Magnetic, Electronic, and Structural Properties of Ferric Chloride Intercalated Graphite.

The magnetic, electronic, and structural properties of intercalated graphite compounds in general, and ferric chloride intercalated graphite compounds in particular, are examined by various experimental and theoretical techniques. Both a microscopic experiment, Mossbauer spectroscopy, and a macroscopic experiment, magnetic susceptibility, indicate that stage 1 and 2 compounds undergo a long-range magnetic phase transition, while evidence is found that stage 4 and 6 compounds do not magnetically order down to 65mK. The magnetic transition temperature dramatically decreases as more diamagnetic graphite planes are added. Therefore, we conclude that the ordering mechanism is influenced by interlayer interactions thus providing direct evidence that magnetic ordering in these compounds is a three-dimensional effect. By using Mossbauer spectroscopy as a characterization tool, we find a sample dependent number of iron vacancies, which dramatically influences the susceptibility curves of the samples. Thus these two experiments also help elucidate the role of iron vacancies in disturbing long-range order thus causing some of the iron spins to acquire spin-glass like characteristics. The electronic properties of these compounds are also examined by Mossbauer spectroscopy. Below 100K donated electrons from the graphite lattice are localized on some ferric chloride sites to change these iron sites from ferric to ferrous sites. The Mossbauer data indicate that at low temperatures the ferric and ferrous sites are not randomly situated, and may form a unique chemical superlattice. The localization process is studied by Mossbauer spectroscopy and two possible explanations of the data are presented. We also examine the role of iron vacancies on the acceptor site. We find that chlorine atoms surrounding iron vacancies, when present in sufficient number, may act as the primary acceptor site for the electrons donated by the graphite to the intercalant. The effects of long-term exposure to air on these compounds is also studied by Mossbauer spectroscopy. A simple model of staging in graphite intercalation compounds is presented which yields only the staged structures which are observed experimentally. We show that for some intercalants, no other structures should be observed while providing physical guidelines for identifying materials in which more complex structures may be realized.