Multivariate Statistical Characterization of Charged and Uncharged Domain Walls in Multiferroic Hexagonal YMnO₃ Single Crystal Visualized by a Spherical Aberration-Corrected STEM

Abstract

A state-of-the-art spherical aberration-corrected STEM was fully utilized to directly visualize the multiferroic domain structure in a hexagonal YMnO3 single crystal at atomic scale. With the aid of multivariate statistical analysis (MSA), we obtained unbiased and quantitative maps of ferroelectric domain structures with atomic resolution. Such a statistical image analysis of the transition region between opposite polarizations has confirmed atomically sharp transitions of ferroelectric polarization both in antiparallel (uncharged) and tail-to-tail 180° (charged) domain boundaries. Through the analysis, a correlated subatomic image shift of Mn-O layers with that of Y layers, exhibiting a double-arc shape of reversed curvatures, have been elucidated. The amount of image shift in Mn-O layers along the c-axis is statistically significant as small as 0.016 nm, roughly one-third of the evident image shift of 0.048 nm in Y layers. Interestingly, a careful analysis has shown that such a subatomic image shift in Mn-O layers vanishes at the tail-to-tail 180° domain boundaries. Furthermore, taking advantage of the annular bright field (ABF) imaging technique combined with MSA, the tilting of MnO5 bipyramids, the very core mechanism of multiferroicity of the material, is evaluated.

Resistive switching in polycrystalline YMnO3 thin films

“…38 In addition to the grain boundaries acting as charged regions, in YMnO 3 also a charged DWs exist. [14][15][16] HH and TT DWs are screened by accumulation or repulsion of the free charge carriers. This applies also to point defects and impurities distributed within the oxide.…”

“…10,11 This work investigates the resistive switching properties of polycrystalline hexagonal YMnO 3 which has been reported as an improper multiferroic with T N ≈ 70 K and T C ≈ 920 K 12,13 and possess partially charged DWs. [14][15][16] In YMnO 3 spontaneous polarization is aligned along the c-axis perpendicular to the M-O plane and it originates from tilting and distortion of MnO 5 bipyramids and displacement of Y ions. 12,17 These transitions are driven by electrostatic and geometry effects and they lead to the formation of kaleidoscopic topology of ferroelectric trimerization-polarization DWs.…”

“…are also charged domain walls where the opposite polarizations are facing each other: the positively head to head (HH) DWs and the negatively charged tail to tail (TT) DWs. [14][15][16] In addition, it was shown that the density of vortex cores which are formed during a spontaneous symmetry-breaking phase transition, i.e. at T C , depends on the cooling rate of YMnO 3 .…”

Manipulation of Nanoscale Domain Switching Using an Electron Beam with Omnidirectional Electric Field Distribution

“…This method requires no prepoling, no electrode, and no physical contact with a tip or any other manipulator and, therefore, would be ideal for manufacturing miniature and integrated electronic devices. Our results also indicate that caution is needed in electron microscopy investigation of FD structures to avoid any artificial effect caused by e-beam illumination [40].…”

“…Four red dots are marked in Fig. 3(b), which indicate the positions of yttrium ions and these positions are used to identify the polarization direction [17,40]. Figure 3(c) shows the result after e-beam irradiation at the blue-circled area.…”