Nucleation Processes in Thin Permalloy Films

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Abstract
Normally, wall motion in thin Permalloy films starts from nuclei of reversed magnetization at the edges of the film, which are created by the demagnetizing field. Therefore, for the investigation of nucleation processes inside the film, the edge effects have to be suppressed. This has been done by two methods: The first is based on the use of inhomogeneous driving fields, and the second on the formation of a high coercive force barrier between the edges and the central area of the film. This barrier prevents the edge domains from moving into the central area. Depending on the maximum amplitude of the driving field, different modes of nucleation are possible, leading to different hysteresis loops. Since the domain nucleation must be attributed to a rotational process, the starting field is measured as a function of the uniaxial anisotropy field which is changed by bending the film. The results agree with the dependence found by Preisach for Permalloy wires under stress.

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