Abstract
We report the effects of longitudinal magnetic field annealing (MFA) on the microstructure, magnetic domain structure, and magnetic softness of Co substituted amorphous Fe89−x−yCoyBxZr11 alloys. A two-phase structure characterized by bcc Fe(Co) nanocrystals (size <15 nm) embedded in residual amorphous matrix was obtained in samples annealed below 873 K. Room temperature saturation magnetization (MS) of Fe89−x−yCoyBxZr11 alloys not only increases from 93 to 127 emu/g in the amorphous state upon Co substitution, but also enhances to 173 emu/g with MFA. Coercivity (HC) increases significantly when annealed up to 673 K and decreases slightly beyond 673 K. All samples annealed at 923 K showed large HC (>100 Oe) due to the formation of Fe(Co)–Zr compounds. Large MS (173 emu/g) and low HC (0.4 Oe) were obtained for an Fe69Co10B10Zr11 alloy annealed at 823 K. Lorentz microscopy results reveal that the average size of the domains decreases with increasing Co content and magnetic ripple structures are observed in samples annealed above 823K. The observed enhancement in magnetic softness is correlated with the microstructure and magnetic domain structure.
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