Anomalous Galvanomagnetic Properties of Graphite in Strong Magnetic Fields

Our experiments on the galvanomagnetic effects of graphite in strong magnetic fields revealed that 1) σ_xyB is not a constant but depends on the field strength, 2) the resistivity at low temperatures has a field dependence of ρ≅B/(p+qBⁿ), n≅1, and 3) in an applied magnetic field the ρ vs T curve has a maximum at T=20 K~25 K. These results can not be explained by simple theory. However, if the transitions: D⁺+(−e)→D° and/or A^-+(+e)→A° are induced in strong fields, where D corresponds to donor and A represents acceptor, then co-existence of ionized impurity scattering and neutral impurity scattering can explain the qualitative feature of the (B, T)-dependence of the resistivity at low temperatures. At high temperatures it is necessary to consider phonon scattering and carrier-carrier scattering. Without the carrier-carrier scattering the (B, T)-dependence of ρ for T>25 K can not be explained.