Magnetic microstructure of Fe84Nb7B9 alloys observed by electron holography

The microstructure, magnetic properties and magnetic structure of crystallized Fe84Nb7B9 samples are studied in this article. It is found that the size of the body-centered-cubic Fe crystallites is independent of the annealing temperature. The volume fraction of the amorphous phase decreases with an increase in annealing temperature and iron boride precipitates form at temperatures over 973 K. Excellent soft magnetic properties are obtained in the sample annealed at 923 K which has large uniform domains with smooth and straight walls, whereas precipitates of Fe boride in the sample annealed at 973 K degrade the magnetic softness. Their magnetization processes are pure magnetization rotation dominated by uniaxial anisotropy. The thick amorphous phase matrix and strong internal stray field in the sample annealed at 773 K lead to a magnetic ripple structure. The domain wall movement is strongly pinned by anisotropy fluctuations. The longitudinal wavelength of the magnetic ripples increases with a decrease in temperature, and disappears at temperatures below 230 K. (C) 2003 American Institute of Physics.