Spin-torque driven magnetic vortex self-oscillations in perpendicular magnetic fields

TL;DR

This study uses micromagnetic simulations to analyze how spin-torque induces self-oscillations of magnetic vortices in a nanopillar under perpendicular magnetic fields, aligning well with experimental observations.

Contribution

It provides a comprehensive simulation approach including coupled spin-torque and magnetostatic effects to understand vortex dynamics in spin-valve structures.

Findings

Vortex moves along a quasi-elliptical trajectory expanding with current

Frequency shifts to higher values (blue-shift) with increased current

Simulation results agree with experimental magnetoresistance and frequency data

Abstract

We have employed complete micromagnetic simulations to analyze dc current driven self-oscillations of a vortex core in a spin-valve nanopillar in a perpendicular field by including the coupled effect of the spin-torque and the magnetostatic field computed self-consistently for the entire spin-valve. The vortex in the thicker nanomagnet moves along a quasi-elliptical trajectory that expands with applied current, resulting in blue-shifting of the frequency, while the magnetization of the thinner nanomagnet is non-uniform due to the bias current. The simulations explain the experimental magnetoresistance-field hysteresis loop and yield good agreement with the measured frequency vs. current behavior of this spin-torque vortex oscillator.