The origin of delta noise in square-loop ferrites

Previous observations suggest that each grain of a square-loop ferrite supports one (or two) plane 180-degree domain wall(s), and atremanence the wall is near to a grain boundary. Following Néel, the wall energy should fluctuate with wall position so that, in effect, its motion across the grain under the influence of an external field is impeded by a series of obstacles, and here their magnitude is assumed to be scattered in a Gaussian way about some mean value. On the basis of this model, it was possible to calculate the mean displacement of all the walls when subjected to a given sequence of drive fields. In particular, the delta noise flux was computed either as a function of the magnitude of the disturb field or the magnetization change produced by the first disturb, all in reduced units. The predictions were compared with the results of ballistic measurements upon a ring of manganese-magnesium ferrite and quite good agreement was obtained, without recourse to any adjustable parameters.