Lorentz electron microscopy

A method to observe magnetic domain structures of a ferromagnetic material using a TEM. Electrons passing through a ferromagnetic material undergo a Lorentz force that depends on the magnetization direction, thus their traveling direction changes (electrons are deflected). Adjoining magnetic domains experience different deflections, thus producing contrast between the magnetic domains. "Lorentz electron microscopy" has two modes: Fresnel mode and Foucault mode. In the Fresnel mode (defocus mode), the deflected electron-beams from the adjoining domains are superposed at the domain boundary, thus boundaries are observed as the light or dark line. In the Foucault mode (infocus mode), diffraction spots produced by the adjoining domains are displaced a little to each other on the back focal plane. When one of the two spots is selected for image formation, a bright image is obtained for the domain corresponding to the selected diffraction spot, whereas the dark image appears for the domain corresponding to the unselected diffraction spot. In an ordinary TEM, since the specimen is placed in a strong magnetic field, the entire specimen exhibits a single magnetic domain. To overcome this problem, a dedicated objective lens that applies nearly no magnetic field to the specimen position is used.