Spin-half paramagnetism in graphene induced by point defects

The possibility to induce a magnetic response in graphene by the introduction of defects has been generating much interest, as this would expand the already impressive list of its special properties and allow novel devices where charge and spin manipulation could be combined. So far there have been many theoretical studies (for reviews, see refs 1-3) predicting that point defects in graphene should carry magnetic moments mu similar to mu(B) and these can in principle couple (anti) ferromagnetically(1-12). However, experimental evidence for such magnetism remains both scarce and controversial(13-16). Here we show that point defects in graphene-(1) fluorine adatoms in concentrations x gradually increasing to stoichiometric fluorographene CFx=1.0 (ref. 17) and (2) irradiation defects (vacancies)-carry magnetic moments with spin 1/2. Both types of defect lead to notable paramagnetism but no magnetic ordering could be detected down to liquid helium temperatures. The induced paramagnetism dominates graphene's low-temperature magnetic properties, despite the fact that the maximum response we could achieve was limited to one moment per approximately 1,000 carbon atoms. This limitation is explained by clustering of adatoms and, for the case of vacancies, by the loss of graphene's structural stability. Our work clarifies the controversial issue of graphene's magnetism and sets limits for other graphitic compounds.