29 results on '"Wittrock, Steffen"'
Search Results
2. Tailoring Optical Excitation to Control Magnetic Skyrmion Nucleation
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Kern, Lisa-Marie, Pfau, Bastian, Schneider, Michael, Gerlinger, Kathinka, Deinhart, Victor, Wittrock, Steffen, Sidiropoulos, Themistoklis, Engel, Dieter, Will, Ingo, Günther, Christian M., Litzius, Kai, Wintz, Sebastian, Weigand, Markus, Büttner, Felix, and Eisebitt, Stefan
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Condensed Matter - Materials Science ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
In ferromagnetic multilayers, a single laser pulse with a fluence above an optical nucleation threshold can create magnetic skyrmions, which are randomly distributed over the area of the laser spot. However, in order to study the dynamics of skyrmions and for their application in future data technology, a controllable localization of the skyrmion nucleation sites is crucial. Here, it is demonstrated that patterned reflective masks behind a thin magnetic film can be designed to locally tailor the optical excitation amplitudes reached, leading to spatially controlled skyrmion nucleation on the nanometer scale. Using x-ray microscopy, the influence of nanopatterned back-side aluminum masks on the optical excitation is studied in two sample geometries with varying layer sequence of substrate and magnetic Co/Pt multilayer. Surprisingly, the masks' effect on suppressing or enhancing skymion nucleation reverses when changing this sequence. Moreover, optical near-field enhancements additionally affect the spatial arrangement of the nucleated skyrmions. Simulations of the spatial modulation of the laser excitation, and the following heat transfer across the interfaces in the two sample geometries are employed to explain these observations. The results demonstrate a reliable approach to add nanometer-scale spatial control to optically induced magnetization processes on ultrafast timescales.
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- 2022
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3. Stabilization of phase noise in spin torque nano oscillators by a phase locked loop
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Wittrock, Steffen, Kreißig, Martin, Lacoste, Bertrand, Litvinenko, Artem, Talatchian, Philippe, Protze, Florian, Ellinger, Frank, Ferreira, Ricardo, Lebrun, Romain, Bortolotti, Paolo, Buda-Prejbeanu, Liliana, Ebels, Ursula, and Cros, Vincent
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Physics - Applied Physics ,Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
The main limitation in order to exploit spin torque nano-oscillators (STNOs) in various potential applications is their large phase noise. In this work, we demonstrate its efficient reduction by a highly reconfigurable, compact, specifically on-chip designed PLL based on custom integrated circuits. First, we thoroughly study the parameter space of the PLL+STNO system experimentally. Second, we present a theory which describes the locking of a STNO to an external signal in a general sense. In our developed theory, we do not restrict ourselves to the case of a perfect phase locking but also consider phase slips and the corresponding low offset frequency $1/f^2$ noise, so far the main drawback in such systems. Combining experiment and theory allows us to reveal complex parameter dependences of the system's phase noise. The results provide an important step for the optimization of noise properties and thus leverage the exploitation of STNOs in prospective real applications.
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- 2021
4. Non-hermiticity in spintronics: oscillation death in coupled spintronic nano-oscillators through emerging exceptional points
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Wittrock, Steffen, Perna, Salvatore, Lebrun, Romain, Ho, Katia, Dutra, Roberta, Ferreira, Ricardo, Bortolotti, Paolo, Serpico, Claudio, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
The emergence of exceptional points (EPs) in the parameter space of a non-hermitian (2D) eigenvalue problem is studied in a general sense in mathematical physics, and has in the last decade successively reached the scope of experiments. In coupled systems, it gives rise to unique physical phenomena, which enable novel approaches for the development of seminal types of highly sensitive sensors. Here, we demonstrate at room temperature the emergence of EPs in coupled spintronic nanoscale oscillators and hence exploit the system's non-hermiticity. We describe the observation of amplitude death of self-oscillations and other complex dynamics, and develop a linearized non-hermitian model of the coupled spintronic system, which properly describes the main experimental features. Interestingly, these spintronic nanoscale oscillators are deployment-ready in different applicational technologies, such as field, current or rotation sensors, radiofrequeny and wireless devices and, more recently, novel neuromorphic hardware solutions. 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. Furthermore, the exploitation of EPs in spintronics devises a new paradigm for ultrasensitive nanoscale sensors and the implementation of complex dynamics in the framework of non-conventional computing.
