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Direct Transition from a Disordered to a Multiferroic Phase on a Triangular Lattice

Department of Physics ETH Zurich. Direct Transition from a Disordered to a Multiferroic Phase on a Triangular Lattice.

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Direct Transition from a Disordered to a Multiferroic Phase on a Triangular Lattice

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  1. Department of Physics ETH Zurich Direct Transition from a Disordered to a Multiferroic Phase on a Triangular Lattice The first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic phase is reported in the triangular lattice antiferromagnet RbFe(MoO4)2. Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment . B A D A: Specific heat divided by the temperature C/T vs Temperature measured using a SiC membrane microcalorimeter in a 15 T superconducting magnet. Only at m0H = 3T a double transition is observed (inset). B: Zero-field temperature dependence of the magnetic Bragg intensity observed at Q=(1/3,1/3,q), compared to the temperature dependence of the ferroelectric polarization Palong the c-axis . C C: H-T phase diagram for magnetic field applied along the [1 -1 0] direction, obtained through neutron diffraction (solid black circles), specific heat (solid green circles), dielectric (solid blue squares represent peaks as a function of field, solid blue diamonds and triangles indicate anomalies as a function of temperature), and pyroelectric measurements (solid red circles). The order temperature T ≈ 3.8 K. Open circles represent the end of a magnetization plateau as a function of field [7]). The color gradient indicates the estimated increasing magnetization as a function of magnetic field. The commensurate and the high-field incommensurate magnetic order coexist in a narrow field region for μ0H ≈ 9 T. D: Structure of RFMO, belonging to the trigonal space group 3P. Shown are the Fe in red and O ions in yellow . M. Kenzelmann, G. Lawes, A.B. Harris, G. Gasparovic, C. Broholm, A.P. Ramirez, G.A. Jorge, M. Jaime, S. Park, Q. Huang, A.Y. Shapiro and L.A. Demianets Phys. Rev. Lett. 98 267205 (2007).

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