Current-Induced Pinwheel Oscillations in Perpendicular Magnetic Anisotropy Spin Valve Nanopillars

Choi, Richard; Katine, J. A.; Mangin, Stéphane; Fullerton, Eric E.

doi:10.1109/tmag.2016.2577628

Cited by 8 publications

(6 citation statements)

References 19 publications

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“…3(c). As determined experimentally and numerically in previous studies [15][16][17], the frequency increases with an increase of |J|. Note that the shape of spikes can also be tuned by controlling the switching time ratio through materials engineering of the two layers (M s , P etc.).…”

Section: Resultsmentioning

confidence: 54%

“…It has been predicted, as well as experimentally observed that this torque configuration can generate a windmill-like motion of the two magnetizations [15][16][17]. The equations of motion of the magnetizations are given by the Landau-Lifschitz-Gilbert-Slonczewski (LLGS) equation [9,10,32] :…”

Section: Modelmentioning

confidence: 99%

“…Therefore, it is interesting to exploit the multifunctionality and tunability of spin-torque to imitate the sharp neuron spikes. Here we propose a simple way to imitate neuron spiking in high-magnetoresistance nanoscale spin valves where both magnetic layers are free and thin enough to be switched through spin torque [15][16][17]. We study these devices through macrospin and micromagnetic simulations [18].…”

Section: Introductionmentioning

confidence: 99%

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Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

et al. 2019

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Spintronic neurons which emit sharp voltage spikes are required for the realization of hardware neural networks enabling fast data processing with low-power consumption. In many neuroscience and computer science models, neurons are abstracted as non-linear oscillators. Magnetic nanooscillators called spin-torque nano-oscillators are interesting candidates for imitating neurons at nanoscale. These oscillators, however, emit sinusoidal waveforms without spiking while biological neurons are relaxation oscillators that emit sharp voltage spikes. Here we propose a simple way to imitate neuron spiking in high-magnetoresistance nanoscale spin valves where both magnetic layers are free and thin enough to be switched by spin torque. Our numerical-simulation results show that the windmill motion induced by spin torque in the proposed spintronic neurons gives rise to spikes whose shape and frequency, set by the charging and discharging times, can be tuned through the amplitude of injected dc current. We also found that these devices can exhibit chaotic oscillations. Chaotic-like neuron dynamics has been observed in the brain, and it is desirable in some neuromorphic computing applications whereas it should be avoided in others. We demonstrate that the degree of chaos can be tuned in a wide range by engineering the magnetic stack and anisotropies and by changing the dc current. The proposed spintronic neuron is a promising building block for hardware neuromorphic chips leveraging non-linear dynamics for computing. * rie-matsumoto@aist.go.jp

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Section: Resultsmentioning

confidence: 54%

Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

et al. 2019

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“…Such behavior causes a second threshold in the write-voltage, above which additional write-error would occur. [14][15][16][17][18] To mitigate these issues, it is essential to fully understand the STT-related magnetic dynamics on both sides of the tunnel barrier in an p-MTJ.…”

Section: Introductionmentioning

confidence: 99%

Interface moment dynamics and its contribution to spin-transfer torque switching process in magnetic tunnel junctions

Safranski¹,

Sun²

2019

Phys. Rev. B

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A practical problem for memory applications involving perpendicularly magnetized magnetic tunnel junctions is the reliability of switching characteristics at high-bias voltage. Often it has been observed that at high-bias, additional error processes are present that cause a decrease in switching probability upon further increase of bias voltage. We identify the main cause of such error-rise process through examination of switching statistics as a function of bias voltage and applied field, and the junction switching dynamics in real time. These experiments show a coincidental onset of error-rise and the presence of a new low-frequency microwave emission well below that dictated by the anisotropy field. We show that in a few-macrospin coupled numerical model, this is consistent with an interface region with concentrated perpendicular anisotropy, and where the magnetic moment has limited exchange coupling to the rest of the layers. These results point to the important role high-frequency interface magnetic moment dynamics play in determining the switching characteristics of these tunnel junction devices.

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“…Most STOs studied up to date are effectively zerodimensional (0D) because the spin current in these devices is applied to a nanometer-scale region of the ferromagnet. Examples of such oscillators include (i) nanopillar spin valves [22][23][24][25][26][27] and nanoscale magnetic tunnel junctions [12,[28][29][30][31], (ii) nanocontacts to magnetic films and multilayers [32][33][34][35][36][37][38][39] and planar nanoconstriction spin Hall oscillators (SHOs) [40][41][42]. It was recently demonstrated that effectively one-dimensional (1D) SHOs can be realized in ferromagnetic nanowires where several low frequency spin wave eigenmodes are simultaneously driven into large-amplitude auto-oscillations by pure spin Hall current uniformly applied to a micrometer-scale active region of the nanowire [43][44][45][46].…”

Section: Introductionmentioning

confidence: 99%

Dimensional crossover in spin Hall oscillators

Smith,

Sobotkiewich,

Khan

et al. 2020

Preprint

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Auto-oscillations of magnetization driven by direct spin current have been previously observed in multiple quasi-zero-dimensional (0D) ferromagnetic systems such as nanomagnets and nanocontacts. Recently, it was shown that pure spin Hall current can excite coherent auto-oscillatory dynamics in quasi-one-dimensional (1D) ferromagnetic nanowires but not in quasi-two-dimensional (2D) ferromagnetic films. Here we study the 1D to 2D dimensional crossover of current-driven magnetization dynamics in wire-based Pt/Ni80Fe20 bilayer spin Hall oscillators via varying the wire width. We find that increasing the wire width results in an increase of the number of excited auto-oscillatory modes accompanied by a decrease of the amplitude and coherence of each mode. We also observe a crossover from a hard to a soft onset of the auto-oscillations with increasing the wire width. The amplitude of auto-oscillations rapidly decreases with increasing temperature suggesting that interactions of the phase-coherent auto-oscillatory modes with incoherent thermal magnons plays an important role in suppression of the auto-oscillatory dynamics. Our measurements set the upper limit on the dimensions of an individual spin Hall oscillator and elucidate the mechanisms leading to suppression of coherent auto-oscillations with increasing oscillator size.

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Current-Induced Pinwheel Oscillations in Perpendicular Magnetic Anisotropy Spin Valve Nanopillars

Cited by 8 publications

References 19 publications

Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

Interface moment dynamics and its contribution to spin-transfer torque switching process in magnetic tunnel junctions

Dimensional crossover in spin Hall oscillators

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