Influence of NiFe quality on bubble devices

Abstract

It is anticipated that as the period of bubble devices decreases, undesired effects due to loss of permeability of the NiFe overlay will become increasingly important, even for half-disk elements. The failure mechanism of "I-bar crossing " in H-I tracks, which leads to high values of the minimum drive field Hxy(min), was studied for both 8 and 20 μm bubble periods as a means of gaining insight into such effects. Direct Ferrofluid observations, along with measurements of the parameter H bb1 which characterizes the coercivity of an individual H bar, confirmed that the I-bar crossing phenomenon originated in high coercivity, and hence high remanence and low permeability of the NiFe. This interpretation was supported by a study of the effects on a sample of a series of annealing treatments at increasing temperatures, a process known to increase NiFe coercivity. The annealing studies demonstrated that for a given NiFe thickness Hbbl was better correlated with Hxy(min) than was the sheet-film coercivity Hc, showing that measurements of Hc must be interpreted with caution. Furthermore it was found that Hbb1 and Hxy(min) decreased with increasing NiFe thickness.