Characterisation of Ferromagnetic Rings for Zernike Phase Plates using the Aharonov-Bohm effect

TL;DR

This paper demonstrates that ferromagnetic cobalt rings can produce precise phase shifts in electron microscopy via the Aharonov-Bohm effect, enabling small, effective phase plates for improved imaging.

Contribution

It provides experimental validation of magnetic flux-induced phase shifts in ferromagnetic rings, proposing their use as compact phase plates in electron microscopy.

Findings

Magnetised cobalt rings exhibit onion and vortex states.

Phase shifts in electron paths agree with Aharonov-Bohm theory.

Cobalt rings can produce a pi/2 phase difference with sub-30 nm width.

Abstract

Holographic measurements on magnetised thin-film cobalt rings have demonstrated both onion and vortex states of magnetisation. For a ring in the vortex state, the difference between phases of electron paths that pass through the ring and those that travel outside it was found to agree very well with Aharonov-Bohm theory within measurement error. Thus the magnetic flux in thin-film rings of ferromagnetic material can provide the phase shift required for phase plates in transmission electron microscopy. When a ring of this type is used as a phase plate, scattered electrons will be intercepted over a radial range similar to the ring width. A cobalt ring of thickness 20 nm can produce a phase difference of pi/2 from a width of just under 30 nm, suggesting that the range of radial interception for this type of phase plate can be correspondingly small.