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 _{x y} B is not a constant but depends on the field strength, 2) the resistivity at low temperatures has a field dependence of \(\rho{\cong}B/(p{+}qB^{n})\), \(n{\cong}1\), 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 ⁰ and/or A ^- +(+e)→A ⁰ 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.