Direct observation of domain structure and magnetization reversal of magnetic thin films using Lorentz transmission electron microscopy

Lorentz transmission electron microscopy (LTEM) was used to characterize the domain structure and the magnetization reversal process of Ni₈₀Fe₂₀ and Co films fabricated using magnetron sputtering. In-situ magnetizing experiments were performed in Fresnel imaging mode, while a long camera length mode ("reverse mode") was employed for Foucault imaging. At low fields, magnetization ripple in the Co films showed higher magnetic contrast and angular distribution than in the NiFe films, which was due to the high anisotropy of Co. The NiFe films reversed via rapid wall motion while the Co films reversed mainly via slow moment rotation followed by wall motion. It is confirmed that domain wall mobility in the NiFe films is higher than that in the Co films. Profound columnar texture of the Co films observed in conventional transmission electron microscopy may enhance wall pinning and thus hinder wall mobility.