Insulating behavior of magnetic spots in proton-bombarded graphite

Kelvin probe force microscopy measurements on micrometer small magnetic spots produced by proton bombardment on bulk graphite reveal a charge transfer from the center of the spot to an external ring with potential variation on the order of 50 mV. The total charge in the spot is neutral. The results can be well understood in terms of practically unscreened potentials, an insulating property, although the nonbombarded, surrounding graphite region exhibits good conductance. Scanning transmission x-ray microscopy measurements on magnetic spots prepared on graphitic films reveal similar charge distribution. The insulating behavior is fundamental to understand the magnetism in graphite.