Regensburg 2010 – scientific programme
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KR: Fachverband Kristallographie
KR 10: Poster: Multiferroics (with MA, DF, KR, DS)
KR 10.23: Poster
Tuesday, March 23, 2010, 10:45–13:45, Poster A
Magnetic structure in multiferroic pyroxenes: (Na, Li)FeSi2O6 — •Max Baum1, Alexander Komarek1, Navid Qureshi1, Petra Becker2, Ladislav Bohatý2, Martin Meven3, Astrid Schneidewind3, Peter Link3, Maria Fernandez-Diaz4, Paul Steffens4, and Markus Braden1 — 1II. Phys. Inst., Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany — 2Inst. für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany — 3Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Lichtenbergstr. 1, 85747 Garching, Germany — 44 Institut Laue-Langevin, BP 156, 6 rue Jules Horowitz, 38042 Grenoble Cedex 9, France
(Na/Li)FeSi2O6 both exhibit multiferroic properties. In NaFeSi2O6 magnetic ordering is incommensurate with a temperature independent modulation k=(0, 0.23, 0). The antiferromagnetic order occurs below 8K and additionally ferroelectric ordering below 6K. Polarized neutron diffraction shows that at this transition chiral magnetic components develop. Ferroelectric order in NaFeSi2O6 seems thus to arise from the inverse Dzyaloshinski-Moriya interaction. Similarly, magnetically driven ferroelectricity is detected in LiFeSi2O6 below 18K but only at applied magnetic field. In both these compounds the electric polarization can be strongly modified by magnetic fields. Our measurement on a single crystal reveals the Shubnikov group P21/c’. On the basis of the magnetic structure we calculated the totoidal moment for LiFeSi2O6: T=-0.037muB/Å2. This is about ten times larger than in LiCoPO4, the first compound where ferrotoroidicity was unambiguously observed.