<I>In Situ</I> Lorentz Microscopy and Electron Holography of Magnetization Process in Ferrite Magnets

Abstract

The magnetic domain structures and magnetization processes of anisotropic Ba and Sr ferrite magnets are investigated by Lorentz microscopy and electron holography. By utilizing a sharp magnetic needle made of a sintered Nd-Fe-B magnet in a transmission electron microscope, the magnetization process in ferrite magnets is visualized for the first time by in situ Lorentz microscopy. In the anisotropic Ba ferrite specimen, magnetization reversal occurs suddenly along the grain boundaries over a large volume, which includes the volumes of some grains located around the specimen edges. On the other hand, in the anisotropic Sr ferrite specimen, magnetization reversal is not observed due to the large coercivity of the specimen. During the magnetization process from the demagnetized state in the Sr ferrite specimen, the domain wall inside a grain moves gradually along the grain boundary and then stops at the grain boundary.