Abstract
AbstractFerroelectric 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.
Highlights
IntroductionHexagonal rare-earth manganites (h-RMnO3, R = Sc, Y, Ho-Lu) have been found to exhibit improper ferroelectricity, antiferromagnetism and novel topological vortex domain structures.[1,2,3]
Hexagonal rare-earth manganites (h-RMnO3, R = Sc, Y, Ho-Lu) have been found to exhibit improper ferroelectricity, antiferromagnetism and novel topological vortex domain structures.[1,2,3]Among these manganites, hexagonal YMnO3 (h-YMO) is one of the well-studied multiferroic materials with the coexistence of ferroelectricity (Tc ~ 1,000 K) and antiferromagnetism (TN ~ 90 K).[4]
Chae et al.[8] pointed out that this vortex pattern is related with a kind of topological defects with which the structural and antiphase domain walls are interlocked with each other, leading to various intriguing phenomena, such as vortex walls, structural translation walls and antiferromagnetic walls
Summary
Hexagonal rare-earth manganites (h-RMnO3, R = Sc, Y, Ho-Lu) have been found to exhibit improper ferroelectricity, antiferromagnetism and novel topological vortex domain structures.[1,2,3] Among these manganites, hexagonal YMnO3 (h-YMO) is one of the well-studied multiferroic materials with the coexistence of ferroelectricity (Tc ~ 1,000 K) and antiferromagnetism (TN ~ 90 K).[4] Its ferroelectric polarisation is originated from the periodic tilting of MnO53+ polyhedral and displacements of Y3+ ions along a line in parallel with the c axis. It is quite interesting that the tilting of MnO53+ polyhedral induces a trimerisation of Mn3+ ions in each Mn layer This trimerisation results in a unique crystallographic domain pattern that consists of six domains with the [α+, γ−, β+, α−, γ+, β−] configuration. The topologically vortex structures and mutual-domain coupling in h-YMO were studied by using first-principles density functional theory.[21,22,23,24]
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