Correlation between the vacancy defects and ferromagnetism in graphite

Vacancies and vacancy clusters produced by carbon ion implantation in highly oriented pyrolytic graphite, and their annealing behavior associated with the ferromagnetism of the implanted sample are studied using positron annihilation in conjunction with ferromagnetic moment measurements using a superconducting quantum interferometer device magnetometer. The results indicate that the magnetic moments are closely correlated to the existence of the vacancy defects in the samples and this is supported by theoretical calculations using density functional theory. The mechanism of magnetic order in the implanted sample is discussed.