbit interactions. Beyond the TMR, our robust 30- and 40-band k · p numerical methods reveal the strong peculiarity of the spin-currents in the antiparallel state with the evidence of a tunneling anomalous Hall effect. Using the boundary conditions corresponding to heavy-hole (HH)-to-light-hole (LH) mixing of the relevant C2v symmetry at III-V interfaces of the junctions, we demonstrate that the efficiency of the transverse spin-current necessary to STT is surprisingly enhanced by the HH-to-LH mixing taking benefit of the lighter mass of the LH state.
  • J. Tornos, F. Gallego, S. Valencia, Y. H. Liu, V. Rouco, V. Lauter, R. Abrudan, C. Luo, H. Ryll, Q. Wang, D. Hernandez-Martin, G. Orfila, M. Cabero, F. Cuellar, D. Arias, F. J. Mompean, M. Garcia-Hernandez, F. Radu, T. R. Charlton, A. Rivera-Calzada, Z. Sefrioui, S. G. E. te Velthuis, C. Leon, J. Santamaria, Ferroelectric Control of Interface Spin Filtering in Multiferroic Tunnel Junctions. Physical Review Letters. 122, 037601 (2019).
    Résumé : The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}/{\mathrm{BaTiO}}_{3}/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics.

  • J. Varignon, M. Bibes, A. Zunger, Origin of band gaps in 3 d perovskite oxides. Nature Communications. 10, 1658 (2019).
    Résumé : It is often stated that first principles studies of transition metal oxides require dynamically correlated methods to correctly produce gap formation, magnetism and structural distortions. Varignon et al. show instead that static correlations are sufficient to capture these features in the ABO3 oxide series.

  • J. Varignon, M. Bibes, A. Zunger, Mott gapping in 3d ABO3 perovskites without Mott-Hubbard interelectronic repulsion energy U. Physical Review B. 100, 035119 (2019).
    Résumé : The existence of band gaps in Mott insulators such as perovskite oxides with partially filled 3d shells has been traditionally explained in terms of strong, dynamic interelectronic repulsion codified by the on-site repulsion energy U in the Hubbard Hamiltonian. The success of the ``DFT+U approach'' where an empirical on-site potential term U is added to the exchange- and correlation density functional theory (DFT) raised questions on whether U in DFT+U represents interelectronic correlation in the same way as it does in the Hubbard Hamiltonian, and if empiricism in selecting U can be avoided. Here we illustrate that ab initio DFT without any U is able to predict gapping trends and structural symmetry breaking (octahedra rotations, Jahn-Teller modes, bond disproportionation) for all $3d\phantom{\rule{0.16em}{0ex}}AB{\mathrm{O}}_{3}$ perovskites from titanates to nickelates in both spin-ordered and spin-disordered paramagnetic phases. Thus, the mechanism of gap formation due to the Hubbard Hamiltonian dynamic interelectronic correlation is not a requirement in these $3d$ electron compounds. We describe the paramagnetic phases as a supercell where individual sites can have different local environments thereby allowing DFT to develop finite moments on different sites as long as the total cell has zero moment. We use the recently developed strongly constrained appropriately normed exchange and correlation functional (SCAN) that is sanctioned by the usual single-determinant, mean-field DFT paradigm with static correlations, but has a more precise rendering of self-interaction cancelation. Our results suggest that strong dynamic electronic correlations are not playing a universal role in gapping of $3d\phantom{\rule{0.16em}{0ex}}AB{\mathrm{O}}_{3}$ Mott insulators, and opens the way for future applications of DFT for studying a plethora of complexity effects that depend on the existence of gaps, such as doping, defects, and band alignment in $AB{\mathrm{O}}_{3}$ oxides.

  • J. Varignon, J. Santamaria, M. Bibes, Electrically Switchable and Tunable Rashba-Type Spin Splitting in Covalent Perovskite Oxides. Physical Review Letters. 122, 116401 (2019).
    Résumé : In transition-metal perovskites ($AB{\mathrm{O}}_{3}$) most physical properties are tunable by structural parameters such as the rotation of the $B{\mathrm{O}}_{6}$ octahedra. Examples include the N\'eel temperature of orthoferrites, the conductivity of mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides often hold large internal electric dipoles and can accommodate heavy elements, they also emerge as prime candidates to display Rashba spin-orbit coupling, through which charge and spin currents may be efficiently interconverted. However, despite a few experimental reports in ${\mathrm{SrTiO}}_{3}$-based interface systems, the Rashba interaction has been little studied in these materials, and its interplay with structural distortions remains unknown. In this Letter, we identify a bismuth-based perovskite with a large, electrically switchable Rashba interaction whose amplitude can be controlled by both the ferroelectric polarization and the breathing mode of oxygen octahedra. This particular structural parameter arises from the strongly covalent nature of the Bi-O bonds, reminiscent of the situation in perovskite nickelates. Our results not only provide novel strategies to craft agile spin-charge converters but also highlight the relevance of covalence as a powerful handle to design emerging properties in complex oxides.

