Magnetic domain walls in thin molybdenum permalloy films observed under external magnetic fields by electron microscopy

Dynamic observations of domain walls have been made using the Lorentz Microscopy technique. The aim of the investigations was to study the influence of magnetic fields on the domain wall stability and also to study the influence of structural features such as grain boundaries, twins' inclusions and second-phase particles on the initial permeability. Most of the thin foils used had thicknesses less than 100 nm hence the specimens could be referred to as thin films. Cross-tie walls which were noted to occur in materials with high permeability, i.e. materials of low crystal anisotropy,K_i, were observed at intermediate thicknesses of the thin foils. Both the cross-tie length and period are dependent upon film thickness, each becoming shorter with increasing thickness. The influence of the applied field on the cross-tie wall stability depends on both the magnitude and direction of the applied field. Secondly, it was observed experimentally that besides the transition from the Néel wall to the Bloch wall, transitions also occur as a function of the applied WA Structura! features such as grain boundaries, twins, inclusions, which may take many forms as holes or cracks, etc., had a very strong pinning effect on the domain wall motion, leading to a reduction in permeability.