Lorentz Microscope

Daisuke Shindo^a and Zentaro Akase^a

^aInstitute of Multidisciplinary Research for Advanced Materials, Tohoku University

Abstract: Principles and application of Lorentz microscopes are presented. First, the mechanism of the so-called Lorentz lens which is an objective lens with weak magnetic field at the specimen position is explained. Then observation modes of Lorentz microscopy of domain structure are presented. It is shown that the defocusing method and in-focus method are useful to locate domain walls and domains, respectively. Phase information analysis with the transport of intensity equation and scanning Lorentz microscopy are also noted. Finally, various kinds of magnetizing systems are explained. As a simple magnetizing method, the specimen tilt, by which a part of the magnetic field of the objective lens can be introduced in the specimen plane, is explained. Also a conventional magnetizing system consisting of a specimen holder with an electromagnet is explained.  Furthermore, by installing a sharp magnetic needle made of a permanent magnet in a piezodriving holder, dynamic observation of nucleation process of magnetization reversal in Nd-Fe-B is carried out. On the other hand, by utilizing an alternating current magnetizing system, dynamic motion of domain walls in electrical steel sheets is studied by Lorentz microscopy. It is observed that the domain walls are strongly pinned at the precipitates.

Key words: Lorentz microscope, Lorentz lens, magnetizing system, magnetic domain wall, magnetization process