Imaging stray magnetic field of individual ferromagnetic nanotubes

TL;DR

This study employs a scanning SQUID to map the magnetic fields of individual ferromagnetic nanotubes, revealing vortex-based magnetization reversal and the influence of geometrical imperfections.

Contribution

It introduces a method for high-resolution magnetic field imaging of nanotubes and compares experimental results with micromagnetic simulations to understand reversal mechanisms.

Findings

Magnetic reversal involves vortex states in nanotubes.

Geometrical imperfections affect stray-field patterns.

Vortex configurations depend on nanotube length and field orientation.

Abstract

We use a scanning nanometer-scale superconducting quantum interference device to map the stray magnetic field produced by individual ferromagnetic nanotubes (FNTs) as a function of applied magnetic field. The images are taken as each FNT is led through magnetic reversal and are compared with micromagnetic simulations, which correspond to specific magnetization configurations. In magnetic fields applied perpendicular to the FNT long axis, their magnetization appears to reverse through vortex states, i.e.\ configurations with vortex end domains or -- in the case of a sufficiently short FNT -- with a single global vortex. Geometrical imperfections in the samples and the resulting distortion of idealized mangetization configurations influence the measured stray-field patterns.