Noise-Induced Transition of Mutual Phase Synchronization in Coupled Spin Torque Nano Oscillators

The magnetization dynamics of a pair of the magneto-statically coupled spin torque nano oscillators (STNOs) have been investigated by using the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with a macro-spin approximation. First, we simulated the deterministic dynamics of the coupled STNOs. Numerical simulations show that the dipole coupling mediates in-phase or out-of-phase synchronization states in the pair of the STNOs. Moreover, we found that a bistable state consisting of both in-phase and out-of phase synchronization states can exist by adjusting the experimental parameters. Second, we simulated the stochastic dynamics of the coupled STNOs under common noisy current injection. It is found that the noisy current injection into the STNOs induces to chastic state transition from the out-of-phase synchronization state to the in-phase. Such state transition arises from the cooperative effects between the noise-induced synchronization and the magneto static interactions.