  • D. - C. Vaz, P. Noël, A. Johansson, B. Göbel, F. Y. Bruno, G. Singh, S. McKeown-Walker, F. Trier, L. - M. Vicente-Arche, A. Sander, S. Valencia, P. Bruneel, M. Vivek, M. Gabay, N. Bergeal, F. Baumberger, H. Okuno, A. Barthélémy, A. Fert, L. Vila, I. Mertig, J. - P. Attane, M. Bibes, Mapping spin–charge conversion to the band structure in a topological oxide two-dimensional electron gas. Nature Materials. 18, 1187-1193 (2019).
    Résumé : A very large spin-to-charge conversion arising from a combination of the Rashba effect and topologically non-trivial states is realized at the interface of strontium titanate and aluminium, with implications for the role of topology in memory and transistor designs.

  • L. Vistoli, W. Wang, A. Sander, Q. Zhu, B. Casals, R. Cichelero, A. Barthélémy, S. Fusil, G. Herranz, S. Valencia, R. Abrudan, E. Weschke, K. Nakazawa, H. Kohno, J. Santamaria, W. Wu, V. Garcia, M. Bibes, Giant topological Hall effect in correlated oxide thin films. Nature Physics. 15, 67 (2019).
    Résumé : A strong Hall effect is observed in a material with spin textures and strong electron correlations. This hints that correlation effects can amplify real-space topological spin transport.

  • S. Wittrock, S. Tsunegi, K. Yakushiji, A. Fukushima, H. Kubota, P. Bortolotti, U. Ebels, S. Yuasa, G. Cibiel, S. Galliou, E. Rubiola, V. Cros, Low offset frequency 1/f flicker noise in spin-torque vortex oscillators. Physical Review B. 99, 235135 (2019).
    Résumé : Low-frequency noise close to the carrier remains little explored in spin-torque nano-oscillators. However, it is crucial to investigate as it limits the oscillator's frequency stability. This work addresses the low offset frequency flicker noise of a spin-torque vortex oscillator in the regime of large-amplitude steady oscillations. We first phenomenologically expand the nonlinear auto-oscillator theory, aiming to reveal the properties of this noise. We then present a thorough experimental study of the oscillator's $1/f$ flicker noise and discuss the results based on the theoretical predictions. Thereby, we connect the oscillator's nonlinear dynamics with the concept of flicker noise and furthermore refer to the influence of a standard $1/f$ noise description based on the Hooge formula, taking into account the nonconstant magnetic oscillation volume, which contributes to the magnetoresistance.

  • V. Zatko, M. Galbiati, S. Dubois, M. Och, P. Palczynski, C. Mattevi, P. Brus, O. Bezencenet, M. - B. Martin, B. Servet, J. - C. Charlier, F. Godel, A. Vecchiola, K. Bouzehouane, S. Collin, F. Petroff, B. Dlubak, P. Seneor, Band-Structure Spin-Filtering in Vertical Spin Valves Based on Chemical Vapor Deposited WS2. ACS Nano. 13, 14468 (2019).
    Résumé : We report on spin transport in WS2-based 2D-magnetic tunnel junctions (2D-MTJs), unveiling a band structure spin filtering effect specific to the transition metal dichalcogenides (TMDCs) family. WS2 mono-, bi-, and trilayers are derived by a chemical vapor deposition process and further characterized by Raman spectroscopy, atomic force microscopy (AFM), and photoluminescence spectroscopy. The WS2 layers are then integrated in complete Co/Al2O3/WS2/Co MTJ hybrid spin-valve structures. We make use of a tunnel Co/Al2O3 spin analyzer to probe the extracted spin-polarized current from the WS2/Co interface and its evolution as a function of WS2 layer thicknesses. For monolayer WS2, our technological approach enables the extraction of the largest spin signal reported for a TMDC-based spin valve, corresponding to a spin polarization of PCo/WS2 = 12%. Interestingly, for bi- and trilayer WS2, the spin signal is reversed, which indicates a switch in the mechanism of interfacial spin extraction. With the support of ab initio calculations, we propose a model to address the experimentally measured inversion of the spin polarization based on the change in the WS2 band structure while going from monolayer (direct bandgap) to bilayer (indirect bandgap). These experiments illustrate the rich potential of the families of semiconducting 2D materials for the control of spin currents in 2D-MTJs.


