Preparation of epitaxial hexagonal YMnO3 thin films and observation of ferroelectric vortex domains

Ferroelectric vortex is one of unique domain structures in the hexagonal RMnO3 (R=Sc, Y, Ho-Lu) systems. This vortex pattern is quite sensitive to crystal imperfections, such as lattice defects and oxygen vacancies, which has been previously observed and studied in a single-crystal structure. Here we report epitaxial growth of hexagonal YMnO3 thin films on platinum-coated Al2O3 (0001) substrates. High-quality epitaxial YMnO3(0001)/Pt(111)/Al2O3(0001) heterostructures with sharp interfaces have been achieved and characterised by using X-ray diffractometry and transmission electron microscopy. Reversible ferroelectric domain structures have been achieved and observed with well-established piezoresponse hysteresis. Furthermore, the ferroelectric vortex domain patterns with a typical size of ~20 nm have been observed, representing a significant progress in the fabrication and exploration of topological vortices in hexagonal RMnO3 thin films.