Synchronization of propagating and localized spin-wave modes in a double-contact spin-torque oscillator: a micromagnetic study

The possibility of synchronizing two or more interacting spin-transfer oscillators (STO) has been studied with the aim of amplifying the overall output power and spectral purity [1]. Here, we numerically characterize a double nanocontact STO within a computational region of 1 μm x 1 μm [2]. The study is performed in the cases of normal and in-plane external bias field, where the corresponding excited modes are propagating and localized, respectively. Synchronization phenomena are examined as a function of the applied current and the distance between the contacts, deriving the characteristic locking bandwidth in each case. To realize the physical phenomenon responsible for the synchronization (dipolar or spin-wave coupling), simulations are also performed by cutting the ferromagnetic material separating the two contacts [3,4]. Interestingly, we observe that in the case of in-plane field a frequency pulling can take place between localized modes excited by closely-positioned contacts but no kind of interaction occurs in the cut geometry.