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Compressive strain induced enhancement of exchange interaction and short-range magnetic order in Sr2IrO4 investigated by Raman spectroscopy

A. Seo, P. P. Stavropoulos, H.-H. Kim, K. Fürsich, M. Souri, J. G. Connell, H. Gretarsson, M. Minola, H. Y. Kee, and B. Keimer
Phys. Rev. B 100, 165106 – Published 4 October 2019
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  • INTRODUCTION
  • EXPERIMENTAL DETAILS
  • EXPERIMENTAL RESULTS
  • COMPUTATIONAL RESULTS
  • DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr2IrO4 under in-plane misfit strain. With in-plane biaxial compression, the energy of the two-magnon peak increases and the peak remains observable over a wider temperature range above the Néel temperature, indicating a strain-induced enhancement of the superexchange interactions between Jeff=1/2 pseudospins. From density functional theory calculations, we have found an increase of the nearest-neighbor hopping parameter and exchange interaction with increasing biaxial compressive strain, in agreement with the experimental observations. Our experimental and theoretical results provide perspectives for systematic, theory-guided strain control of the primary exchange interactions in 5d transition-metal oxides.

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    • Received 17 September 2018
    • Revised 7 August 2019

    DOI:https://doi.org/10.1103/PhysRevB.100.165106

    ©2019 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Epitaxial strainMagnonsSpin-orbit coupling
    1. Physical Systems
    AntiferromagnetsIridatesMott insulatorsStrongly correlated systemsThin films
    1. Techniques
    DFT+UDensity functional calculationsRaman spectroscopy
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    A. Seo1,2, P. P. Stavropoulos3, H.-H. Kim2, K. Fürsich2, M. Souri1, J. G. Connell1, H. Gretarsson2, M. Minola2, H. Y. Kee3,4, and B. Keimer2

    • 1Department of Physics and Astronomy, University of Kentucky, 500 Rose Street, Lexington, Kentucky 40506, USA
    • 2Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany
    • 3Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7
    • 4Canadian Institute for Advanced Research, Quantum Materials Program, Toronto, Ontario, Canada M5G 1Z8

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    Issue

    Vol. 100, Iss. 16 — 15 October 2019

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    Images

    • Figure 1
      Figure 1

      (a) X-ray reciprocal space maps around the pseudocubic 103 reflection of STO and LSAT substrates. Q//≡2π/a and Q⊥≡2π/c, where a and c are in-plane and out-of-plane lattice parameters, respectively. The 1118̲ reflections from the Sr2IrO4 thin films are visible. The average lattice parameters of the Sr2IrO4 thin films are obtained and listed in Table 1. (b) Raman spectra of Sr2IrO4/STO, Sr2IrO4/LSAT, and Sr2IrO4/LAO taken at 10 K using the z(xx)z¯ channel (A1g and B1g). Oxygen-deficient Sr2IrO4 is known to exhibit an oxygen-vacancy-related mode (VO) at the Raman shift indicated by the dotted line (∼258cm−1) [19], which is not observed in these spectra. The peaks at ∼278cm−1 are an A1g phonon mode of Sr2IrO4 [20].

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    • Figure 2
      Figure 2

      (a) Temperature-dependent Raman spectra of B2g modes for Sr2IrO4/STO and Sr2IrO4/LSAT. The black triangles (▼) indicate the two-magnon peak energies at the lowest temperature (10 K). Sharp peaks at lower energies (<800cm−1) are B2g phonons. (b) Raman spectra of B2g modes for Sr2IrO4/STO and Sr2IrO4/LSAT at 10 K. The solid lines are curve fits using two Lorentz oscillators for the broad, asymmetric two-magnon peaks above 900cm−1. The obtained two-magnon peak positions show a blueshift of ∼50cm−1 from Sr2IrO4/STO to Sr2IrO4/LSAT.

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    • Figure 3
      Figure 3

      (a) The two-magnon peak energies of Sr2IrO4/STO and Sr2IrO4/LSAT as a function of temperature. (b) The two-magnon peak widths of Sr2IrO4/STO and Sr2IrO4/LSAT as a function of temperature. The inset shows magnetizations vs temperature measured with field cooling at H=100Oe for the Sr2IrO4/STO and Sr2IrO4/LSAT samples. (c) The normalized spectral weights, i.e., the integrated intensities from 900 to 2500cm−1, of the two-magnon peaks as a function of temperature. The vertical dashed lines of blue and red color indicate TN of Sr2IrO4/STO and Sr2IrO4/LSAT samples, respectively, obtained from the inset of Fig. 3.

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