Propagation and control of nanoscale magnetic-droplet solitons

Abstract

The propagation and controlled manipulation of strongly nonlinear, two-dimensional solitonic states in a thin, anisotropic ferromagnet are theoretically demonstrated. It has been recently proposed that spin-polarized currents in a nanocontact device could be used to nucleate a stationary dissipative droplet soliton. Here, an external magnetic field is introduced to accelerate and control the propagation of the soliton in a lossy medium. Soliton perturbation theory corroborated by two-dimensional micromagnetic simulations predicts several intriguing physical effects, including the acceleration of a stationary soliton by a magnetic field gradient, the stabilization of a stationary droplet by a uniform control field in the absence of spin torque, and the ability to control the soliton's speed by use of a time-varying, spatially uniform external field. Soliton propagation distances approach 10 µm in low loss media, suggesting that droplet solitons could be viable information carriers in future spintronic applications, analogous to optical solitons in fiber optic communications.

Observation of droplet soliton drift resonances in a spin-transfer-torque nanocontact to a ferromagnetic thin film

“…Here, we report observation of drift instabilities 10,18 in droplet-soliton excitations at room temperature. We studied the effect of magnetic fields and current densities on the droplet dynamics.…”

Generation linewidth of mode-hopping spin torque oscillators

“…STT describes the momentum transfer from spin-polarized electrons to a local magnetization and therefore provides a direct coupling between dc charge currents and magnetization dynamics. Depending on external conditions, a rich variety of physical phenomena with technologically interesting outcomes are possible, including different modes of spin wave generation [3][4][5][6][7][8], vortex gyration [9][10][11][12], and the nucleation and manipulation of magnetic droplet solitons [13][14][15][16]. Regardless of the particular magnetization dynamics, devices where a stable oscillatory state can be achieved are generally referred to as spin torque oscillators [17,18] (STOs), and are typically composed of two ferromagnetic layers decoupled by a non-magnetic spacer (although recent studies also report on STOs based on single ferromagnet layers [19]).…”

Phase-locking of multiple magnetic droplets by a microwave magnetic field

“…In free layers with perpendicular magnetic anisotropy (PMA), the STT has been predicted to induce a localized oscillation mode-dissipative magnetic droplet soliton. 9,10 Recent experiments have confirmed this type of localized oscillation soliton mode generated in NC region, [11][12][13][14][15] which has been considered as a promising candidate for the STOs. In such devices, the energy dissipation due to magnetic damping is compensated by the energy input from the current-induced STT effect.…”