Two-dimensional overdamped simulations of droplet solitons activated by spin transfer torque

Gabriel D Chaves-O’Flynn,D L Stein

doi:10.1063/9.0000055

Abstract

We present overdamped micromagnetic simulations of the time evolution of magnetic droplet solitons which are formed in a thin film with perpendicular magnetic anisotropy by injecting a spin polarized current through a circular nanocontact. The overdamped dynamics help explore the effective energy landscape of these structures and permit identification of stationary states that are either energy extrema or saddle configurations. Our micromagnetic simulations start with configurations that are numerical solutions of a one-dimensional model where the magnetization depends only on the radial distance to the center of the nanocontact. We verify that these solutions correspond either to energy minima or saddle states, and use them to estimate thermal activation barriers for various current strengths. From the two-dimensional micromagnetic simulations, we identify a new persistent state which does not appear in the one-dimensional model.

Highlights

ΔE is the height of the barrier that separates two energy minima, and the prefactor f 0 is an attempt frequency of the order of GHz
Droplet solitons are dynamic states in thin-film materials having a strong magnetic anisotropy perpendicular to the plane of the film.1. Since they were first predicted by Kosevich et al.,2 numerous analytical and theoretical papers have been published on the properties of these objects
The activation barriers predicted by the 1D model are smaller than those obtained from the two-dimensional simulations, which likely arises from exchange energy contributions that result from variations of the azimuthal angle Φ, which the 1D model assumes to be spatially uniform

Summary

Introduction

ΔE is the height of the barrier that separates two (local or global) energy minima, and the prefactor f 0 is (roughly speaking) an attempt frequency of the order of GHz. Droplet solitons are dynamic states in thin-film materials having a strong magnetic anisotropy perpendicular to the plane of the film.1 Since they were first predicted by Kosevich et al.,2 numerous analytical and theoretical papers have been published on the properties of these objects.

Results

Conclusion