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Impact of Device Variability and Circuit Phase Shift in Synchronized Spin Torque Oscillators

  • Johan Persson (a1), Yan Zhou (a1) and Johan Akerman (a1)


Current-induced magnetization dynamics in a system composed of two electrically coupled spin torque oscillators (STOs) is examined. The dynamics of the STOs is modeled by the Landau–Lifshitz–Gilbert equations modified with a Slonczewski spin-transfer torque term. To study the impact of realistic process variations on STO synchronization we let the two STOs have different in-plane anisotropy fields (H k ). The simulation also provides for a time delay τ. We construct a phase diagram of the STO synchronization as a function of H k and direct current (I dc) at different τ. The phase diagram turns out to be quite rich with different types of synchronized precession modes. While the synchronized state is originally very sensitive to STO process variations and can only sustain up to 4% H k variation, the addition of a small time delay dramatically improves its robustness and allows as much as 145% H k variation in the entire out-of-plane precession regime. It is also shown that the two STOs can not only be locked in frequency, but also in phase at a given τ and the phase difference between the two STOs can be tuned by varying the dc current.



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