Regensburg 1998 – wissenschaftliches Programm
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AM: Magnetismus
AM 11: Postersitzung
AM 11.70: Poster
Dienstag, 24. März 1998, 16:15–20:00, B
Fast Paramagnetic Relaxation in Mössbauer Spectra of Ferrocenium Salts — •M. Abraham1, W. Wagener1, H.-H. Klauss1, F.J. Litterst1, A. Hofmann2, and M. Herberhold2 — 1Institut für Metallphysik und Nukleare Festkörperphysik, TU Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig — 2Laboratorium für Anorganische Chemie, Universität Bayreuth, D-95447 Bayreuth
57Fe Mössbauer effect measurements have been performed on samples of unsubstituted and substituted ferrocenium tetrafluoroborate in the temperature range between 4 K and 300 K. The spectra show one broad non-symmetric absorption line. The shape’s asymmetry and width increase with decreasing temperature. We interpret this as the slowing down of magnetic fluctuations of the low spin Fe(III) atom in the center of the ferrocenium complex. Even at 4 K, however, the relaxation rate is too fast to allow the observation of fully resolved magnetic hyperfine spectra.
Fits using a simple stochastic relaxation model lead to rather good agreement with the spectra. The influence of the substituents at the cyclopentadienyle rings on the relaxation rate has been investigated. Experiments in applied magnetic fields will give further insight into the relaxation process. The relaxation rate can be separated in temperature independent spin-spin fluctuations and temperature dependent spin-lattice fluctuations. Details of the relaxation behaviour will be discussed in terms of the electronic structure of Fe(III) in these compounds.