Sharp Films as Memory Elements

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Abstract
The concept of sharp films results from a study of the behavior of the magnetization vector at the edge of a thin film. In that study it was shown that many of the effects of the demagnetizing field at the edge of a film can be predicted by assuming a local shape edge‐anisotropy field, whose easy axis lies parallel to the edge of the film. According to this theory, square films have a low nucleation threshold because the edges of the film perpendicular to the easy axis have an edge anisotropy that subtracts from the ordinary field‐induced anisotropy yielding a region of low resultant anisotropy. Sharp films are memory elements in which the angle between the film edge and the easy axis is everywhere small. Consequently, the resultant anisotropy field along the edge is the sum instead of the difference of the two anisotropy fields, and the nucleation threshold is high. In fact, reverse domains in these films generally form in the center rather than at the edge. Sharp films have typical Hc values of 3 Oe for films of 4½ to 5 Oe Hk, while the reversible limit (creep threshold for zero easy axis field) will be 0.1 Oe less than H̄k. Since magnetization creep is the principle limitation of thin film memory elements and since sharp films have creep thresholds far larger than films of ordinary shape deposited on the same substrate at the same time, new fast, low‐power NDRO memory modes are possible with sharp films. These modes involve rotationally switching the films from one saturated state to another and use fields that are ⅔ Hc and ⅔ Hk so that no unselected films are disturbed.

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