| 1. |
- Bainsla, Lakhan, et al.
(författare)
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Ultrathin Ferrimagnetic GdFeCo Films with Low Damping
- 2022
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 32:23, s. 2111693-
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Tidskriftsartikel (refereegranskat)abstract
- Ferromagnetic materials dominate as the magnetically active element in spintronic devices, but come with drawbacks such as large stray fields and low operational frequencies. Compensated ferrimagnets provide an alternative as they combine the ultrafast magnetization dynamics of antiferromagnets with a ferromagnet-like spin-orbit-torque behavior. However, to use ferrimagnets in spintronic devices their advantageous properties must be retained also in ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1−x thin films in the thickness range t = 2–20 nm are grown on high resistance Si(100) substrates and studied using broadband ferromagnetic resonance measurements at room temperature. By tuning their stoichiometry, a nearly compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1−x ultrathin films for the first time, with an effective magnetization of (Formula presented.) = 0.02 T and a low effective Gilbert damping constant of α = 0.0078, comparable to the lowest values reported so far in 30 nm films. These results show great promise for the development of ultrafast and energy efficient ferrimagnetic spintronic devices.
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| 2. |
- Behera, Nilamani, et al.
(författare)
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Ultra-Low Current 10 nm Spin Hall Nano-Oscillators
- 2024
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Ingår i: Advanced Materials. - 0935-9648 .- 1521-4095. ; 36:5
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Tidskriftsartikel (refereegranskat)abstract
- Nano-constriction based spin Hall nano-oscillators (SHNOs) are at the forefront of spintronics research for emerging technological applications, such as oscillator-based neuromorphic computing and Ising Machines. However, their miniaturization to the sub-50 nm width regime results in poor scaling of the threshold current. Here, it shows that current shunting through the Si substrate is the origin of this problem and studies how different seed layers can mitigate it. It finds that an ultra-thin Al2O3 seed layer and SiN (200 nm) coated p-Si substrates provide the best improvement, enabling us to scale down the SHNO width to a truly nanoscopic dimension of 10 nm, operating at threshold currents below 30 (Formula presented.) A. In addition, the combination of electrical insulation and high thermal conductivity of the Al2O3 seed will offer the best conditions for large SHNO arrays, avoiding any significant temperature gradients within the array. The state-of-the-art ultra-low operational current SHNOs hence pave an energy-efficient route to scale oscillator-based computing to large dynamical neural networks of linear chains or 2Darrays.
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| 3. |
- Behera, Nilamani, et al.
(författare)
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Ultra-low-current Spin Hall Nano-oscillators
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. - 9798350338362
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Konferensbidrag (refereegranskat)abstract
- We report on the magnetodynamic properties and the magnetization auto-oscillations of ultra-low current 20 nm width nano-constriction spin Hall nano-oscillators (SHNOs) fabricated on different substrates and seed layers. Combining an optimized W88Ta12 alloy, low damping CoFeB, and a moderate perpendicular magnetic anisotropy, we push the threshold current down to 35 μA in the best devices. The best overall magnetodynamic properties and lowest threshold currents are obtained when using a 3 nm thick AlOx seed layer in between the high-resistance Si substrate and the W88Ta12 layer.
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| 4. |
- Fulara, Himanshu, et al.
(författare)
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Giant voltage-controlled modulation of spin Hall nano-oscillator damping
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong non-linear properties providing robust large-scale mutual synchronization in chains and two-dimensional arrays. While SHNOs can be tuned via magnetic fields and the drive current, neither approach is conducive to individual SHNO control in large arrays. Here, we demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the voltage-dependent perpendicular magnetic anisotropy tunes the frequency and, thanks to nano-constriction geometry, drastically modifies the spin-wave localization in the constriction region resulting in a giant 42% variation of the effective damping over four volts. As a consequence, the SHNO threshold current can be strongly tuned. Our demonstration adds key functionality to nano-constriction SHNOs and paves the way for energy-efficient control of individual oscillators in SHNO chains and arrays for neuromorphic computing. Spin Hall nano-oscillators can be tuned via magnetic fields and the drive current, but individual oscillator control in large arrays remains a challenge. Here, the authors provide individual control of the threshold current and the auto-oscillation frequency by voltage-controlled magnetic anisotropy.
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| 5. |
- Fulara, Himanshu, et al.
(författare)
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Spin-orbit torque–driven propagating spin waves
- 2019
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:9
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Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2019 The Authors, Spin-orbit torque (SOT) can drive sustained spin wave (SW) auto-oscillations in a class of emerging microwave devices known as spin Hall nano-oscillators (SHNOs), which have highly nonlinear properties governing robust mutual synchronization at frequencies directly amenable to high-speed neuromorphic computing. However, all demonstrations have relied on localized SW modes interacting through dipolar coupling and/or direct exchange. As nanomagnonics requires propagating SWs for data transfer and additional computational functionality can be achieved using SW interference, SOT-driven propagating SWs would be highly advantageous. Here, we demonstrate how perpendicular magnetic anisotropy can raise the frequency of SOT-driven auto-oscillations in magnetic nanoconstrictions well above the SW gap, resulting in the efficient generation of field and current tunable propagating SWs. Our demonstration greatly extends the functionality and design freedom of SHNOs, enabling long-range SOT-driven SW propagation for nanomagnonics, SW logic, and neuromorphic computing, directly compatible with CMOS technology.
