Domain Wall Spin Structures in Mesoscopic Fe Rings probed by High Resolution SEMPA

TL;DR

This study combines simulations and high-resolution imaging to analyze the stability and variety of domain wall spin structures in mesoscopic Fe rings, revealing the influence of geometry, material properties, and metastability on magnetic configurations.

Contribution

It provides a comprehensive phase diagram of domain wall configurations in Fe rings, incorporating both experimental observations and micromagnetic simulations, highlighting the role of metastability and asymmetric walls.

Findings

Transverse and vortex domain walls are predicted and observed.

Asymmetric transverse domain walls are prevalent in certain geometries.

Material properties, defects, and thermal effects significantly influence domain wall states.

Abstract

We present a combined theoretical and experimental study of the energetic stability and accessibility of different domain wall spin configurations in mesoscopic magnetic iron rings. The evolution is investigated as a function of the width and thickness in a regime of relevance to devices, while Fe is chosen as a material due to its simple growth in combination with attractive magnetic properties including high saturation magnetization and low intrinsic anisotropy. Micromagnetic simulations are performed to predict the lowest energy states of the domain walls, which can be either the transverse or vortex wall spin structure, in good agreement with analytical models, with simulations revealing the expected low temperature configurations observable on relaxation of the magnetic structure from saturation in an external field. In the latter case, following the domain wall nucleation process, transverse domain walls are found at larger widths and thicknesses than would be expected by comparing the competing energy terms demonstrating the importance of metastability of the states. The simulations are compared to high resolution experimental images of the magnetization using scanning electron microscopy with polarization analysis to provide a phase diagram of the various spin configurations. In addition to the vortex and simple symmetric transverse domain wall, a significant range of geometries are found to exhibit highly asymmetric transverse domain walls with properties distinct from the symmetric transverse wall. Simulations of the asymmetric walls reveal an evolution of the domain wall tilting angle with ring thickness. Analysis of all the data reveals that in addition to the geometry, the influence of materials properties, defects and thermal activation all need to be taken into account in order to understand and reliably control the experimentally accessible states, as needed for devices.