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Establishing effective measurement method for distinguishing spin states – by direct observations of different spin states in both bulk crystal and thin film crystals

The University of Tokyo
RIKEN
Nara Institute of Science and Technology (NAIST)

Overview:

A research group including graduate student Yuichi Yokoyama and Associate Professor Hiroki Wadati at the Institute for Solid State Physics (ISSP) of the University of Tokyo and Yuichi Yamasaki at National Institute for Materials Science (NIMS) measured resonant inelastic soft X-ray scattering (RIXS) for a perovskite lanthanum-cobalt oxide (LaCoO3) using BL07LSU, which is a beam line of ISSP at SPring-8, the world’s largest synchrotron radiation facility. Thin films and bulk crystal of LaCoO3 were synthesized by the research group at the University of Tokyo and RIKEN.

It was indicated that the different spin-states from the bulk crystal were realized in the LaCoO3 thin films because of the epitaxial strain effects from the substrates. The research group observed that the spectral shape of the inelastic scattering at the Co L absorption edge changed according to the magnitude of the tensile-strain for the thin films. By comparing with the spectra obtained by the theoretical calculations performed by the group of Nara Institute of Science and Technology, the spin states of Co ions were revealed to be different between the bulk crystal and the thin film crystals.

Although it is difficult to observe the strain effects on the spin states with conventional X-ray absorption spectroscopic (XAS) measurements, clear difference can be probed with the use of RIXS.

Details of the study was published in the 17 May issue of Physical Review Letters online.

FIG. 1 : Comparison of RIXS spectra for LaCoO3 with different tensile strains obtained by the experiments and the calculations. HS (Oh) and LS (Oh) denote the high-spin state and low-spin state, while HS (D2h) indicates the high-spin state with D2h symmetry of CoO6. In the thin film with 1.0% tensile strain, a different peak observed at 1.0 eV could be assigned to the spin state HS (D2h).
FIG. 1 : Comparison of RIXS spectra for LaCoO3 with different tensile strains obtained by the experiments and the calculations. HS (Oh) and LS (Oh) denote the high-spin state and low-spin state, while HS (D2h) indicates the high-spin state with D2h symmetry of CoO6. In the thin film with 1.0% tensile strain, a different peak observed at 1.0 eV could be assigned to the spin state HS (D2h).
Reference:
  • Journal:Physical Review Letters
  • Title:Tensile-strain-dependent spin states in epitaxial LaCoO3 thin films
  • Author:Y. Yokoyama, Y. Yamasaki, M. Taguchi, Y. Hirata, K. Takubo, J. Miyawaki, Y. Harada, D. Asakura, J. Fujioka, M. Nakamura, H. Daimon, M. Kawasaki, Y. Tokura, and H. Wadati
  • DOI: https://doi.org/10.1103/PhysRevLett.120.206402
(Published on: Wednesday May 23rd, 2018)