A STUDY ON MAGNETIC CONTRAST AND MAGNETIC FIELD MEASUREMENT IN THE SCANNING ELECTRON MICROSCOPY

Abstract

Electron microscopy is one of the more important tools to image and quantify the micro-magnetic fields. In this study, a new electron beam tomographic technique to reconstruct three-dimensional micro-magnetic fields is described. Type-I magnetic contrast in the scanning electron microscope (SEM) is the contrast in the secondary electron (SE) image modulated by the fringe fields from magnetic specimens such as magnetic recording media and head. The modeling of the Type-I magnetic contrast in the SEM has not been well understood. In the first part of the thesis, a more accurate analytical modeling of the Type-I magnetic contrast with energy filtering in the SEM has been proposed and simulated. In the second part of the thesis, an algorithm based on algebraic reconstruction techniques (ART) has been developed to quantify micro-magnetic fields from magnetic recording heads using the deflection of low energy primary electron beam by the micro-magnetic fields. Existing tomography algorithms for the reconstruction of micro-magnetic fields have the disadvantages of partial reconstruction due to insufficient data points and slow reconstruction. An entirely new algorithm has been developed for the high resolution reconstruction of micro-magnetic fields using a ray tracing technique combined with an efficient version of ART. This new algorithm, which will overcome the shortcomings mentioned above, has been verified using numerical simulation. It has also been proven to be more efficient and accurate than the existing algorithms. A versatile experimental system has been designed and developed to image and quantify the micro-magnetic fields.