Ion Irradiation Induced Magnetism in Carbon-based Compounds

Because of the biological compatibility, light weight and low cost, the possibility of having a room temperature carbon-based metal-ion free magnet attracts currently the interest of the scientific community. The search for magnetic ordering in carbon-based materials started, however, more than 15 years ago as Makarova [1] recently reviewed in detail. First claims on the existence of carbon-based ferromagnets with room temperature spontaneous magnetization were published beginning of the 90’s [2-4]. Some of the reports of carbonaceous materials show a saturation magnetization at room temperature Ms ~ 10 emu/g [3], just a tenth of that for magnetite (Fe3O4)! Theoretical work [5-7] pointed out on the possibility of having ferromagnetic carbon with a large magnetization (larger than α-Fe !). Ferromagnetic loops up to 800 K were reported in photo-assisted polymerised fullerene C60 [8]. At room temperature the magnetic samples showed a saturation magnetization Ms ~ 0.15 emu/g, which would indicate a magnetic moment of about 0.1 μB per C60. This result has been recently reproduced independently [9]. A ten times larger saturation magnetization was found in hydrofullerite C60H24, however the magnetization was not stable at room temperature after one year [10]. In spite of the above cited work this topic was not taken into account seriously by the main stream of scientists working on magnetism. We guess that poor reproducibility added to an insufficient characterization of the impurity concentration at every step of the sample preparation and measurement were the reasons that hindered a broad discussion on the magnetism in carbonaceous materials.