Dislocation-mediated period adaptation in magnetic "bubble" arrays

(Received 14 June 1993, accepted in final form 21 October 1993)

Abstract
Dislocation-mediated mechanisms of stress relaxation, generating disorder in magnetic bubble arrays in response to temperature-induced period adaptation, are described. In contrast to the response of assemblies of rigid particles, the stress-induced evolution of dense magnetic domain patterns is characterized by the interplay of lattice topology and bubble domain size and shape. Such coupling of topological and geometrical degrees of freedom determines the local transformations which mediate lattice expansion ("coarsening") and govern dislocation dynamics : these are shown to be predicated upon adjustments in the number density of bubbles via bubble collapse. Elementary processes underlying the translation of dislocations, the dissociation ("splitting") of dislocation cores and the formation of virtual pairs as well as interstitials in the form of dislocation clusters of zero net Burgers vector are examined. Later stages of coarsening are shown to permit pattern "healing" via annihilation of interstitials. Examination of the close connection between the elementary processes of dislocation dynamics and the topological transformations of polygonal networks ("froths") reveals the elimination of 5-sided cells to play a central role.