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- 2021
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5. Flicker and random telegraph noise between gyrotropic and dynamic C-state of a vortex based spin torque nano oscillator
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Wittrock, Steffen, Talatchian, Philippe, Romera, Miguel, Garcia, Mafalda Jotta, Cyrille, Marie-Claire, Ferreira, Ricardo, Lebrun, Romain, Bortolotti, Paolo, Ebels, Ursula, Grollier, Julie, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science ,Condensed Matter - Other Condensed Matter - Abstract
Vortex based spin torque nano oscillators (STVOs) can present more complex dynamics than the spin torque induced gyrotropic (G) motion of the vortex core. The respective dynamic modes and the transition between them can be controlled by experimental parameters such as the applied dc current. An interesting behavior is the stochastic transition from the G- to a dynamic C-state occurring for large current densities. Moreover, the C-state oscillations exhibit a constant active magnetic volume. We present noise measurements in the different dynamic states that allow accessing specific properties of the stochastic transition, such as the characteristic state transition frequency. Furthermore,we confirm, as theoretically predicted, an increase of flicker noise with $I_{dc}^2$ when the oscillation volume remains constant with the current. These results bring insight into the potential optimization of noise properties sought for many potential rf applications with spin torque oscillators. Furthermore, the investigated stochastic characteristics open up new potentialities, for instance in the emerging field of neuromorphic computing schemes.
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- 2021
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6. Spin-torque Dynamics for Noise Reduction in Vortex-based Sensors
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Garcia, Mafalda Jotta, Moulin, Julien, Wittrock, Steffen, Tsunegi, Sumito, Yakushiji, Kay, Fukushima, Akio, Kubota, Hitoshi, Yuasa, Shinji, Ebels, Ursula, Pannetier-Lecoeur, Myriam, Fermon, Claude, Lebrun, Romain, Bortolotti, Paolo, Solignac, Aurélie, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Performance of magnetoresistive sensors is today mainly limited by their 1/f low-frequency noise. Here, we study this noise component in vortex-based TMR sensors. We compare the noise level in different magnetization configurations of the device, i.e vortex state or uniform parallel or antiparallel states. We find that the vortex state is at least an order of magnitude noisier than the uniform states. Nevertheless, by activating the spin-transfer induced dynamics of the vortex configuration, we observe a reduction of the 1/f noise, close to the values measured in the AP state, as the vortex core has a lower probability of pinning into defect sites. Additionally, by driving the dynamics of the vortex core by a non-resonant rf field or current we demonstrate that the 1/f noise can be further decreased. The ability to reduce the 1/f low-frequency noise in vortex-based devices by leveraging their spin-transfer dynamics thus enhances their applicability in the magnetic sensors' landscape.
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- 2020
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7. Beyond the gyrotropic motion: dynamic C-state in vortex spin torque oscillators
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Wittrock, Steffen, Talatchian, Philippe, Rabasa, Miguel Romera, Menshawy, Samh, Garcia, Mafalda Jotta, Cyrille, Marie-Claire, Ferreira, Ricardo, Lebrun, Romain, Bortolotti, Paolo, Ebels, Ursula, Grollier, Julie, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science ,Condensed Matter - Other Condensed Matter - Abstract
In the present study, we investigate a dynamical mode beyond the gyrotropic (G) motion of a magnetic vortex core in a confined magnetic disk of a nano-pillar spin torque nano oscillator. It is characterized by the in-plane circular precession associated to a C-shaped magnetization distribution. We show a transition between G and C-state mode which is found to be purely stochastic in a current-controllable range. Supporting our experimental findings with micromagnetic simulations, we believe that the results provide novel opportunities for the dynamic and stochastic control of STOs, which could be interesting to be implemented for example in neuromorphic networks.
