Synchronization of spin-torque-driven nano-oscillators for point contacts on a quasi-one-dimensional nanowire: Micromagnetic simulations

Abstract

In this paper we present numerical simulation studies of the synchronization of two coupled spin-torque nano-oscillators (STNO) in the quasi-one-dimensional (1D) geometry: magnetization oscillations are induced in a thin NiFe nanostripe by a spin-polarized current injected via square-shaped CoFe nanomagnets on the top of this stripe. In a sufficiently large out-of-plane field, a propagating oscillation mode appears in such a system. Due to the absence of the geometrically caused wave decay in 1D systems, this mode is expected to enable a long-distance synchronization between STNOs. Indeed, our simulations predict that synchronization of two STNOs on a nanowire is possible up to the intercontact distance $\ensuremath{\Delta}L=3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ (for the nanowire width $w=50\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$). However, we have also found several qualitatively important features of the synchronization behavior for this system, which make the achievement of a stable synchronization in this geometry a highly nontrivial task. In particular, there exists a minimal distance between the nanocontacts, below which a synchronization of STNOs cannot be achieved. Further, when the current value in the first contact is kept constant, the synchronized oscillation power depends nonmonotonously on the current value in the second contact. Finally, for one and the same current values through the contacts, there might exist several synchronized states (with different frequencies), depending on the initial conditions.