Magnetization reversal driven by low dimensional chaos in a nanoscale ferromagnet

Montoya, Eric; Perna, Salvatore; Chen, Yujin; Katine, J. A.; d’Aquino, M.; Serpico, C.; Krivorotov, I. N.

doi:10.1038/s41467-019-08444-2

Cited by 40 publications

(28 citation statements)

References 73 publications

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“…4(a)) and out-of-plane magnetized spin valves ( Fig. 4(b)) (the structure of the in-plane magnetized spin valve, SV IP1 , and its parameters are shown in This chaotic switching of in-plane spin valves [35] under windmill motion can be interpreted in the following way. For windmill motion, the switching of one layer toggles the switching of the other.…”

Section: Resultsmentioning

confidence: 99%

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: 99%

Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

et al. 2019

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“…Second, spin-dependent transport effects, such as spin transfer torques [17], which allow magnetization dynamics to be driven by electrical currents, and magnetoresistance, which allows such dynamics to be detected electrically, offer promising avenues for integration into micro-and nanoelectronics. In these systems, chaos can appear as a result of periodic driving [18,19], as delayed-feedback effects [20], in the dynamics of coupled vortices [21], and during magnetization reversal [22].…”

mentioning

confidence: 99%

Chaos in Magnetic Nanocontact Vortex Oscillators

et al. 2019

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We present an experimental study of spin-torque driven vortex self-oscillations in magnetic nanocontacts. We find that above a certain threshold in applied currents, the vortex gyration around the nanocontact is modulated by relaxation oscillations, which involve periodic reversals of the vortex core. This modulation leads to the appearance of commensurate but also more interestingly here, incommensurate states, which are characterized by devil's staircases in the modulation frequency. We use frequency-and time-domain measurements together with advanced time-series analyses to provide experimental evidence of chaos in incommensurate states of vortex oscillations, in agreement with theoretical predictions.

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“…1(a)) are separated by an energy barrier arising from perpendicular magnetic anisotropy of the free layer. Thermal fluctuations lead to stochastic assisted switching of magnetization over the barrier [44][45][46][47] . As a result, switching takes place at a different magnetic field value in each hysteresis loop forming a statistical distribution of fields for P → AP and AP → P switching.…”

Section: Results Perpendicular Magnetic Tunnel Junctionsmentioning

confidence: 99%

“…In-situ switching experiments. In order to study the effects of gamma irradiation on the dynamics of thermally-activated switching of the pMTJ free layer 48 , we utilize a circular pMTJ with a thicker MgO layer and a superparamagnetic free layer 47 , where the free layer stochastically switches between the P and AP states at a www.nature.com/scientificreports www.nature.com/scientificreports/ characteristic rate of a few hundred Hz. The superparamagnetic free layer is a result of reduced perpendicular magnetic anisotropy such that the energy barrier for switching is comparable to the thermal energy 49 .…”

Section: Spin Transfer Torque Switching Experiments Directly After Fmentioning

confidence: 99%

Immunity of nanoscale magnetic tunnel junctions with perpendicular magnetic anisotropy to ionizing radiation

Montoya

Chen

Ngelale

et al. 2020

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Spin transfer torque magnetic random access memory (Stt-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of Stt-MRAM is that its core component, the nanoscale magnetic tunneling junction (MtJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMtJs) required for scalable applications. particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMtJs used in Stt-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the currentinduced switching before and after irradiation. our results demonstrate that all these key properties of nanoscale MtJs relevant to Stt-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. these results indicate that nanoscale MtJs are promising building blocks for radiation-hard non-von neumann computing. Spin transfer torque random access memory (STT-MRAM) is a next-generation non-volatile memory technology 1-4 that has the advantage of fast write times 5-7 , relatively low power consumption 8-11 , and shows promise of scalability down to at least 7 nm CMOS technology node 12,13. STT-MRAM has already found its applications in the form of stand-alone nonvolatile memory 14 , and efforts to realize embedded versions of STT-MRAM are under way 15,16. The core component of STT-MRAM is a nanoscale magnetic tunnel junction (MTJ) 17-19 that consists of ferromagnetic metallic layers separated by a non-magnetic insulating tunnel barrier as illustrated in Fig. 1(a). Since the MTJ does not contain semiconductor components, STT-MRAM can be radiation hard, i.e. robust to the effects of ionizing radiation. This makes STT-MRAM potentially attractive for applications in space and military technologies, particle accelerators, and nuclear reactors 20,21. In fact previous studies have shown the promise of the radiation hardness of MTJs 22-24 ; however, the effects of ionizing radiation on spin transfer torque switching in MTJs with properties required for scalable STT-MRAM technology have not been experimentally studied. An STT-MRAM bit is written by a current pulse that applies spin torque 25 to magnetization of the free layer ferromagnet and reverses its direction thereby changing the relative alignment of magnetic moments of the free and pinned layers of the MTJ between parallel and antiparallel 26-28. This free layer switching leads to a change of the MTJ resistance due to the tunneling magneto-resistance (TMR) effect 28 , which allows resi...

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Magnetization reversal driven by low dimensional chaos in a nanoscale ferromagnet

Cited by 40 publications

References 73 publications

Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators

Chaos in Magnetic Nanocontact Vortex Oscillators

Immunity of nanoscale magnetic tunnel junctions with perpendicular magnetic anisotropy to ionizing radiation

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