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Wittrock S, Perna S, Lebrun R, Ho K, Dutra R, Ferreira R, Bortolotti P, Serpico C, Cros V. Non-hermiticity in spintronics: oscillation death in coupled spintronic nano-oscillators through emerging exceptional points. Nat Commun 2024; 15:971. [PMID: 38302454 PMCID: PMC10834588 DOI: 10.1038/s41467-023-44436-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 12/13/2023] [Indexed: 02/03/2024] Open
Abstract
The emergence of exceptional points (EPs) in the parameter space of a non-hermitian (2D) eigenvalue problem has long been interest in mathematical physics, however, only in the last decade entered the scope of experiments. In coupled systems, EPs give rise to unique physical phenomena, and enable the development of highly sensitive sensors. Here, we demonstrate at room temperature the emergence of EPs in coupled spintronic nanoscale oscillators and exploit the system's non-hermiticity. We observe amplitude death of self-oscillations and other complex dynamics, and develop a linearized non-hermitian model of the coupled spintronic system, which describes the main experimental features. The room temperature operation, and CMOS compatibility of our spintronic nanoscale oscillators means that they are ready to be employed in a variety of applications, such as field, current or rotation sensors, radiofrequeny and wireless devices, and in dedicated neuromorphic computing hardware. Furthermore, their unique and versatile properties, notably their large nonlinear behavior, open up unprecedented perspectives in experiments as well as in theory on the physics of exceptional points expanding to strongly nonlinear systems.
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Affiliation(s)
- Steffen Wittrock
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France.
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany.
| | - Salvatore Perna
- Department of Electrical Engineering and ICT, University of Naples Federico II, 80125, Naples, Italy
| | - Romain Lebrun
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Katia Ho
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Roberta Dutra
- Centro Brasileiro de Pesquisas Fésicas (CBPF), Rua Dr. Xavier Sigaud 150, Rio de Janeiro, 22290-180, Brazil
| | - Ricardo Ferreira
- International Iberian Nanotechnology Laboratory (INL), 471531, Braga, Portugal
| | - Paolo Bortolotti
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Claudio Serpico
- Department of Electrical Engineering and ICT, University of Naples Federico II, 80125, Naples, Italy
| | - Vincent Cros
- Laboratoire Albert Fert, CNRS, Thales, Université Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France.
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2
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Shreya S, Jenkins AS, Rezaeiyan Y, Li R, Böhnert T, Benetti L, Ferreira R, Moradi F, Farkhani H. Granular vortex spin-torque nano oscillator for reservoir computing. Sci Rep 2023; 13:16722. [PMID: 37794052 PMCID: PMC10550924 DOI: 10.1038/s41598-023-43923-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Accepted: 09/30/2023] [Indexed: 10/06/2023] Open
Abstract
In this paper, we investigate the granularity in the free layer of the magnetic tunnel junctions (MTJ) and its potential to function as a reservoir for reservoir computing where grains act as oscillatory neurons while the device is in the vortex state. The input of the reservoir is applied in the form of a magnetic field which can pin the vortex core into different grains of the device in the magnetic vortex state. The oscillation frequency and MTJ resistance vary across different grains in a non-linear fashion making them great candidates to be served as the reservoir's outputs for classification objectives. Hence, we propose an experimentally validated area-efficient single granular vortex spin-torque nano oscillator (GV-STNO) device in which pinning sites work as random reservoirs that can emulate neuronal functions. We harness the nonlinear oscillation frequency and resistance exhibited by the vortex core granular pinning of the GV-STNO reservoir computing system to demonstrate waveform classification.
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Affiliation(s)
- S Shreya
- Electrical and Computer Engineering Department, Aarhus University, 8200, Aarhus, Denmark.
| | - A S Jenkins
- International Iberian Nanotechnology Laboratory (INL), Braga, Portugal
| | - Y Rezaeiyan
- Electrical and Computer Engineering Department, Aarhus University, 8200, Aarhus, Denmark
| | - R Li
- Electrical and Computer Engineering Department, Aarhus University, 8200, Aarhus, Denmark
| | - T Böhnert
- International Iberian Nanotechnology Laboratory (INL), Braga, Portugal
| | - L Benetti
- International Iberian Nanotechnology Laboratory (INL), Braga, Portugal
| | - R Ferreira
- International Iberian Nanotechnology Laboratory (INL), Braga, Portugal
| | - F Moradi
- Electrical and Computer Engineering Department, Aarhus University, 8200, Aarhus, Denmark
| | - H Farkhani
- Electrical and Computer Engineering Department, Aarhus University, 8200, Aarhus, Denmark.
