Micromagnetic study of flux-closure states in Fe dots using quantitative Lorentz Microscopy

TL;DR

This paper combines Lorentz Microscopy and micromagnetic simulations to quantitatively analyze flux-closure states, asymmetric Bloch domain walls, and surface vortices in epitaxial Fe dots, revealing detailed magnetic structures and dynamics.

Contribution

It introduces a combined experimental and simulation approach to accurately characterize magnetic domain walls and vortex behavior in Fe dots.

Findings

Quantitative measurement of asymmetric Bloch domain wall width.

Identification of magnetic surface vortex propagation.

Enhanced magnetic sensitivity through novel image analysis.

Abstract

A micromagnetic study of epitaxial micron-sized iron dots is reported through the analysis of Fresnel contrast in Lorentz Microscopy. Their use is reviewed and developed through analysis of various magnetic structures in such dots. Simple Landau configuration is used to investigate various aspects of asymmetric Bloch domain walls. The experimental width of such a complex wall is first derived and its value is discussed with the help of micromagnetic simulations. Combination of these two approaches enables us to define what is really extracted when estimating asymmetric wall width in Lorentz Microscopy. Moreover, quantitative data on the magnetization inside the dot is retrieved using phase retrieval as well as new informations on the degrees of freedom of such walls. Finally, it is shown how the existence and the propagation of a surface vortex can be characterized and monitored. This demonstrates the ability to reach a magnetic sensitivity a priori hidden in Fresnel contrast, based on an original image treatment and backed-up by the evaluation of contrasts obtained from micromagnetic simulations.