On the use of divergent wall images in the fresnel mode of Lorentz microscopy for the measurement of the widths of very narrow domain walls

In the Fresnel mode of Lorentz microscopy, domain wall widths are often estimated using the linear extrapolation method in which the widths of divergent domain wall images recorded with different defocus distances are extrapolated to zero defocus. This paper examines the validity of the technique for very narrow walls by analysing images synthesized on a computer. The results show that the method is only of limited reliability for the estimation of very narrow wall widths. Methods of improving the accuracy are suggested.