  • R. Aeschlimann, D. Preziosi, P. Scheiderer, M. Sing, S. Valencia, J. Santamaria, C. Luo, H. Ryll, F. Radu, R. Claessen, C. Piamonteze, M. Bibes, A Living‐Dead Magnetic Layer at the Surface of Ferrimagnetic DyTiO3 Thin Films. Advanced Materials. 30, 1707489 (2018).

  • M. Alouini, J. Frougier, A. Joly, G. Baili, D. Dolfi, J. - M. George, VSPIN: a new model relying on the vectorial description of the laser field for predicting the polarization dynamics of spin-injected V(e)CSELs. Optics Express. 26, 6739-6757 (2018).
    Résumé : A new vectorial model (VSPIN) based on the Jones formalism is proposed to describe the polarization dynamics of spin injected V(e)CSELs. This general modelling framework accounts for spin injection effects as a gain circular dichroism in the active medium and provides guidelines for developing functional spin-controlled lasers. We investigate the detrimental role of phase anisotropy on polarization switching and show that it can be overcome by preparing the laser cavity to achieve efficient polarization switching under low effective spin injection. The VSPIN model predictions have been confirmed experimentally and explain the polarization behavior of spin-VCSELs reported in the literature.

  • Q. Barbedienne, J. Varignon, N. Reyren, A. Marty, C. Vergnaud, M. Jamet, C. Gomez-Carbonell, A. Lemaître, P. le Fèvre, F. Bertran, A. Taleb-Ibrahimi, H. Jaffrès, J. - M. George, A. Fert, Angular-resolved photoemission electron spectroscopy and transport studies of the elemental topological insulator a-Sn. Physical Review B. 98, 195445 (2018).
    Résumé : Gray tin, also known as $\ensuremath{\alpha}$-Sn, can be turned into a three-dimensional topological insulator (3D-TI) by strain and finite-size effects. Such room-temperature 3D-TI is peculiarly interesting for spintronics due to the spin-momentum locking along the Dirac cone (linear dispersion) of the surface states. Angle-resolved photoemission spectroscopy (ARPES) has been used to investigate the dispersion close to the Fermi level in thin (001)-oriented epitaxially strained films of $\ensuremath{\alpha}$-Sn for different film thicknesses as well as for different capping layers (Al, ${\mathrm{AlO}}_{x}$, and MgO). Indeed a proper capping layer is necessary to be able to use $\ensuremath{\alpha}$-Sn surface states for spintronic applications. In contrast with free surfaces or surfaces coated with Ag, coating the $\ensuremath{\alpha}$-Sn surface with Al or ${\mathrm{AlO}}_{x}$ leads to a drop in the Fermi level below the Dirac point, and an important consequence for electronic transport is the presence of bulk states at the Fermi level. $\ensuremath{\alpha}$-Sn films coated by ${\mathrm{AlO}}_{x}$ are studied by electrical magnetotransport: Despite magnetotransport properties of the bulk electronic states of the ${\mathrm{\ensuremath{\Gamma}}}_{8}$ band playing an important role as suggested by ab initio calculations, there is clear evidence of surface states revealed by Shubnikov--de Haas oscillations corresponding to the ARPES observation.

  • S. Boyn, A. Chanthbouala, S. Girod, C. Carrétéro, A. Barthélémy, M. Bibes, J. Grollier, S. Fusil, V. Garcia, Real-time switching dynamics of ferroelectric tunnel junctions under single-shot voltage pulses. Applied Physics Letters. 113, 232902 (2018).
    Résumé : In ferroelectric memory devices, information is stored within the polarization direction whose reversal usually occurs by the nucleation and propagation of domains. In ultrathin ferroelectrics, ultrafast dynamics may be achieved by nucleation-limited switching, avoiding the inherently speed-limited propagation of domain walls. Here, we investigate polarization reversal dynamics in ultrathin ferroelectric films by transient current measurements. Thanks to the tunnel electroresistance, the start of polarization reversal induces sharp variations of the transmitted current under voltage pulses. These single-shot measurements show extremely fast switching with durations down to 3 ns that is only limited by the current device geometry. While the OFF-to-ON switching shows finite nucleation times that scale with the pulse amplitude, the ON-to-OFF switching speed cannot be detected under such rectangular pulses. Resorting to triangular pulse excitations allows us to detect the dynamics of this switching direction....

