Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators
Chaos and Relaxation Oscillations in Spin-Torque Windmill Spiking Oscillators
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DOI：
10.1103/physrevapplied.11.044093
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发表时间：
2018-10
影响因子：
4.6
通讯作者：
R. Matsumoto;S. Lequeux;H. Imamura;J. Grollier
中科院分区：
文献类型：
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作者：
R. Matsumoto;S. Lequeux;H. Imamura;J. Grollier
能够发射尖峰电压的自旋电子神经元是实现硬件神经网络所必需的，它能够以低功耗实现快速数据处理。在许多神经科学和计算机科学模型中，神经元被抽象为非线性振子。磁性纳米振荡器称为自旋扭矩纳米振荡器，是在纳米尺度上模拟神经元的有趣候选者。然而，这些振荡器发出没有尖峰的正弦波形，而生物神经元是松弛振荡器，发出尖锐的电压尖峰。在这里，我们提出了一种简单的方法来模拟高磁阻纳米级自旋阀中的神经元尖峰，其中两个磁层都是自由的，并且足够薄，可以通过自旋扭矩来切换。我们的数值模拟结果表明，在所提出的自旋电子神经元中，由自旋扭矩引起的风车运动产生尖峰，其形状和频率由充电和放电时间设置，可以通过注入的直流电流的幅度来调节。我们还发现，这些器件可以表现出混沌振荡。在大脑中观察到了类混沌神经元动力学，它在一些神经形态计算应用中是可取的，而在另一些应用中应该避免。我们证明，通过改变磁堆栈和各向异性以及改变直流电流，可以在很大范围内调节混沌程度。提出的自旋电子神经元是利用非线性动力学进行计算的硬件神经形态芯片的一个很有前途的构建块。
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 nano-oscillators 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.