TABLE OF CONTENTS Electron holography is an electron microscope imaging technique that permits quantitative measurement of magnetic fields with spatial resolution approaching the nanometer scale. The theoretical background and usual experimental setup for electron holography are first briefly described. Applications of the technique to magnetic materials and nanostructures are then discussed in more detail. Future prospects are summarized.
The transmission electron microscope (TEM) is an essential tool that is in widespread use for microstructural characterization. Although there are many different TEM imaging modes, most cannot be used to characterize magnetic fields within or surrounding a sample because they are insensitive to changes in the phase of the electron beam. Lorentz microscopy, as described in Chap. 4, uses defocused imaging to distinguish magnetic features such as domain walls [1] , [2]. In this approach, which has several closely related variants [3], high-energy electrons of the incident beam are deflected sideways by the magnetic field of the sample to produce bands of light and dark contrast that correspond to local changes in the magnetic field strength or orientation. Compared with electron holography, these Lorentz imaging modes have the advantages that real-time observation of changing domains is possible and no vacuum reference wave is required. However, longer-range magnetic fields are not easily mapped, and compositional contributions to the contrast from the edges of nanostructured elements may be significant, so that magnetic nanostructures become more difficult to characterize as their dimensions are reduced.
Electron holography offers an...
