Wave optical effects in Lorentz microscopic images of magnetic domain walls

Abstract

Intensity distributions in Lorentz microscopic defocused images of magnetic domain walls were numerically calculated using wave optics. Constants used in the calculation were generalized by the deflection angle φ and the wall width 2 x 0 so that the result was able to apply to any magnetic films. 180° walls in amorphous Gd-Fe films were observed by transmission Lorentz microscopy operating at 200 kV in the defocused mode. Numbers of well resolved intereference fringes were apparently observed in convergent images when the illumination angle was kept less than about 2 x 10 −6 and their intensity varied in consistent way to the calculated images with the defocusing distance. Series of convergent images of each wall were compared with the calculated ones by a through focus fitting method and the deflection angle and the wall width were accurately determined at a time. The measured example for a Gd-Fe film of 510 Å in thickness was φ = 2.65 × 10 −5 and 2x 0 = 1320 A ̊ .