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 (DELTA-g) 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 DELTA-g(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 E3 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 DELTA-g-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.