| 1. |
- Houshang, Afshin, et al.
(author)
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Phase-Binarized Spin Hall Nano-Oscillator Arrays: Towards Spin Hall Ising Machines
- 2022
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In: Physical Review Applied. - 2331-7019. ; 17:1
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Journal article (peer-reviewed)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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| 2. |
- Litvinenko, A., et al.
(author)
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Tunable Magnetoacoustic Oscillator with Low Phase Noise
- 2021
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In: Physical Review Applied. - 2331-7019. ; 15:3
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Journal article (peer-reviewed)abstract
- A frequency-tunable low-phase-noise magnetoacoustic resonator is developed on the base of a parallel plate straight-edge bilayer consisting of an yttrium-iron-garnet (YIG) layer grown on a substrate of a gallium gadolinium garnet (GGG). When a YIG-GGG sample forms an ideal parallel plate, it supports a series of high-quality-factor acoustic modes standing along the plate thickness. Due to the magnetostriction of the YIG layer the ferromagnetic resonance (FMR) mode of the YIG layer can strongly interact with the acoustic thickness modes of the YIG-GGG structure, when the modes' frequencies match. A particular acoustic thickness mode used for the resonance excitations of the hybrid magnetoacoustic oscillations in a YIG-GGG bilayer is chosen by the YIG-layer FMR frequency, which can be tuned by the variation of the external bias magnetic field. A composite scheme of a magnetoacoustic oscillator, which includes a FMR-based resonance preselector, is developed to guarantee satisfaction of the Barkhausen criteria for a single-acoustic-mode oscillation regime. The developed low-phase-noise composite magnetoacoustic oscillator can be tuned from 0.84 to 1 GHz with an increment of about 4.773 MHz (frequency distance between the adjacent acoustic thickness modes in a YIG-GGG parallel plate), and demonstrates the phase noise of & minus;116 dBc/Hz at the offset frequency of 10 kHz.
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| 3. |
- Mazraati, Hamid, Industrial PhD Student, 1989-, et al.
(author)
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Mutual Synchronization of Constriction-Based Spin Hall Nano-Oscillators in Weak In-Plane Magnetic Fields
- 2022
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In: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 18:1
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Journal article (peer-reviewed)abstract
- We study mutual synchronization in double nanoconstriction-based spin Hall nano-oscillators (SHNOs) under weak in-plane magnetic fields (mu H-0(IP) = 30-40 mT) and also investigate its angular dependence. We compare SHNOs with different nanoconstriction spacings of 300 and 900 nm. In all devices, mutual synchronization occurs below a certain critical angle, which is higher for the 300 nm spacing than for the 900 nm spacing, reflecting the stronger coupling at shorter distances. Alongside the synchronization, we observe a strong second harmonic consistent with predictions that the synchronization may be mediated by the propagation of second-harmonic spin waves. However, although Brillouin light scattering microscopy confirms the synchronization, it fails to detect any related increase of the second harmonic. Micromagnetic simulations instead explain the angular-dependent synchronization as predominantly due to magnetodipolar coupling between neighboring SHNOs.
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| 4. |
- Ovcharov, Roman, 1997, et al.
(author)
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Antiferromagnetic Bloch Line Driven by Spin Current as Room-Temperature Analogue of a Fluxon in a Long Josephson Junction
- 2023
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In: Physical Review Applied. - 2331-7019. ; 20:3
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Journal article (peer-reviewed)abstract
- Antiferromagnets (AFMs) are promising materials for future high-frequency field-free spintronic applications. Self-localized spin structures can enhance their capabilities and introduce alternative functionalities to AFM-based devices. Here we consider a domain wall (DW), a topological soliton that bridges a connection between two ground states, similar to a Josephson junction link between two superconductors. We demonstrate the similarities between DWs in biaxial AFM with easy-axis primary anisotropy, driven by a spin current, and long Josephson junctions (LJJs). We found that the Bloch line (BL) in DWs resembles the fluxon state of Josephson junctions, creating a close analogy between the two systems. We propose a scheme that allows us to create, move, read, and delete such BLs. This transmission line operates at room temperature and can be dynamically reconfigured in contrast to superconductors. Results of a developed model were confirmed by micromagnetic simulations for Cr2O3 and DyFeO3, i.e., correspondingly with weak and strong in-plane anisotropy. Overall, the proposed scheme has significant potential for use in magnetic memory and logic devices.
