Domain-Wall Structure in Permalloy Films

Abstract

Domain‐wall structure in Permalloy films in the thickness range 25 to 2000 A has been studied by the Bitter technique. A new type of 180° wall has been observed: the main wall is cut at regular intervals by short, right‐angle ``cross ties'' which terminate in free, single ends. The cross‐tie period and length are dependent on film thickness, each becoming shorter with decreasing thickness. These patterns can be understood in terms of a new model for the structure of domain walls in thin films of low‐anisotropy material. In the conventional model the atomic moments within the wall rotate about an axis perpendicular to the wall. In a thin film such a configuration leads to a large energy contribution from the large demagnetization factor normal to the film. In the new model, the axis of rotation is itself thought to rotate about the axis of the wall to give a ``corkscrew'' configuration of spins and a large decrease in associated magnetostatic energy. Of several experiments which have been performed which support this model, one is briefly described.