Three-dimensional domain identification in a single hexagonal manganite nanocrystal

Abstract

The three-dimensional domain structure in ferroelectric materials determines many of their physical and technological properties, including their electrostatic stability, coercive field and surface charge. The domain structure can be particularly complex in improper ferroelectrics such as the hexagonal manganites since the polarization is a slave to a non-ferroelectric primary order parameter that drives the domain formation. In antiferromagnetic YMnO3 , for example, this leads to an unusual hexagonal vortex domain pattern with topologically protected domain walls, which have been shown to exhibit electrical conductivity and a net magnetic dipole moment at the sample surface. Characterizing the three-dimensional structure of these domains and domain walls has been elusive, however, due to a lack of suitable imaging techniques. Here, we present a multi-Bragg coherent x-ray diffraction imaging (BCDI) determination of the domain walls and domain types in a single YMnO3 nanocrystal. By reconstructing high-resolution, three-dimensional images of the structure and the full strain tensor field, we resolve two ferroelectric domains separated by a domain wall and confirm that the primary atomic displacements occur along the crystallographic c-axis throughout the nanocrystal. By correlating the BCDI experiment with atomistic simulation, we are able to verify the "Mexican hat" symmetry model of domain formation in the hexagonal manganites, and establish that the two domains correspond to adjacent minima in the Mexican hat with opposite ferroelectric polarization and adjacent trimerization domains. Finally, using a circular mean comparison we show that for this sample the two domains correspond to a clockwise winding around the brim of the hat. Our results highlight the potential of multi-Bragg CDI combined with atomistic simulations for revealing and identifying ferroelectric domain structures.

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Identifiers

ORCID for David Serban: orcid.org/0000-0003-4335-4522

ORCID for Marcus C. Newton: orcid.org/0000-0002-4062-2117

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