Lorentz TEM characterisation of magnetic and physical structure of nanostructure magnetic thin films
The work presented in this thesis is an investigation which aims to quantitatively characterise the physical microstructure, magnetic structure and micromagnetic behaviour of nanostructured thin films for magnetic recording and spintronics application. The nanostructures in the present work involve continuous and patterned thin films. Chapters 1, 2, and 3 present the overview backgrounds directly relevant to the work. Chapter 4 focuses on vortex structure in magnetic nanodots. The results confirm that the behaviour of the vortex can be modified by changing the edge geometry of the dots. It is demonstrated a practical method to determine the out-of-plane component of the vortex core with high accuracy and speed. Additionally in-plane curling magnetisation of the vortex is also mapped by reconstructing the electron phase using the transport-of-intensity equation. However this method is susceptible to spurious low spatial frequency and this aspect is explored to show limitations of the method. Chapter 5 deals with the characterisation of magnetic structure in nanoconstrictions intended to trap domain walls (DWs) in the nanoconstrictions. A structure was fabricated with two micron-sized pads as the sources for creation of DWs. A DW can be driven to be pinned at the nanoconstriction resulting in a change of magnetoresistance due to the contribution of the DW to the resistance of the device. The magnetisation configuration around the constriction is studied during the reversal process. It is apparent that that understanding the magnetisation rotation around the constriction and into the pads is the key to the magnetoresistance measurements and the DW resistance is part of this process. Evidences of DW compression at the nanoconstriction were noted. In Chapter 6 the investigation of the physical structure and micromagnetism of CoIr film is described. A hexagonal crystal structure with a [0001] texture normal to the film plane was characterised. Weak anisotropy is observed in the film denoted by a complex reversal on the hard axis due to incoherent rotation of magnetic moments. The film exhibits typical soft magnetic behaviour it merits compared to other soft materials are discussed in light of the results obtained here. Chapter 7 concludes with a discussion of the outcomes of the present thesis. Additionally possible directions for future research in topics discussed in this thesis are proposed.