Magnetic order in proton irradiated graphite: Curie temperatures and magnetoresistance effect

Defect induced magnetic order is a new phenomenon in material science that refers to the triggering and manipulation of magnetic order and magnetic moments in nominally non-magnetic materials by lattice defects and/or non-magnetic add atoms. A noticeable example of this effect is the magnetic order at room temperature produced by proton irradiation of graphite. In this work we have managed to increase the ferromagnetic signal by cooling the graphite samples down to 110 K during proton irradiation, diminishing in this way annealing effects. SQUID measurements of the magnetization show a fluence dependent Curie temperature. The longitudinal magnetoresistance shows an irreversible behavior similar to that found in ferromagnetic films indicating spin/domain reorientation effects. The observed magnetoresistance effects and Curie temperatures above room temperature are promising facts that may lead to useful carbon-based devices in the near future.