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arXiv · 1011.1152

Local electronic structure of Fe$^{2+}$ impurities in MgO thin films: Temperature-dependent soft x-ray absorption spectroscopy study

T. Haupricht·R. Sutarto·M. W. Haverkort·H. Ott·A. Tanaka·H. H. Hsieh·H. -J. Lin·C. T. Chen·Z. Hu·L. H. Tjeng
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Abstract

We report on the local electronic structure of Fe impurities in MgO thin films. Using soft x-ray absorption spectroscopy (XAS) we verified that the Fe impurities are all in the 2+ valence state. The fine details in the line shape of the Fe $L_{2,3}$ edges provide direct evidence for the presence of a dynamical Jahn-Teller distortion. We are able to determine the magnitude of the effective $D_{4h}$ crystal field energies. We also observed a strong temperature dependence in the spectra which we can attribute to the thermal population of low-lying excited states that are present due to the spin-orbit coupling in the Fe 3d. Using this Fe$^{2+}$ impurity system as an example, we show that an accurate measurement of the orbital moment in Fe$_3$O$_4$ will provide a direct estimate for the effective local low-symmetry crystal fields on the Fe$^{2+}$ sites, important for the theoretical modeling of the formation of orbital ordering.

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T. Haupricht, R. Sutarto, M. W. Haverkort, H. Ott, A. Tanaka, H. H. Hsieh, H. -J. Lin, C. T. Chen, Z. Hu, L. H. Tjeng. 2010-11-04. Local electronic structure of Fe$^{2+}$ impurities in MgO thin films: Temperature-dependent soft x-ray absorption spectroscopy study. https://doi.org/10.1103/physrevb.82.035120

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