Regensburg 2019 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 7: Multiferroics

KFM 7.8: Talk

Monday, April 1, 2019, 17:50–18:10, H47

The ultrathin limit of improper ferroelectricity — •Johanna Nordlander¹, Marco Campanini², Marta D. Rossell², Rolf Erni², Quintin N. Meier¹, Andres Cano^1,3, Nicola A. Spaldin², Manfred Fiebig¹, and Morgan Trassin¹ — ¹Department of Materials – ETH, Zurich, Switzerland — ²Electron Microscopy Center – EMPA, Dübendorf, Switzerland — ³Institut Néel – CNRS, Grenoble, France

The secondary nature of spontaneous polarization in improper ferroelectrics is known to promote functional properties beyond those of conventional ferroelectrics. In technologically relevant ultrathin films, however, the improper ferroelectric behavior remains largely unexplored. Using state-of-the-art in-situ second harmonic generation and transmission electron microscopy, we probe the coupled improper polarization and primary order parameter in YMnO₃ thin films. The polarization displays a pronounced thickness dependence, which we show to originate from the strong modification of the primary order at epitaxial interfaces. Finite-size effects reduce the temperature of the phase transition, allowing us to reveal its order-disorder character with atomic resolution. Our results lay the foundation for understanding the emergence of improper ferroelectricity within the confinement of ultrathin films – essential for the successful implementation of these exotic materials in nanoscale devices.