Successive magnetic phase transitions and multiferroicity in quasi-two-dimensional triangular lattice Heisenberg antiferromagnets Ba$_{3}$CoNb$_{2}$O$_{9}$ and Ba$_{3}$MnNb$_{2}$O$_{9}$

ORAL

Abstract

We have measured magnetic, dielectric and thermodynamic properties of quasi-two-dimensional triangular lattice antiferromagnet (TLAF), Ba$_{3}$CoNb$_{2}$O$_{9}$ (S$=$ 1/2) and Ba$_{3}$MnNb$_{2}$O$_{9}$ (S$=$ 3/2). At zero magnetic field, Ba$_{3}$CoNb$_{2}$O$_{9}$ undergoes a two-step transition at 1.36 K and 1.10 K and enters a 120 degree ordered state. By applying magnetic fields, a series of magnetic phases with fractional saturation magnetization (1/3, 1/2, 2/3 (or $\sqrt 3 $/3Ms) are observed. The collinear spin phase with 1/3 Ms becomes more robust at lower temperatures due to quantum fluctuations. For Ba$_{3}$MnNb$_{2}$O$_{9}$, the 120 degree ordered state is stabilized below 3.10 K at zero field. Under the magnetic field, successive magnetic phase transitions are observed with fractional magnetization 1/3 and 1/2 Ms. The 1/3 Ms phase becomes more stable at higher temperatures due to thermal fluctuations. The ferroelectricity emerges in all spin states in both compounds regardless of the spin chirality. Therefore, Ba$_{3}$CoNb$_{2}$O$_{9}$ and Ba$_{3}$MnNb$_{2}$O$_{9}$ are unique TLAFs exhibiting not only a series of magnetic phase transitions but also multiferroicity.

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Authors

  • M. Lee

    National High Magnetic Field Laboratory, FL, USA

  • J. Hwang

    National High Magnetic Field Laboratory, FL, USA

  • E.S. Choi

    National High Magnetic Field Laboratory, FSU, Tallahassee, Florida 32306, USA, Appl. Supercond. Ctr.\& Natl. High Magnetic Field Lab, Florida State Univ., National High Magnetic Field Laboratory, FL, USA

  • J. Ma

    Oak Ridge National Laboratory, TN, USA

  • C.R. Dela Cruz

    Oak Ridge Nat Lab, Oak Ridge National Laboratory, Oak Ridge National Laboratory, TN, USA

  • M. Zhu

    Michigan State University, MI, USA

  • X. Ke

    Michigan State University, Michigan State University, MI, USA

  • Z.L Dun

    University of Tennessee, University of Tennessee, Knoxville, University of Tennessee, TN, USA

  • H.D. Zhou

    University of Tennessee and National High Magnetic Field Laboratory, Florida State University, University of Tennessee - Knoxville, Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, 37996, Department of Physics and Astronomy, University of Tennessee, University of Tennessee, Department of Physics and Astronomy, University of Tennessee - Knoxville, University of Tennessee, TN, USA