2. Lorentz microscopy: Theoretical basis and image simulations

Magnetization configurations in real engineering materials can be studied both qualitatively and quantitatively in a variety of ways. This chapter reviews the basic theory of Lorentz microscopy, a set of observation modes that are commonly used in either a conventional transmission electron microscope (CTEM) or a scanning transmission electron microscope (STEM). The behavior of relativistic electrons in a magnetic field is examined in the chapter, using first a classical and then a quantum mechanical approach. In the chapter, the various observation modes (Fresnel, Foucault, and derived techniques) are presented and the way the transmission electron microscope (TEM) can be used to obtain qualitative pictures of the magnetization configuration in a thin foil is discussed. The chapter presents quantitative observation modes, which produce direct maps of the sample magnetization configuration. These include differential phase contrast, which can be used in CTEM and STEM versions. It also describe the way Lorentz images can be simulated for a given magnetization configuration.