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- 2020
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8. Influence of flicker noise and nonlinearity on the frequency spectrum of spin torque nano-oscillators
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Wittrock, Steffen, Talatchian, Philippe, Tsunegi, Sumito, Crété, Denis, Yakushiji, Kay, Bortolotti, Paolo, Ebels, Ursula, Fukushima, Akio, Kubota, Hitoshi, Yuasa, Shinji, Grollier, Julie, Cibiel, Gilles, Galliou, Serge, Rubiola, Enrico, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics - 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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- 2020
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9. Spin-current manipulation of photoinduced magnetization dynamics in heavy metal / ferromagnet double layer based nanostructures
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Wittrock, Steffen, Meyer, Dennis, Müller, Markus, Ulrichs, Henning, Walowski, Jakob, Mansurova, Maria, Martens, Ulrike, and Münzenberg, Markus
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
Spin currents offer a way to control static and dynamic magnetic properties, and therefore they are crucial for next-generation MRAM devices or spin-torque oscillators. Manipulating the dynamics is especially interesting within the context of photo-magnonics. In typical $3d$ transition metal ferromagnets like CoFeB, the lifetime of light-induced magnetization dynamics is restricted to about 1 ns, which e.g. strongly limits the opportunities to exploit the wave nature in a magnonic crystal filtering device. Here, we investigate the potential of spin-currents to increase the spin wave lifetime in a functional bilayer system, consisting of a heavy metal (8 nm of $\beta$-Tantalum (Platinum)) and 5 nm CoFeB. Due to the spin Hall effect, the heavy metal layer generates a transverse spin current when a lateral charge current passes through the strip. Using time-resolved all-optical pump-probe spectroscopy, we investigate how this spin current affects the magnetization dynamics in the adjacent CoFeB layer. We observed a linear spin current manipulation of the effective Gilbert damping parameter for the Kittel mode from which we were able to determine the system's spin Hall angles. Furthermore, we measured a strong influence of the spin current on a high-frequency mode. We interpret this mode an an exchange dominated higher order spin-wave resonance. Thus we infer a strong dependence of the exchange constant on the spin current.
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- 2019
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10. Low offset frequency $1/f$ flicker noise in spin torque vortex oscillators
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Wittrock, Steffen, Tsunegi, Sumito, Yakushiji, Kay, Fukushima, Akio, Kubota, Hitoshi, Bortolotti, Paolo, Ebels, Ursula, Yuasa, Shinji, Cibiel, Gilles, Galliou, Serge, Rubiola, Enrico, and Cros, Vincent
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Condensed Matter - Mesoscale and Nanoscale Physics ,Condensed Matter - Materials Science ,Physics - Applied Physics - Abstract
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 TMR-based 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. Hereby, 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 non-constant magnetic oscillation volume, which contributes to the magnetoresistance., Comment: 10 pages
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- 2019
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11. Spin-transfer torque switching at ultra low current densities
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Leutenantsmeyer, Johannes Christian, Zbarsky, Vladyslav, Wittrock, Steffen, Walter, Marvin, Peretzki, Patrick, Schuhmann, Henning, Thomas, Andy, Rott, Karsten, Reiss, Guenter, Kim, Tae Hee, Seibt, Michael, and Muenzenberg, Markus
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Condensed Matter - Materials Science - Abstract
The influence of the tantalum buffer layer on the magnetic anisotropy of perpendicular Co-Fe-B/MgO based magnetic tunnel junctions is studied using magneto-optical Kerr-spectroscopy. Samples without a tantalum buffer are found to exhibit no perpendicular magnetization. The transport of Boron into the tantalum buffer is considered to play an important role on the switching currents of those devices. With the optimized layer stack of a perpendicular tunnel junction, a minimal critical switching current density of only 9.2 kA/cm$^2$ is observed. As of today, this value is the lowest reported value for current-induced magnetization reversal.
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- 2014
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12. Spin-transfer torque switching below 20 kA/cm$^2$ in perpendicular magnetic tunnel junctions
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Leutenantsmeyer, Johannes Christian, Walter, Marvin, Wittrock, Steffen, Peretzki, Patrick, Schuhmann, Henning, Seibt, Michael, and Münzenberg, Markus
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Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
We demonstrate the reduction of critical spin-transfer torque (STT) switching currents in Co-Fe-B/MgO based magnetic tunnel junctions (MTJ) with perpendicular magnetization anisotropy (PMA). The junctions yield tunnel magnetoresistance (TMR) ratios of up to 64% at 4 monolayer (ML) tunnel barrier thickness. In this paper, the reduction of the critical switching current density is studied. By optimizing the applied bias field during DC-STT measurements, ultra low critical switching current densities of less than 20 kA/cm$^2$, even down to 9 kA/cm$^2$, are found. With the reduced switching currents, our samples are ideal candidates for further experimental studies such as the theoretical predicted thermally driven spin-transfer torque effect., Comment: 3 pages, 2 figures
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- 2013
13. Non-hermiticity in spintronics: oscillation death in coupled spintronic nano-oscillators through emerging exceptional points
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Wittrock, Steffen, primary, Perna, Salvatore, additional, Lebrun, Romain, additional, Ho, Katia, additional, Dutra, Roberta, additional, Ferreira, Ricardo, additional, Bortolotti, Paolo, additional, Serpico, Claudio, additional, and Cros, Vincent, additional
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- 2023
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14. Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He+-Ion Irradiation
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Kern, Lisa-Marie, primary, Pfau, Bastian, additional, Deinhart, Victor, additional, Schneider, Michael, additional, Klose, Christopher, additional, Gerlinger, Kathinka, additional, Wittrock, Steffen, additional, Engel, Dieter, additional, Will, Ingo, additional, Günther, Christian M., additional, Liefferink, Rein, additional, Mentink, Johan H., additional, Wintz, Sebastian, additional, Weigand, Markus, additional, Huang, Meng-Jie, additional, Battistelli, Riccardo, additional, Metternich, Daniel, additional, Büttner, Felix, additional, Höflich, Katja, additional, and Eisebitt, Stefan, additional
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- 2022
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15. Exceptional points controlling oscillation death in coupled spintronic nano-oscillators
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Wittrock, Steffen, primary, Perna, Salvatore, additional, Lebrun, Romain, additional, Dutra, Roberta, additional, Ferreira, Ricardo, additional, Bortolotti, Paolo, additional, Serpico, Claudio, additional, and Cros, Vincent, additional
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- 2022
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16. Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He+‑Ion Irradiation.
