Feedback voltage driven chaos in a three-terminal spin-torque oscillator

In this work, we report an excitation of chaos and a nontrivial magnetization switching via transient chaos in a three-terminal spin-torque oscillator (STO). The driving force of the chaos is a voltage-controlled magnetic anisotropy (VCMA) effect generated by a feedback signal from the STO since the feedback effect is known to be effective in exciting chaos in a dynamical system. Solving the Landau-Lifshitz-Gilbert equation numerically and applying temporal and statistical analyses to its solution, the existence of the chaos driven by the feedback VCMA effect is identified. Simultaneously, however, transient chaos is also observed, where the magnetization initially shows chaotic behavior but finally switches its direction. This transient dynamics from chaos to magnetization switching was unexpected because the sign of the feedback VCMA effect was chosen so that the switching current increases and, as a result, the situation rather favors the condition for sustaining chaos. It is implied that this switching happens when narrowing a stable region of the magnetic potential energy by the feedback effect and magnetization precession pointing to a saddle point coincidentally occur simultaneously.