TABLE OF CONTENTS Magnetic nanocrystals and nanostructured magnetic materials occupy very important positions in cutting edge technologies. The applications of magnetic materials include permanent magnets, magnetic recording, magnetic memory. magnetic sensors, etc. Lorentz microscopy in TEM is a convenient way to image the magnetic structure with the highest achievable resolution.
Electrons passing though a magnetic domain experience Lorentz deflection given by
where e is the electron charge, B is the magnetic induction, ? is the electron wavelength, d is the thickness of the domain and h is the Plank's constant. This deflection angle for 100 kV electrons passing a 200 nm Fe specimen is in the order of 0.4 milliradians. This deflection can be used to image the magnetic domain in either conventional TEM or in a scanning TEM (STEM). The deflection of the electron beam results in diffraction contrast as observed by bright-field TEM imaging using a very small objective aperture, in which the contrast is introduced due to the decrease in number of electrons propagating along the incident beam direction. This allows a direct imaging of local domain structure.
TEM is based on magnetic lenses. To image magnetic specimens, it is necessary to avoid any change of the magnetic structure caused by the magnetic field of the objective lens. A simple solution is to switch off the objective lens, and a lens for magnetic imaging can be mounted at a...
