Stochastic Computing Implemented by Skyrmionic Logic Devices

Magnetic skyrmions, which are a topologically nontrivial spin texture, have been considered as promising information carriers in future electronic devices because of their nanoscale size, low depinning current density, and high motion velocity. Despite the broad interest in skyrmion racetrack memory, researchers have recently been exploiting logic functions enabled by using the particlelike behavior of skyrmions. These functions can be applied to unconventional computing, such as stochastic computing (SC), which treats data as probabilities and is superior to binary computing due to its simplicity of logic operation. In this paper, we demonstrate SC implemented by the use of skyrmionic logic devices. We propose a skyrmionic AND OR logic device as a multiplier in the stochastic domain and two skyrmionic multiplexer (MUX) logic devices as stochastic adders. With the assistance of voltage-controlled magnetic anisotropy (VCMA), precise control of skyrmion collisions is not required in the skyrmionic AND OR logic device, thus improving the operational robustness. In the two MUX logic devices, skyrmions can be driven by the Zhang-Li torque or the spin-orbit torque (SOT). In particular, we can regulate the skyrmion motion flexibly by using VCMA or voltage-controlled Dzyaloshinskii-Moriya interaction in the SOT case. Furthermore, a 3-bit stochastic multiplier and adder are demonstrated by micromagnetic simulations. Simulations in synthetic antiferromagnets show that the performance of our skyrmionic logic gates can be optimized through the use of advanced materials. Our work opens up possibilities for implementing SC using skyrmionic logic devices.