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MA: Fachverband Magnetismus
MA 9: Joint Session "Multiferroics II - Hexagonal Manganites / Incommensurate Multiferroics" (jointly with DF, DS, KR, TT)
MA 9.3: Talk
Monday, March 26, 2012, 15:45–16:00, EB 301
Hexagonal InMnO3 - An Outsider Among The Family Of Multiferroic Hexagonal Manganites — •Martin Lilienblum1, Yu Kumagai1, Alexei A. Belik2, Naemi Leo1, Nicola A. Spaldin1, and Manfred Fiebig1 — 1Department of Materials, ETH Zurich — 2International Center for Materials Nanoarchitectonics, NIMS
So far, it was believed that hexagonal (h-) InMnO3 exhibit the same type of multiferroic order as the other compounds from the h-RMnO3 family (R = Sc, Y, Dy - Lu), including, in particular, a unit-cell-tripling improper ferroelectric order. Here we present experimental evidence for the absence of ferroelectricity in hexagonal InMnO3 based on three different techniques: x-ray diffraction (XRD), piezoresponse force microscopy (PFM) and optical second harmonic generation (SHG). XRD data are ambiguous because they can be described likewise by the non-ferroelectric P3c structure and by the ferroelectric P63cm structure present in the other h-RMnO3 compounds. However, PFM at room temperature and SHG measurements at low temperature uniquely reveal the absence of ferroelectric order in InMnO3. We therefore propose that InMnO3 exhibits antiferrodistortive, but non-ferroelectric order according to the P3c symmetry. Density functional calculations show that the relative energy between the P3c and P63cm structures is determined by a competition between electrostatic and covalency effects, with an absence of covalency favoring the ferroelectric structure.
We gratefully acknowledge the support by DFG through SFB 608.