Observation of vortex-nucleated magnetization reversal in individual ferromagnetic nanotubes

TL;DR

This study observes vortex nucleation as the initial step in magnetization reversal in individual ferromagnetic nanotubes, revealing how vortex entry depends on field angle and end surface orientation, supported by experiments and simulations.

Contribution

It provides the first direct observation of vortex nucleation in ferromagnetic nanotubes and demonstrates control over vortex entry influenced by end surface geometry.

Findings

Vortex entry marks the onset of magnetization reversal.

The vortex entry field varies with the angle between the nanotube end and the magnetic field.

Micromagnetic simulations confirm the experimental observations.

Abstract

The reversal of a uniform axial magnetization in a ferromagnetic nanotube (FNT) has been predicted to nucleate and propagate through vortex domains forming at the ends. In dynamic cantilever magnetometry measurements of individual FNTs, we identify the entry of these vortices as a function of applied magnetic field and show that they mark the nucleation of magnetization reversal. We find that the entry field depends sensitively on the angle between the end surface of the FNT and the applied field. Micromagnetic simulations substantiate the experimental results and highlight the importance of the ends in determining the reversal process. The control over end vortex formation enabled by our findings is promising for the production of FNTs with tailored reversal properties.