Effect of crystallization on magnetic domain structure of thinned amorphous FeSiBCuNb ribbons

Crystallization and associated magnetic domain structure of Fe_73.5Cu₁Nb₃Si_13.5B₉ amorphous ribbons have been investigated in in-situ annealing studies by electron transmission microscopy (TEM). Two stages of crystallization, which occurred at 380°C and 650°C, have been observed. The crystals associated with these temperatures are spherical nuclei with diameters less than 5 nm or clusters of ultrafine grains whose diameters are in the range of 15-20 nm respectively. The products formed at both stages are identified as the α-Fe(Si) phase. The magnetic domain structure of the as-quenched specimen is composed of large and simple domains. There is no evident change in domain structure. Upon the offset of the first crystallization. However, the second stage of crystallization leads to emergence of magnetic ripple. The origin of magnetic ripple is discussed within the framework of the random anisotropy model. From the analysis, effective uniaxial anisotropy <k> in the nanocrystalline alloy may be considered as local random anisotropy and is therefore likely to be the cause of the magnetic ripple. The estimated mean wavelength, λ, of the magnetic ripple is approximately 160 nm