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 L2,3 edges provide direct evidence for the presence of a dynamical Jahn-Teller distortion. We are able to determine the magnitude of the effective D4h 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 Fe2+ impurity system as an example, we show that an accurate measurement of the orbital moment in Fe3O4 will provide a direct estimate for the effective local low-symmetry crystal fields on the Fe2+ sites, important for the theoretical modeling of the formation of orbital ordering.
@article{arxiv.1011.1152,
title = {Local electronic structure of Fe$^{2+}$ impurities in MgO thin films: Temperature-dependent soft x-ray absorption spectroscopy study},
author = {T. Haupricht and R. Sutarto and M. W. Haverkort and H. Ott and A. Tanaka and H. H. Hsieh and H. -J. Lin and C. T. Chen and Z. Hu and L. H. Tjeng},
journal= {arXiv preprint arXiv:1011.1152},
year = {2011}
}