Domain Wall Engineering

The physical properties of a ferroic material may change drastically in the vicinity of a domain wall. At the wall, the symmetry is lower so that new effects may arise. For example multiferroic hexagonal YMnO₃ is not magnetoelectric in the bulk but at its (coupled) antiferromagnetic and ferroelectric domain walls. In addition, domain walls represent dielectric and magnetic discontinuities. If ferroelectric domains meet head-on (i.e. with the wall oriented perpendicular to the spontaneous polarization) mobile positive or negative charges have to screen the diverging potential at the domain wall.

Effects like these can be used for tailoring the properties and coupling effects at the domain walls. Because of this, domain walls can be regarded as functional interfaces. However, a major advantage in comparison to "conventional" oxide interfaces is that domain walls remain mobile even after the sample has been grown whereas interfaces in heterostructures are spatially fixed once fabricated.

In our group we explore ways to measure and engineer the physical properties of the domain walls, create walls with novel types of functionalities (such as tunable conductance) and move the walls in a controlled way so that we can manipulate their properties at will.

Observation of coupled magnetic und electric domains. [1] C-AFM image: Domain walls appear as lines of different brightness, reflection their different conductance. [2] Contact-free probing of functional ferroelectric domain walls by X-ray photoemission electron microscopy (X-PEEM). The conducting domain walls show brighter contrast then the surrounding insulating bulk. [3] Optimized domain-wall currents in cation-doped ErMnO ₃. [4]

Reference

M. Fiebig, T. Lottermoser, D. Fröhlich, A.V. Goltsev, R.V. Pisarev: Observation of Coupled Magnetic and Electric Domains, Nature 419, 818 (2002)
D. Meier, J. Seidel, A. Cano, K. Delaney, Y. Kumagai, M. Mostovoy, N. A. Spaldin, R. Ramesh, M. Fiebig: Anisotropic Conductance at Improper Ferroelectric Domain Walls, Nature Materials 11, 284 (2012)
J. Schaab, I. P. Krug, F. Nickel, D. M. Gottlob, H. Doğanay, A. Cano, M. Hentschel, Z. Yan, E. Bourret, C. M. Schneider, R. Ramesh, D. Meier: Imaging and Characterization of Conducting Ferroelectric Domain Walls by Photoemission Electron Microscopy, Applied Physics Letters 104, 232904 (2014)
J. Schaab, A. Cano, M. Lilienblum, Z. Yan, E. Bourret,R. Ramesh, M. Fiebig, D. Meier: Optimization of Electronic Domain-Wall Properties by Aliovalent Cation Substitution, Advanced Electronic Materials 2, 1500195 (2016)