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Kern, Lisa-Marie, Pfau, Bastian, Deinhart, Victor, Schneider, Michael, Klose, Christopher, Gerlinger, Kathinka, Wittrock, Steffen, Engel, Dieter, Will, Ingo, Günther, Christian M., Liefferink, Rein, Mentink, Johan H., Wintz, Sebastian, Weigand, Markus, Huang, Meng-Jie, Battistelli, Riccardo, Metternich, Daniel, Büttner, Felix, Höflich, Katja, and Eisebitt, Stefan
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- 2022
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17. Spin–torque dynamics for noise reduction in vortex-based sensors
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Jotta Garcia, Mafalda, primary, Moulin, Julien, additional, Wittrock, Steffen, additional, Tsunegi, Sumito, additional, Yakushiji, Kay, additional, Fukushima, Akio, additional, Kubota, Hitoshi, additional, Yuasa, Shinji, additional, Ebels, Ursula, additional, Pannetier-Lecoeur, Myriam, additional, Fermon, Claude, additional, Lebrun, Romain, additional, Bortolotti, Paolo, additional, Solignac, Aurélie, additional, and Cros, Vincent, additional
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- 2021
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18. Flicker and random telegraph noise between gyrotropic and dynamic C-state of a vortex based spin torque nano oscillator
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Wittrock, Steffen, primary, Talatchian, Philippe, additional, Romera, Miguel, additional, Garcia, Mafalda Jotta, additional, Cyrille, Marie-Claire, additional, Ferreira, Ricardo, additional, Lebrun, Romain, additional, Bortolotti, Paolo, additional, Ebels, Ursula, additional, Grollier, Julie, additional, and Cros, Vincent, additional
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- 2021
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19. Beyond the gyrotropic motion: Dynamic C-state in vortex spin torque oscillators
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Wittrock, Steffen, primary, Talatchian, Philippe, additional, Romera, Miguel, additional, Menshawy, Samh, additional, Jotta Garcia, Mafalda, additional, Cyrille, Marie-Claire, additional, Ferreira, Ricardo, additional, Lebrun, Romain, additional, Bortolotti, Paolo, additional, Ebels, Ursula, additional, Grollier, Julie, additional, and Cros, Vincent, additional
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- 2021
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20. Du bruit & la stabilité à la synchronisation & la dynamique complexe dans les nano-oscillateurs à base de transfert de spin
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Wittrock, Steffen, Unité mixte de physique CNRS/Thales (UMPhy CNRS/THALES), Centre National de la Recherche Scientifique (CNRS)-THALES, Université Paris-Saclay, and Vincent Cros
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Points exceptionnels ,Exceptional points ,Bruit ,Synchronisation ,[PHYS.COND.CM-GEN]Physics [physics]/Condensed Matter [cond-mat]/Other [cond-mat.other] ,Spintronique ,Spintronics ,Spin torque nano-Oscillators ,Synchronization ,Noise ,Dynamique couplée ,Coupled dynamics ,Nano-Oscillateurs magnétiques - Abstract
Spin torque nano-oscillators (STNOs) present unique potential functionalities for rf-communications, energy harvesting or next-generation computing. Therewith, they unify hardware multifunctional key capabilities in the framework of Industry 4.0 and emphasize the potentialities of spintronics, even beyond the paradigm of CMOS. Along with the STNO’s nano-size, radiation-hardness, frequency tunability, low energy consumption and CMOS compatibility, their key characteristics is their strong nonlinearity, which opens up the path to various interesting physical phenomena. However, their nonlinearity also causes the oscillators’ poor spectral coherence, which so far limits their applicability in real practical devices. This PhD thesis aims at providing a deeper understanding of the STNO’s noise in the framework of nonlinearity. Generalizable to all types of spintronic oscillators, we experimentally and theoretically study the contribution of 1/f flicker noise at low frequency offsets in vortex based STNOs. We discuss the influence of this type of noise on the oscillation’s spectral shape and demonstrate potential means for efficient coherence improvements. Moreover, this PhD thesis is also dedicated to the coupling and synchronization of several STNOs, since these capabilities facilitate different applicational schemes in prospective technologies. Indeed, beyond synchronization, novel complex phenomena are experimentally demonstrated and studied, such as the emergence of exceptional points in the coupled system. In summary, the obtained results open up new perspectives not only for the fundamental research on STNOs, but also for novel types of future applications.; Les nano-oscillateurs à transfert de spin (STNOs) présentent des fonctionnalités uniques pour les communications