Magnetoresistance Effect of Thin Films Made of Single Graphite Crystals

Abstract

The magnetic field dependence of the transverse magnetoresistance Δρ/ ρ₀ and the Hall coefficient R_H was measured for the graphite films of various thickness ranging from around 20 to 110 nm at temperatures between 4.2 K and 300 K. High quality of the crystallinity of these graphite films prepared by cleaving could be confirmed from the observation of Shubnikov-de Haas oscillation in R_H. The saturation tendency revealed in the resistivity ρ versus magnetic field B characteristics for graphite films thinner than about 50 nm in the strong magnetic field region at low temperature, while as for all graphite films in this study, ρ varied in proportion to Bⁿ (n>1) in the strong magnetic field region at high temperature. According to the transport theory for the simple two carriermodel in the strong magnetic field region, this saturation tendency should be due to the differencebetween electron and hole densities. It may be caused by some change of energy band structure in thin films. Furthermore, at high temperature, ρ versus B characteristics, common to all these graphite films, may be explained by the equal number density ofelectrons and holes due to thermal excitation.