# Fresnel Magnetic Imaging of Ultrasmall Skyrmion Lattices

## TL;DR

Researchers used a special electron microscopy technique to study tiny magnetic skyrmion lattices and found unexpected contrast patterns due to imaging limitations.

## Contribution

The study reveals periodic chiral-reversal in ultrasmall skyrmion imaging and identifies its origin in the sinusoidal contrast transfer function.

## Key findings

- Periodic chiral-reversal phenomenon is observed in ultrasmall skyrmion lattice imaging.
- Chiral misinterpretations are attributed to sinusoidal modulation of the contrast transfer function.
- Findings highlight limitations of conventional Fresnel contrast analysis for nanoscale magnetic imaging.

## Abstract

Magnetic skyrmions with ultrasmall nanometric dimensions hold significant promise for next‐generation high‐density spintronic devices. Direct real‐space imaging of these topological spin textures is critical for elucidating their emergent properties at the nanoscale. Here, Lorentz transmission electron microscopy studies of nanometric skyrmion lattices in B20‐structured Mn0.5Fe0.5Ge crystals are presented using the Fresnel mode. According to conventional chiral discrimination methods relying on static bright‐dark contrast, an abnormal periodic chiral‐reversal phenomenon is demonstrated, retrieved through the transport of intensity equation analysis of defocus‐dependent Fresnel images. Through systematic off‐axis electron holography experiments and numerical simulations, these chiral misinterpretations are attributed to the sinusoidal modulation mechanism of the contrast transfer function that correlates with both defocus values and skyrmion dimensions. The findings establish quantitative limitations of conventional Fresnel contrast analysis for ultrasmall skyrmions while revealing fundamental insights into defocus‐mediated phase‐to‐intensity conversion processes in nanoscale magnetic imaging.

This study uncovers periodic contrast reversal in ultrasmall skyrmion lattice imaging through defocus‐modulated Fresnel magnetic microscopy, elucidating its origin in the sinusoidal contrast transfer function mechanism and providing fundamental insights into defocus‐mediated phase‐to‐intensity conversion processes in nanoscale magnetic imaging.