Spin-half paramagnetism in graphene induced by point defects

Abstract

The presence, or otherwise, of magnetism in graphene has been the subject of much debate. A systematic study of point defects—a widely suggested source of ferromagnetism in graphene—suggests that although they can exhibit net spin, they remain paramagnetic, even at liquid helium temperature. 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, 2, 3) predicting that point defects in graphene should carry magnetic moments μ∼μB and these can in principle couple (anti)ferromagnetically1,2,3,4,5,6,7,8,9,10,11,12. However, experimental evidence for such magnetism remains both scarce and controversial13,14,15,16. 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.