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3
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Imai Y, Taniguchi T. Associative memory by virtual oscillator network based on single spin-torque oscillator. Sci Rep 2023; 13:15809. [PMID: 37737250 PMCID: PMC10517175 DOI: 10.1038/s41598-023-42951-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 09/16/2023] [Indexed: 09/23/2023] Open
Abstract
A coupled oscillator network may be able to perform an energy-efficient associative memory operation. However, its realization has been difficult because inhomogeneities unavoidably arise among the oscillators during fabrication and lead to an unreliable operation. This issue could be resolved if the oscillator network were able to be formed from a single oscillator. Here, we performed numerical simulations and theoretical analyses on an associative memory operation that uses a virtual oscillator network based on a spin-torque oscillator. The virtual network combines the concept of coupled oscillators with that of feedforward neural networks. Numerical experiments demonstrate successful associations of 60-pixel patterns with various memorized patterns. Moreover, the origin of the associative memory is shown to be forced synchronization driven by feedforward input, where phase differences among oscillators are fixed and correspond to the colors of the pixels in the pattern.
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Affiliation(s)
- Yusuke Imai
- National Institute of Advanced Industrial Science and Technology (AIST), Research Center for Emerging Computing Technologies, Tsukuba, Ibaraki, 305-8568, Japan
| | - Tomohiro Taniguchi
- National Institute of Advanced Industrial Science and Technology (AIST), Research Center for Emerging Computing Technologies, Tsukuba, Ibaraki, 305-8568, Japan.
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4
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Spontaneous generation and active manipulation of real-space optical vortices. Nature 2022; 611:48-54. [PMID: 36224392 DOI: 10.1038/s41586-022-05229-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 08/11/2022] [Indexed: 11/09/2022]
Abstract
Optical vortices are beams of light that carry orbital angular momentum1, which represents an extra degree of freedom that can be generated and manipulated for photonic applications2-8. Unlike vortices in other physical entities, the generation of optical vortices requires structural singularities9-12, but this affects their quasiparticle nature and hampers the possibility of altering their dynamics or making them interacting13-17. Here we report a platform that allows the spontaneous generation and active manipulation of an optical vortex-antivortex pair using an external field. An aluminium/silicon dioxide/nickel/silicon dioxide multilayer structure realizes a gradient-thickness optical cavity, where the magneto-optic effects of the nickel layer affect the transition between a trivial and a non-trivial topological phase. Rather than a structural singularity, the vortex-antivortex pairs present in the light reflected by our device are generated through mathematical singularities in the generalized parameter space of the top and bottom silicon dioxide layers, which can be mapped onto real space and exhibit polarization-dependent and topology-dependent dynamics driven by external magnetic fields. We expect that the field-induced engineering of optical vortices that we report will facilitate the study of topological photonic interactions and inspire further efforts to bestow quasiparticle-like properties to various topological photonic textures such as toroidal vortices, polarization and vortex knots, and optical skyrmions.
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Martins L, Jenkins AS, Alvarez LSE, Borme J, Böhnert T, Ventura J, Freitas PP, Ferreira R. Non-volatile artificial synapse based on a vortex nano-oscillator. Sci Rep 2021; 11:16094. [PMID: 34373533 PMCID: PMC8352962 DOI: 10.1038/s41598-021-95569-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2021] [Accepted: 07/07/2021] [Indexed: 02/07/2023] Open
Abstract
In this work, a new mechanism to combine a non-volatile behaviour with the spin diode detection of a vortex-based spin torque nano-oscillator (STVO) is presented. Experimentally, it is observed that the spin diode response of the oscillator depends on the vortex chirality. Consequently, fixing the frequency of the incoming signal and switching the vortex chirality results in a different rectified voltage. In this way, the chirality can be deterministically controlled via the application of electrical signals injected locally in the device, resulting in a non-volatile control of the output voltage for a given input frequency. Micromagnetic simulations corroborate the experimental results and show the main contribution of the Oersted field created by the input RF current density in defining two distinct spin diode detections for different chiralities. By using two non-identical STVOs, we show how these devices can be used as programmable non-volatile synapses in artificial neural networks.
