Stability of second kind of dumbbell domains subjected to an in-plane field at different bias fields

The softening process of the second kind of dumbbell domains(IIDs) in garne t bubble films subjected to an in-plane held H-ip at different static bias field H-b was studied experimentally. It was found that when H-b is larger, the remaining percentage of IID, R-IID, drops sharply at a certain H-ip, a nd with the increase of H-b the drop occurs at lower H-ip and becomes more intensive. We have confirmed that this is related to the "spontaneous-shrin k" of IIDs, which plays an important role for the breakdown of vertical Blo ch line chains of IIDs subjected to joint fields H-ip and H-b.