  • L. Bégon-Lours, V. Rouco, Q. Qiao, A. Sander, M. A. Roldán, R. Bernard, J. Trastoy, A. Crassous, E. Jacquet, K. Bouzehouane, M. Bibes, J. Santamaría, A. Barthélémy, M. Varela, J. - E. Villegas, Factors limiting ferroelectric field-effect doping in complex oxide heterostructures. Physical Review Materials. 2, 084405 (2018).
    Résumé : Ferroelectric field-effect doping has emerged as a powerful approach to manipulate the ground state of correlated oxides, opening the door to a different class of field-effect devices. However, this potential is not fully exploited so far, since the size of the field-effect doping is generally much smaller than expected. Here we study the limiting factors through magnetotransport and scanning transmission electron and piezoresponse force microscopy in ferroelectric/superconductor $(\mathrm{YB}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{7\text{\ensuremath{-}}\ensuremath{\delta}}/\mathrm{BiFe}{\mathrm{O}}_{3})$ heterostructures, a model system showing very strong field effects. Still, we find that they are limited in the first place by an incomplete ferroelectric switching. This can be explained by the existence of a preferential polarization direction set by the atomic terminations at the interface. More importantly, we also find that the field-effect carrier doping is accompanied by a strong modulation of the carrier mobility. Besides making quantification of field effects via Hall measurements not straightforward, this finding suggests that ferroelectric poling produces structural changes (e.g., charged defects or structural distortions) in the correlated oxide channel. Those findings have important consequences for the understanding of ferroelectric field effects and for the strategies to further enhance them.

  • F. Cadiz, A. Djeffal, D. Lagarde, A. Balocchi, B. Tao, B. Xu, S. Liang, M. Stoffel, X. Devaux, H. Jaffrès, J. - M. George, M. Hehn, S. Mangin, H. Carrere, X. Marie, T. Amand, X. Han, Z. Wang, B. Urbaszek, Y. Lu, P. Renucci, Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field. Nano Letters. 18, 2381 (2018).
    Résumé : Electrical Initialization of Electron and Nuclear Spins in a Single Quantum Dot at Zero Magnetic Field
    Mots-clés : Semiconductors and Spintronics.

  • S. - J. Carreira, M. - H. Aguirre, J. Briatico, E. Weschke, L. - B. Steren, Tuning the interfacial charge, orbital, and spin polarization properties in La0.67Sr0.33MnO3/La1−xSrxMnO3 bilayers. Applied Physics Letters. 112, 032401 (2018).
    Résumé : The possibility of controlling the interfacial properties of artificial oxide heterostructures is still attracting researchers in the field of materials engineering. Here, we used surface sensitive techniques and high-resolution transmission electron microscopy to investigate the evolution of the surface spin-polarization and lattice strains across the interfaces between La0.66Sr0.33MnO3 thin films and low-doped manganites as capping layers. We have been able to fine tune the interfacial spin-polarization by changing the capping layer thickness and composition. The spin-polarization was found to be the highest at a critical capping thickness that depends on the Sr doping. We explain the non-trivial magnetic profile by the combined effect of two mechanisms: On the one hand, the extra carriers supplied by the low-doped manganites that tend to compensate the overdoped interface, favouring locally a ferromagnetic double-exchange coupling. On the other hand, the evolution from a tensile-strained structure of t...

