The variation of ferromagnetism induced by 12C+ ion implantation in highly oriented pyrolytic graphite was systematically studied by using Raman spectroscopy in conjunction with magnetic moment measurements and annealing treatments. It was found that the magnetization of the implanted sample was closely correlated with the density of the defects, which was characterized by the Raman spectra, produced by the implantation. It was clear that by using consecutive implantation steps at different energies to increase the vacancy defects in the implanted layer, the magnetization of the sample increases with the number of the implantation steps until the fourth step of implantation, which caused the near-surface layer to be highly disordered or amorphous, weakening the magnetic coupling and thus resulting in the decrease in magnetization. Annealing treatments of the sample indicated that the ferromagnetism induced by the implantations was stable at room temperature. However, when the sample was annealed at 473K (Wigner energy release temperature), the density of vacancies and interstitials was abruptly decreased and the magnetism induced by the implantations was extinguished. This finding gave a clear indication of the key role of the defects produced by C+ ion implantation in graphite.

Raman Study of Correlation Between Defects and Ferromagnetism in Graphite. Z.He, H.Xia, X.Zhou, X.Yang, Y.Song, T.Wang: Journal of Physics D, 2011, 44[8], 085001