Domain wall behaviour in magnetic nanoelements and wires

Domain walls in magnetic nanoelements and wires have markedly different properties from their counterparts in either thin films or bulk material. An understanding of their structure and their behaviour under external stimuli is of fundamental interest and also necessary if reliable nanomagnetic devices are to be developed. In this lecture, following a brief introduction to domains and domain walls (DWs), I shall describe how magnetic imaging can provide much of the necessary information in a direct and accessible way. Various imaging techniques exist and here the focus will be on transmission electron microscopy. In addition to offering high spatial resolution it is well suited to in-situ experimentation.

The structure of DWs in elements or wires fabricated from soft magnetic materials such as permalloy is rarely simple and three dimensional magnetic features, such as vortices, occur frequently. Moreover, the domain and DW structure in multilayer and single layer elements with the same total magnetic thickness can be quite different. This leads to fertile ground for research and offers opportunities for tailoring properties towards specific applications.

In the final part of the lecture I will discuss briefly in situ experimentation whereby transport measurements and DW observation can be combined. Specifically I will discuss how DWs can be driven by spin-polarised current rather than by magnetic field. Some key observations from these experiments will be described.