Third type of domain wall in soft magnetic nanostrips

TL;DR

This paper reports the discovery of a third type of magnetic domain wall in permalloy nanostrips, characterized by a unique 3D flux closure structure, expanding the understanding of domain wall configurations.

Contribution

The study identifies and characterizes a new third type of domain wall in permalloy nanostrips, supported by numerical simulations and magnetic imaging, and provides an extended phase diagram.

Findings

Discovery of a third domain wall type with 3D flux closure structure

Experimental confirmation of the new domain wall in permalloy nanostrips

Demonstration of domain wall mobility under external magnetic field

Abstract

Magnetic domain walls (DWs) in nanostructures are low-dimensional objects that separate regions with uniform magnetisation. Since they can have different shapes and widths, DWs are an exciting playground for fundamental research, and became in the past years the subject of intense works, mainly focused on controlling, manipulating, and moving their internal magnetic configuration. In nanostrips with in-plane magnetisation, two DWs have been identified: in thin and narrow strips, transverse walls are energetically favored, while in thicker and wider strips vortex walls have lower energy. The associated phase diagram is now well established and often used to predict the low-energy magnetic configuration in a given magnetic nanostructure. However, besides the transverse and vortex walls, we find numerically that another type of wall exists in permalloy nanostrips. This third type of DW is characterised by a three-dimensional, flux closure micromagnetic structure with an unusual length and three internal degrees of freedom. Magnetic imaging on lithographically-patterned permalloy nanostrips confirms these predictions and shows that these DWs can be moved with an external magnetic field of about 1mT. An extended phase diagram describing the regions of stability of all known types of DWs in permalloy nanostrips is provided.