  • J. - Y. Chauleau, W. Legrand, N. Reyren, D. Maccariello, S. Collin, H. Popescu, K. Bouzehouane, V. Cros, N. Jaouen, A. Fert, Chirality in Magnetic Multilayers Probed by the Symmetry and the Amplitude of Dichroism in X-Ray Resonant Magnetic Scattering. Phys. Rev. Lett. 120, 037202 (2018).
    Résumé : Chirality in condensed matter has recently become a topic of the utmost importance because of its significant role in the understanding and mastering of a large variety of new fundamental physical mechanisms. Versatile experimental approaches, capable to reveal easily the exact winding of order parameters, are therefore essential. Here we report x-ray resonant magnetic scattering as a straightforward tool to reveal directly the properties of chiral magnetic systems. We show that it can straightforwardly and unambiguously determine the main characteristics of chiral magnetic distributions: i.e., its chiral nature, the quantitative winding sense (clockwise or counterclockwise), and its type, i.e., N\textbackslash'eel [cycloidal] or Bloch [helical]. This method is model independent, does not require a priori knowledge of the magnetic parameters, and can be applied to any system with magnetic domains ranging from a few nanometers (wavelength limited) to several microns. By using prototypical multilayers with tailored magnetic chiralities driven by spin-orbit-related effects at $\textbackslashmathrm{Co}\textbar\textbackslashmathrm{Pt}$ interfaces, we illustrate the strength of this method.
    Mots-clés : Spinorbitronics.

  • P. Chen, M. - N. Grisolia, H. J. Zhao, O. E. González-Vázquez, L. Bellaiche, M. Bibes, B. - G. Liu, J. Íñiguez, Energetics of oxygen-octahedra rotations in perovskite oxides from first principles. Physical Review B. 97, 024113 (2018).
    Résumé : From superconductivity to magnetoelectricity, perovskite oxides exhibit a wealth of appealing physical properties, often controlled by subtle structural details. Especially critical are the `tilt' distortion modes involving rotations of the oxygen octahedra that constitute the backbone of the perovskite lattice, which motivates today's interest in better understanding and tuning such tilts. Here, the authors present a thorough first-principles investigation of the energy landscape relevant to this matter, revealing the main competitors among different tilt modes as well as their trends across the perovskite family.

  • D. Crete, A. Sene, A. Labbe, E. Pawlowski Recoba, J. Kermorvant, Y. Lemaitre, B. Marcilhac, E. Parzy, E. Thiaudiere, C. Ulysse, Evaluation of Josephson Junction Parameter Dispersion Effects in Arrays of HTS SQUIDs. IEEE Transactions on Applied Superconductivity. 28, 1602506 (2018).

  • S. Delprat, M. Galbiati, S. Tatay, B. Quinard, C. Barraud, F. Petroff, P. Seneor, R. Mattana, Molecular spintronics: the role of spin-dependent hybridization. Journal of Physics D: Applied Physics. 51, 473001 (2018).
    Résumé : Spin-dependent hybridization at the ferromagnet/molecule interface has recently unveiled a promising new potential for spintronics. By projecting the spintronic properties (i.e. induced spin polarization) from a given ferromagnet electrode to the highly versatile and tailorable molecular layer, spin-dependent hybridization has opened up new opportunities to tailor spintronic device properties at the molecular scale. Here we focus on the potential and impact of this hybridization on spintronic devices. Depending on the coupling strength at the ferromagnet/molecule interface, the induced spin polarization can be enhanced or even inversed. In the first part of the paper, we introduce the concept of spin-dependent hybridization and, in particular, we show that it allows the magnetoresistive response of spintronic devices to be tuned. In the second part, we review the experimental evidence emphasizing spin-dependent hybridization in molecular layers and single molecules. In the last part, we highlight how this spin-dependent hybridization can play a key role in tunnelling magnetoresistance and tunnelling anisotropic magnetoresistance.

  • A. Djeffal, F. Cadiz, M. Stoffel, D. Lagarde, X. Gao, H. Jaffrès, X. Devaux, S. Migot, X. Marie, H. Rinnert, S. Mangin, J. - M. George, P. Renucci, Y. Lu, Co-Fe-B/MgO/Ge Spin Photodiode Operating at Telecommunication Wavelength with Zero Applied Magnetic Field. Physical Review Applied. 10, 044049 (2018).
    Résumé : The spin photodiode is essential for decoding circularly polarized light for future applications in optical telecommunication. However, most spin photodiodes only work with a large applied magnetic field, because of the in-plane magnetization of the spin detector. The authors investigate the growth and spin-polarized photocurrent of a perpendicularly magnetized Co-Fe-B/MgO spin detector on germanium. Without using any magnetic field, they obtain asymmetry in photocurrent helicity that is detectable at room temperature, for 1310-nm light. This work will impact the development of devices for the optical transport of spin information.
    Mots-clés : Semiconductors and Spintronics.