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| 5. |
- Ovcharov, Roman, 1997, et al.
(author)
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Spin Hall Nano-Oscillator Based on an Antiferromagnetic Domain Wall
- 2022
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In: Physical Review Applied. - 2331-7019. ; 18:2
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Journal article (peer-reviewed)abstract
- We propose here a high-frequency spin-Hall nano-oscillator based on a simple magnetic texture, such as a domain wall, located in an antiferromagnet with an easy-axis anisotropy type. We show that the spin current, polarized along the anisotropy axis, excites a conical precession of the Neel vector in such a domain wall, which allows obtaining a robust ac output signal-contrary to the planar precession in a uniform uniaxial antiferromagnet, where ac output is hard to achieve. The frequency of the auto-oscillations is easily tunable by the applied current up to the terahertz range, and the threshold current vanishes for a pure uniaxial antiferromagnet. By micromagnetic simulations, we demonstrate that the pinning of the domain wall is crucial for the oscillator design, which can be achieved in the nanoconstriction layout of the free layer.
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| 6. |
- Rajabali, Mona, et al.
(author)
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Injection Locking of Linearlike and Soliton Spin-Wave Modes in Nanoconstriction Spin Hall Nano-oscillators
- 2023
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In: Physical Review Applied. - 2331-7019. ; 19:3
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Journal article (peer-reviewed)abstract
- We study injection locking of two different spin wave (SW) modes (a field-localized linearlike interior mode and a self-localized SW bullet soliton) in a single nanoconstriction-based spin Hall nano-oscillator. Mode selection is achieved by varying the oblique magnetic field angle and magnitude. The two modes show dramatically different responses to injection locking, in terms of locking bandwidth and linewidth and output power in the locked state. Extracting the locking range graphically from the experimental data yields apparent thresholds for the required injected power, with the bullet mode showing a larger threshold than the linearlike mode. By instead fitting the full detuning behavior using a model including thermal noise, the apparent threshold vanishes, while the very different locking behavior of the two modes can instead be ascribed to the order of magnitude difference in their mode volumes.
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| 7. |
- Sulymenko, O. R., et al.
(author)
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Terahertz-Frequency Spin Hall Auto-oscillator Based on a Canted Antiferromagnet
- 2017
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In: Physical Review Applied. - 2331-7019. ; 8:6
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Journal article (peer-reviewed)abstract
- We propose a design of a terahertz-frequency signal generator based on a layered structure consisting of a current-driven platinum (Pt) layer and a layer of an antiferromagnet (AFM) with easy-plane anisotropy, where the magnetization vectors of the AFM sublattices are canted inside the easy plane by the Dzyaloshinskii-Moriya interaction (DMI). The dc electric current flowing in the Pt layer creates due to the spin Hall effect, a perpendicular spin current that, being injected in the AFM layer, tilts the DMI-canted AFM sublattices out of the easy plane, thus exposing them to the action of a strong internal exchange magnetic field of the AFM. The sublattice magnetizations, along with the small net magnetization vector m(DMI) of the canted AFM, start to rotate about the hard anisotropy axis of the AFM with the terahertz frequency proportional to the injected spin current and the AFM exchange field. The rotation of the small net magnetization mDMI results in the terahertz-frequency dipolar radiation that can be directly received by an adjacent (e.g., dielectric) resonator. We demonstrate theoretically that the radiation frequencies in the range f = 0.05-2 THz are possible at the experimentally reachable magnitudes of the driving current density, and we evaluate the power of the signal radiated into different types of resonators. This power increases with the increase of frequency f, and it can exceed 1 mu W at f similar to 0.5 THz for a typical dielectric resonator of the electric permittivity epsilon similar to 10 and a quality factor Q similar to 750.
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