Magnetic-Field-Free Objective Lens around a Specimen for Observing Fine Structure of Ferromagnetic Materials in a Transmission Electron Microscope

In order to observe the fine structures of ferromagnetic materials or to observe their magnetic domain structures, special magnetic-field-free lenses in which specimens are set in the upper pole-piece have been developed. In these objective lenses, the spherical aberration depends largely on the shape of the lens, especially, (1) the distance between the positions of the specimen and the peak of the lens field, (2) the diameters of the pole-piece bores and the top face of the upper pole-piece, and (3) the gap length. In a lens with a pole-piece of optimum dimensions, the resulting resolution reached 0.7 nm and the leakage field strength was 0.35 mT. Complicated domain structures of ferromagnetic materials could be clearly observed.