  • M. Evelt, L. Soumah, A. B. Rinkevich, S. O. Demokritov, A. Anane, V. Cros, J. B. Youssef, G. de Loubens, O. Klein, P. Bortolotti, V. E. Demidov, Emission of Coherent Propagating Magnons by Insulator-Based Spin-Orbit-Torque Oscillators. Physical Review Applied. 10, 041002 (2018).
    Résumé : The emerging field of $m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}s$ utilizes propagating coherent magnons (collective excitations of electron spins) as carriers of information. Scaling down magnonic devices requires finding new approaches to the efficient excitation of magnons at nanoscale. This study demonstrates an approach to excite coherent GHz-frequency magnons in magnetic insulators by means of dc electric currents. The proposed method opens a route for implementing highly efficient nanomagnonic computing systems.

  • A. Fert, Peter Grünberg, a great name in the field of magnetism and 2007 laureate of Nobel Prize in Physics passed away on April 7, 2018. Journal of Magnetism and Magnetic Materials. 466, A1-A2 (2018).

  • A. Fert, Peter Grünberg (1939-2018). Nature. 557, 638 (2018).
    Résumé : Physicist who revolutionized data storage with work on magnetism in nanomaterials.

  • T. Fördös, K. Postava, H. Jaffrès, D. Q. To, J. Pištora, H. - J. Drouhin, Mueller matrix ellipsometric study of multilayer spin-VCSEL structures with local optical anisotropy. Applied Physics Letters. 112, 221106 (2018).
    Résumé : Spin-laser structures such as spin-polarized vertical-cavity surface-emitting lasers are semiconductor devices in which the radiative recombination processes involving spin-polarized carriers result in an emission of circularly polarized photons. Nevertheless, additional linear in-plane anisotropies in the cavity, e.g., interfacial and surface anisotropies, generally lead to preferential linearly polarized laser emission and to possible coupling between modes. We present Mueller matrix ellipsometric study of non-intentionally doped InGaAs/GaAsP laser structures devoted for optical pumping operations in the spectral range from 0.73 to 6.4 eV in order to disentangle surface and quantum wells contributions to the linear optical birefringence of the structures. The measurement of full 4 × 4 Mueller matrix for multiple angles of incidence and in-plane azimuthal angles in combination with proper parametrization of optical functions has been used for extraction of optical permittivity tensor components along [11...

  • M. Galbiati, A. Vecchiola, S. Mañas-Valero, J. Canet-Ferrer, R. Galceran, M. Piquemal-Banci, F. Godel, A. Forment-Aliaga, B. Dlubak, P. Seneor, E. Coronado, A Local Study of the Transport Mechanisms in MoS2 Layers for Magnetic Tunnel Junctions. ACS Applied Materials & Interfaces. 10, 30017 (2018).
    Résumé : A Local Study of the Transport Mechanisms in MoS2 Layers for Magnetic Tunnel Junctions

  • J. Hu, B. Ernst, S. Tu, M. Kuveždić, A. Hamzić, E. Tafra, M. Basletić, Y. Zhang, A. Markou, C. Felser, A. Fert, W. Zhao, J. - P. Ansermet, H. Yu, Anomalous Hall and Nernst Effects in Co2TiSn and Co2Ti0.6V0.4Sn Heusler Thin Films. Physical Review Applied. 10, 044037 (2018).
    Résumé : The cobalt-based Heusler alloys are promising for spintronic applications, thanks to their high spin polarization and half-metallic character. This work investigates the spin-dependent transport and thermoelectric effects in epitaxial Co${}_{2}$TiSn thin films, with and without V doping. The anomalous Nernst angle and anomalous Hall angle are both determined, and the relationship between these two important parameters is discussed. These experimental results are a step toward realizing spin-caloritronic devices for efficient on-chip energy harvesting of waste heat.

  • T. Huong Dang, D. Quang To, E. Erina, T. L. Hoai Nguyen, V. I. Safarov, H. Jaffrès, H. - J. Drouhin, dans Journal of Magnetism and Magnetic Materials (2018)vol. 459p. 37-42.
    Résumé : We report on the investigation of carrier tunneling asymmetry at ferromagnet-semiconductor junctions. By an analytical 2 x 2 spin model, we show that, when Dresselhaus interactions is included in the conduction band of III-V semiconductors (T-d or D-2d symmetry group), the electrons may undergo a difference of transmission vs. the sign of their incident parallel wavevector normal to the in-plane magnetization. The asymmetry of transmission also exists in the valence band of semiconductors owing to the inner atomic spin-orbit strength and free of asymmetric potentials in bulk or at interfaces. We present advanced multiband 14 x 14 and 30 x 30 k.p tunneling models together with tunneling transport perturbation calculations based on Green's function techniques corroborating these results. Those demonstrate that a tunneling spin-current normal to the interface can generate a transverse surface charge current, the so-called Anomalous Tunnel Hall Effect. (C) 2017 Elsevier B.V. All rights reserved.

