Fermiology of Acceptor Graphite Intercalation Compounds Using de Haas-Van Alphen and Shubnikov-De Haas Measurements.

A number of well-staged acceptor Graphite Intercalation Compounds (GIC) have been prepared using a variety of intercalation techniques (isothermal, two-zone vapor transport, electrochemical). The host material was Highly Oriented Pyrolitic Graphite (HOPG). (00 l) x-ray diffraction measurements were performed to assure the purity of stage for each sample. Magnetooscillatory phenomena were studied as a function of an external magnetic field (0-19 Tesla). Using an inductive technique, both the magnetic susceptibility and magnetoresistance oscillations (de Haas-van Alphen, dHvA, and Shubnikov-de Haas, ShdH, effects, respectively) were observed. From the periodicity of the magnetooscillations as a function of the inverse magnetic field, the extremal cross-sections of the Fermi surfaces and the amount of charge transferred per carbon atom for each compound were inferred. The cyclotron effective mass and the Dingle Temperature, hence the average scattering time of the electrons or holes, for each cross sectional Fermi surface (FS) area were also inferred from the temperature dependence (1.9^circ -25^circK) of the amplitudes of the magnetooscillations. The number of frequencies present in the magnetooscillation spectra was stage-dependent and usually larger than that predicted by the simple two-dimensional Single Sandwich (SS) model. In-plane superlattices can produce new secondary FS, hence "extra" frequencies, while Magnetic Interaction (MI) effects can lead to mixing and harmonic frequencies in the dHvA spectrum. It is shown that these effects can be sorted out of the experimental spectra and that the remaining "primitive" FS sections are in good agreement with the SS model. Direct evidence of Magnetic B reakdown (MB) and Magnetic I nterference effects (MIF) due to the existence of in-plane superlattices were observed for the first time in GIC's. The results were consistent with the superlattices predicted by x-ray diffraction measurements performed on the same samples. MI effects and field-induced transitions were also observed for the first time in GIC's. In a secondary project, a tungsten-carbide anvil cell was modified and used to perform ungasketed measurements of the resistivity of HOPG, single crystal pristine graphite and FeCl_3 stage I GIC as a function of pressure (0-96 kbar) at room temperature, using a modified two-probe technique. The results are off by a factor of three or more when compared with the theory. A number of suggestions are given for the improvement of the cell for gasketed pressure experiments.