Noise-induced synchronization of spin-torque oscillators

Abstract

Noise-induced synchronization is a phenomenon where several oscillators with different initial conditions show synchronized motion, even in the absence of a coupling between them, when common stochastic input signals are injected. The phenomenon has attracted attention from nonlinear science, as well as applied physics, because it enables environmental noise to be used to synchronize many oscillators and is a necessary condition for brain-inspired computing. Here we develop a theoretical analysis of noise-induced synchronization in spin-torque oscillators (STOs). The analytical form for the Lyapunov exponent for the present model we derive indicates that there are two contributions from input signal to noise-induced synchronization in STOs. The first is that the input signal directly aligns the phases of the magnetizations, and the second is that the input signal changes the oscillating amplitude, and the amplitude-phase coupling results in synchronization. The validity of the analytical results was qualitatively confirmed by numerical simulation. We also show the existence of on-off intermittency at finite temperature, whose statistical properties are similar to those of other oscillator systems.