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Affiliation(s)
- Leandro Martins
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal ,grid.5808.50000 0001 1503 7226IFIMUP-IN, Rua do Campo Alegre, 678, 4169-007 Porto, Portugal
| | - Alex S. Jenkins
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal
| | | | - Jérôme Borme
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal
| | - Tim Böhnert
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal
| | - João Ventura
- grid.5808.50000 0001 1503 7226IFIMUP-IN, Rua do Campo Alegre, 678, 4169-007 Porto, Portugal
| | - Paulo P. Freitas
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal
| | - Ricardo Ferreira
- grid.420330.60000 0004 0521 6935INL, Avenida Mestre José Veiga, s/n, 4715-330 Braga, Portugal
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Wittrock S, Talatchian P, Tsunegi S, Crété D, Yakushiji K, Bortolotti P, Ebels U, Fukushima A, Kubota H, Yuasa S, Grollier J, Cibiel G, Galliou S, Rubiola E, Cros V. Influence of flicker noise and nonlinearity on the frequency spectrum of spin torque nano-oscillators. Sci Rep 2020; 10:13116. [PMID: 32753722 PMCID: PMC7403434 DOI: 10.1038/s41598-020-70076-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Accepted: 07/22/2020] [Indexed: 11/23/2022] Open
Abstract
The correlation of phase fluctuations in any type of oscillator fundamentally defines its spectral shape. However, in nonlinear oscillators, such as spin torque nano-oscillators, the frequency spectrum can become particularly complex. This is specifically true when not only considering thermal but also colored 1/f flicker noise processes, which are crucial in the context of the oscillator’s long term stability. In this study, we address the frequency spectrum of spin torque oscillators in the regime of large-amplitude steady oscillations experimentally and as well theoretically. We particularly take both thermal and flicker noise into account. We perform a series of measurements of the phase noise and the spectrum on spin torque vortex oscillators, notably varying the measurement time duration. Furthermore, we develop the modelling of thermal and flicker noise in Thiele equation based simulations. We also derive the complete phase variance in the framework of the nonlinear auto-oscillator theory and deduce the actual frequency spectrum. We investigate its dependence on the measurement time duration and compare with the experimental results. Long term stability is important in several of the recent applicative developments of spin torque oscillators. This study brings some insights on how to better address this issue.
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Affiliation(s)
- Steffen Wittrock
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France.
| | - Philippe Talatchian
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France.,Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, 20899-6202, MD, USA
| | - Sumito Tsunegi
- National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki, 305-8568, Japan
| | - Denis Crété
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Kay Yakushiji
- National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki, 305-8568, Japan
| | - Paolo Bortolotti
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Ursula Ebels
- Univ. Grenoble Alpes, CEA, INAC-SPINTEC, CNRS, SPINTEC, 38000, Grenoble, France
| | - Akio Fukushima
- National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki, 305-8568, Japan
| | - Hitoshi Kubota
- National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki, 305-8568, Japan
| | - Shinji Yuasa
- National Institute of Advanced Industrial Science and Technology (AIST), Spintronics Research Center, Tsukuba, Ibaraki, 305-8568, Japan
| | - Julie Grollier
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
| | - Gilles Cibiel
- Centre National d'Études Spatiales (CNES), 18 av. Edouard Belin, 31401, Toulouse, France
| | - Serge Galliou
- FEMTO-ST Institute, CNRS, Univ. Bourgogne Franche Comté, 25030, Besançon, France
| | - Enrico Rubiola
- FEMTO-ST Institute, CNRS, Univ. Bourgogne Franche Comté, 25030, Besançon, France
| | - Vincent Cros
- Unité Mixte de Physique CNRS, Thales, Univ. Paris-Sud, Univ. Paris-Saclay, 1 Avenue Augustin Fresnel, 91767, Palaiseau, France
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7
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Jenkins AS, Alvarez LSE, Freitas PP, Ferreira R. Digital and analogue modulation and demodulation scheme using vortex-based spin torque nano-oscillators. Sci Rep 2020; 10:11181. [PMID: 32636523 PMCID: PMC7341870 DOI: 10.1038/s41598-020-68001-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 05/18/2020] [Indexed: 11/09/2022] Open
Abstract
In conventional communications systems, information is transmitted by modulating the frequency, amplitude or phase of the carrier signal, which often occurs in a binary fashion over a very narrow bandwidth. Recently, ultra-wideband signal transmission has gained interest for local communications in technologies such as autonomous local sensor networks and on-chip communications, which presents a challenge for conventional electronics. Spin-torque nano-oscillators (STNOs) have been studied as a potentially low power highly tunable frequency source, and in this report we expand on this to show how a specific dynamic phase present in vortex-based STNOs makes them also well suited as Wideband Analogue Dynamic Sensors (WADS). This multi-functionality of the STNOs is the basis of a new modulation and demodulation scheme, where nominally identical devices can be used to transmit information in both a digital or analogue manner, with the potential to allow the highly efficient transmittance of data.
