Electron spin resonance in graphite

Electron spin resonance in three- and quasi-two-dimensional graphites has been investigated between liquid-helium and room temperatures. The g shift (Δg) of three-dimensional graphite first increases with lowering temperature (T) so as to form a peak at 20 K, and then steeply falls off. An expression for Δg(T) proposed on the basis of the Dresselhaus-Dresselhaus Hamiltonian implies that the peak is produced in a way similar to that for the diamagnetic susceptibility. Curve fitting to the data, in which the divergence of the ${\mathit{E}}_3$ band is removed by considering the energy uncertainty, reproduces the temperature dependence fairly well by using the spin-orbit coupling constants with the correct order magnitude but with negative sign. The origin of such a difficulty involved in the calculation is discussed in connection with subtle balance between the electron and hole contributions. Specimens of quasi-two-dimensional graphite show behavior of Δg-versus-T similar to that observed for the three dimensional; this behavior is affected by localized spins especially at low temperatures. The absorption lines of all the specimens examined are narrowed with increasing temperature above 20 K by an averaging process of the g values of conduction carriers in k space.