rf, la collecte d'énergie ou encore de nouvelles approches de calcul. Ils unifient ainsi les capacités clés multifonctionnelles des nanodispositifs dans le cadre de l'industrie 4.0 et mettent l'accent sur les potentialités de la spintronique, même au-delà du paradigme du CMOS. En plus de leur taille nanométrique, leur résistance aux rayonnements, leur agilité en fréquence, leur faible consommation d’énergie et compatibilité CMOS, une de leurs propriétés clé est leur forte non-linéarité, qui ouvre la voie vers des divers phénomènes physiques intéressants. Toutefois, cette non-linéarité est également à l'origine de la faible cohérence spectrale des oscillateurs, ce qui est un des obstacles jusqu'à présent dans les développements applicatifs. Cette thèse vise à fournir une compréhension plus approfondie du bruit du STNO sous l’influence de la non-linéarité. Généralisable à tous les types d'oscillateurs spintroniques, nous avons étudié à la fois expérimentalement et théoriquement la contribution du bruit de scintillement en 1/f dans le signal proche porteuse de STNO à base de vortex. Par ailleurs, l'influence de ce type de bruit sur la forme spectrale de l'oscillation a été étudiée et des moyens potentiels d'améliorer efficacement la cohérence sont proposés. Un autre axe de ce travail a été consacrée à l'étude du couplage et de la synchronisation de plusieurs STNOs, puisque ces capacités facilitent différents schémas d'application dans les technologies prospectives. En effet, au-delà de la synchronisation, de nouveaux phénomènes complexes sont démontrés et étudiés expérimentalement, tels que l'émergence de points exceptionnels dans le système couplé. En résumé, les résultats obtenus ouvrent de nouvelles perspectives non seulement pour la recherche fondamentale sur les STNOs, mais aussi pour de nouveaux types d'applications futures.
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- 2020
21. THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices.
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Ulrichs, Henning, Meyer, Dennis, Müller, Markus, Wittrock, Steffen, Mansurova, Maria, Walowski, Jakob, and Münzenberg, Markus
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COBALT compounds ,ELASTIC waves ,BAND gaps ,SUBMILLIMETER waves ,SYMMETRY (Physics) - Abstract
In this article, we present the observation of coherent elastic dynamics in a nano-scale phononic superlattice, which consists of only 4 bilayers. We demonstrate how ultra-short light pulses with a length of 40 fs can be utilized to excite a coherent elastic wave at 0.535 THz, which persist over about 20 ps. In later steps of the elastic dynamics, modes with frequency of 1.7 THz and above appear. All these modes are related to acoustic band gaps. Thus, the periodicity strongly manifests in the wave physics, although the system under investigation has only a small number of spatial periods. To further illustrate this, we show how by breaking the translational invariance of the superlattice, these features can be suppressed. Discussed in terms of phonon blocking and radiation, we elucidate in how far our structures can be considered as useful building blocks for phononic devices. [ABSTRACT FROM AUTHOR]
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- 2016
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22. Influence of flicker noise and nonlinearity on the frequency spectrum of spin torque nano-oscillators
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Wittrock, Steffen, primary, Talatchian, Philippe, additional, Tsunegi, Sumito, additional, Crété, Denis, additional, Yakushiji, Kay, additional, Bortolotti, Paolo, additional, Ebels, Ursula, additional, Fukushima, Akio, additional, Kubota, Hitoshi, additional, Yuasa, Shinji, additional, Grollier, Julie, additional, Cibiel, Gilles, additional, Galliou, Serge, additional, Rubiola, Enrico, additional, and Cros, Vincent, additional
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- 2020
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23. Low frequency noise in vortex spin torque nano-oscillators
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Wittrock, Steffen, Yakushiji, Kay, Fukushima, Akio, Kubota, Hitoshi, Bortolotti, Paolo, Ebels, Ursula, Yuasa, Shinji, Cibiel, Gilles, Galliou, Serge, Rubiola, Enrico, Université Paris-Sud - Paris 11 (UP11), Spintronics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), THALES, Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Centre National d'Études Spatiales [Toulouse] (CNES), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), THALES [France], Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), and Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)
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[SPI.OTHER]Engineering Sciences [physics]/Other ,Condensed Matter::Materials Science - Abstract
International audience; 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. Starti...