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Affiliation(s)
- Alex S Jenkins
- International Iberian Nanotechnology Laboratory, INL, Av. Mestre José Veiga s/n, 4715-330, Braga, Portugal.
| | - Lara San Emeterio Alvarez
- International Iberian Nanotechnology Laboratory, INL, Av. Mestre José Veiga s/n, 4715-330, Braga, Portugal
| | - Paulo P Freitas
- International Iberian Nanotechnology Laboratory, INL, Av. Mestre José Veiga s/n, 4715-330, Braga, Portugal
| | - Ricardo Ferreira
- International Iberian Nanotechnology Laboratory, INL, Av. Mestre José Veiga s/n, 4715-330, Braga, Portugal
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8
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Nanoscale true random bit generator based on magnetic state transitions in magnetic tunnel junctions. Sci Rep 2019; 9:15661. [PMID: 31666671 PMCID: PMC6821798 DOI: 10.1038/s41598-019-52236-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 09/16/2019] [Indexed: 11/08/2022] Open
Abstract
We present an investigation into the in-plane field induced free layer state transitions found in magnetic tunnel junctions. By applying an ac current into an integrated field antenna, the magnetisation of the free layer can be switched between the magnetic vortex state and the quasi-uniform anti-parallel state. When in the magnetic vortex state, the vortex core gyrates a discrete number of times, and at certain frequencies there is a 50% chance of the core gyrating n or n - 1 times, leading to the proposal of a novel nanoscale continuous digital true random bit generator.
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9
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Mutual synchronization of spin torque nano-oscillators through a long-range and tunable electrical coupling scheme. Nat Commun 2017; 8:15825. [PMID: 28604670 PMCID: PMC5472782 DOI: 10.1038/ncomms15825] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 05/01/2017] [Indexed: 11/24/2022] Open
Abstract
The concept of spin-torque-driven high-frequency magnetization dynamics, allows the potential construction of complex networks of non-linear dynamical nanoscale systems, combining the field of spintronics and the study of non-linear systems. In the few previous demonstrations of synchronization of several spin-torque oscillators, the short-range nature of the magnetic coupling that was used has largely hampered a complete control of the synchronization process. Here we demonstrate the successful mutual synchronization of two spin-torque oscillators with a large separation distance through their long range self-emitted microwave currents. This leads to a strong improvement of both the emitted power and the linewidth. The full control of the synchronized state is achieved at the nanoscale through two active spin transfer torques, but also externally through an electrical delay line. These additional levels of control of the synchronization capability provide a new approach to develop spin-torque oscillator-based nanoscale microwave-devices going from microwave-sources to bio-inspired networks. 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 power and signal linewidth.
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Self-Injection Locking of a Vortex Spin Torque Oscillator by Delayed Feedback. Sci Rep 2016; 6:26849. [PMID: 27241747 PMCID: PMC4886513 DOI: 10.1038/srep26849] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 05/06/2016] [Indexed: 11/25/2022] Open
Abstract
The self-synchronization of spin torque oscillators is investigated experimentally by re-injecting its radiofrequency (rf) current after a certain delay time. We demonstrate that the integrated power and spectral linewidth are improved for optimal delays. Moreover by varying the phase difference between the emitted power and the re-injected one, we find a clear oscillatory dependence on the phase difference with a 2π periodicity of the frequency of the oscillator as well as its power and linewidth. Such periodical behavior within the self-injection regime is well described by the general model of nonlinear auto-oscillators including not only a delayed rf current but also all spin torque forces responsible for the self-synchronization. Our results reveal new approaches for controlling the non-autonomous dynamics of spin torque oscillators, a key issue for rf spintronics applications as well as for the development of neuro-inspired spin-torque oscillators based devices.
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