The domain structure in the multiferroic hexagonal manganites, h-RMnO3 (R Sc, Y, Dy-Lu),is currently intensely investigated, motivated by the observation of nanoscale electricalconductivity at the domain walls and intriguing sixfold topological defects at their meetingpoints, as well as reports of coupling between ferroelectricity, magnetism and structuralantiphase domains. The detailed structure of the domain walls, as well as the origin of suchcouplings, however, was previously unknown. Here we use first-principles electronic structurecalculations to elucidate the structure and properties of the structural domain walls inthe hexagonal manganites. Our results allow us to explain why ferroelectric domain wallsare always simultaneously antiphase walls, propose a mechanism for ferroelectric switchingthrough domain-wall motion, suggest a structure for the observed sixfold topological defectsand predict a topological protection of experimentally observed stripe domains in hexagonalmanganites.
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