Strange non-chaotic attractors in spin valve systems

Highlights: • Magnetization dynamics. • Nonlinear dynamics and chaos. • Complex systems. The current-driven magnetization dynamics in spin torque oscillators is investigated because of its high potential for high-frequency applications. The system consists of a pinned layer with a fixed magnetization and a single-domain free layer, such that it is governed by the Landau-Lifshitz-Gilbert-Slonczewski equation. In particular, we study the effect of a time-dependent quasi-periodic current. We numerically characterize the dynamical behavior of the system by monitoring the Lyapunov exponents, and by calculating the Fourier spectra. We find a rather complicated landscape of sometimes closely intermingled chaotic and non-chaotic areas in the parameters space. Finally, we compute a phase diagram of the existence of the strange non-chaotic attractors.