Berlin 2018 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 69: Multiferroic Oxide Thin Films and Heterostructures II (joint session KFM/TT/MA)

TT 69.4: Vortrag

Mittwoch, 14. März 2018, 16:00–16:15, EMH 225

In-situ characterization of improper ferroelectricity in ultrathin multiferroic h-YMnO₃ films — •Johanna Nordlander¹, Marta D. Rossell², Rolf Erni², Manfred Fiebig¹, and Morgan Trassin¹ — ¹ETH, Zürich, Switzerland — ²EMPA, Dübendorf, Switzerland

Improper ferroelectrics are materials whose ferroelectricity is driven by another, primary, order parameter. This type of ferroelectricity can lead to exotic properties that do not exist in standard ferroelectrics. In the case of bulk hexagonal manganites, the structural trimerization results in a topologically protected vortex domain structure. Due to their potential for extending existing technological applications with complex functional properties, there has been a revival of interest in hexagonal manganite thin films. Here we demonstrate the growth of highly oriented, epitaxial hexagonal YMnO₃ thin films using pulsed laser deposition. We use in-situ optical second harmonic generation (SHG) to non-invasively probe, in real time during and after the deposition process, the ferroic state of the films in the ultrathin regime. With the complementary use of reflection high-energy electron diffraction (RHEED), the emerging polarization of YMnO₃ is resolved with monolayer precision. The characteristic improper ferroelectric domain pattern in the ultrathin YMnO₃ films is investigated using scanning transmission electron microscopy. This work provides new insights in the early stage of improper ferroelectricity and domain state in hexagonal YMnO₃ thin films - especially the drastic influence of epitaxial strain and reduced dimensions on the ferroelectric Curie temperature.