Magnetic signals of proton irradiated spots created on highly oriented pyrolytic graphite surface

We demonstrate that a proton microbeam produces ferromagnetic spots on highly oriented pyrolytic graphite surface. The micrometer wide spots were characterized by magnetic force microscopy. This technique reveals clear irreversible behavior of the magnetic signal at the spots after application of an external DC field. Our results leave no doubts on the intrinsic nature of the ferromagnetism in a metal-free carbon structure.