Percolation-Type Ferromagnetic Order in Epitaxial Strained LaCoO$_3$ Thin Films

ORAL

Abstract

Support for percolation-type ferromagnetic order in LaCoO$_3$ thin films is provided by x-ray diffraction and Co $K$-edge x-ray absorption fine structure (XAFS) spectroscopy. X-ray diffraction shows considerable changes in structure with respect to bulk LaCoO$_3$, and extended XAFS (EXAFS) demonstrates a large Jahn-Teller like distortion of the oxygen octahedra in highly strained films. Structural distortions of the oxygen octahedra are strongly coupled to the hybridization between orbitals of Co and O atoms, as shown by x-ray absorption near edge spectroscopy (XANES). Our results indicate that increased Co-O hybridization, and therefore increased magnetic exchange energy, does not cause ferromagnetism to occur in LaCoO$_3$ thin films. Instead, we suggest that the strain-induced distortions of the oxygen octahedra increase the population of $e_g$ electrons and concurrently depopulate $t_{2g}$ electrons beyond a stabilization threshold for ferromagnetic order.

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Authors

  • George Sterbinsky

    • National Institute of Standards and Technology

  • Philip Ryan

    • Argonne National Laboratory
    • Advanced Photon Source, Argonne National Laboratory

  • Jong-Woo Kim

    • Argonne National Lab
    • Argonne National Laboratory
    • Advanced Photon Source, Argonne National Laboratory

  • Evguenia Karapetrova

    • Advanced Photon Source, Argonne National Laboratory

  • J. Ma

    • Department of Physics, University of California, Riverside

  • Jing Shi

    • Department of Physics and Astronomy, University of California, Riverside
    • Department of Physics and Astronomy, University of California Riverside
    • University of California, Riverside
    • Department of Physics, University of California, Riverside

  • Joseph Woicik

    • National Institute of Standards and Technology
    • NIST