Competing Exchange Interactions and Multiferroic Behavior of a Molecule-Based Magnet

 · Invited

Abstract

Multiferroic behavior sensitively depends on the microscopic interactions between spins. The molecule-based magnet (NH4)2FeCl5 (H2O) exhibits a complex magnetic-field or pressure versus temperature phase diagram with three multiferroic phases observed by magnetization, neutron diffraction, and Raman spectroscopy measurements. Both low-field phases contain spin cycloids with electric polarization P along the a axis produced by the inverse Dzyalloshinskii-Moriya interaction. Above the spin-reorientation transition at roughly 4 T, the spins form a canted antiferromagnetic state and P rotates to the c axis. The electric polarization at high fields is believed to be caused by p-d orbital hybridization. We evaluate the magnetic interactions in the low-field multiferroic phase by comparing inelastic neutron scattering spectra of a single crystal with a simple Heisenberg model containing five exchange interactions mediated by intermolecular hydrogen and halogen bonds. Two competing exchange interactions in every bc plane produce a cycloid with spins in the ac plane, helicity Si x Sj along the b axis, and ordering wavevector Q = (0, 0, 0.23) r.l.u. along the c axis. Using this wavevector as a constraint, we obtain excellent agreement between the observed and predicted inelastic spectra at zero field. With some small but clear differences, the zero-field exchange and anisotropy parameters also provide excellent agreement with the inelastic neutron-scattering spectra of the high-field phase. The resulting exchange and anisotropy parameters are compared with the predictions of first-principle calculations.

*Research sponsored by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Research conducted at ORNL's Spallation Neutron Source and High Flux Isotope Reactor was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U. S. Department of Energy.

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Presenters

  • Randy Fishman

    • Oak Ridge National Lab
    • Oak Ridge National Laboratory

Authors

  • Randy Fishman

    • Oak Ridge National Lab
    • Oak Ridge National Laboratory

  • Xiaojian Bai

    • Oak Ridge National Lab

  • Vasile Garlea

    • Oak Ridge National Laboratory
    • Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN
    • Oak Ridge National Lab
    • Neutron Scattering Division, Oak Ridge National Laboratory

  • Tao Hong

    • Neutron Scattering Division, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory
    • Oak Ridge National Lab

  • Jaime Fernandez-Baca

    • Oak Ridge National Lab
    • Oak Ridge National Laboratory

  • Huibo Cao

    • Oak Ridge National Lab
    • Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    • Neutron Scattering, Oak Ridge National Laboratory
    • Oak Ridge National Laboratory

  • Wei Tian

    • Oak Ridge National Laboratory, Oak Ridge
    • Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
    • Oak Ridge National Lab

  • Minseong Lee

    • National High Magnetic Field Laboratory
    • Pulsed Field Facility, Los Alamos National Lab
    • National High Magnetic Field Laboratory, Los Alamos National Laboratory
    • Los Alamos National Lab
    • Los Alamos National Laboratory

  • Vivien Zapf

    • Los Alamos Natl Lab
    • National High Magnetic Field Lab, Los Alamos National Lab
    • Pulsed Field Facility, Los Alamos National Lab
    • Los Alamos National Lab
    • Los Alamos National Laboratory

  • Junhee Lee

    • Ulsan National Institute of Science and Technology

  • Amanda J Clune

    • University of Tennessee

  • Kendall D Hughey

    • Department of Chemistry, University of Tennessee
    • University of Tennessee

  • Janice Musfeldt

    • University of Tennessee
    • Department of Physics and Astronomy, Rutgers University
    • Department of Chemistry, University of Tennessee