Bloch line interaction in coarsely crystalline permalloy films

Data storage in thin permalloy films has failed to reach its promise partly because domain walls do not maintain their configuration in the presence of disturb fields. The phenomena associated with the motion of a domain wall, both creep and coercivity, are generally determined by the interactions between the wall and its host magnetic film. Some of these interactions are isolated and studied. When a domain wall moves across a specimen, it interacts with many defects at a given time. In order to minimize the complexity of the system, a physical model is described, in which a Bloch line moving along a cross-tie wall in a coarsely crystalline permalloy film is treated like a segment of a Bloch wall. In this model adjacent Bloch wall segments are completely decoupled from each other. The Bloch line is then studied with Lorentz microscopy to determine factors that strongly affect its motion. The experimental work is compared to a mathematical model in which a partial breakoff of exchange coupling across grain boundaries is used to explain the observed behavior. Some implications of these results are discussed.