Abstract
Spin transition has attracted the interest of researchers in various fields since the early 1930s, with thousands of examples now recognized, including those in minerals and biomolecules. However, so far the metal centres in which it has been found to occur are almost always octahedral six-coordinate 3d4 to 3d7 metals, such as Fe(II). A five-coordinate centre is only rarely seen. Here we report that under pressure SrFe(II)O2, which features a four-fold square-planar coordination, exhibits a transition from high spin (S = 2) to intermediate spin (S = 1). This is accompanied by a transition from an antiferromagnetic insulating state to a ferromagnetic so-called half-metallic state: only half of the spin-down (dxz,dyz) states are filled. These results highlight the square-planar coordinated iron oxides as a new class of magnetic and electric materials.
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Acknowledgements
This work was supported by Science Research on Priority Areas (Novel States of Matter Induced by Frustration) and also partly by the Ministry of Education, Culture, Sports, Science and Technology of Japan. Research at Oak Ridge National Laboratory was sponsored by the Division of Materials Sciences and Engineering, US Department of Energy, under contract with UT-Battelle. This research used resources of the National Energy Research Computing Center, which is supported by the Office of Science of the US Department of Energy. This work was supported by the University of Vienna through the University Focus Research Area Materials Science (Multi-scale Simulations of Materials Properties and Processes in Materials).
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H.K. designed and coordinated the overall study seeking advice from M.T. (experiment) and C.L.F. (theory). N.H. conceived the high-pressure Mössbauer study, and X-Q.C. conceived the theoretical studies. Y.T., with support from K.Y., synthesized the material. T.K., S.S., K.H., Y.S. and Y.M. conducted high-pressure Mössbauer and electrical resistivity experiments, and T.K. analysed the data (with the help of M.T. and S.N.). Y.T., C.T., A.K., T.O. and T.Y. performed high-pressure X-ray diffraction experiments, and Y.T. and C.T. analysed the data. X-Q.C., C.L.F. and R.P. performed the theoretical work and analysis. H.K. and T.K. co-wrote the experimental part and C.L.F. and X-Q.C. co-wrote the theoretical part, with comments from R.P. All contributed to the discussion of the results.
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Kawakami, T., Tsujimoto, Y., Kageyama, H. et al. Spin transition in a four-coordinate iron oxide. Nature Chem 1, 371–376 (2009). https://doi.org/10.1038/nchem.289
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DOI: https://doi.org/10.1038/nchem.289
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