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Competing Exchange Interactions on the Verge of a Metal-Insulator Transition in the Two-Dimensional Spiral Magnet Sr3Fe2O7

J.-H. Kim, Anil Jain, M. Reehuis, G. Khaliullin, D. C. Peets, C. Ulrich, J. T. Park, E. Faulhaber, A. Hoser, H. C. Walker, D. T. Adroja, A. C. Walters, D. S. Inosov, A. Maljuk, and B. Keimer
Phys. Rev. Lett. 113, 147206 – Published 3 October 2014
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    Abstract

    We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr3Fe2O7, which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe4+ moments adopt incommensurate spiral order below TN=115  K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr3Fe2O7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.

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    • Received 15 July 2014

    DOI:https://doi.org/10.1103/PhysRevLett.113.147206

    © 2014 American Physical Society

    Authors & Affiliations

    J.-H. Kim1, Anil Jain1,2, M. Reehuis3, G. Khaliullin1, D. C. Peets1, C. Ulrich1,4,5, J. T. Park6, E. Faulhaber6, A. Hoser3, H. C. Walker7, D. T. Adroja7,8, A. C. Walters1, D. S. Inosov1,9, A. Maljuk1,10, and B. Keimer1,*

    • 1Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany
    • 2Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
    • 3Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany
    • 4School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia
    • 5Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia
    • 6Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), D-85748 Garching, Germany
    • 7ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11-0QX, United Kingdom
    • 8Physics Department, Highly Correlated Matter Research Group, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa
    • 9Institut für Festkörperphysik, TU Dresden, D-01069 Dresden, Germany
    • 10Leibniz Institut für Festkörper-und Werkstoffforschung, D-01171 Dresden, Germany

    • *b.keimer@fkf.mpg.de

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    Vol. 113, Iss. 14 — 3 October 2014

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    • Figure 1
      Figure 1

      Neutron powder diffraction data of Sr3Fe2O7 at 2 K. The helical spin modulation vector in Sr3Fe2O7 was found to be k→=[0.1410.1411] (in the tetragonal setting). The upper symbols and line represent experimental data and calculated results, respectively. A small amount of SrFeO3 (TN=133  K) in our powder sample manifests its helical magnetic phase with k→=[0.129,0.129,0.129], consistent with fully oxygenated SrFeO3 [23]. The upper, middle, and bottom bars indicate the calculated positions of Sr3Fe2O7 nuclear, Sr3Fe2O7 magnetic, and SrFeO3 reflections, respectively, and the bottom line is a residual.

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    • Figure 2
      Figure 2

      Helical magnetic structure of Sr3Fe2O7 projected onto the (a) ab and (b) ac planes. The rectangle indicates the tetragonal unit cell. Spheres and octahedra represent the Fe ions and FeO6 units, respectively. Arrows indicate the spin directions. Lines indicate the spin exchange couplings J included in the theoretical fits.

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    • Figure 3
      Figure 3

      Contour maps of spin-wave dispersions in Sr3Fe2O7 at 7 K along the (a) [H00], (b) [HH0], (c),(d) [HH5], and (e) [HH7] directions. The intensities in (a) and (b) were multiplied by E to enhance the upper band. (f)–(j) show the theoretical dispersions and neutron scattering intensities (convoluted with the instrumental resolution), calculated with the parameters described in the text.

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