Magnetoplasma and Cyclotron Phenomena in the High- Temperature X-Band Electron Paramagnetic Resonance Spectra of Graphite

The X-band electron paramagnetic resonance (EPR) spectra at 100-400 K of a few distinct samples of graphite have revealed the new phenomena of an unidentified broad signal dependent on the specimen size and a transition from a Dysonian sharp EPR signal to a Lorentzian shape at a low microwave power. A detailed study of the dependences of these signals on the temperature, microwave power, specimen orientation relative to the direction of the magnetic field, and specimen size led to the attribution of the broad signal to plasma absorption combined with cyclotron resonance at room temperature. In addition, the microwave field was found to cause essential heating of the charge carrier subsystem, which drove the charge carrier subsystem out of thermal equilibrium.