Study of Spin Configuration of Hexagonal Shaped Ferromagnetic Structures

Abstract

This thesis work consists of two distinct parts: the set-up of a unique characterisation system and the study of spin configurations in hexagonal ferromagnetic structures. The characterisation system developed is able to perform in-situ magnetic imaging, structural modification and electrical transport measurement on ferromagnetic structures. For the latter, hexagonal ferromagnetic structures were investigated due to its uniqueness of having a vortex state with well-defined, symmetric and moderate stray field for desirable magnetostatic interaction, which is not found in the vortices of circular disk structures. The vortex structure in hexagonal elements is stable over a wide thickness range. By arranging the hexagons in ring networks, we found that there is an occurrence of alternating chirality configuration in the vortices when the inter-element spacing is small. The results imply that, in addition to the strength, the symmetry of the stray field also plays an important role in determining the relative chirality of individual hexagons. To explore potential applications of hexagonal elements, the investigation of composite structures showed that it is possible to cause magnetisation reversal in the composite structures by spin-transfer torque effect.