With advances in the fabrication and processing technology of nanoscale magnetic materials, characterization methods are being pushed to their limits. It is necessary to correlate the observed magnetic properties with the microstructure as well as the magnetic structure of the material. Transmission electron microscopy provides the ability to characterize both the microstructure and the magnetic structure with high spatial resolution. Lorentz microscopy has been used traditionally for investigating the magnetic induction maps of thin foils. However, the observations are typically only two dimensional projections and do not give a clear idea of the entire three dimensional (3D) magnetic induction.;In this work, we present a novel method to characterize the 3D magnetic structure of the sample using Lorentz microscopy and tomography techniques. Tomography enables us to obtain 3D information of the property under observation by recording a series of 2D projections by tilting the sample. The electron-optical phase shift of the electrons in a TEM is essentially a 2D projection of the electrostatic and the magnetic vector potentials of the sample. Thus, combining the phase shift data recorded from a TEM with tomographic reconstruction methods, we can determine the 3D magnetic induction and the magnetic vector potential of the sample. This method is called Vector Field Electron Tomography (VFET) since it reconstructs a vector field using electron tomography data.;In this thesis, the mathematical theory for VFET is developed and a theoretical proof-of-concept is shown. With the aid of simulation assisted Lorentz microscopy, the ability of VFET to reconstruct the 3D magnetic induction and the magnetic vector potential of various magnetization states is demonstrated. Some experimental applications are shown along with an analysis of the reconstructed fields.
展开▼
