Electron holography of nanocrystalline magnetic materials

Electron holography study on magnetic domain structures of nanocrystalline magnetic materials was overviewed mainly based on the experimental results recently obtained by the author and his colleagues. Electron holography system which was established by modifying a conventional analytical electron microscope, i.e., introducing a biprism and a special pole piece for magnetic domain observation shows the resolution of several nanometers under the magnetic field less than 1600 A/m at the specimen position. With this system, firstly magnetic domain structures of nanocrystalline soft magnetic materials Fe-Cu-Nb-Si-B with various heat treatments are clarified. Furthermore, by introducing the residual magnetic field of the objective lens in the thin film plane, magnetization process of the soft magnetic materials is observed. On the other hand, in nano-granular films Co-Zr-O, the dependence of both microstructures and magnetic domain structures on the composition is clarified in detail. It is found that the strength of the magnetic anisotropy field in the film directly depends on the magnetization distribution clarified by electron holography. Finally, in the nanocomposite magnets Nd-Fe-B, the detailed distribution of lines of magnetic flux at a nanometer scale is visualized. It is found that the distribution of lines of magnetic flux observed is directly related to the magnetic properties, such as coercivity and remanence. These results clearly demonstrate the usefulness and the potential of electron holography for the analysis of detailed magnetic domain structures of advanced magnetic materials such as nanocrystalline magnetic materials.