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One-Dimensional Magnetic Fluctuations in the Spin-2 Triangular Lattice α−NaMnO2

C. Stock, L. C. Chapon, O. Adamopoulos, A. Lappas, M. Giot, J. W. Taylor, M. A. Green, C. M. Brown, and P. G. Radaelli
Phys. Rev. Lett. 103, 077202 – Published 11 August 2009
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    Abstract

    The S=2 anisotropic triangular lattice α−NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at T≤45  K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Δ≃7.5  meV) has been analyzed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/kB≃73  K), along the monoclinic b axis and a sizable easy-axis magnetic anisotropy (|D|/kB≃3  K) are considered. Despite earlier suggestions for two-dimensional spin interactions, the dynamics illustrate strongly coupled antiferromagnetic S=2 chains and cancellation of the interchain exchange due to the lattice topology. α−NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions.

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    • Received 30 January 2009

    DOI:https://doi.org/10.1103/PhysRevLett.103.077202

    ©2009 American Physical Society

    Authors & Affiliations

    C. Stock1,*, L. C. Chapon1, O. Adamopoulos2,3, A. Lappas2,†, M. Giot1,2, J. W. Taylor1, M. A. Green4,5, C. M. Brown4, and P. G. Radaelli1

    • 1ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxon, OX11 0QX, United Kingdom
    • 2Institute for Electronic Structure and Laser, Foundation of Research and Technology-Hellas, Vassilika Vouton, 71110 Heraklion, Greece
    • 3Department of Chemistry, University of Crete, Voutes, 71003 Heraklion, Greece
    • 4NIST Center for Neutron Research, 100 Bureau Drive, Gaithersburg, Maryland 20899-6102, USA
    • 5Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115, USA

    • *Corresponding author. chris.stock@stfc.ac.uk
    • †Corresponding author. lappas@iesl.forth.gr

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    Vol. 103, Iss. 7 — 14 August 2009

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    Images

    • Figure 1
      Figure 1
      (a) Mn3+ ions (projected in the basal plane); the thick red or dark gray lines illustrate the chains, with J1 (red or dark gray) and J2 (blue or gray) marking the intrachain and interchain interactions. (b) Constant-Q cuts taken on the DCS spectrometer. (c)–(e) T evolution of MARI spectra illustrate the strong magnetic fluctuations at higher temperatures.Reuse & Permissions
    • Figure 2
      Figure 2
      (a) The magnetic density of states integrated over the range of 1.0<Q<2.5  Å−1 (T=5  K). The solid and dashed lines are calculations based on the 1D and 2D SMA models, respectively. (b) The low-energy spectrum on MARI, with Ei=30  meV; the white spaces are due to gaps in the detectors. (c) The excitation spectrum measured with Ei=150  meV illustrates the dispersion and the location of the top of the magnetic band. The solid line is the single crystal dispersion, taking Q∥ to the Mn chains.Reuse & Permissions
    • Figure 3
      Figure 3
      (a) The calculated intensity contours for the 1D SMA described in the text. (b) The measured magnetic intensity on MARI, with Ei=85  meV at T=5  K.Reuse & Permissions
    • Figure 4
      Figure 4
      The momentum (a) and the energy (b) integrated intensities, with Ei=85  meV at T=5  K. Solid lines in both panels are the results of the SMA calculation. The dashed line in panel (b) is a calculation introducing interchain interactions through RPA.Reuse & Permissions
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