Magnetic vortex nucleation modes in static magnetic fields

Marek Vaňatka,Tomáš Šikola,Vojtěch Uhlíř,Lukáš Flajšman,Michal Urbánek,Jan Michalička,Mi-Young Im,Meena Dhankhar,Roman Jíra

doi:10.1063/1.5006235

Abstract

The magnetic vortex nucleation process in nanometer- and micrometer-sized magnetic disks undergoes several phases with distinct spin configurations called the nucleation states. Before formation of the final vortex state, small submicron disks typically proceed through the so-called C-state while the larger micron-sized disks proceed through the more complicated vortex-pair state or the buckling state. This work classifies the nucleation states using micromagnetic simulations and provides evidence for the stability of vortex-pair and buckling states in static magnetic fields using magnetic imaging techniques and electrical transport measurements. Lorentz Transmission Electron Microscopy and Magnetic Transmission X-ray Microscopy are employed to reveal the details of spin configuration in each of the nucleation states. We further show that it is possible to unambiguously identify these states by electrical measurements via the anisotropic magnetoresistance effect. Combination of the electrical transport and magnetic imaging techniques confirms stability of a vortex-antivortex-vortex spin configuration which emerges from the buckling state in static magnetic fields.

Highlights

Magnetic vortices are flux-closing magnetization configurations known to occur in micro- or nano-size disks or polygons fabricated from soft magnetic materials like Permalloy
They consist of a magnetization curling in the disk plane and of a vortex core located at the center, where the magnetization points perpendicular to that plane.[1,2,3]
Recent studies have shown magnetic vortices as spin wave emitters[9] using two antiferromagnetically coupled disks in a heterostructure providing a system with much higher eigenfrequencies when compared to a single magnetic disk with a vortex state

Summary

Introduction

LTEM images show a good agreement between the simulated and measured magnetic contrast for both the vortex-pair state [Figs. 2. Simulation and LTEM imaging of vortex nucleation states in magnetic field.

Results

Conclusion