Ultrafast annular-magnetic-field-driven vortex-core reversals

Zhenyu Wang,Ruifang Wang

doi:10.1063/1.4973536

Abstract

By micromagnetic numerical simulations, we investigate the dynamics of vortex-core reversal in a soft magnetic nanodisk under the excitation of annular, perpendicular, resonant magnetic fields. The non-fundamental radial modes of the nanodisk are characterized into alternating radial-phase-regions for which two adjacent regions across a node point are in antiphase. We show that radial spin-waves excited by fields applied in the in-phase regions are in phase, and therefore generate strong magnetization oscillations resulting from constructive spin-wave interference. Such annular magnetic fields can substantially speed up the vortex-core reversal and lower the threshold field amplitude in comparison with the global field. Our work provides an efficient mechanism for spin-wave excitation and ultrafast vortex-core switching.

Highlights

The magnetic vortex (MV) is a common ground state of soft ferromagnetic structures in the scale range of a few microns to tens of nanometers.[1,2] In such confined systems, the competition between the exchange interaction and the magnetic dipole interaction favors an in-plane circulation of magnetization around a core where the magnetization tilts out-of-plane
The VC polarity reversal occurs through the creation and annihilation of a vortex–antivortex pair, when the VC accelerates to a critical velocity of a few hundred meters per second.[17,18]
When an out-ofplane AC magnetic field is applied to excite the radial spin-wave mode, the VC polarity switches within one nanosecond and causes no translational motion of the VC.[19,20,21,22,23,24]

Summary

Introduction

The magnetic vortex (MV) is a common ground state of soft ferromagnetic structures in the scale range of a few microns to tens of nanometers.[1,2] In such confined systems, the competition between the exchange interaction and the magnetic dipole interaction favors an in-plane circulation of magnetization around a core where the magnetization tilts out-of-plane. We performed micromagnetic simulations to demonstrate a far more efficient excitation for non-fundamental modes when the magnetic field is applied in selected annular regions of a circular vortex.

Results

Conclusion