  Recent observations of chaos in nanomagnet suggest a possibility of new
spintronics applications such as random-number generator and neuromorphic
computing. However, large amount of electric current and/or magnetic field are
necessary for the excitation of chaos, which are unsuitable for energy-saving
applications. Here, we propose an excitation of chaos in three-terminal
spin-torque oscillator (STO). The driving force of the chaos is
voltage-controlled magnetic anisotropy (VCMA) effect, which enables us to
manipulate magnetization dynamics without spending electric current or magnetic
field, and thus, energy efficient. In particular, we focus on the VCMA effect
generated by feedback signal from the STO since feedback effect is known to be
effective in exciting chaos in dynamical system. Solving the
Landau-Lifshitz-Gilbert (LLG) equation numerically and applying temporal and
statistical analyses to its solution, the existence of the chaotic and
transient-chaotic magnetization dynamics driven by the feedback VCMA effect is
identified.
