Electron holography study on magnetization process in nanocrystalline and microcrystalline Fe_73.5Si_13.5B₉Nb3́ Cu₁ Films

Magnetic domain structures in Fe_73.5Si_13.5B ₉Nb₃Cu₁ alloys annealed at different temperatures have been observed in situ under external magnetic fields by electron holography. Under a weak magnetic field of less than several A/m, a typical magnetization process of the high permeability material is observed in the specimen annealed at 823 K consisting of the bcc Fe-Si nanocrystalline and the amorphous matrix phase. On the other hand, in the specimen annealed at 973 K consisting of large Fe-Si grains and Fe-B compounds, many domain walls are observed at the boundaries between Fe-Si grains and also between Fe-B grains. Under a strong magnetic field of more than several kA/m, domain walls are observed only between Fe-B grains. The result indicates that the boundaries between Fe-B grains act as stronger pinning sites of domain walls than the boundaries between Fe-Si grains and those between Fe-Si and Fe-B grains in the Fe_73.5Si_13.5B₉Nb₃Cu₁ alloy annealed at 973 K.