Electron Holography Study on Magnetization Process in Nanocrystalline and Microcrystalline Fe_{73.5}Si_{13.5}B_{9}Nb_{3}Cu_{1} Films

Magnetic domain structures in Fe73:5Si13:5B9Nb3Cu1 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 823K consisting of the bcc Fe–Si nanocrystalline and the amorphous matrix phase. On the other hand, in the specimen annealed at 973K 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 Fe73:5Si13:5B9Nb3Cu1 alloy annealed at 973K.