Abstract
$^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy was employed to investigate electronic charge transfer as well as the local structural and magnetic properties of stage-2 ${\mathrm{FeCl}}_{3}$-graphite in the temperature range from 1.5 to 300 K. Both ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ ions were clearly identified in the intercalant layers. The highly textured absorbers, with the graphite c axis preferentially normal to the absorber plane, were investigated in different orientations with respect to the \ensuremath{\gamma} rays. In this way, the relative amount of ${\mathrm{Fe}}^{2+}$ ions could be determined over the whole temperature range as 19%, independent of temperature, in disagreement with previous reports. The relaxationlike M\"ossbauer spectra observed at temperatures between 40 and 100 K reveal a thermally induced electron hopping between ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ sites, with an activation energy of 45\ifmmode\pm\else\textpm\fi{}20 meV. In addition, the Debye-Waller factor was found to be anisotropic as a consequence of a larger in-plane Fe vibrational amplitude. The magnetically split M\"ossbauer spectra at temperatures below 4.2 K, which were also studied in external magnetic fields, favor a spin-glass type of magnetic ordering of the intercalant layers.
Published Version
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