Internal Structure of Cross-Tie Walls in Thin Permalloy Films through High-Resolution Bitter Techniques

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Abstract
The use of a water immersion objective with the optical microscope for Bitter pattern studies has resulted in a significant improvement in resolution. A discussion of technique in using such an objective is presented. Applied to the study of cross‐tie domain walls in thin Permalloy films, this technique has revealed details of internal wall structure. In the proposed model for such walls the magnetization within the wall is thought to be predominantly in the plane of the film, with periodic transition regions in which the magnetization is normal to the film. This configuration reduces the large magnetostatic energy which would be associated with a conventional 180° wall. Areas of low particle density are observed at the intersection of the main wall and cross‐ties and in the main wall midway between cross‐ties. From conventional ideas of colloid‐pattern formation, these areas might be expected to have a high particle density because they are the transition regions in which the magnetization is normal to the film. The apparent conflict is resolved by assuming that these regions are large compared to the colloid particle size so that the fringing field at the edge of the region governs the particle distribution. In support of the model, convincing evidence is presented of the reported shift of colloid particles when an external field is applied normal to the film.

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