Cylindrical-domain propagation by Permalloy bar stray fields

The field gradients of magnetic stray fields which affect the propagation of cylindrical domains in a T-bar pattern are investigated. The magnetization of the Permalloy bars which gives rise to the propagating field gradient is found to be influenced by the stray field of the cylindrical domain itself. Considering this interaction, the propagating field gradients are calculated first for single bars and then for a geometric arrangement as it occurs in a T-bar pattern. Those forces leading to a forward propagation and those leading to a trapping of the domain are studied. Useful relations for the distance between the adjacent bars are deduced. The calculated propagating field gradient is found to have considerable local variations. This causes corresponding velocity variations of the domain. The marked velocity minima which occur along the domain path represent a strong restriction to high data rates in domain memory devices. Average propagation fields for the different propagation steps are shown as a function of the bar width.