  • A. Labbé, E. Parzy, E. Thiaudière, P. Massot, J. - M. Franconi, C. Ulysse, Y. Lemaître, B. Marcilhac, D. Crété, J. Kermorvant, Effects of flux pinning on the DC characteristics of meander-shaped superconducting quantum interference filters with flux concentrator. Journal of Applied Physics. 124, 214503 (2018).
    Résumé : Superconducting quantum interference filters, or SQIFs, are a promising class of highly sensitive magnetometers benefiting from a highly peaked and symmetric magnetic response at zero-input flux. They can be used in magnetometry, e.g., in wideband applications. A simple solution to increase further their sensitivity is to add a superconducting flux concentrator (SFC) to their design. Using the ion irradiation process, we designed a meander-shaped SQIF enhanced with an SFC. The SFC improved the SQIF transfer factor by a factor of 8.4. However, high temperature superconducting (HTSc) devices are vulnerable to flux pinning, which can severely hinder their response. On the one hand, HTSc technologies alleviate the burden of cryogenics. On the other hand, applications that use SFCs in noisy and unshielded environments will become possible only if a better understanding of how this flux impacts the device’s properties is achieved. We studied the relationship between the field present during the cooling process ...
    Mots-clés : Supra.

  • W. Legrand, J. - Y. Chauleau, D. Maccariello, N. Reyren, S. Collin, K. Bouzehouane, N. Jaouen, V. Cros, A. Fert, Hybrid chiral domain walls and skyrmions in magnetic multilayers. Science Advances. 4, eaat0415 (2018).
    Résumé : <p>Noncollinear spin textures in ferromagnetic ultrathin films are currently the subject of renewed interest since the discovery of the interfacial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric exchange interaction selects a given chirality for the spin textures and allows stabilizing configurations with nontrivial topology including chiral domain walls (DWs) and magnetic skyrmions. Moreover, it has many crucial consequences on the dynamical properties of these topological structures. In recent years, the study of noncollinear spin textures has been extended from single ultrathin layers to magnetic multilayers with broken inversion symmetry. This extension of the structures in the vertical dimension allows room temperature stability and very efficient current-induced motion for both Néel DWs and skyrmions. We show how, in these multilayered systems, the interlayer interactions can actually lead to hybrid chiral magnetization arrangements. The described thickness-dependent reorientation of DWs is experimentally confirmed by studying demagnetized multilayers through circular dichroism in x-ray resonant magnetic scattering. We also demonstrate a simple yet reliable method for determining the magnitude of the DMI from static domain measurements even in the presence of these hybrid chiral structures by taking into account the actual profile of the DWs. The existence of these novel hybrid chiral textures has far-reaching implications on how to stabilize and manipulate DWs, as well as skymionic structures in magnetic multilayers.</p>

  • W. Legrand, N. Ronceray, N. Reyren, D. Maccariello, V. Cros, A. Fert, Modeling the Shape of Axisymmetric Skyrmions in Magnetic Multilayers. Physical Review Applied. 10, 064042 (2018).
    Résumé : Magnetic skyrmions (arrangements of spins featuring topological properties) are candidates to implement information bits in devices for combined data storage and logic processing. A prerequisite is the further optimization of the host magnetic multilayers, to obtain sufficiently stable and mobile skyrmions below 10 nm in size. This study develops an extensive model of skyrmions in magnetic multilayers, allowing analysis or prediction of their size, magnetic structure, and dynamical behavior. This model establishes guidelines for optimizing multilayer properties on the way to applications of magnetic skyrmions.

