| 1. |
- 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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| 2. |
- 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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| 3. |
- Jiang, Sheng, et al.
(författare)
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Using Magnetic Droplet Nucleation to Determine the Spin Torque Efficiency and Asymmetry in Co-x(Ni,Fe)(1-x) Thin Films
- 2018
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how to extract the material-dependent spin-torque efficiency (epsilon) and asymmetry (lambda) from the field-current nucleation boundaries of magnetic droplet solitons in orthogonal nano-contact spintorque oscillators with Co-x(Ni80Fe20)(1-x), (x = 0 -1), fixed layers. As the perpendicular component of the fixed-layer magnetization plays a central role in governing droplet nucleation, the nucleation boundaries exhibit monotonic shifts towards higher perpendicular magnetic fields when the fixed-layer magnetization mu M-0(s, p) is tuned from 1.04 to 1.7 T. We then extract epsilon and lambda from fits to the nucleation boundaries and find that while epsilon does not vary with composition,lambda increases from 1.5 to 3 with increasing Co content. The analysis of droplet nucleation boundaries is hence a useful tool for the systematic study of both epsilon and lambda as functions of material composition.
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| 4. |
- Mazraati, Hamid, Industrial PhD Student, 1989-, et al.
(författare)
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Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields
- 2018
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally study the auto-oscillating spin-wave modes in Ni(80)Fc(20)/beta-W constriction-based spin Hall nano-oscillators as a function of bias current, strength of the in-plane applied field, and azimuthal field angle in the low-field range of 40-80 mT. We observe two different spin-wave modes: (i) a linearlike mode confined to the internal field minima near the edges of the nanoconstriction, and only weakly dependent on the bias current and the applied-field angle, and (ii) a second, lower-frequency mode with significantly higher threshold current and stronger dependence on both the bias current and the externalfield angle. Micromagnetic modeling qualitatively reproduces the experimental data and reveals that the second mode is a spin-wave bullet and that the spin Hall nano-oscillator mode hops between the two modes, resulting in a substantial increase in linewidths. In contrast to the linearlike mode, the bullet is localized in the middle of the constriction and shrinks with increasing bias current. Using intrinsic frequency doubling at zero field angle, we can reach frequencies above 9 GHz in fields as low as 40 mT, which is important for the development of low-field spintronic oscillators with applications in microwave-signal generation and neuromorphic computing.
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| 5. |
- Mazraati, Hamid, Industrial PhD Student, 1989-, et al.
(författare)
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Mutual Synchronization of Constriction-Based Spin Hall Nano-Oscillators in Weak In-Plane Magnetic Fields
- 2022
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 18:1
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Nguyen, T. N. Anh, et al.
(författare)
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Depth-Dependent Magnetization Profiles of Hybrid Exchange Springs
- 2014
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Ingår i: Physical Review Applied. - 2331-7019. ; 2:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetization depth profile of a hybrid exchange-spring system in which a Co/Pd multilayer with perpendicular anisotropy is coupled to a CoFeB thin film with in-plane anisotropy. The competition between these two orthogonal anisotropies promotes a strong depth dependence of the magnetization orientation. The angle of the magnetization vector is sensitive both to the strength of the individual anisotropies and to the local exchange constant and is thus tunable by changing the thickness of the CoFeB layer and by substituting Ni for Pd in one layer of the Co/Pd stack. The resulting magnetic depth profiles are directly probed by element-specific x-ray magnetic circular dichroism of the Fe and Ni layers located at different average depths. The experimental results are corroborated by micromagnetic simulations.
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| 7. |
- Ovcharov, Roman, 1997, et al.
(författare)
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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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Ingår i: Physical Review Applied. - 2331-7019. ; 20:3
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Rajabali, Mona, et al.
(författare)
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Injection Locking of Linearlike and Soliton Spin-Wave Modes in Nanoconstriction Spin Hall Nano-oscillators
- 2023
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Ingår i: Physical Review Applied. - 2331-7019. ; 19:3
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Xing, X. J., et al.
(författare)
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Paving Spin-Wave Fibers in Magnonic Nanocircuits Using Spin-Orbit Torque
- 2017
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies reveal that domain walls in magnetic nanostructures can serve as compact, energy-efficient spin-wave waveguides for building magnonic devices that are considered promising candidates for overcoming the challenges and bottlenecks of today's CMOS technologies. However, imprinting long strip-domain walls into magnetic nanowires remains a challenge, especially in bent geometries. Here, through micromagnetic simulations, we present a method for writing strip-domain walls into bent magnetic nanowires using spin-orbit torque. We employ Y-shaped magnetic nanostructures as well as an S-shaped magnetic nanowire to demonstrate the injection process. In addition, we verify that the Y-shaped nanostructures that incorporate strip-domain walls can function as superb spin-wave multiplexers and that spin-wave propagation along each conduit can be controllably manipulated. This spin-wave multiplexer based on strip-domain walls is expected to become a key signal-processing component in magnon spintronics.
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