Theory for a dissipative droplet soliton excited by a spin torque nanocontact

TL;DR

This paper predicts a new dissipative droplet soliton in spin torque oscillators with perpendicular anisotropy, deriving conditions for its formation and confirming its stability through numerical simulations, with insights into its potential instabilities.

Contribution

It introduces a novel dissipative droplet soliton model in spin torque systems and derives conditions for its nucleation and stability using asymptotic and numerical methods.

Findings

Dissipative droplet solitons can form with sufficient perpendicular anisotropy.

Stability of the droplet is confirmed against typical experimental perturbations.

A drift instability can cause the droplet to propagate away and be destroyed.

Abstract

A novel type of solitary wave is predicted to form in spin torque oscillators when the free layer has a sufficiently large perpendicular anisotropy. In this structure, which is a dissipative version of the conservative droplet soliton originally studied in 1977 by Ivanov and Kosevich, spin torque counteracts the damping that would otherwise destroy the mode. Asymptotic methods are used to derive conditions on perpendicular anisotropy strength and applied current under which a dissipative droplet can be nucleated and sustained. Numerical methods are used to confirm the stability of the droplet against various perturbations that are likely in experiments, including tilting of the applied field, non-zero spin torque asymmetry, and non-trivial Oersted fields. Under certain conditions, the droplet experiences a drift instability in which it propagates away from the nanocontact and is then destroyed by damping.