Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA.
Department of Electrical Engineering and Information Technology, University of Naples Federico II, 80125, Naples, Italy.
Nat Commun. 2019 Feb 1;10(1):543. doi: 10.1038/s41467-019-08444-2.
Energy-efficient switching of magnetization is a central problem in nonvolatile magnetic storage and magnetic neuromorphic computing. In the past two decades, several efficient methods of magnetic switching were demonstrated including spin torque, magneto-electric, and microwave-assisted switching mechanisms. Here we experimentally show that low-dimensional magnetic chaos induced by alternating spin torque can strongly increase the rate of thermally-activated magnetic switching in a nanoscale ferromagnet. This mechanism exhibits a well-pronounced threshold character in spin torque amplitude and its efficiency increases with decreasing spin torque frequency. We present analytical and numerical calculations that quantitatively explain these experimental findings and reveal the key role played by low-dimensional magnetic chaos near saddle equilibria in enhancement of the switching rate. Our work unveils an important interplay between chaos and stochasticity in the energy assisted switching of magnetic nanosystems and paves the way towards improved energy efficiency of spin torque memory and logic.
能量高效的磁化切换是非易失性磁存储和磁神经形态计算中的一个核心问题。在过去的二十年中，已经展示了几种高效的磁切换方法，包括自旋扭矩、磁电和微波辅助切换机制。在这里，我们通过实验证明了由交变自旋扭矩引起的低维磁混沌可以强烈地增加纳米级铁磁体中热激活磁切换的速率。这种机制在自旋扭矩幅度中表现出明显的阈值特性，并且其效率随着自旋扭矩频率的降低而增加。我们提出了分析和数值计算，定量地解释了这些实验结果，并揭示了鞍点附近的低维磁混沌在提高切换速率方面所起的关键作用。我们的工作揭示了磁纳米系统中能量辅助切换过程中混沌和随机性之间的重要相互作用，为提高自旋扭矩存储和逻辑的能量效率铺平了道路。