  • Y. Li, X. de Milly, O. Klein, V. Cros, J. Grollier, G. De Loubens, Selective control of vortex polarities by microwave field in two robustly synchronized spin-torque nano-oscillators. Applied Physics Letters. 112, 022405 (2018).
    Résumé : Manipulating operation states of coupled spin-torque nano-oscillators (STNOs), including their synchronization, is essential for applications such as complex oscillator networks. In this work, we experimentally demonstrate selective control of two coupled vortex STNOs through microwave-assisted switching of their vortex core polarities. First, the two oscillators are shown to synchronize due to the dipolar interaction in a broad frequency range tuned by an external biasing field. Coherent output is demonstrated along with strong linewidth reduction. Then, we show individual vortex polarity control of each oscillator, which leads to synchronization/desynchronization due to accompanied frequency shift. Our methods can be easily extended to multiple-element coupled oscillator networks.

  • Z. Liao, N. Gauquelin, R. J. Green, K. Müller-Caspary, I. Lobato, L. Li, S. V. Aert, J. Verbeeck, M. Huijben, M. - N. Grisolia, V. Rouco, R. El Hage, J. - E. Villegas, A. Mercy, M. Bibes, P. Ghosez, G. A. Sawatzky, G. Rijnders, G. Koster, Metal–insulator-transition engineering by modulation tilt-control in perovskite nickelates for room temperature optical switching. Proceedings of the National Academy of Sciences. 115, 9515-9520 (2018).
    Résumé : <p>In transition metal perovskites ABO<sub>3</sub>, the physical properties are largely driven by the rotations of the BO<sub>6</sub> octahedra, which can be tuned in thin films through strain and dimensionality control. However, both approaches have fundamental and practical limitations due to discrete and indirect variations in bond angles, bond lengths, and film symmetry by using commercially available substrates. Here, we introduce modulation tilt control as an approach to tune the ground state of perovskite oxide thin films by acting explicitly on the oxygen octahedra rotation modes—that is, directly on the bond angles. By intercalating the prototype SmNiO<sub>3</sub> target material with a tilt-control layer, we cause the system to change the natural amplitude of a given rotation mode without affecting the interactions. In contrast to strain and dimensionality engineering, our method enables a continuous fine-tuning of the materials’ properties. This is achieved through two independent adjustable parameters: the nature of the tilt-control material (through its symmetry, elastic constants, and oxygen rotation angles), and the relative thicknesses of the target and tilt-control materials. As a result, a magnetic and electronic phase diagram can be obtained, normally only accessible by A-site element substitution, within the single SmNiO<sub>3</sub> compound. With this unique approach, we successfully adjusted the metal–insulator transition (MIT) to room temperature to fulfill the desired conditions for optical switching applications.</p>

  • L. Lόpez-Mir, C. Frontera, H. Aramberri, K. Bouzehouane, J. Cisneros-Fernández, B. Bozzo, L. Balcells, B. Martínez, Anisotropic sensor and memory device with a ferromagnetic tunnel barrier as the only magnetic element. Scientific Reports. 8, 861 (2018).
    Résumé : Multiple spin functionalities are probed on Pt/La2Co0.8Mn1.2O6/Nb:SrTiO3, a device composed by a ferromagnetic insulating barrier sandwiched between non-magnetic electrodes. Uniquely, La2Co0.8Mn1.2O6 thin films present strong perpendicular magnetic anisotropy of magnetocrystalline origin, property of major interest for spintronics. The junction has an estimated spin-filtering efficiency of 99.7% and tunneling anisotropic magnetoresistance (TAMR) values up to 30% at low temperatures. This remarkable angular dependence of the magnetoresistance is associated with the magnetic anisotropy whose origin lies in the large spin-orbit interaction of Co2+ which is additionally tuned by the strain of the crystal lattice. Furthermore, we found that the junction can operate as an electrically readable magnetic memory device. The findings of this work demonstrate that a single ferromagnetic insulating barrier with strong magnetocrystalline anisotropy is sufficient for realizing sensor and memory functionalities in a tunneling device based on TAMR.

  • D. Maccariello, W. Legrand, N. Reyren, K. Garcia, K. Bouzehouane, S. Collin, V. Cros, A. Fert, Electrical detection of single magnetic skyrmions in metallic multilayers at room temperature. Nature Nanotechnology. 13, 233 (2018).
    Résumé : <p>Single magnetic skyrmions are electrically detected in magnetic multilayers at room temperature, and their main contribution to the signal, which is enhanced for tracks approaching the size of the skyrmions, comes from the anomalous—rather than topological—Hall effect.</p>
    Mots-clés : Spinorbitronics.

  • 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; // Series in Materials Sciencep. .

  • 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).

  • 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>

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