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1. Lateral inhibition in magnetic domain wall racetrack arrays for neuromorphic computing

   https://doi.org/10.1117/12.2568870  

   Cui, Can ; Akinola, Otitoaleke G. ; Hassan, Naimul ; Bennett, Christopher H. ; Marinella, Matthew J. ; Friedman, Joseph S. ; Incorvia, Jean Anne ( August 2020 , Proc. SPIE, Spintronics XIII)

   Drouhin, Henri-Jean M. ; Wegrowe, Jean-Eric ; Razeghi, Manijeh (Ed.)

   Neuromorphic computing captures the quintessential neural behaviors of the brain and is a promising candidate for the beyond-von Neumann computer architectures, featuring low power consumption and high parallelism. The neuronal lateral inhibition feature, closely associated with the biological receptive eld, is crucial to neuronal competition in the nervous system as well as its neuromorphic hardware counterpart. The domain wall - magnetic tunnel junction (DW-MTJ) neuron is an emerging spintronic arti cial neuron device exhibiting intrinsic lateral inhibition. This work discusses lateral inhibition mechanism of the DW-MTJ neuron and shows by micromagnetic simulation that lateral inhibition is eciently enhanced by the Dzyaloshinskii-Moriya interaction (DMI).
2. Intrinsic Lateral Inhibition Facilitates Winner-Take-All in Domain Wall Racetrack Arrays for Neuromorphic Computing

   https://doi.org/10.1109/ISCAS48785.2022.9937784  

   Cui, Can ; Akinola, Otitoaleke G. ; Hassan, Naimul ; Bennett, Christopher H. ; Marinella, Matthew J. ; Friedman, Joseph S. ; Incorvia, Jean Anne ( May 2022 , 2022 IEEE International Symposium on Circuits and Systems (ISCAS))

   Neuromorphic computing is a promising candidate for beyond-von Neumann computer architectures, featuring low power consumption and high parallelism. Lateral inhibition and winner-take-all (WTA) features play a crucial role in neuronal competition of the nervous system as well as neuromorphic hardwares. The domain wall - magnetic tunnel junction (DWMTJ) neuron is an emerging spintronic artificial neuron device exhibiting intrinsic lateral inhibition. In this paper we show that lateral inhibition parameters modulate the neuron firing statistics in a DW-MTJ neuron array, thus emulating soft-winner-take-all (WTA) and firing group selection.
3. Three Artificial Spintronic Leaky Integrate-and-Fire Neurons

   https://doi.org/10.1142/S2010324720400032  

   Brigner, Wesley H. ; Hu, Xuan ; Hassan, Naimul ; Jiang-Wei, Lucian ; Bennett, Christopher H. ; Garcia-Sanchez, Felipe ; Akinola, Otitoaleke ; Pasquale, Massimo ; Marinella, Matthew J. ; Incorvia, Jean Anne ; et al ( January 2020 , SPIN)

   Due to their non-volatility and intrinsic current integration capabilities, spintronic devices that rely on domain wall (DW) motion through a free ferromagnetic track have garnered significant interest in the field of neuromorphic computing. Although a number of such devices have already been proposed, they require the use of external circuitry to implement several important neuronal behaviors. As such, they are likely to result in either a decrease in energy efficiency, an increase in fabrication complexity, or even both. To resolve this issue, we have proposed three individual neurons that are capable of performing these functionalities without the use of any external circuitry. To implement leaking, the first neuron uses a dipolar coupling field, the second uses an anisotropy gradient, and the third uses shape variations of the DW track.
4. A perspective on electrical generation of spin current for magnetic random access memories

   https://doi.org/10.1063/5.0084551  

   Safranski, Christopher ; Sun, Jonathan Z. ; Kent, Andrew D. ( April 2022 , Applied Physics Letters)

   Spin currents are used to write information in magnetic random access memory (MRAM) devices by switching the magnetization direction of one of the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar. Different physical mechanisms of conversion of charge current to spin current can be used in two-terminal and three-terminal device geometries. In two-terminal devices, charge-to-spin conversion occurs by spin filtering in the MTJ's ferromagnetic electrodes and present day MRAM devices operate near the theoretically expected maximum charge-to-spin conversion efficiency. In three-terminal devices, spin–orbit interactions in a channel material can also be used to generate large spin currents. In this Perspective article, we discuss charge-to-spin conversion processes that can satisfy the requirements of MRAM technology. We emphasize the need to develop channel materials with larger charge-to-spin conversion efficiency—that can equal or exceed that produced by spin filtering—and spin currents with a spin polarization component perpendicular to the channel interface. This would enable high-performance devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars without need of a symmetry breaking field. We also discuss MRAM characteristics essential for CMOS integration. Finally, we identify critical research needs for charge-to-spin conversion measurements and metrics that can be used to optimize device channel materials andmore »interface properties prior to full MTJ nanopillar device fabrication and characterization.« less
5. Magnetic memory driven by topological insulators

   https://doi.org/10.1038/s41467-021-26478-3  

   Wu, Hao ; Chen, Aitian ; Zhang, Peng ; He, Haoran ; Nance, John ; Guo, Chenyang ; Sasaki, Julian ; Shirokura, Takanori ; Hai, Pham Nam ; Fang, Bin ; et al ( October 2021 , Nature Communications)

   Giant spin-orbit torque (SOT) from topological insulators (TIs) provides an energy efficient writing method for magnetic memory, which, however, is still premature for practical applications due to the challenge of the integration with magnetic tunnel junctions (MTJs). Here, we demonstrate a functional TI-MTJ device that could become the core element of the future energy-efficient spintronic devices, such as SOT-based magnetic random-access memory (SOT-MRAM). The state-of-the-art tunneling magnetoresistance (TMR) ratio of 102% and the ultralow switching current density of 1.2 × 10⁵ A cm⁻²have been simultaneously achieved in the TI-MTJ device at room temperature, laying down the foundation for TI-driven SOT-MRAM. The charge-spin conversion efficiencyθ_SHin TIs is quantified by both the SOT-induced shift of the magnetic switching field (θ_SH = 1.59) and the SOT-induced ferromagnetic resonance (ST-FMR) (θ_SH = 1.02), which is one order of magnitude larger than that in conventional heavy metals. These results inspire a revolution of SOT-MRAM from classical to quantum materials, with great potential to further reduce the energy consumption.