Contrasting Magnetic Properties of Thermally and Chemically Reduced Graphene Oxide

We report the observation of enhanced magnetization in graphene oxide (GO) after thermal annealing. We have also proposed that this enhancement in magnetization is due to the increased density of zigzag edges. We conjecture that on annealing the random epoxy groups in the native GO migrate over the GO surface by acquiring thermal energy and self-assemble to form several long chains of epoxy groups. Subsequently, upon thermal reduction the GO sheet is unzipped along these long chains giving rise to more zigzag edges, resulting in enhancement of magnetization. We also found out that the density of epoxy groups plays an important role in the unzipping process. If the density of epoxy groups is low, then unzipping of GO is not possible. Chemical reduction of GO does not favor unzipping.