Domain Wall Width Measurement in Cobalt Films by Lorentz Microscopy

A recent report by Suzuki et al. indicates that the domain wall width of 76% Ni–Fe alloy films with thickness 200 to 1800 Å is much wider than those calculated on the basis of the simple wall models. It was suggested that theoretical calculations might be in serious error due to gross overestimation of the magnetostatic stray field energy. In the present work, similar measurements of domain wall width have been made by the defocused mode of Lorentz microscopy for evaporated polycrystalline Co films with thickness from 200 to 1500 Å. Only the intensity profiles of the divergent wall images were taken into account, and a small out-of-focus distance (1.1 mm) was used, so that classical interpretation of the image would be allowable. The present study indicates (1) the wall width in Co is much greater than predicted by present theories with minimum value of 3000 Å at 500-Å film thickness and (2) the change in wall width with film thickness is much less than in the case of Ni–Fe films.