The Electron-Beam Shadow Method of Investigating Magnetic Properties of Crystals

Abstract

This chapter presents the electron-beam shadow method of investigating magnetic properties of crystals. Magnetic-powder techniques have shown that needle- or plate-shaped magnetic domains exist in an unmagnetized single crystal of hexagonal cobalt. In the electron-beam method, crystals for examination are usually mounted, within the vacuum, on a specimen holder which allows the position of the crystal to be moved, to some extent, with respect to the electron beam. Considering that electrostatic charging produces disturbances of the electron beam, which may be mistaken for magnetic effects, it is essential that crystals, particularly those which are poor electrical conductors, first be coated with a thin layer of a good conducting substance. The electrons produce an elongated illuminated area on the screen, and it is possible to observe the shadow of a much larger edge-length of the specimen. In electron shadow experiments, the electron beam that interacts with the field of the crystal generally makes a small angle with the crystal face and approaches nearest to the face at the lower edge of the crystal. The chapter suggests that the electron beam method of investigation may be used to study magnetic transformations, estimate domain sizes, and to obtain information about reduction of the leakage field by means of closure domains.