Conductivity of Vortexlike Ferroelectric Domain Patterns in Multiferroic YMnO3

YMnO3 is a typical member of the hexagonal manganites RMnO3 that form a unique class of multiferroics (materials with simultaneous magnetic and polar order) where a geometrically-driven mechanism triggers improper ferroelectricity. Interestingly, in these materials, vortex-like ferroelectric domain patterns occur where the vortex cores represent stable topological defects. Moreover, the ferroelectric domain walls (DWs) have significantly different conductivity than the domains. Taken together, these unusual properties enable possible applications in microelectronics that could make use of the nanoscale DWs in these materials instead of the domains themselves as active device elements. For this purpose, the conductivity contrast between the DWs and the domains should be as high as possible.

Until now, it was not possible to obtain unequivocal information on the absolute values of the conductivity of the DWs. In cooperation with the groups of Profs. Fiebig (ETH Zurich) and Meier (Norwegian University of Science and Technology, Trondheim), we have used a careful equivalent-circuit analysis of dielectric spectra (see Figure) to deconvolute the electrical properties of the domains and DWs in YMnO3. For the first time we have deduced the conductivity of the less-conducting DWs in a hexagonal manganite and demonstrate that tunneling of localized charge carriers is the dominant charge-transport process. The conductivity contrast between the bulk domains and the DWs is revealed to reach up to a factor 500 at room temperature, much higher than previously thought. Such information is of high relevance for the design of new DW-based microelectronic devices.

Spectra of the dielectric constant ε' and conductivity σ' of YMnO3 at various temperatures. The complex frequency dependence arises from a combination of contributions from the material itself ("bulk"), from domain walls, and from insulating surface layers at the electrodes (see inset). A careful analysis of these spectra allows to deduce the technically relevant domain-wall conductivity.

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Conductivity Contrast and Tunneling Charge Transport in the Vortexlike Ferroelectric Domain Patterns of Multiferroic Hexagonal YMnO3
E. Ruff et al., Phys. Rev. Lett. 118, 036803 (2017).