Corner clusters in thin soft magnetic layers. III. Conversions in corner clusters

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Abstract
The domain structure in thin soft magnetic films is considered as a concatenation of domain-wall clusters, being collections of domain walls that have one intersection line—the so-called cluster knot—in common. The transformations in the domain structure are accompanied by the addition and the disappearance of clusters to and from the configuration, respectively. The discussion is confined to the reversible conversions in the corner clusters, whose cluster knots coincide with corners in the magnetic film. The situation in corners is unique because a singularity in the field in this region can be generated by a moderate external stimulus. Only domain walls whose ‘‘feet,’’ or the part most adjacent to the corner, coincide with one of the edges of the corner can be present in these high-field regions. This feature of the field distribution is of decisive significance to the conversions in the magnetization distribution, which is accompanied by the penetration of domain walls into the non-field-free region near the corners whose bounding edges form angles η smaller than π. In corners with larger angles, conversion between two continuous magnetization modes is possible, one mode characterized by the singularity in the field and the other one by a rotation segment with sector angle η-π. In this rotation segment, being a sector in which the magnetization rotates circularly around the cluster knot, the same reversible conversions as those previously discussed for free clusters can take place. The theoretical findings are supported by experimental observations conducted with the Bitter technique in 3500-Å-thick permalloy layers.