Suppression of vortex–antivortex structures by anti-trimer point defects in hexagonal manganites.

The topologically protected vortex–antivortex (V–AV) domain structure in ferroelectric hexagonal manganites has been highly concerned recently, but its stability against intrinsic defects remains to be understood, given the claim that a topological structure would be robust against defects and other perturbations. In fact, it is also known that the V–AV structure is sensitive to the sample quality, and such a well-developed structure is hardly observed in thin films and defective single crystals. In this work, we investigate the influence of anti-trimer point defects on the stability of the V–AV domain structure by employing the phase-field simulation based on the Landau–Devonshire phenomenological theory. It is revealed that the characteristic V–AV structure essentially relies on the anti-trimer point defects under consideration. These defects lower the trimerization transition temperature on one hand and produce pinning effect on the vortex cores/walls on the other hand. However, the V–AV structure does remain robust if the anti-trimer magnitude of these defects is relatively weak but will be eventually destroyed if the anti-trimer magnitude is strong. [ABSTRACT FROM AUTHOR]