Single skyrmion true random number generator using local dynamics and interaction between skyrmions

Magnetic skyrmions are topologically protected quasi-particles that can exist in certain magnetic materials. They are of great interest to both fundamental research and technological applications. Of particular interest is their potential for applications in logic-in-memory and unconventional computing devices. Magnetic skyrmions exhibit many desirable properties including stability, small size, and highly efficient controllability, which make them effective carriers in racetrack memory devices. In this talk, we show that the local dynamics of skyrmions, in contrast to the global dynamics of a skyrmion, can be introduced to provide effective functionalities for versatile computing. Our physical system is a magnetic multilayer with perpendicular magnetic anisotropy, substrate/Ta(1.6 nm)/Co₄₀Fe₄₀B₂₀(CoFeB) (0.95 nm)/MgO(1.6 nm)/TaO_x(2.0 nm). We can generate a single or multiple skyrmion(s). A single skyrmion interacting with local pinning centers under thermal effects can fluctuate in time and switch between a small-skyrmion (S) and a large-skyrmion (L) state, thereby serving as a robust true random number generator (TRNG) for probabilistic computing. The skyrmion mimics a robust stochastic neuron. We demonstrate that the probability of a skyrmion being in the S state or in the L state can be tuned by an applied magnetic field and/or spin current due to the effects of the Zeeman-energy variation and spin-orbit torque. Furthermore, we also discovered that neighboring skyrmions exhibit an anti-correlated coupling in their fluctuation dynamics. Both the switching probability and the dynamic coupling strength can be tuned by modifying the applied magnetic field and spin current. All these attributes offer opportunities to implement skyrmionic devices based on either a single skyrmion or a skyrmion network with a high degree of tunability and controllability. With a better understanding of the local dynamics of skyrmions, versatile skyrmionic devices can be designed and realized experimentally.