| 1. |
- Albertsson, D. I., et al.
(författare)
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Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators
- 2019
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Ingår i: Ieee Transactions on Magnetics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9464 .- 1941-0069. ; 55:10
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Tidskriftsartikel (refereegranskat)abstract
- Emerging spin-torque nano oscillators (STNOs) and spin-Hall nano oscillators (SHNOs) are potential candidates for microwave applications. Recent advances in three-terminal magnetic tunnel junction (MTJ)-based SHNOs opened the possibility to develop more reliable and well-controlled oscillators, thanks to individual spin Hall-driven precession excitation and read-out paths. To develop hybrid systems by integrating three-terminal SHNOs and CMOS circuits, an electrical model able to capture the analog characteristics of three-terminal SHNOs is needed. This model needs to be compatible with current electric design automation (EDA) tools. This work presents a comprehensive macrospin-based model of three-terminal SHNOs able to describe the dc operating point, frequency modulation, phase noise, and output power. Moreover, the effect of voltage-controlled magnetic anisotropy (VCMA) is included. The model shows good agreement with experimental measurements and could be used in developing hybrid three-terminal SHNO/CMOS systems.
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| 2. |
- Albertsson, Dagur Ingi, et al.
(författare)
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Ultrafast Ising Machines using spin torque nano-oscillators
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:11
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Tidskriftsartikel (refereegranskat)abstract
- Combinatorial optimization problems are known for being particularly hard to solve on traditional von Neumann architectures. This has led to the development of Ising Machines (IMs) based on quantum annealers and optical and electronic oscillators, demonstrating speed-ups compared to central processing unit (CPU) and graphics processing unit (GPU) algorithms. Spin torque nano-oscillators (STNOs) have shown GHz operating frequency, nanoscale size, and nanosecond turn-on time, which would allow their use in ultrafast oscillator-based IMs. Here, we show using numerical simulations based on STNO auto-oscillator theory that STNOs exhibit fundamental characteristics needed to realize IMs, including in-phase/out-of-phase synchronization and second harmonic injection locking phase binarization. Furthermore, we demonstrate numerically that large STNO network IMs can solve Max-Cut problems on nanosecond timescales.
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| 3. |
- Awad, Ahmad, et al.
(författare)
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Width dependent auto-oscillating properties of constriction based spin Hall nano-oscillators
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 116:23
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Tidskriftsartikel (refereegranskat)abstract
- We study the current tunable microwave signal properties of nano-constriction-based spin Hall nano-oscillators in oblique magnetic fields as a function of the nano-constriction width, w = 50 - 140 nm. The threshold current is found to scale linearly with w, defining a constant threshold current density of Jth = 1.7 x 10(8) A/cm(2). While the current dependence of the microwave frequency shows the same generic non-monotonic behavior for all w >= 80 nm, the quality of the generated microwave signal improves strongly with w, as the total power increases and the linewidth decreases linearly with w. As a consequence, the peak power for a 140 nm nano-constriction is about an order of magnitude higher than that for an 80 nm nano-constriction. The smallest nano-constriction, w = 50 nm, exhibits a different behavior with a higher power and a worse linewidth, indicating a crossover into a qualitatively different narrow-constriction regime.
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| 4. |
- 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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| 5. |
- Behera, Nilamani, et al.
(författare)
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Energy-Efficient W100-xTax/ Co-Fe-B/MgO Spin Hall Nano-Oscillators
- 2022
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Ingår i: Physical Review Applied. - 2331-7019. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate a W-Ta alloying route to reduce the auto-oscillation threshold current densities and the power consumption of nanoconstriction based spin Hall nano-oscillators. Using spin-torque ferromagnetic resonance measurements on microbars of W100-xTax(5 nm)/Co-Fe-B(t)/MgO stacks with t=1.4, 1.8, and 2.0 nm, we measure a substantial improvement in both the spin-orbit torque efficiency and the spin Hall conductivity. We demonstrate a 34% reduction in auto-oscillation threshold current density, which translates into a 64% reduction in power consumption as compared with pure W-based spin Hall nano-oscillators. Our work demonstrates the promising aspects of W-Ta alloying for the energy-efficient operation of emerging spintronic devices.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- Jiang, Sheng, et al.
(författare)
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Reduced spin torque nano-oscillator linewidth using He+ irradiation
- 2020
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 116:7
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an approach for improving the spectral linewidth of a spin torque nano-oscillator (STNO). Using He + ion irradiation, we tune the perpendicular magnetic anisotropy (PMA) of the STNO free layer such that its easy axis is gradually varied from strongly out-of-plane to moderate in-plane. As the PMA impacts the non-linearity N of the STNO, we can, in this way, control the threshold current, the current tunability of the frequency, and, in particular, the STNO linewidth, which dramatically improves by two orders of magnitude. Our results are in good agreement with the theory for nonlinear auto-oscillators, confirm theoretical predictions of the role of the nonlinearity, and demonstrate a straightforward path toward improving the microwave properties of STNOs.
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| 10. |
- Mazraati, Hamid, Industrial PhD Student, 1989-, et al.
(författare)
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Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting
- 2018
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 113:9
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of hafnium (Hf) dusting on the magnetodynamical properties of NiFe/Pt bilayers using spin-torque-induced ferromagnetic resonance measurements on 6 mu m wide microstrips on high-resistive Si substrates. Based on two series of NiFe(t(NiFe))/Hf(t(Hf))/Pt(5) stacks, we first demonstrate that the zero-current magnetodynamic properties of the devices benefit from Hf dusting: (i) the effective magnetization of the NiFe layer increases by 4%-8% with Hf present and (ii) the damping a decreases linearly with tHf by up to 40%. The weaker anisotropic magnetoresistance (AMR similar or equal to 0.3%-0.4%) of the 3 nm NiFe series is largely unaffected by the Hf, while the stronger AMR of the 5 nm NiFe series drops from 0.7% to 0.43% with increasing t(Hf). We find that the spin Hall efficiency zeta(SH) is independent of the NiFe thickness, remaining unaffected (zeta(SH) = 0.115) up to t(Hf) = 0.4 nm and then decreasing linearly for higher t(Hf). The different trends of alpha and zeta(SH) suggest that there is an optimum Hf thickness (similar or equal to 0.4 nm) for which the threshold current for auto-oscillation should have a minimum, while the much lower damping should improve mutual synchronization. Our results also indicate that the spin-orbit torque is entirely damping-like with no field-like torque component. Finally, the internal spin Hall angle of Pt is estimated to be theta(SH) = 0.22 by calculating the transparency of the interface. Published by AIP Publishing.
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