Induced anisotropy in nanocrystalline FeCuNbSiB

The kinetics of induced anisotropy K_ind was studied in nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5 B₉, as well as in the amorphous precursor and in amorphous Fe₇₈B₁₃Si₉. The nanocrystalline alloy was produced from the precursor by annealing at 813 K for 1 h and possessed an average FeSi grain size of 13 nm, as determined from X-ray diffraction. Annealing in a 0.2 T field at 723-773 K, above T_c of the amorphous phase, resulted in low values of K_ind. The data were compared to the micromagnetic theory of Kronmuller to determine activation energy spectra. K_ind for the nanocrystalline alloy is well described by this theory, however, with an activation energy spectrum that is much narrower than for the amorphous alloys. The limiting value of the anisotropy is K_∞ ≈13 J/m³ consistent with that expected for the anisotropy in Fe-20at%.Si with the DO₃ structure