Berlin 2012 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 4: Multiferroics II (jointly with MA, DS, KR, TT)

DF 4.3: 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.