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| 6. |
- González, Victor Hugo, 1993, et al.
(författare)
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Voltage control of frequency and effective damping in nano-constriction-based spin Hall nano-oscillators
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings. - 9798350338362
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Konferensbidrag (refereegranskat)abstract
- Using micromagnetic simulations, we study the tunability of strongly voltage-controlled magnetic anisotropy (VCMA), ΔK = ±200 kJ/m3, in voltage-gated W/CoFeB/MgO based nano-constriction spin Hall nano-oscillators. The VCMA modifies the local magnetic properties such that the magnetodynamics transitions between regimes of i) confinement, ii) tuning, and iii) separation, with qualitatively different behavior. As a consequence, voltage control remains efficient over a very large frequency range, and subsequent manufacturing advances could allow SHNOs to be easily integrated into next-generation electronics for further fundamental studies and industrial applications.
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| 7. |
- González, Victor Hugo, 1993, et al.
(författare)
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Voltage control of frequency, effective damping, and threshold current in nano-constriction-based spin Hall nano-oscillators
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:25
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Tidskriftsartikel (refereegranskat)abstract
- Using micromagnetic simulations, we study the interplay between strongly voltage-controlled magnetic anisotropy (VCMA), Δ K = ±200 kJ/m3, and gate width, w = 10-400 nm, in voltage-gated W/CoFeB/MgO based nano-constriction spin Hall nano-oscillators. The VCMA modifies the local magnetic properties such that the magnetodynamics transitions between regimes of (i) confinement, (ii) tuning, and (iii) separation with qualitatively different behaviors. We find that the strongest tuning is achieved for gate widths of the same size as the constriction width, for which the effective damping can be increased an order of magnitude compared to its intrinsic value. As a consequence, voltage control remains efficient over a very large frequency range, and subsequent manufacturing advances could allow spin Hall nano-oscillators to be easily integrated into next-generation electronics for further fundamental studies and industrial applications.
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| 8. |
- Haidar, M., et al.
(författare)
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Compositional effect on auto-oscillation behavior of Ni 100 -Fe-x(x)/Pt spin Hall nano-oscillators
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the compositional effect on the magnetodynamic and auto-oscillation properties of Ni 100 - xFe(x)/Pt (x=10-40) nanoconstriction-based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance performed on microstrips, we measure a significant reduction in both damping and spin Hall efficiency with the increasing Fe content, which lowers the spin pumping contribution. The strong compositional effect on spin Hall efficiency is primarily attributed to the increased saturation magnetization in Fe-rich devices. As a direct consequence, higher current densities are required to drive spin-wave auto-oscillations at higher microwave frequencies in Fe-rich nanoconstriction devices. Our results establish the critical role of the compositional effect in engineering the magnetodynamic and auto-oscillation properties of spin Hall devices for microwave and magnonic applications.
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| 9. |
- Houshang, Afshin, et al.
(författare)
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Phase-Binarized Spin Hall Nano-Oscillator Arrays: Towards Spin Hall Ising Machines
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- Ising machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths between its binary spins. Using its intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest-energy state, which is the solution to the CO problem. IMs have been implemented on different platforms, and interacting nonlinear oscillators are particularly promising candidates. Here we demonstrate a pathway towards an oscillator-based IM using arrays of nanoconstriction spin Hall nano-oscillators (SHNOs). We show how SHNOs can be readily phase binarized and how their resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states, we use phase-resolved Brillouin-light-scattering microscopy and directly observe the individual phase of each nanoconstriction. Micromagnetic simulations corroborate our experiments and confirm that our proposed IM platform can solve CO problems, showcased by how the phase states of a 2 x 2 SHNO array are solutions to a modified max-cut problem. Compared with the commercially available D-Wave Advantage (TM), our architecture holds significant promise for faster sampling, substantially reduced power consumption, and a dramatically smaller footprint.
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| 10. |
- Houshang, Afshin, et al.
(författare)
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Spin transfer torque driven higher-order propagating spin waves in nano-contact magnetic tunnel junctions
- 2018
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Short wavelength exchange-dominated propagating spin waves will enable magnonic devices to operate at higher frequencies and higher data transmission rates. While giant magnetoresistance (GMR)-based magnetic nanocontacts are efficient injectors of propagating spin waves, the generated wavelengths are 2.6 times the nano-contact diameter, and the electrical signal strength remains too weak for applications. Here we demonstrate nano-contact-based spin wave generation in magnetic tunnel junctions and observe large-frequency steps consistent with the hitherto ignored possibility of second-and third-order propagating spin waves with wavelengths of 120 and 74 nm, i.e., much smaller than the 150-nm nanocontact. Mutual synchronization is also observed on all three propagating modes. These higher-order propagating spin waves will enable magnonic devices to operate at much higher frequencies and greatly increase their transmission rates and spin wave propagating lengths, both proportional to the much higher group velocity.
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