We have investigated highly-oriented pyrolytic graphite (HOPG) with a mosaic spread (ZYH) by employing electron spin resonance (ESR) measurements in comparison to high-grade virgin HOPG (ZYA) and proton-irradiated ZYA (Irr-ZYA). In spite of ferromagnetism found in ZYH as in Irr-ZYA, the ESR spectra in ZYH resemble those in ZYA rather than those in Irr-ZYA, only giving a conduction electron signal. Distinct characteristics of the conduction electron signals were investigated, the g-values and the linewidths being interpreted in terms of the carrier density and the magnetic susceptibility in relation to defects in the systems.
