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MA: Fachverband Magnetismus
MA 20: Multiferroics
MA 20.3: Vortrag
Mittwoch, 27. Februar 2008, 14:30–14:45, EB 202
Pyroxenes: a new class of multiferroics — •Sven Jodlauk1, Petra Becker1, John Mydosh2, Daniel Khomskii2, Thomas Lorenz2, Sergej Streltsov2, and Ladislav Bohatý1 — 1Inst. f. Kristallographie, Universität Köln — 2II. Physikalisches Institut, Universität Köln
We present the results of our dielectric and magnetic investigations on pyroxenes with the general formula AMSi2O6 (A = mono- or divalent metal, M = di- or trivalent metal). They are shown to be a new class of multiferroic materials. In particular, we have found so far that NaFeSi2O6 becomes ferroelectric in a magnetically ordered state below ≈ 6 K. Similarly, magnetically driven ferroelectricity is also detected in the Li homologues, LiFeSi2O6 (TC≈18 K) and LiCrSi2O6 (TC≈11 K). In all these monoclinic systems the electric polarization can be strongly modified by magnetic fields. We present measurements of magnetic susceptibility, pyroelectric current and dielectric constants performed in various magnetic fields using a natural crystal of aegirine (NaFeSi2O6) and synthetic crystals of LiFeSi2O6 and LiCrSi2O6 grown from melt solution. For NaFeSi2O6 we propose a temperature versus magnetic field phase diagram. The possibility of a spiral magnetic structure caused by frustration to be the origin of the multiferroic behaviour taking into account computed exchange constants is discussed. We propose that other pyroxenes may also be multiferroic, and that the versatility of this family offers an exceptional opportunity to study general conditions for and mechanisms of magnetically driven ferroelectricity. This work was supported by the DFG via SFB 608.
Reference: J. Phys.: Condens. Matter 19 (2007) 432201