- Published
- 2018
24. Low offset frequency 1/f flicker noise in spin-torque vortex oscillators
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Wittrock, Steffen, primary, Tsunegi, Sumito, additional, Yakushiji, Kay, additional, Fukushima, Akio, additional, Kubota, Hitoshi, additional, Bortolotti, Paolo, additional, Ebels, Ursula, additional, Yuasa, Shinji, additional, Cibiel, Gilles, additional, Galliou, Serge, additional, Rubiola, Enrico, additional, and Cros, Vincent, additional
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- 2019
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25. Spin-Current Manipulation of Photo-Induced Magnetization Dynamics in Heavy Metal/Ferromagnet Double Layer-Based Nanostructures
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Wittrock, Steffen, primary, Meyer, Dennis, additional, Muller, Markus, additional, Ulrichs, Henning, additional, Walowski, Jakob, additional, Mansurova, Maria, additional, Martens, Ulrike, additional, and Munzenberg, Markus, additional
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- 2017
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26. Spin-current manipulation of photoinduced magnetization dynamics in Ta|CoFeB based nanostructures
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Wittrock, Steffen
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- 2016
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27. Hybrid PLL system for spin torque oscillators utilizing custom ICs in 0.18 μm BiCMOS
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Kreisig, Martin, primary, Wittrock, Steffen, additional, Protze, Florian, additional, Lebrun, Romain, additional, Merazzo, Karla J., additional, Cyrille, Marie-Claire, additional, Ferreira, Ricardo, additional, Bortolotti, Paolo, additional, Ebels, Ursula, additional, Cros, Vincent, additional, and Ellinger, Frank, additional
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- 2017
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28. Spin-Transfer Torque Switching at Ultra Low Current Densities
- Author
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Leutenantsmeyer, Johannes Christian, primary, Zbarsky, Vladyslav, additional, von der Ehe, Marvin, additional, Wittrock, Steffen, additional, Peretzki, Patrick, additional, Schuhmann, Henning, additional, Thomas, Andy, additional, Rott, Karsten, additional, Reiss, Günter, additional, Kim, Tae Hee, additional, Seibt, Michael, additional, and Münzenberg, Markus, additional
- Published
- 2015
- Full Text
- View/download PDF
29. Deterministic Generation and Guided Motion of Magnetic Skyrmions by Focused He + -Ion Irradiation.
- Author
-
Kern LM, Pfau B, Deinhart V, Schneider M, Klose C, Gerlinger K, Wittrock S, Engel D, Will I, Günther CM, Liefferink R, Mentink JH, Wintz S, Weigand M, Huang MJ, Battistelli R, Metternich D, Büttner F, Höflich K, and Eisebitt S
- Abstract
Magnetic skyrmions are quasiparticles with nontrivial topology, envisioned to play a key role in next-generation data technology while simultaneously attracting fundamental research interest due to their emerging topological charge. In chiral magnetic multilayers, current-generated spin-orbit torques or ultrafast laser excitation can be used to nucleate isolated skyrmions on a picosecond time scale. Both methods, however, produce randomly arranged skyrmions, which inherently limits the precision on the location at which the skyrmions are nucleated. Here, we show that nanopatterning of the anisotropy landscape with a He
+ -ion beam creates well-defined skyrmion nucleation sites, thereby transforming the skyrmion localization into a deterministic process. This approach allows control of individual skyrmion nucleation as well as guided skyrmion motion with nanometer-scale precision, which is pivotal for both future fundamental studies of skyrmion dynamics and applications.- Published
- 2022
- Full Text
- View/download PDF
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