Ultra-fast artificial neuron: generation of picosecond-duration spikes in a current-driven antiferromagnetic auto-oscillator

Roman Khymyn,Ivan Lisenkov,Olga Sulymenko,James Voorheis,Oleksandr Prokopenko,Vasil Tiberkevich,Andrei Slavin,Johan Akerman

doi:10.1038/s41598-018-33697-0

Abstract

We demonstrate analytically and numerically, that a thin film of an antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being driven by an external spin-transfer torque signal, can be used for the generation of ultra-short “Dirac-delta-like” spikes. The duration of the generated spikes is several picoseconds for typical AFM materials and is determined by the inplane magnetic anisotropy and the effective damping of the AFM material. The generated output signal can consist of a single spike or a discrete group of spikes (“bursting”), which depends on the repetition (clock) rate, amplitude, and shape of the external control signal. The spike generation occurs only when the amplitude of the control signal exceeds a certain threshold, similar to the action of a biological neuron in response to an external stimulus. The “threshold” behavior of the proposed AFM spike generator makes possible its application not only in the traditional microwave signal processing but also in the future neuromorphic signal processing circuits working at clock frequencies of tens of gigahertz.

Highlights

We demonstrate analytically and numerically, that a thin film of an antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being driven by an external spin-transfer torque signal, can be used for the generation of ultra-short “Dirac-delta-like” spikes
The film exhibits a biaxial magnetic anisotropy: the anisotropy easy plane is perpendicular to the axis nh, and its effective magnetic field is Hh, while the anisotropy easy axis is directed along the vector ne, and its effective magnetic field is He20
The spin dynamics of the AFM with bi-axial anisotropy under the action of an external spin torque is described by the set of two coupled Landau-Lifshitz equations for the magnetization of each of the AFM sublattices M1 and M2, see Methods section for details

Summary

Introduction

We demonstrate analytically and numerically, that a thin film of an antiferromagnetic (AFM) material, having biaxial magnetic anisotropy and being driven by an external spin-transfer torque signal, can be used for the generation of ultra-short “Dirac-delta-like” spikes. The spike generation occurs only when the amplitude of the control signal exceeds a certain threshold, similar to the action of a biological neuron in response to an external stimulus. A similar type of pulse-encoded signals is used in nervous systems of biological objects, where response of a neuron to an input stimulus is a single spike, or a train of spikes with a certain sequence frequency, which is called an action potential in the cell biology[1]. The modern concepts of neuromorphic computing and signal processing include spike generators as a mandatory element of their architecture[2,3] Another peculiarity of a nervous system is the neuron’s threshold behavior, in a sense, that a neuron generates a response only when the input stimulus is above a certain critical value (threshold). The optical comb generators offering microwave frequency spacing, based on the phase modulation in Fabry-Perot cavities[7], multi-frequency lasers[8], Brillouin-enhanced fiber lasers[9] and phase modulation within an amplified fiber loop[10] can have a substantially wider frequency span (> 100 GHz), but are rather complex devices, incompatible with the existing on-chip technology

Methods

Results

Conclusion