The bimodal state of magnetization in annealed cylindrical permalloy films

The shapes of commonly observed nonideal Belson traces in cylindrical Permalloy films have been derived by considering a bimodal distribution of easy axes induced by annealing multidomain films in a hard-direction field. In the bimodal state the film behaves like a mixture of two differently skewed regions, each of which contributes additively to the Belson curve. In the simplest bimodal case, symmetrical traces are derived from which the intrinsic skew and dispersion angles can be determined. In general, complex asymmetrical Belson traces result when the effect of mode population and nonzero initial skew are considered. Bimodal traces can be avoided by setting the wire in a single domain state prior to hard field annealing. Erasure of a bimodal distribution requires the application of an easy direction field at a sufficiently high temperature for a sufficient period of time.